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

Teleosts show varied master sex determining (MSD) genes and sex
determination (SD) mechanisms, with frequent turnovers of sex chromosomes.
Tracing the origins of MSD genes and turnovers of sex chromosomes in a
taxonomic group is of particular interest in evolutionary biology. Oyster
pompano (Trachinotus anak), a marine fish, belongs to the family
Carangidae, in which 17b-hydroxysteroid dehydrogenase 1 (hsd17b1) has
repeatedly evolved to a MSD gene. Using whole genome resequencing, a
single SNP at Chromosome 24 was identified to be strictly associated with
phenotypic sex, with females being the heterozygous sex. This SNP is
located in a splicing site at the first exon/intron boundary of hsd17b1.
The Z-linked SNP results in malfunction of all spliced isoforms, whereas
the W-linked isoforms were predicted to have open reading frames (ORF)
that are conserved among vertebrates, suggesting that hsd17b1 is a female
determining gene. The differential alternative splicing patterns of ZZ and
ZW genotypes were consistently observed both in undifferentiated stages
and differentiated gonads. We observed elevated recombination around the
SD locus and no differentiation between Z and W chromosomes. The extreme
diversity of mutational mechanisms that hsd17b1 evolves to a MSD gene
highlights frequent in situ turnovers between sex chromosomes in the
Carangidae.