Abstract
Oreochromis fishes exhibit variability of sex-determination (SD) genes whose characterization contributes to understanding of the sex differentiation network, and to effective tilapia farming, which requires all-male culture. However, O. niloticus (On) amh is the only master-key regulator (MKR) of SD that has been mapped (XY/XX SD-system on LG23). In O. aureus (Oa), LG3 controls a WZ/ZZ SD-system that has recently been delimited to 9.2 Mbp, with an embedded interval rich with female-specific variation, harboring two paics genes and banf2. Developing genetic markers within this interval and using a hybrid Oa stock that demonstrates no recombination repression in LG3, we mapped the critical SD region to 235 Kbp on the orthologous On physical map (p < 1.5 × 10−26). DNA-seq assembly and peak-proportion analysis of variation based on Sanger chromatograms allowed the characterization of copy-number variation (CNV) of banf2. Oa males had three exons capable of encoding 90-amino-acid polypeptides, yet in Oa females, we found an extra copy with an 89-amino-acid polypeptide and three non-conservative amino acid substitutions, designated as banf2w. CNV analysis suggested the existence of two to five copies of banf2 in diploidic Cichlidae. Disrupting the Hardy–Weinberg equilibrium (p < 4.2 × 10−3), banf2w was concordant with female determination in Oa and in three cichlids with LG3 WZ/ZZ SD-systems (O. tanganicae, O. hornorum and Pelmatolapia mariae). Furthermore, exclusive RNA-seq expression in Oa females strengthened the candidacy of banf2w as the long-sought LG3 SD MKR. As banf genes mediate nuclear assembly, chromatin organization, gene expression and gonad development, banf2w may play a fundamental role inducing female nucleus formation that is essential for WZ/ZZ SD.
Highlights
A master key regulator (MKR) of sex determination (SD) is a gene capable of turning on an alternative gene-regulation program to that maintained at the default homogametic state (XX or ZZ) [1,2,3]
One of the female-specific haplotypes had a large deletion in an intronic region, but it did not differ at the protein level from the corresponding male form
We describe banf2 genes of four cichlid species (Oa, Oreochromis tanganicae (Ot), O. urolepis hornorum (Oh) and Pelmatolapia mariae (Pm))
Summary
A master key regulator (MKR) of sex determination (SD) is a gene capable of turning on an alternative gene-regulation program to that maintained at the default homogametic state (XX or ZZ) [1,2,3]. MKR controlling it, i.e., sex-determining region Y (SRY) [4,5]. Exhibit a remarkable variability of genetic and environmental mechanisms for SD [8] with distinct MKRs in different or even closely related species [9,10]. According to the dominant gene hypothesis, the heterogametic sex chromosomes (Y or W) often differentiate from their X or Z counterparts by an extra gene copy, which is structurally different from its autosomal ortholog [8]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have