Receptivity of the Human Male and Female Fetal Caudal Genital Ligament to Gonadal Hormones

In first-trimester human fetuses, caudal genital ligaments in both sexes express receptors for androgens, estrogens, and INSL3 — the "passive female default" model doesn't hold in humans

Journal: Reproduction (Cambridge, England) | Published: 2026-04-05 | Type: Journal Article | PMID: 41949886 Authors: Desdoits-Lethimonier C et al. (Irset/Inserm & Centre Hospitalier Universitaire de Rennes) Funding/COI: Public funding (Inserm, Université de Rennes, EHESP). No COI declared.

Summary

Standard embryology frames testicular descent as hormone-driven (male) and the female caudal genital ligament (CGL) as developing by passive default — in the absence of male hormones. This study challenges that framing using actual human fetal tissue. First-trimester CGLs in both sexes express receptors for androgens, estrogens (ESR1), and INSL3 (via RXFP2), with multiple receptor subtypes rising as gestation progresses. The finding that female CGLs are hormonally receptive — not inert — raises pointed questions about xenoestrogen exposure during early development.

Claims

• CGLs from both male and female first-trimester human fetuses express RXFP2 (INSL3 receptor), androgen receptor (AR), estrogen receptors, and TGF-beta family receptors
• RXFP2 expression increased with gestational age in both sexes; expression was spatially heterogeneous and not linked to cell proliferation
• AR expression tended to increase with age, more markedly in males
• SRD5A2 (5α-reductase type 2) and ESR1 mRNA both increased significantly with age in both sexes, but with clear sexual dimorphism in their patterns
• ACVR2B and BMPR1B (TGF-beta receptors) decreased with age in both sexes; AMHR2 was stable
• In boys with uni- or bilateral cryptorchidism, receptor gene expression was consistent regardless of age, ligament position, or gross appearance

Study Quality

This is a descriptive molecular study using scarce human first-trimester fetal tissue, supplemented by CGL samples from cryptorchidism cases. The methodological approach is appropriately multimodal: real-time qPCR for quantification, in situ hybridization for spatial localization, and immunostaining where material permitted. Using three complementary techniques reduces reliance on any single method and strengthens confidence in the expression findings.

The abstract does not report sample sizes — a significant omission for work built on rare biological specimens. First-trimester human fetal tissue is inherently scarce, and statistical power for detecting age-related trends in such samples is almost certainly limited. This is a hypothesis-generating, not mechanistic, study: it identifies what receptors are present, not whether they are functionally active or what downstream effects they produce.

Red Flags

• Sample size not disclosed in abstract; these studies typically involve very small n by necessity
• Descriptive design only — receptor mRNA expression is not evidence of functional signaling response
• No receptor activity, binding assay, or downstream pathway readout reported
• The inference from "female CGLs express ESR1" to "xenoestrogen vulnerability" is speculative and untested within this study
• Cryptorchidism findings are essentially null: expression consistency across varied presentations tells you the receptor layer isn't where cryptorchid and normal cases diverge, but offers no alternative explanation

Strengths

• Rare human fetal tissue — most mechanistic CGL literature is from rodents; first-trimester human data carries genuine informational value
• Multi-method approach (qPCR + ISH + immunostaining) is appropriate for the tissue type
• Includes cryptorchidism tissue alongside healthy fetal samples, adding clinical context
• Public funding, no declared conflicts of interest
• Directly addresses a known gap: rodent models have dominated this field, and their translatability to humans has been assumed rather than tested

Verdict

This paper earns its place in the literature by doing something genuinely difficult — characterizing receptor expression in human first-trimester fetal tissue rather than inferring it from mice. The core finding, that female CGLs are not hormonally inert but actively express androgen and estrogen receptors with age-dependent increases, is worth taking seriously as a foundation for future mechanistic work. The cryptorchidism arm is the weakest section: uniform receptor expression across affected boys is interesting but uninterpretable without a clear comparator or functional endpoint. Read this as a map of the molecular landscape, not a mechanistic account. The xenoestrogen hypothesis it floats at the end is the most policy-relevant implication, but this study doesn't test it — that work remains to be done.