Research paper Expression analysis and characterization of an autosome-localized tesk1 gene in half-smooth tongue sole (Cynoglossus semilaevis) Wenteng Xu a,b , Hailong Li a,b , Ning Zhang a,b , Zhongdian Dong a,b , Na Wang a,b , Changwei Shao a,b , Songlin Chen a,b, ⁎ a Yellow Sea Fisheries Research Institute, CAFS, Key Lab for Sustainable Development of Marine Fisheries, Ministry of Agriculture, Qingdao 266071, China b Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China abstract article info Article history: Received 12 November 2015 Received in revised form 21 January 2016 Accepted 4 February 2016 Available online 8 February 2016 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. Phy- logenetic 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 con- firmed its major localization in oocyte cells. Comparison of methylation patterns in different sexual genotypes re- veals 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 expres- sion and in view of this, we postulate that AlTesk1 might be involved in some cellular processes specific in ovary, e.g. oogenesis. © 2016 Elsevier B.V. All rights reserved. Keywords: Cynoglossus semilaevis Altesk1 Expression pattern Methylation profile Oogenesis 1. Introduction As one of the most important economic aquaculture species in China, half-smooth tongue sole (Cynoglossus semilaevis) has emerged as a new model to study sex determination and differentiation for its deciphered genome, obvious sexual dimorphism, and sex reversal phe- nomenon (Chen et al., 2014). Half-smooth tongue sole employs ZW/ZZ sex chromosome system and the female fish can be phenotypically re- versed to male, namely pseudo-male, in certain environmental condi- tions, e.g. high temperature (Chen et al., 2014; Shao et al., 2014). Since the body size of female fish usually reaches 2–4 times as big as that of male or pseudo-male ones, researchers aim to increase female ratio of population for enhancing productivity (Chen et al., 2007). One theoret- ical solution is to cross the female (ZW) and pseudo-male (ZW) to ob- tain WW super female, which could be then utilized for full-female breeding. However, the pseudo-male cannot produce the functional W sperm (Chen et al., 2014), thus exploiting genes involved in spermatogenesis would benefit for understanding the molecular mech- anism of W sperm absence and possibly provide feasible solutions. As is well known, protein kinases participate in almost all cellular processes and their involvement in spermatogenesis to affect fertiliza- tion is frequently discussed in recent work (Jenardhanan and Mathur, 2014; Kornbluth and Fissore, 2015), so testis-specific protein kinase 1 (tesk1) gene family has been selected as the promising candidates be- cause of its conserved function in mammalian spermatogenesis. Tesk1 represents a group of serine/threonine protein kinases and is nominated due to its first identification in testis, specific in testicular germ cells of mouse and rat after 18 or 20–22 postnatal days, respectively (Toshima et al., 1995; Toshima et al., 1998). The findings strongly suggested its function in spermatogenesis, or to be more specific, spermiogenesis process. Soon after that, Toshima et al. found an alternative transcript of tesk1 that showed ubiquitous tissue distribution and via promoter- linked lacZ method they proposed that tesk1 might participate in nerve development apart from spermatogenesis (Toshima et al., 1999, 2001). Subsequent study obtained accumulating evidence about the in- teraction of Tesk1 and Sprouty, which exerted effect on nerve formation by regulating microtubule- and actin cytoskeleton (Leeksma et al., 2002; Tsumura et al., 2005; Chandramouli et al., 2008; Johne et al., 2008). In a more recent work, up-regulation of tesk1 after rat nerve in- jury further supported its role in nerve regeneration (Lou et al., 2012). The versatile behavior of mammalian Tesk1 has greatly enlarged our Gene 582 (2016) 161–167 Abbreviations: A, adenosine; aa, amino acid(s); bp, base pair(s); C, cytidine; G, guanosine; S, second; T, thymidine; tesk1, testis-specific protein kinase 1; TGD, teleost- specific duplication event; WGD, whole genome duplication. ⁎ Corresponding author. E-mail address: chensl@ysfri.ac.cn (S. Chen). http://dx.doi.org/10.1016/j.gene.2016.02.010 0378-1119/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Gene journal homepage: www.elsevier.com/locate/gene