Gene expression of male pathway genes sox9 and amh during early sex differentiation in a reptile departs from the classical amniote model

Abstract

Background Sex determination is the process whereby the bipotential embryonic gonads become committed to differentiate into testes or ovaries. In genetic sex determination (GSD), the sex determining trigger is encoded by a gene on the sex chromosomes, which activates a network of downstream genes; in mammals these include SOX9, AMH and DMRT1 in the male pathway, and FOXL2 in the female pathway. Although mammalian and avian GSD systems have been well studied, few data are available for reptilian GSD systems. Results We conducted an unbiased transcriptome-wide analysis of gonad development throughout differentiation in central bearded dragon (Pogona vitticeps) embryos with GSD. We found that sex differentiation of transcriptomic profiles occurs at a very early stage, before the gonad consolidates as a body distinct from the gonad-kidney complex. The male pathway genes dmrt1 and amh and the female pathway gene foxl2 play a key role in early sex differentiation in P. vitticeps, but the central player of the mammalian male trajectory, sox9, is not differentially expressed in P. vitticeps at the bipotential stage. The most striking difference from GSD systems of other amniotes is the high expression of the male pathway genes amh and sox9 in female gonads during development. We propose that a default male trajectory progresses if not repressed by a W-linked dominant gene that tips the balance of gene expression towards the female trajectory. Further, weighted gene expression correlation network analysis revealed novel candidates for male and female sex differentiation. Conclusion Our data reveal that interpretation of putative mechanisms of GSD in reptiles cannot solely depend on lessons drawn from mammals.

Sexual antagonism and sex determination in three syngnathid species alongside a male pregnancy gradient

“…In HE, among the SBGs with the highest log fold-change and Fst in both organs was amh – one of the key genes involved in vertebrate gonadal differentiation pathway (Morrish and Sinclair 2002; Yatsu et al 2016; Nagahama et al 2021; Wagner et al 2023). Besides that, amh also appears to have functions in the brain (Pfennig et al 2015; Silva and Giacobini 2021).…”

AMHY and sex determination in egg-laying mammals

“…In therians, AMH expression is upregulated in response to increased SOX9 expression after gonad specification in the developing mouse testis by E12.5 when it results in loss of the Müllerian ducts in males 43 . Echidna AMHY expression is more similar to non-mammalian vertebrates (chicken, turtle, American alligator and bearded dragon, P. vitticeps) in which Amh expression also precedes that of Sox9 54,55,56,57 . Such co-expression of autosomal Amh and sex determining Amhy in the gonad during sexual differentiation is also seen in the Northern Pike (Esox lucius) 27 .…”

Understanding the genetic sex-determining mechanism in Hyla eximia treefrog inferred from H-Y antigen

“…In vertebrates, sex-determining mechanisms can be mainly subdivided into two types according to the nature of the main sex-determining factor [1,2]: (1) genetic sex determination (GSD) in which the genomic factor plays a relevant biological role (such as chromosomal) or (2) environmental sex determination (ESD) in which the main factor is an environmental cue (such as temperature or light). In mammals (including humans) and birds, sex-determining mechanisms are controlled by XX/XY (XX females/XY male heterogamety) or ZZ/ZW (ZW females heterogamety/ZZ males) chromosomes, respectively [3][4][5]; which contain either a dominant gene on the heteromorphic sex chromosome (such as SRY in humans) or a dosage-sensitive gene on the homomorphic sex chromosome (such as DMRT1 in birds). In many reptiles and fish, the environment can determine or influence the sex of developing embryos [6].…”