Multiple evidences suggest sox2 as the main driver of a young and complex sex determining ZW/ZZ system in turbot (Scophthalmus maximus)
Matínez, Paulino; Robledo, Diego; Taboada, Xoana; Blanco, Andrés; Gómez-Tato, Antonio; Álvarez-Blázquez, B. (Blanca); Cabaleiro, Santiago; Piferrer, Francesc; Bouza, Carmen; Viñas, Ana M.
A major challenge in evolutionary biology is to find an explanation for the variation in
sex-determining (SD) systems across taxa and to understand the mechanisms driving
sex chromosome differentiation. We studied the turbot, holding a ZW/ZZ SD system
and no sex chromosome heteromorphism, by combining classical genetics and
genomics approaches to disentangle the genetic architecture of this trait. RAD-Seq was
used to genotype 18,214 SNPs on 1,135 fish from 36 families and a genome wide
association study (GWAS) identified a ~ 6 Mb region on LG5 associated with sex (P <
0.05). The most significant associated markers were located close to sox2, dnajc19 and
fxr1 genes. A segregation analysis enabled narrowing down the associated region and
evidenced recombination suppression in a region overlapping the candidate genes. A
Nanopore/Illumina assembly of the SD region using ZZ and WW individuals identified
a single SNP fully associated with Z and W chromosomes. RNA-seq from 5-90 day-old
fish detected the expression along the gonad differentiation period of a short non-coding
splicing variant (ncRNA) included in a vertebrate-conserved long non-coding RNA
overlapping sox2. qPCR showed that sox2 was the only differentially expressed gene
between males and females at 50-55 days post fertilization, just prior the beginning of
gonad differentiation. More refined information on the involvement of secondary
genetic and environmental factors and their interactions on SD was gathered after the
analysis of a broad sample of families. Our results confirm the complex nature of SD in
turbot and support sox2 as its main driver.
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