Comparative Transcriptomic Dynamics During Embryonic Gonadal Development in Turtles with Genotypic and Temperature-Dependent Sex Determination

In vertebrates, the sex of an individual is determined by its genotype (Genotypic Sex Determination or GSD) or by the environmental temperature experienced during the thermosensitive period (TSP) of embryogenesis (Temperature-dependent Sex Determination or TSD). Here, I leverage the transcriptomes of three turtles – Chrysemys picta (TSD), Podocnemis expansa (TSD) and Apalone spinifera (GSD) using bioinformatics approaches to test the hypothesis that the TSD and GSD networks are essentially the same, but that qualitative and/or quantitative differences in expression of key elements results in sex determination by temperature rather than by genotypic constitution. Our RNA-seq dataset from these turtles incubated at male- and female- producing temperature (high/low for GSD), span five developmental stages including the thermosensitive period. We used the newly assembled C. picta genome to perform a genome-guided assembly of the transcriptomes. The transcriptomes of A. spinifera and P. expansa are assembled de novo to account for the evolutionary divergence between these species and C. picta, which could skew genome-guided assemblies. Results from the subsequent transcript quantification, abundance normalization and differential expression analyses to identify differentially regulated genes between male- and female- producing temperatures across developmental stages, along with the composition and regulation of the GSD and TSD gene networks will be discussed. These data will help uncover novel genes underlying different biological pathways that participate in gonadogenesis and candidate thermosensitive TSD genes. This study sheds light on the genetic basis of a complex system (sexual phenotype), its environmental susceptibility (TSD v GSD), and evolutionary potential (divergence among species).