Gene Variant of Barrier to Autointegration Factor 2 (Banf2w) Is Concordant with Female Determination in Cichlids

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.

A Chromosome-Level Genome Assembly of Mozambique Tilapia (Oreochromis mossambicus) Reveals the Structure of Sex Determining Regions

“…hornorum and P . mariae with ZW sex determining system ( Curzon et al, 2021 ). However, the W-specific banf was not identified in the female fish of Family2 with ZW sex determining system based on the re-sequencing data, suggesting the existence of a different female sex determiner in O .…”

“…hornorum and P . mariae ( Curzon et al, 2021 ). The major sex-determination gene on LG23 is a duplication of amh , which is known to play an important role in the vertebrate sex-determination network ( Li et al, 2015 ; Pan et al, 2021b ).…”

Absence of Figla-like Gene Is Concordant with Femaleness in Cichlids Harboring the LG1 Sex-Determination System

“…However, different fish species have adopted different MKR genes to initiate the sex cascade, which determines the fate of the bipotential sex gonad [ 11 ]. During the last year, two new MKRs ( bmpr1b and banf2w ) have been suggested [ 12 , 13 ], in addition to ten SD MKRs detected previously [ 11 ]. In most cases in fishes, as in other vertebrates, Y and W differ from X and Z, respectively, in the number of copies and sequences [ 11 , 14 ].…”

“…In general, purebred species of tilapia possess monofactorial SD systems such as WZ/ZZ and XX/XY [ 30 , 31 ]. Nevertheless, On , Oa , and their hybrids have been reported to segregate for three SD loci on LGs 1 [ 32 , 33 ], 3 [ 12 , 34 ], and 23 [ 14 , 35 , 36 ]. Purebred Oa and On have been reported to segregate for the SD systems on LGs 3 (WZ/ZZ) and 23 (XX/XY), respectively.…”

A single intronic single nucleotide polymorphism in splicing site of steroidogenic enzyme hsd17b1 is associated with phenotypic sex in oyster pompano, Trachinotus anak

“…Genotypic sex determination (GSD) systems have evolved independently and repeatedly, involving various master sex determining (MSD) genes [3,4]. In teleosts, almost all the identified MSD genes are members of gene families involved in gonad development, including DMRT1, members of the SOXA and B1 protein families and TGF-β signalling pathway as reviewed by Pan et al [5] or genes that interact with these pathways [6,7], except for a few exceptions [8,9]. A recent study in the fish genus Seriola revealed that a steroidogenic enzyme gene, hsd17b1 evolved to be an MSD gene, providing an exceptional case of the diversity of MSD genes [10].…”