Molecular characterization of a novel, developmentally regulated small embryonic chaperone from Caenorhabditis elegans.

Low molecular weight chaperones inhibit protein aggregation and facilitate refolding of partially denatured polypeptides in cells subjected to physical and chemical stresses. The nematode Caenorhabditis elegans provides a system amenable for investigations on roles for chaperone proteins in normal homeostasis and development. We characterized a C. elegans gene and cDNAs that encode a novel, small embryonic chaperone-like protein (SEC-1) that is composed of 159 amino acids. The central core of SEC-1 (residues 45-126) is approximately 40% identical with a corresponding segment of mammalian Hsp27 and alphaB crystallin. Expression of SEC-1 in Escherichia coli confers thermotolerance on the bacterium. SEC-1 mRNA is evident only in C. elegans oocytes and developing embryos. Translation and accumulation of SEC-1 protein is temporally coupled with a prolonged burst of intense protein synthesis and rapid mitogenesis during early embryogenesis. As the rate of protein synthesis decreases during late embryogenesis, levels of SEC-1 and its cognate mRNA decline precipitously. Induction/deinduction of SEC-1 is precisely regulated by intrinsic developmental factors rather than extrinsic stresses. In vivo injection of C. elegans oocytes with antisense oligonucleotides that complement the 5'-end of SEC-1 mRNA arrests nematode development at an early stage after fertilization. Thus, SEC-1 appears to be adapted to perform essential functions in early embryogenesis.