Discovery of Two Distinct Small Heat Shock Protein (HSP) Families in the Desert Fish Poeciliopsis

Abstract

The availability of a genetically pedigreed fish colony at the University of Connecticut has made possible a detailed investigation of the heat shock response of a Poikilothermic vertebrate. During the past 12 years, two tropical species, six desert species and numerous interspecific hybrids of viviparous fishes in the genus Poeciliopsis have been studied. In the natural environment, these animals occupy thermally distinct niches that range in latitude from southern Arizona, through the Sonora Desert of northwestern Mexico across tropical southern Mexico and Central America into Columbia in South America. The diverse habitats include: (1) relatively stable tropical rivers with narrow annual and daily temperature ranges, (2) unstable streams that cross subtropical desert where temperatures range from 4 to 40°C seasonally and undergo rapid daily changes of as much as 22°C in 3h, and (3) pristine headwaters at higher elevations in the foothills of the Sierra Madre Occidental. When we began these studies, no detailed analysis of diversity in HSP families had been attempted. In fact, many investigators considered heat shock genes to be so highly conserved evolutionarily, that a search for variation would be fruitless. This view turned out to be overly pessimistic. Our approach to exploring HSP diversity employed high resolution two-dimensional Polyacrylamide gels to display protein isoforms at the level of denatured polypeptide chains. This strategy allowed a relatively rapid screening of multiple HSP families compared with the time required to clone and sequence all of the members of even one multigene family. Analyses of protein patterns also had the advantage of screening out nonfunctional genes and allowing a comparison of the levels of expression of different isoforms.