Molecular cloning and characterization of meichroacidin (male meiotic metaphase chromosome-associated acidic protein).

We have isolated a cDNA clone encoding a germ cell specific protein from an expression cDNA library prepared from the mouse testis, using testis-specific polyclonal antibodies. Sequence analysis of the cDNA revealed that the deduced amino acid sequence consisted of 284 residues, including a nominal repeat structure in the N-terminal region. Northern blot analysis revealed the presence of a transcript of 1.3 kb exclusively expressed in the testis and ovary, but at relatively low levels in the ovary. In contrast, no other tissues and organs expressed significant levels of the transcript. Expression of the mRNA in the testis was first detected on day 14 in postnatal development. Western blot analysis showed the presence of the protein with a molecular weight of approximately 40 kDa and an isoelectric point of 4.9. The protein was exclusively found in the testis and ovary, but in a far lesser amount in the ovary as was the case with the transcript. Immunohistochemical examination revealed that the protein was predominantly present in the cytoplasm in pachytene spermatocytes through to round spermatids. However, during the disappearance of the nuclear envelope at both the first and second meiotic divisions, the protein was localized around the metaphase chromosomes and spindles. Because of this, the name meichroacidin which stands for male meiotic metaphase chromosome-associated acidic protein is proposed for this antigen. The highly regulated stage-specific expression of meichroacidin and its specific association with the metaphase chromosomes and spindles suggest that the protein plays important roles in male meiosis. Copyright 1998 Academic Press.