Expression and localization of five members of the testis-specific serine kinase (Tssk) family in mouse and human sperm and testis

Abstract

Members of the testis-specific serine/threonine kinases (Tssk) family may have a role in sperm differentiation in the testis and/or fertilization. To gain insight into the functional relevance of these kinases, their expression was examined both at the mRNA and protein levels. Quantitative PCR analysis confirmed that all five Tssk mRNAs are almost exclusively expressed postmeiotically in the testis. Recombinant mouse and human Tssks were cloned and used for validation of an array of commercial and custom-made antibodies against Tssks. Immunolocalization in mouse testis, and in mouse and human sperm, showed that Tssk1, Tssk2, Tssk4 and Tssk6, but not Tssk3, were present in mouse sperm and in germ cells from mouse testis. TSSK1, TSSK2 and TSSK6 were also detected in human sperm, while TSSK3 was absent. In both mouse and human sperm, Tssk1 was partially soluble, while Tssk2, Tssk4 and Tssk6 were insoluble in non-ionic detergents. In vitro recombinant TSSK2 activity assays showed maximum enzymatic activity at 5 mM Mg(2+) and a Km for ATP of ∼10 µM. These, observations together with findings that the Tssk1/Tssk2 double knock-out as well as the Tssk6 null mice are sterile without presenting other detectable defects, suggest that these kinases could be used as targets for male contraception.

Taf7l cooperates with Trf2 to regulate spermiogenesis

“…A second group of Taf7l-regulated genes [Odf1, testis-specific serine kinase 6 (Tssk6), sperm motility kinase 2a/b (Smok2a/b), and Smok3a/b] have been implicated in sperm structure and motility during late stages of spermatogenesis ( Fig. 2 B and C) (27)(28)(29)(30). Additionally, a group of genes that have generally been classified as ones involved in metabolism are significantly down-regulated in the testis upon loss of Taf7l and likely reflect both metabolic and spermatogenesis functions.…”

Heat Shock Protein 90 Functions to Stabilize and Activate the Testis-specific Serine/Threonine Kinases, a Family of Kinases Essential for Male Fertility

“…TSSK3 protein could not be detected in testis or sperm by Western blotting or immunofluorescence, although the TSSK3 mRNA was detected (9). It was proposed that TSSK3 protein may only exist transiently in vivo and, thus, is not readily detected (9).…”

“…For example, null male mice for CAMK4, casein kinase 2␣Ј catalytic subunit, and cyclin-dependent kinase 2 (CDK2) 3 are infertile (6 -8). The testis-specific serine/threonine kinases (TSSKs) are exclusively expressed in spermatids (9), and three of them, namely TSSK1, -2, and -6 (also known as small serine/threonine kinase (SSTK)), have been evaluated by genetic deletion in mice and shown to be essential for male fertility (10 -12). The TSSK family consists of six members but TSSK5 does not appear to possess all the subdomains that are required for a kinase (9).…”

“…The testis-specific serine/threonine kinases (TSSKs) are exclusively expressed in spermatids (9), and three of them, namely TSSK1, -2, and -6 (also known as small serine/threonine kinase (SSTK)), have been evaluated by genetic deletion in mice and shown to be essential for male fertility (10 -12). The TSSK family consists of six members but TSSK5 does not appear to possess all the subdomains that are required for a kinase (9). The TSSKs have high homology to one another, with TSSK3 and -6 as the smallest members consisting of only N-and C-lobes of the kinase catalytic domain (9,11).…”

“…The TSSK family consists of six members but TSSK5 does not appear to possess all the subdomains that are required for a kinase (9). The TSSKs have high homology to one another, with TSSK3 and -6 as the smallest members consisting of only N-and C-lobes of the kinase catalytic domain (9,11). TSSK4 has a 13-amino acid extension at the N terminus, a 36-amino acid extension at the C terminus, and an insertion of 11 amino acids between the kinase subdomains VII and VIII in the C-lobe.…”