Title

Analysis of diversity in the heat shock response of the desert topminnow {\it Poeciliopsis\/}

Date of Completion

January 1997

Keywords

Biology, Molecular|Biology, Cell|Biology, Zoology

Degree

Ph.D.

Abstract

The heat shock response is an adaptive response mounted at the cellular level when organisms are exposed to many types of environmental stress, and involves the increased synthesis of a specific set of proteins. These proteins, the heat shock proteins (HSPs), appear to be involved in short-term survival of stressful conditions. It was found that inducible HSPs exhibited significant diversity within and among a group of closely related fish species (genus Poeciliopsis), in contrast to what might be predicted from the highly conserved nature of HSPs across diverse taxa. The distribution of HSP diversity in these species was consistent with what is known about their evolutionary history; also, differences in the make-up of HSP families between tropical and desert species indicated HSP families could be subject to both natural selection and genetic drift over a relatively short evolutionary time frame. However, constitutively expressed members of the Hsp70 family were identical in all species, indicating that they were subject to a much higher degree of evolutionary constraint. This may indicate that the two classes of Hsp70, even though they are highly related, may play different roles in the cell.^ A detailed characterization of HSPs and the regulation of their synthesis was performed in one species, P. lucida. Identification of different HSPs was accomplished by comparison to similar HSPs from other organisms, taking advantage of the ability of heterologous DNA probes and antibodies to interact with Poeciliopsis HSP sequences. An unusual characteristic of the heat shock response in P. lucida was the induction of multiple divergent small HSPs (sHSPs). Through sequence analysis, one sHSP was shown to be homologous to the human Hsp27 while another was homologous to Xenopus Hsp30. This was the first demonstration that members of two distinct sHSP families are present in a single species. ^