TSKS, testis-specific serine kinase substrate, is expressed in the testis and is downregulated in cancerous testicular tissue, in comparison with adjacent normal tissue. TSKS expression is very low to undetectable in seminoma, teratocarcinoma, embryonal, and Leydig cell tumours, while high in testicular tissue adjacent to tumours which contain pre-malignant carcinoma in situ [1]. Recently it has been shown in human testis to be localised to the equatorial segment of ejaculated human sperm. The finding of a TSKS family member in mature sperm suggests that this family of kinases might play a role in sperm function [2]. TSKS is localised during spermiogenesis to the centrioles of post-meiotic spermatids, where it reaches its greatest concentration during the period of flagellogenesis [3].

1: Identification and characterization of a novel human testis-specific kinase substrate gene which is downregulated in testicular tumors. Scorilas A, Yousef GM, Jung K, Rajpert-De Meyts E, Carsten S, Diamandis EP; Biochem Biophys Res Commun. 2001;285:400-408. PMID:11444856

2: Expression analysis of the human testis-specific serine/threonine kinase (TSSK) homologues. A TSSK member is present in the equatorial segment of human sperm. Hao Z, Jha KN, Kim YH, Vemuganti S, Westbrook VA, Chertihin O, Markgraf K, Flickinger CJ, Coppola M, Herr JC, Visconti PE; Mol Hum Reprod. 2004;10:433-444. PMID:15044604

3: TSKS concentrates in spermatid centrioles during flagellogenesis. Xu B, Hao Z, Jha KN, Zhang Z, Urekar C, Digilio L, Pulido S, Strauss JF 3rd, Flickinger CJ, Herr JC; Dev Biol. 2008;319:201-210. PMID:18495105