Creatine kinase in trout male germ cells: purification, gene expression, and localization in the testis.

High creatine kinase (CK) activity (16.5 +/- 7.6 IU/mg) is present in trout spermatozoa. In order to partly characterize the CK isozyme predominantly present in sperm and to study the expression of this protein in spermatogenesis, we purified to homogeneity a CK (s-CK) from trout sperm, by nitrogen cavitation followed by two chromatography steps (DEAE-Trisacryl and Blue Sepharose). Specific antisera to 5-CK were developed. A cDNA encoding for a CK named TCK1, and whose transcript shows enhanced testicular expression, was previously isolated from trout testis (Garber et al., 1990: Biochim Biophys Acta 1087:256-258). A CK subunit expressed in vitro by this cDNA cross-reacts with anti-s-CK. A 21-amino-acid residue sequence near the N-terminus of s-CK is identical to the cDNA-derived sequence of TCK1, which is unlike any previously reported CK sequence. Using in situ hybridization, the TCK1 mRNA was detectable in primary and secondary spermatocytes and in early spermatids. Immunohistochemical staining of testis and various organs revealed that s-CK was confined to testis and, in this organ, to late spermatids and spermatozoa. In gill, some cells exhibited a positive signal, but another study rules out the presence of s-CK in this organ (Garber et al., 1990: Biochim Biophys Acta 1087:256-258). These results demonstrate that s-CK/TCK1 is a germ cell-specific protein, the transcription of which starts in meiotic germ cells, while translation starts in late spermatids.