Expression, regulation and possible function of heat shock genes (Hsp47, Hsp70, Hsp90α and Hsp90β) during normal development and under stress-conditions in zebrafish
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The objectives of my thesis work to examine the similarities and differences that exist among the control and stress induced expression patter of the above mentioned heat shock genes during zebrafish embryogenesis. Northern blot analysis revealed stress- and gene-specific differences in the heat and ethanol-induced activation of these genes. Furthermore, spatial differences in the mRNA distribution of hsp genes following heat shock and ethanol-treatment were identified using whole-mount in situ hybridization. The second aspect of my thesis deals with constitutive expression of 'hsp47' during the embryonic development of zebrafish. Based on biochemical evidence, Hsp47 is regarded as a collagen-specific chaperone. I show that strong expression of 'hsp47' mRNA is co-incident predominantly with expression of the type II collagen gene ('col2al') in a number of chondrogenic and non-chondrogenic tissues including the notochord, otic vesicle and developing fins. Notochordal expression of both genes is disrupted in'floating head' ('flh') and ' no tail' ('ntl') embryos, which lack properly differentiated notochords. Surprisingly, no 'hsp47' mRNA is detectable in the strongly 'col2a1'-expressing cells of the floor plate and hypochord, indicating that the two genes are not strictly co-regulated. In the third part of my thesis I examined the possible roles Hsp90 might play during zebrafish myogenesis as it was suggested by our previous studies that revealed coordinate expression of 'hsp90'α and ' myoD', one of the major myogenic regulatory factors (J. Sass, PhD thesis). Utilizing the Hsp9O-binding agent, geldanamycin (GA), I show that GA-treatment during zebrafish gastrulation and early somitogenesis specifically disrupts the development of a group of muscle cells known as the muscle pioneers. However, development of the notochord, which provides many of the signals required for proper somite patterning, is normal in GA-treated embryos. Furthermore, the PKA-dependent mechanism by which responding cells of the paraxial mesoderm are thought to be specified appears to be intact in treated embryos and the ' myoD'-expressing adaxial cell progenitors of muscle pioneers develop. The data indicate that Hsp90 is required during the conversion of adaxial cells into muscle pioneers and that many of the signaling and differentiation events occurring in the pathway prior to this point are unaffected.