Changes in expression patterns of stress protein genes during population growth of the rotifer Brachionus plicatilis

Abstract

We amplified three kinds of cDNA fragments encoding stress proteins from the rotifer Brachionus plicatilis by polymerase chain reaction in order to investigate the molecular mechanisms underlying mediation of its lifespan. The stress proteins were heat shock protein 70 (HSP70), glucose regulated protein 94 (GRP94) and ubiquitin-conjugating enzyme, which have been suggested to extend the lifespans of fruitfly and yeast. The isolated clones consisted of 579, 776 and 257 bp in the above order, respectively, and their deduced amino acid sequences showed 81, 59 and 48% identities, respectively, with corresponding sequences from the nematode Caenorhabditis elegans. As rotifers in the stationary phase can extend their lifespan we subsequently performed northern blot analysis on rotifers both in the exponential and stationary phases. The mRNA levels of HSP70 and GRP94 in the exponential growth phase were 2.5 and 1.6 times higher, respectively, than those in the stationary phase, whereas those of ubiquitin-conjugating enzyme did not differ between rotifers in the two phases. These results suggest that stress proteins are not directly responsible for the extension of rotifer lifespan, but another factor(s) is possibly involved. Our results, however, demonstrated that these genes are useful as molecular markers for monitoring the population growth of rotifer.