Expression analysis and characterization of an autosome-localized tesk1 gene in half-smooth tongue sole (Cynoglossus semilaevis)

• An autosome-localized Altesk1 gene encoding “long-type” Tesk protein was characterized in half-smooth tongue sole.
• Epigenetic regulation might account for the high expression of Altesk1 in ovary at 210-day and 1-year stage.
• In situ hybridization reveals that Altesk1 is predominantly localized in oocytes.
• This is the first report that tesk1 gene may be involved in female-specific process, e.g. oogenesis.

Testis-specific protein kinase 1 (tesk1) represents a conserved gene family functioning in many cellular processes. In this study, we cloned and characterized an autosome-localized tesk1 gene (Altesk1) from Cynoglossus semilaevis. The open reading frame consists of 2088 nucleotides and encodes a 665 amino acid polypeptide. Phylogenetic analyses show that vertebrate Tesk1s are divided into two clusters based on protein length and AlTesk1 belongs to “long-type” group. Semi-quantitative PCR reveals that Altesk1 is predominantly expressed in ovary, despite of relatively low detection in some other tissues. Among different development stages, Altesk1 transcripts are only observed in ovary samples of 210-day and 1-year fish. In situ hybridization analyses have further confirmed its major localization in oocyte cells. Comparison of methylation patterns in different sexual genotypes reveals the low methylation level of Altesk1 promoter in female, which is consistent with Altesk1 high expression level in female. Taken together, this is the first time that tesk1 gene has been found to show female-biased expression and in view of this, we postulate that AlTesk1 might be involved in some cellular processes specific in ovary, e.g. oogenesis.