Influence of Temperature on the Differential Expression of Sox9 and Foxl2 Genes during Embryonic Development in Nile Tilapia (Oreochromis niloticus) and Their Relationship with Polymorphisms in the Regulatory Region

Abstract

We aimed to characterize the sex differentiation expression of Sox9 and Foxl2 genes and polymorphisms using quantitative polymerase chain reaction and conventional polymerase chain reaction (PCR) method, respectively. We evaluated the coding regions of these genes in two Nile tilapia (Oreochromis niloticus) strains subjected to different temperatures to examine the relationship between polymorphisms within the regulatory region and Sox9 and Foxl2 gene expression during the development phase. The experiment included 64 animals at 6 days post-fertilization (dpf). Animal tissue samples were collected periodically at 7-day intervals, including day zero (0) until day 28. There was a significant difference (P < 0.001) in Sox9 and Foxl2 gene expression and variation over the collection period between treatments and strains. There was a 12–19 dpf moderate increase (*P < 0.05) of Sox9 in the Supreme strain at 35°C. This strain overexpressed Foxl2 1.5- to 2-fold (P < 0.001) at 19 dpf. Temperature (35°C) substantially increased Sox9 and Foxl2 expression at 19 dpf. Only Sox9 exhibited polymorphic regions. Using temperature did not cause significant Sox9 expression in either Oreochromis niloticus strain. Moreover, there was no direct relationship between sex determination and expression regulation of other genes responsible for this. Hence, we could not establish a significant relationship between sex reversal by temperature and gene expression in the Oreochromis niloticus.