A Duplicated, Truncated amh Gene Is Involved in Male Sex Determination in an Old World Silverside

Abstract

A master sex-determining gene, the Y chromosome-linked anti-Müllerian hormone (amhy) gene, has been described in two New World atheriniform species but little is known on the distribution, evolution, and function(s) of this gene in other Atheriniformes. Interestingly, amhy has been found to coexist with temperature-dependent sex determination (TSD), providing a unique opportunity to explore the interplay between genotypic and environmental sex determination. In this study, the search for an amhy homolog was extended to an Old World atheriniform, the cobaltcap silverside Hypoatherina tsurugae (Atherinidae). The full sequences, including the coding and noncoding regions, of the autosomal amh (amha) and a putative amhy were obtained. The deduced Amha and Amhy proteins comprised 511 and 340 amino acids (aa), respectively. PCR analysis with genomic DNA from wild adults and from laboratory-reared juveniles revealed a high, but not complete association of ∼95% between amhy and maleness. The spatiotemporal expression of amhy and amha during gonadal sex differentiation was analyzed by qRT-PCR and in situ hybridization (ISH). amhy transcription (in amhy-positive larvae) started before and peaked during histological differentiation of the gonads whereas amha was negligible during the same period in both genotypes. These results demonstrate that the amhy, although with some structural differences in relation to the amhy of some New World atheriniforms, is strongly associated with maleness and probably important for testicular development in this Old World atheriniform. Thus, amhy is a candidate sex determination gene in cobaltcap silverside and it will be key to scrutinize the mechanism of sex determination in this species.

The rise and fall of the ancient northern pike master sex determining gene

“…Because the conserved Amh domains that are altered in the amhby genes in these two species are needed for proper protein secretion and interaction between Amh and its receptor 3 , it is unclear how these truncated Amhby proteins could still serve as functional MSD proteins. A similar duplication and truncation of an amh MSD gene has already been reported in the cobaltcap silverside (Hypoatherina tsurugae), another teleost 22 . In addition, other cases of MSD genes having evolved through duplication / truncation of their ancestral copy have also been described, such as the sdY MSD gene in Salmonids and the putative amhr2by MSD gene in yellow perch, Perca flavescens, demonstrating that preservation of all ancestral domains is not always necessary for a duplicated protein to assume an MSD role 13,23,24 .…”

“…), poeciliids, tilapiine cichlids, salmonids, and sticklebacks, in which different SD systems, sex chromosomes and MSD genes were found even in closely related species [14][15][16][17][18] . Apart from the Oryzias family [19][20][21][22][23][24][25][26][27][28][29] and the salmonids 18,[30][31][32] , however, relatively few studies have explored the evolution of SD systems and the fate of MSD genes within an entire group of closely related species.…”

Identification of the master sex determining gene in Northern pike (Esox lucius) reveals restricted sex chromosome differentiation

“…bonariensis , the sister species of the Patagonian pejerrey, a male-specific amhy was found to interact with temperature in determining sex [19], and in the ling cod, Ophiodon elongatus , a male-specific duplicate of amh was also identified using molecular marker sequences [43]. More recently, a duplicated copy of amh was found in an Atheriniformes species, Hypoatherina tsurugae , and is suspected to be involved in male sex determination [44]. Besides amh , its canonical receptor, amhrII , has also been shown to play a pivotal role as a MSD gene in the Tiger Pufferfish, Takifugu rubripes [45].…”

Identification of the master sex determining gene in Northern pike (Esox lucius) reveals restricted sex chromosome differentiation

“…Besides these three examples, association of amh duplicates with phenotypic sex was also found in other teleosts: in O. bonariensis , the sister species of the Patagonian pejerrey, a male-specific amhy was found to interact with temperature in determining sex [19], and in the ling cod, Ophiodon elongatus, a male-specific duplicate of amh was also identified using molecular marker sequences [43]. More recently, a duplicated copy of amh was found in an Atheriniformes species, Hypoatherina tsurugae, and is suspected to be involved in male sex determination [44]. Our phylogenetic analysis on Amh sequences from several teleost species revealed that the three confirmed male-specific Amh duplications are independent, lineage-specific events rather than the product of shared ancestry.…”