Impact of ecologically relevant heat shocks on Hsp developmental function in the vetigastropod Haliotis asinina

Heat shock proteins (Hsps) are essential for cellular maintenance, normal differentiation and morphogenesis, and protection against a range of environmental stresses. It is unknown which of these roles takes precedence when they are required simultaneously. Here we examined the impact of thermal stress on the complex developmental expression patterns of HasHsp70 and HasHsp90A in the vetigastropod Haliotis asinina. We find that near-lethal heat shocks do not alter the spatial demarcation of Hsp expression despite such treatments impacting on the external character of the embryos. Using a suite of molecular markers that are both coexpressed with the Hsps (i.e. in ventrolateral ectoderm and prototroch) and expressed in tissues that have lower (basal) Hsp expression (e.g. serotonergic nervous system and shell gland), we determined that Hsp-expressing tissues do not incur markedly less thermal damage than adjacent tissues. To explore the relationship of Hsp expression with sensitivity of specific cell territories to heat shock, we focused on the formation of the prototroch, a tissue where HasHsp70 and HasHsp90A are coexpressed. By heat shocking at specific developmental stages, we determined that the most sensitive period of prototroch development is during its early specification and differentiation, which overlaps with the time the Hsps are expressed at their highest levels in these cells. This correlation is consistent with heat shock impairing the function of Hsps in regions of the H. asinina embryo undergoing morphogenesis.