TISSUE-SPECIFIC EXPRESSION OF AN HSC90 GENE AND NUCLEAR TRANSLOCATIONOF THE HSC90-RELATED PROTEIN DURING AMPHIBIAN EMBRYOGENESIS

Expression and distribution of a constitutive member of the 90 kDa hea t-shock protein family, named HSC90, was investigated during amphibian embryonic development. By Northern blot analysis, two hsp90 transcrip ts (2.5 and 3 kb) which displayed differing developmental regulation w ere detected during embryogenesis. Expression of the larger transcript (3 kb), which encodes an HSC90-related protein, decreased until the g astrula stage. However, zygotic transcription for this hsc90 gene was found to start from the neurula stage, and the corresponding zygotic h sc90 transcript was specifically located by whole mount in situ hybrid ization in the anterior neural tube of a late neurula embryo. Later, i n a tailbud embryo, hsc90 transcripts were detected in the cephalic re gion, neural tube, eye vesicles, branchial and mandibular arches and s omites. Distribution of the HSC90-related protein was also analysed by immunohistochemistry throughout embryogenesis. As expected, the prote in was strongly expressed in the cytoplasm, mainly in the periplasmic area of embryonic tissue cells. Interestingly, HSC90 was also transien tly detected in the nuclear area, with this nuclear transfer depending on the chromatin condensation state, up to the blastula stage. During the process of gastrulation, nuclear translocation of HSC90 was also observed at the level of the blastopore dorsal lip, exclusively in cel ls undergoing invagination.