Title : Relative expression of growth hormone receptor (GHR1) and its truncated variant (GHR1t) in adults and larvae of flatfish Paralichthys adspersus
The flatfish Paralichthys adspersus is a commercial species with sexual dimorphism, in which females growing faster than males. This characteristic will generate that one goal in the coming breeding programs is controlling the sex ratio to encourage a female bias in the culture population. However, another way to modify this growth pattern in P. adspersus is editing males to get higher growth. In that sense, we are testing a hypothesis based on the fact that in early adult stages, females express more levels of ghr1 than males, while males express more ghr1t, a truncated variant of ghr1, than females, acting as a negative regulator of growth. As the first step to test our hypothesis, we assessed the expression levels of ghr1 and ghr1t in the liver and muscle of adult males and females and the ventral section of pre-metamorphic, metamorphic, and post-metamorphic larvae of P. adspersus. For relative expression, we choose three housekeeping genes (HKGs) based on previous gene expression studies of P. adspersus and Paralichthys olivaceus. HKGs were ß-actin (ACTB), ß-tubulin (TUBB), and ubiquitin C (UBCE). Our results showed that the expression level of full version of ghr1 (ghr1f) in the liver is not significant in both sexes (P > 0.05), while the expression level of ghr1t is higher in males than in females (P < 0.05), presenting an expression ratio of ghr1t in males to females near 2:1. In the case of muscle, expression levels of ghr1f and ghr1t were not significant for both sexes (P > 0.05). Comparison between tissues showed that expression levels of ghr1f and ghr1t were higher in liver than muscle (P < 0.05), with a higher differential expression for ghr1tf. As a second step, we amplified the intron 8, generating a PCR product of 973 bp. Through the amplification and sequencing of this intron and the ghr1t 3´UTR we were able to characterize the presence of a polyadenylation signal sequence. It remains to be determined why this transcription termination signal is favored in males, increasing the ghr1t levels.