Functional Studies Of Rat Dnaj-like Protein Rdjl

Spermatogenesis is a complex progress of cell division and differentiation leading to the formation of mature spermatozoa, during which many genes are transcripted and translated under stringent temporal and spatial regulation. The identification and study of these differentially expressed genes is of great value to delineate the mechanism of spermatogenesis. In our study, the method of DDRT-PCR combined with segmentation of rat seminiferous tubules was applied to investigate differential gene expression in germ cells between different stages. One of the ESTs identified was used as probe to screen the cDNA library of rat testis and the full-length cDNA of a rat DnaJ like protein (GenBank accession no. AF154849) was obtained. It consisted of 950bp with an open reading frame of 669bp, encoding a 223 amino acid protein. The N-terminal region had a conservative J domain of about 70 amino acid residues, so it was designated rDJL-a novel member of DnaJ protein family. Inspection of the amino acid sequence reveals that rDJL contained only the highly conserved J domain, therefore rDJL belongs to the type III subgroup of DnaJ proteins. Type I and type II DnaJ proteins have a more highly conserved J domain within their own groups and tend to interact with a broader range of substrates, whereas type III J proteins, have a lower level of conservation and a more restricted substrate specificity .It is well established that DnaJ proteins serve as co-chaperones of Hsp70 proteins and are necessary for stimulation of interacting Hsp70 ATPase activity. The chaperone function of Hsp70 proteins is regulated by members of the DnaJ protein family through direct interaction of different Hsp70 and DnaJ-like protein pairs . DnaJ proteins are involved in a variety of functions such as facilitation of protein folding, protein traffic, gene expression regulation, uncoating of clathrin-coated vesicles etc. To date, several DnaJ proteins related to spermatogenesis have been analyzed. MSJ-1 is a DnaJ homolog specifically expressed in germ cells at haploid stages, which interacts with mUBPy and may be important for acrosome formation and centrosome adjustment during spermatid development. Study on the role of type I DnaJ homolog DjA1 revealed that loss of DjA1 in mice led to severe defects in spermatogenesis that involve aberrant androgen signaling.