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Relationship: 3706

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

AR transcriptional activity in GT tissues, reduced leads to FGF10/FGFR2-IIIb signaling in genital tissue, reduced

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

AR transcriptional activity in GT tissues, reduced

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

FGF10/FGFR2-IIIb signaling in genital tissue, reduced

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Androgen receptor antagonism leads to delayed preputial seperation via reduced fibroblast growth factor in genital-tubercle tissues	adjacent			Travis Karschnik (send email)	Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
Mus musculus	Mus musculus	High	NCBI
Rattus norvegicus	Rattus norvegicus	High	NCBI
Homo sapiens	Homo sapiens	Low	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Male	High
Female	Moderate
Unspecific	High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Fetal	High
Foetal	High
Embryo	High
Fetal to Parturition	High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

This KER captures an AR‑dependent regulatory relationship in the genital tubercle in which reduced AR transcriptional activity diminishes Fgfr2‑IIIb and Fgf10 signalling in genital tissues.

AR functions as a ligand‑activated nuclear transcription factor. Upon binding 5α‑dihydrotestosterone (DHT), AR undergoes a ligand‑induced conformational change that stabilizes the receptor and supports recruitment of transcriptional co‑activators (Furutani et al., 2002). In GT organ culture, AR antagonism with flutamide down‑regulates Fgfr2‑IIIb transcripts, and co‑addition of DHT rescues Fgfr2‑IIIb expression, demonstrating AR‑dependent control of Fgfr2‑IIIb in this tissue (Petiot et al., 2005). An in silico stereotypic androgen response element (ARE) is present in the Fgfr2 promoter, suggesting possible direct transcriptional regulation of Fgfr2 by AR in this tissue (Petiot et al., 2005). AR antagonism also reduces Fgf10 transcripts in GT organ culture in a dose‑dependent fashion, although direct versus indirect regulation of Fgf10 by AR remains unresolved (Petiot et al., 2005). FGF10, produced by GT mesenchyme, is the primary ligand for the FGFR2‑IIIb isoform in the adjacent urethral epithelium and surface ectoderm; global loss of Fgf10 or Fgfr2‑IIIb and tissue‑specific deletion of Fgfr2 demonstrate that this axis drives urethral epithelial proliferation, maturation/stratification, tubulogenesis, and prepuce morphogenesis, and that its disruption causes hypospadias (Petiot et al., 2005; Gredler et al., 2015).

When AR activity is reduced by pharmacological antagonism in GT organ culture, Fgfr2‑IIIb and Fgf10 mRNA are downregulated in a dose‑dependent manner, and Fgfr2‑IIIb downregulation is rescued by DHT (Petiot et al., 2005). This reduction in FGF10/FGFR2‑IIIb signaling is sufficient to arrest epithelial progenitor cell proliferation and disrupt stratification and maturation of the urethral plate epithelium, ultimately impairing urethral morphogenesis (Petiot et al., 2005; Gredler et al., 2015).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence for this KER was assembled through a combination of expert knowledge and AI-assisted literature search and synthesis. Specifically, a combination of Claude (Anthropic) using Sonnet 4.6, and EPA AI, using GPT5, was used to identify, retrieve, and summarize relevant primary and secondary literature, and to draft the initial content of this KER page. All citations generated through this process were subsequently reviewed and verified by the KER author against primary sources and DOI resolution checks, prior to inclusion. Users of this KER are advised that AI-assisted evidence assembly may introduce selection bias or gaps in coverage that differ from a fully systematic human-conducted review, and independent verification of the evidence base is encouraged. A copy of the initial prompt is attached to AOP619.

A review of primary experimental literature using the following databases and search strategies was employed:

PubMed and Google Scholar using the following search terms and combinations: "FGF10 FGFR2 androgen receptor genital tubercle," "FGFR2-IIIb androgen response element," "flutamide FGF10 FGFR2 hypospadias," "AR transcriptional activity external genitalia FGF signaling," "FGF10 FGFR2 urethral development masculinization," and "hypospadias FGF8 FGF10 FGFR2 androgen." No formal date restriction was applied. Priority was given to primary experimental studies in rodent genetic and pharmacological models, followed by human genetic and histological studies. Knockout mouse studies, ex vivo culture experiments, in situ hybridization studies, and transcriptome analyses were included. Review articles were used to corroborate mechanistic frameworks.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

AR is a member of the nuclear steroid hormone receptor superfamily and functions as a ligand‑inducible transcription factor. Upon binding DHT, the AR-DHT complex undergoes an agonist‑induced conformational change, dimerizes, translocates to the nucleus, and binds androgen response elements (AREs) composed of two palindromic half‑sites separated by a three‑nucleotide spacer to drive transcription (Gelmann, 2002; Quigley et al., 1995). In developing external genital tissues, testosterone is locally converted to DHT by 5α‑reductase type 2; in the human fetal penis, SRD5A2 is strongly expressed in the stroma along the ventral urethral seam while AR is enriched in the urethral epithelium (Kim et al., 2002). Loss of AR function (e.g., complete androgen insensitivity) leads to female‑appearing external genitalia, and 5α‑reductase type 2 deficiency causes undervirilization and hypospadias, establishing that DHT-AR‑dependent transcription is required for normal external genital development (Quigley et al., 1995; Kim et al., 2002).

Within the genital tubercle (GT), AR antagonism (flutamide) down‑regulates Fgfr2‑IIIb transcripts in a dose‑dependent manner with rescue by DHT, and reduces Fgf10 transcripts at higher antagonist doses, demonstrating AR‑dependent control of the FGF10-FGFR2‑IIIb axis during the developmental period when these genes are expressed (Petiot et al., 2005). The Fgfr2 promoter contains a stereotypic ARE‑like motif identified in silico between nucleotides 1193-1198 within the region 1041-1610 upstream of the transcription start site, providing a plausible direct molecular link between AR transcriptional activity and Fgfr2‑IIIb expression in urethral epithelium; however, GT‑specific AR-DNA binding or reporter evidence has not yet been shown, so direct regulation remains putative (Petiot et al., 2005). Whether AR regulation of Fgf10 in the GT is direct or involves intermediate signals remains unresolved; by analogy, in the prostate FGF10 is a mesenchymal growth cue required for epithelial proliferation and budding, but neonatal prostate data indicate FGF10 is not directly regulated by testosterone (Thomson & Cunha, 1999; Donjacour et al., 2003).

FGF10, produced by GT mesenchyme, acts as a major ligand for the epithelial FGFR2‑IIIb isoform, forming a locally acting epithelial-mesenchymal signaling axis (Ohuchi et al., 2000). Genetic loss‑of‑function and tissue‑specific deletion studies show that reduced FGF10/FGFR2‑IIIb signaling is sufficient to arrest proliferation of urethral epithelial progenitors, disrupt epithelial stratification and maturation, and produce hypospadias; endodermal FGFR2 is required for urethral epithelial maturation and ectodermal FGFR2 for ventral prepuce closure and maintenance of a closed urethral tube (Petiot et al., 2005; Gredler et al., 2015). At the cellular level, FGFR2 signaling in GT epithelia couples G1/S progression with columnar morphogenesis and cell‑adhesion organization, linking the FGF axis to proliferation‑coupled epithelial maturation required for urethral tubulogenesis (Gredler et al., 2015). Taken together, these findings support the biological plausibility of a causal chain in which reduced AR transcriptional activity during the developmental window diminishes FGF10–FGFR2‑IIIb signaling in GT tissues, thereby compromising urethral epithelial progenitor maintenance and stratification required for urethral tubulogenesis and disrupting ectodermal FGFR2‑dependent ventral prepuce closure and external preputial lamina formation—prenatal defects that plausibly predispose to persistent ventral tethering and abnormal postnatal preputial separation (Petiot et al., 2005; Gredler et al., 2015; Harada et al., 2015).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Pharmacological AR antagonism in ex vivo GT organ culture (mouse).

Petiot et al. (2005) showed that flutamide produced a clear, dose‑dependent decrease in Fgfr2‑IIIb transcripts in the urethral plate epithelium of cultured GTs, with no change at 10-5 M, progressively reduced at 10⁻⁴ M and 5×10⁻⁴ M, and markedly diminished/undetectable at 10⁻³ M; importantly, co‑addition of DHT rescued Fgfr2‑IIIb expression and normalized morphology, confirming AR specificity (Petiot et al., 2005). Male and female GTs were cultured separately and showed no differences in response to flutamide (Petiot et al., 2005).

AR antagonism also down‑regulates Fgf10 in GT organ culture. In the same study, flutamide reduced Fgf10 transcripts in a dose‑dependent fashion in both male and female GTs, indicating that androgen‑dependent regulation of the mesenchymal ligand is operative during this developmental window (Petiot et al., 2005).

ARE in the Fgfr2 promoter (molecular plausibility for a direct transcriptional link).

Petiot et al. (2005) identified a stereotypic ARE‑like motif within 1041 to 1610 bp upstream of the Fgfr2 transcription start site, consistent with direct AR‑dependent transcriptional regulation of Fgfr2‑IIIb; they noted, however, that intermediate regulatory steps cannot be excluded and direct AR-DNA binding in GT was not shown.

Disruption of androgen signaling in vivo alters urethral plate cell behavior.

Using lineage tracing, Seifert et al. (2008) showed that flutamide‑treated males failed to undergo urethral septation/internalization and instead retained urethral plate cells to the ventral margin, mimicking untreated females; flutamide‑treated females showed normal urethral positioning. These data confirm that androgen‑dependent signals are required for the morphogenetic cell behaviors distinguishing male from female urethral development and align with the FGFR2 endodermal deletion phenotype (Seifert et al., 2008; Gredler et al., 2015).

Network context and tissue‑specific roles of FGF signaling in GT.

Tissue‑specific Fgfr knockouts demonstrate that mesenchymal FGF signaling is required for early GT outgrowth, ectodermal signaling for urethral tube formation, and endodermal signaling for epithelial stratification/adhesion during later stages, placing the FGF10-FGFR2‑IIIb axis precisely within the epithelial-mesenchymal mechanics of urethral tubulogenesis (Harada et al., 2015).

Computational corroboration.

A multicellular agent‑based model of GT development recapitulated urethral tube closure as an emergent, androgen‑dependent property that is quantitatively sensitive to SHH‑ and FGF10‑driven mesenchymal proliferation and to endodermal apoptosis; androgen insufficiency or delayed androgenization produced feminization or incomplete closure, respectively, providing in silico corroboration of the AR→FGF10/FGFR2‑IIIb linkage’s impact on urethrogenesis (Leung et al., 2016).

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Directionality of Fgf10 regulation: In GT organ culture, flutamide dose‑dependently reduces Fgf10 in both sexes, but whether AR regulates Fgf10 directly or via intermediates is unresolved; in neonatal prostate, FGF10 is not directly regulated by testosterone, supporting an indirect route (Petiot et al., 2005; Thomson & Cunha, 1999; Donjacour et al., 2003).
Possible ARE‑independent regulation of Fgfr2: A putative AR recognition hexamer is present upstream of Fgfr2 and DHT rescues flutamide‑suppressed Fgfr2‑IIIb in GT organ culture, but GT‑specific AR-DNA binding and transactivation have not been demonstrated (no ChIP or promoter‑reporter assays), so direct regulation remains unproven (Petiot et al., 2005).
Species extrapolation: Most mechanistic data are from mouse/rat; the timing and endocrine control of the masculinization programming window differ between rodents and humans, and human genetic/IHC data are correlative, limiting direct inference of timing/magnitude/cell‑type specificity of AR→FGF regulation in humans (Welsh et al., 2008; Sharpe, 2020; Kim et al., 2002).
Tissue‑compartment specificity: AR is present in both GT mesenchyme and urethral epithelium (mouse), and in human fetal penis AR is enriched in urethral epithelium while 5α‑reductase type 2 is concentrated in ventral stroma at the urethral seam; whether AR‑driven Fgfr2 and/or Fgf10 transcription occurs cell‑autonomously in specific GT compartments in vivo remains to be resolved (Petiot et al., 2005; Kim et al., 2002).

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Modulating Factor	Details	Effect on KER	References
DHT availability	Local conversion of testosterone to DHT by 5α‑reductase type 2 in ventral urethral stroma/GT‑derivative tissues; DHT binds/stabilizes AR with higher affinity than testosterone.	Higher DHT increases AR transcriptional activity, upregulating Fgfr2‑IIIb; DHT rescues flutamide‑suppressed Fgfr2‑IIIb in GT organ culture (rescue for Fgf10 was not shown).	Petiot et al., 2005; Quigley et al., 1995; Kim et al., 2002.
5α-Reductase type 2 activity	Enzyme converting testosterone to DHT in GT‑derivative tissues; SRD5A2 is strongly localized to ventral stroma at the urethral seam in human fetal penis.	Reduced 5α‑reductase activity decreases local DHT, lowering AR‑driven Fgfr2‑IIIb (and possibly Fgf10 indirectly) and compromising downstream FGF signaling; human SRD5A2 deficiency is associated with undervirilization/hypospadias.	Kim et al., 2002; Quigley et al., 1995.
Timing of exposure / developmental window (MPW)	In rats, the masculinization programming window is GD15.5-18.5; effects of anti‑androgens are greatest within this window. In humans, the presumptive MPW is ~8-14 gestational weeks.	Anti‑androgenic disruption within the MPW is expected to most strongly reduce AR‑dependent control of FGF10/FGFR2‑IIIb and to yield the most severe urethral defects; disruption outside this window has attenuated effects.	Welsh et al., 2008; Sharpe, 2020
Sex (male vs. female)	Male and female GT explants show similar dose‑dependent down‑regulation of Fgfr2‑IIIb and Fgf10 with flutamide in organ culture; in vivo, AR antagonism during the window feminizes male urethral development, whereas females are largely unaffected.	The molecular AR→FGF10/FGFR2‑IIIb linkage operates in both sexes, but morphogenetic consequences are greater in males	Petiot et al., 2005; Seifert et al., 2008.
Genetic background / FGFR2 variants	Specific FGFR2 coding or regulatory variants were observed uniquely in boys with familial isolated hypospadias in a Swedish cohort.	Such variants may alter receptor function or regulation, increasing susceptibility when AR activity is reduced (gene-environment interaction); functional impact of individual variants remains to be established.	Beleza-Meireles et al. (2007)
SHH pathway activity (upstream of FGF10 in GT)	In GT, Shh regulates growth and positions Fgf10 upstream of epithelial responses; in limb, FGFR2‑IIIb acts upstream of Shh (illustrating pathway inversion across tissues).	Perturbation of SHH can alter Fgf10 independently of AR, potentially modulating the apparent strength of the AR→FGF linkage.	Seifert et al., 2010; Petiot et al., 2005; Revest et al., 2001.
Ligand redundancy for FGFR2‑IIIb	FGFR2‑IIIb binds several ligands (e.g., FGF7, FGF10); FGF10 is a major ligand across epithelia.	Partial compensation by other ligands could blunt the impact of reduced FGF10 on this KER in some contexts.	Ohuchi et al., 2000.

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

The precise in vivo response-response relationship between the degree of AR activity reduction and the magnitude of FGF10/FGFR2‑IIIb signaling decrease is not yet quantified; available dose-response data derive from ex vivo GT cultures and semi‑quantitative in situ hybridization rather than absolute measures of FGF signaling output (e.g., receptor phosphorylation).

Petiot et al. (2005) demonstrated a clear dose-response relationship between flutamide concentration and reduction of Fgfr2‑IIIb transcripts in mouse GT organ culture after 48 h: Fgfr2‑IIIb expression was maintained at 10⁻⁵ M flutamide, progressively reduced at 10⁻⁴ M and 5×10⁻⁴ M, and markedly diminished/undetectable at 10⁻³ M; co‑treatment with DHT (5×10⁻⁶ M) rescued Fgfr2‑IIIb expression, confirming AR specificity (Petiot et al., 2005). Fgf10 transcripts persisted at 10⁻⁵ M but showed progressive down‑regulation at 10⁻⁴-10⁻³ M, including loss of detectable signal at 10⁻³ M in female GT; DHT rescue was shown for Fgfr2‑IIIb (not for Fgf10) (Petiot et al., 2005).

A multicellular agent‑based model of GT development indicated that partial reductions in androgen signaling can produce graded urethral‑closure outcomes—from mild to severe hypospadias—depending on the timing and magnitude of perturbation, providing in silico corroboration of graded AR‑dependent control over FGF‑sensitive epithelial behaviors (Leung et al., 2016).

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

In mouse GT organ culture, AR antagonism produces detectable reductions in Fgfr2‑IIIb (and, at higher doses, Fgf10) within 48 h, and DHT rescues Fgfr2‑IIIb within that same window, indicating an hours‑to‑days timescale for AR‑dependent FGF transcript changes in GT tissue (Petiot et al., 2005; Furutani et al., 2002).

Overall, the KER operates during the androgen‑dependent sexual differentiation phase of GT development. In mouse, the critical programming window for penile masculinization is approximately E14.5-E17.5, while urethral septation/internalization and preputial morphogenesis continue through late gestation to birth (P0) (Amato et al., 2022; Seifert et al., 2008). In rat, the masculinization programming window spans GD15.5-18.5; suppression of androgen action within this window produces the greatest feminization/hypospadias, with much smaller effects outside it (Welsh et al., 2008; Sharpe, 2020). By analogy, the presumptive human window is ~8-14 gestational weeks, although direct human GT mechanistic data are limited (Sharpe, 2020).

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Petiot et al. investigated whether FGFR2‑IIIb regulates AR in a positive feedback loop. Immunohistochemistry at E16.5 showed that AR distribution in Fgfr2‑IIIb null embryos was indistinguishable from wild type, indicating that FGF10/FGFR2‑IIIb signaling does not regulate AR expression in GT at this stage; thus, a downstream‑to‑upstream feedback loop was not detected. Consistently, conditional deletion of Shh at E11.5 did not alter Fgfr2 mRNA levels, arguing against a Shh→Fgfr2 feedback at E14.5 (Gredler et al., 2015).

Conversely, Sonic hedgehog (SHH) signaling interacts with androgen pathways during GT masculinization. SHH is expressed in the urethral plate epithelium and signals via Gli2 in adjacent mesenchyme; Gli2 mutants show reduced expression of androgen‑responsive, sexually dimorphic genes (e.g., Mafb, Fkbp5) and fail to be masculinized by exogenous androgens despite normal testicular testosterone, indicating hedgehog signaling is required to maintain androgen responsiveness in GT mesenchyme (Miyagawa et al., 2011). In GT, SHH also lies upstream of mesenchymal Fgf10 (in contrast to limb, where FGFR2‑IIIb acts upstream of Shh), providing a route by which hedgehog signaling can reinforce the mesenchymal ligand side of the FGF10-FGFR2‑IIIb axis (Petiot et al., 2005; Revest et al., 2001). Taken together, current data support a potential feed‑forward influence wherein SHH/Gli2 enhances androgen responsiveness and promotes Fgf10 expression, indirectly supporting AR‑dependent FGF signaling in GT; direct SHH‑dependent regulation of Fgfr2 has not been observed in GT (Gredler et al., 2015).

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Taxonomy: Empirical applicability is strongest in mice, where genetic loss‑of‑function and pharmacological perturbation studies establish that reduced AR activity diminishes the FGF10-FGFR2‑IIIb axis in GT tissues and produces urethral/preputial defects (Petiot et al., 2005; Gredler et al., 2015). In rats, most evidence comes from in vivo anti‑androgen exposure models within the masculinization programming window (MPW), which feminize urethral development and induce hypospadias, consistent with diminished AR‑dependent control of pathways governing urethrogenesis (Welsh et al., 2008; Seifert et al., 2008; Sinclair et al., 2016). In humans, evidence is indirect and correlative: AR and 5α‑reductase type 2 are present in the right fetal tissues to support local DHT production (Kim et al., 2002), FGFR2 variants have been reported in familial hypospadias (Beleza‑Meireles et al., 2007), FGF10 SNPs associate with risk in a large case-control cohort (Carmichael et al., 2013), and postnatal foreskin from hypospadiac boys shows altered FGF/FGFR2 immunostaining patterns (Haid et al., 2020). Cross‑species extrapolation is biologically plausible given conserved epithelial-mesenchymal FGF signaling in external genital development, but differences in distal urethral morphogenesis and endocrine timing across mammals should be noted (Amato et al., 2022; Sharpe, 2020). Mammalia, given conserved androgen‑responsive epithelial-mesenchymal signaling during external genital development, with caveats on interspecies differences in distal urethral morphogenesis and endocrine control (Amato et al., 2022; Sharpe, 2020)

Life Stage: This KER operates during the androgen‑dependent phase of external genital development. In mouse, the critical programming window for penile masculinization is approximately E14.5-E17.5, with urethral septation/internalization and preputial morphogenesis continuing through late gestation to birth (Seifert et al., 2008; Amato et al., 2022). In rat, the MPW is GD15.5-18.5, during which suppression of androgen action has maximal effects on urethral development (Welsh et al., 2008; Sharpe, 2020). Evidence does not support activity of this specific regulatory relationship in postnatal life; AR‑dependent FGF regulation in adult tissues (e.g., prostate) is context‑specific and not directly informative for prenatal GT (Donjacour et al., 2003).

Sex: The KER has greater downstream morphogenetic consequence for males. In organ culture, both male and female GTs show dose‑dependent down‑regulation of Fgfr2‑IIIb and Fgf10 with flutamide, and DHT rescues Fgfr2‑IIIb, indicating that the AR→FGF10/FGFR2‑IIIb linkage operates in both sexes at the molecular level (Petiot et al., 2005). In vivo, AR antagonism during the programming window feminizes male urethral development, whereas females show little change in urethral position, supporting primary applicability to males with moderate applicability to females (Seifert et al., 2008).

References

List of the literature that was cited for this KER description. More help

Amato, C. M., Yao, H. H.-C., & Zhao, F. (2022). One tool for many jobs: Divergent and conserved actions of androgen signaling in male internal reproductive tract and external genitalia. Frontiers in Endocrinology, 13, 910964. https://doi.org/10.3389/fendo.2022.910964 (PMID: 35846302)

Beleza-Meireles, A., Lundberg, F., Lagerstedt, K., Zhou, X., Omrani, D., Frisén, L., & Nordenskjöld, A. (2007). FGFR2, FGF8, FGF10 and BMP7 as candidate genes for hypospadias. European Journal of Human Genetics, 15(4), 405-410. https://doi.org/10.1038/sj.ejhg.5201777 (PMID: 17264867)

Carmichael, S. L., Ma, C., Choudhry, S., Lammer, E. J., Witte, J. S., & Shaw, G. M. (2013). Hypospadias and genes related to genital tubercle and early urethral development. Journal of Urology, 190(5), 1884-1892. https://doi.org/10.1016/j.juro.2013.05.061 (PMID: 23714460; PMC: PMC4103581)

Donjacour, A. A., Thomson, A. A., & Cunha, G. R. (2003). FGF-10 plays an essential role in the growth of the fetal prostate. Developmental Biology, 261(1), 39-54. https://doi.org/10.1016/S0012-1606(03)00250-1 (PMID: 12941620)

Furutani, T., Watanabe, T., Tanimoto, K., Hashimoto, T., Koutoku, H., Kudoh, M., Shimizu, Y., Kato, S. and Shikama, H. (2002). Stabilization of androgen receptor protein is induced by agonist, not by antagonists. Biochem. Biophys. Res. Commun. 294, 779-784.

Gelmann, E. P. (2002). Molecular biology of the androgen receptor. Journal of Clinical Oncology, 20(13), 3001-3015. https://doi.org/10.1200/JCO.2002.10.018 (PMID: 12089231)

Gredler, M. L., Seifert, A. W., & Cohn, M. J. (2015). Tissue-specific roles of Fgfr2 in development of the external genitalia. Development, 142(12), 2203-2212. https://doi.org/10.1242/dev.119891 (PMID: 26081573; PMC: PMC4483768)

Haid, B., Pechriggl, E., Nägele, F., Dudas, J., Webersinke, G., & Rammer, M. (2020). FGF8, FGF10 and FGF receptor 2 in foreskin of children with hypospadias: An analysis of immunohistochemical expression patterns and gene transcription. Journal of Pediatric Urology, 16(1), 41.e1-41.e10. https://doi.org/10.1016/j.jpurol.2019.10.007 (PMID: 31676182)

Harada, M., Omori, A., Nakahara, C., Nakagata, N., Akita, K., & Yamada, G. (2015). Tissue-specific roles of FGF signaling in external genitalia development. Developmental Dynamics, 244(6), 759-773. https://doi.org/10.1002/dvdy.24277

Kim, K. S., Liu, W., Cunha, G. R., Russell, D. W., Huang, H., Shapiro, E., & Baskin, L. S. (2002). Expression of the androgen receptor and 5 alpha-reductase type 2 in the developing human fetal penis and urethra. Cell and Tissue Research, 307(2), 145-153.

Leung, M. C. K., Hutson, M. S., Seifert, A. W., Spencer, R. M., & Knudsen, T. B. (2016). Computational modeling and simulation of genital tubercle development. Reproductive Toxicology, 64, 151-161. https://doi.org/10.1016/j.reprotox.2016.05.005 (PMID: 27181558)

Miyagawa, S., Moon, A., Haraguchi, R., Inoue, C., Harada, M., Nakahara, C., Suzuki, K., Nakagata, N., Ng, R. C., Akita, K., Yamada, G. (2011). The role of sonic hedgehog-Gli2 pathway in the masculinization of external genitalia. Endocrinology, 152(7), 2894-2903. (PMID: 21586556)

Ohuchi, H., Hori, Y., Yamasaki, M., Harada, H., Sekine, K., Kato, S., & Itoh, N. (2000). FGF10 acts as a major ligand for FGF receptor 2 IIIb in mouse multi-organ development. Biochemical and Biophysical Research Communications, 277(3), 643-649. https://doi.org/10.1006/bbrc.2000.3721

Petiot, A., Perriton, C. L., Dickson, C., & Cohn, M. J. (2005). Development of the mammalian urethra is controlled by Fgfr2-IIIb. Development, 132(10), 2441-2450. https://doi.org/10.1242/dev.01778 (PMID: 15843416)

Quigley, C. A., De Bellis, A., Marschke, K. B., El-Awady, M. K., Wilson, E. M., & French, F. S. (1995). Androgen receptor defects: historical, clinical, and molecular perspectives. Endocrine reviews, 16(3), 271-321.

Revest, J. M., Spencer-Dene, B., Kerr, K., De Moerlooze, L., Rosewell, I., & Dickson, C. (2001). Fibroblast growth factor receptor 2-IIIb acts upstream of Shh and Fgf4 and is required for limb bud maintenance but not for the induction of Fgf8, Fgf10, Msx1, or Bmp4. Developmental Biology, 231(1), 47-62. https://doi.org/10.1006/dbio.2000.0144

Seifert, A. W., Harfe, B. D., & Cohn, M. J. (2008). Cell lineage analysis demonstrates an endodermal origin of the distal urethra and perineum. Developmental Biology, 318(1), 143-152. https://doi.org/10.1016/j.ydbio.2008.03.017 (PMID: 18439576; PMC: PMC3047571)

Seifert, A. W., Zheng, Z., Ormerod, B. K., & Cohn, M. J. (2010). Sonic hedgehog controls growth of external genitalia by regulating cell cycle kinetics. Nature Communications, 1, Article 23. https://doi.org/10.1038/ncomms1020

Sharpe, R. M. (2020). Androgens and the masculinization programming window: Human-rodent differences. Biochemical Society Transactions, 48(4), 1725-1735. https://doi.org/10.1042/BST20200200 (PMID: 32830844)

Sinclair, A. W., Cao, M., Pask, A., Baskin, L., & Cunha, G. R. (2017). Flutamide-induced hypospadias in rats: A critical assessment. Differentiation, 94, 37-57. https://doi.org/10.1016/j.diff.2016.12.001 (PMID: 28043016)

Thomson, A. A., & Cunha, G. R. (1999). Prostatic growth and development are regulated by FGF10. Development, 126(16), 3693-3701.

Welsh, M., Saunders, P. T., Fisken, M., Scott, H. M., Hutchison, G. R., Smith, L. B., & Sharpe, R. M. (2008). Identification in rats of a programming window for reproductive tract masculinization, disruption of which leads to hypospadias and cryptorchidism. The Journal of clinical investigation, 118(4), 1479-1490.