Integrated analysis of hsc70-based mammalian molecular chaperone system

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The mammalian cytosolic hsc70 chaperone system requires type I DnaJ cochaperone(s) for mitochondrial protein import and refolding of denatured proteins in vitro. We reported that two of type I DnaJ cochaperones, DjA1 and DjA2, are ubiquitously present in mammalian tissues and functionally equivalent in the in vitro assays. To explore the function of DjA1 and DjA2 in mouse, we generated DnajA1-null and DnajA2-null mice by targeted disruption. We also generated Tom34-null mice.The mouse Tom34 gene has two alternative initial exons and are transcribed two mRNAs that differs only in the 5'-proximal sequences corresponding to the two initial exons (exon 1a and 1b). Tom34 mRNA with exon 1a (Tom34a) is expressed ubiquitously, while that with exon 1b (Tom34b) is expressed only in mature testicular germ cells. The Tom34-/- mice were viable and grew normally. Male as well as female Tom34-/- mice were fertile. In vitro-preprotein import into isolated mitochondria showed no apparent difference between Tom34-/- and wild-type mice. These results indicate that Tom34 is dispensable for mouse growth and development under optimal conditions.The DnajA1-/- as well as DnajA2-/- male mice showed slight growth retardation and were almost sterile. The weights of testis from DnajA1-/- mice were reduced to about 50% compared to that of DnajA1+/- and wild-type littermates. While those from DnajA2-/- mice were more severely reduced. The cross-section of testis from DnajA1-/- mice revealed sloughing of round spermatids and apparent increase of apoptosis in pachytene-stage spermatocytes. RT-PCR analysis showed marked decreases in expression of several stage-specific genes of germ cells. However, transplantation of GFP-spermatogonia into DnajA1-/- mice indicated defect in supporting somatic cells. While DnajA2-/- mice had defect in spermatocyte.