The distribution of heat shock proteins in the nervous system of the unstressed mouse embryo suggests a role in neuronal and non-neuronal differentiation

Heat shock proteins (Hsps) act as molecular chaperones and are generally co nstitutively expressed in the absence of stress. Hsps are also inducible by a variety of stressors whose effects could be disastrous on the brain. It has been shown previously that Hsps are differentially expressed in glial a nd neuronal cells, as well as in the different structures of the brain. Thi s differential expression has been related to specific functions distinct f rom their general chaperone function, such as intracellular transport. We i nvestigated here the constitutive expression of 5 Hsps (the small Hsp, Hsp2 5, the constitutive Hsc70 and Hsp90 beta, the mainly inducible Hsp70 and Hs p90 alpha), and of a molecular chaperone, TCP-1 alpha during mouse nervous system development. We analyzed, by immunohistochemistry, their distributio n in the central nervous system and in the ganglia of the peripheral nervou s system from day 9.5 (E9.5) to day 17.5 (E17.5) of gestation. Hsps are exp ressed in different cell classes (neuronal, glial, and vascular). The diffe rent proteins display different but often overlapping patterns of expressio n in different regions of the developing nervous system, suggesting unique roles at different stages of neural maturation. Their putative function in cell remodeling during migration or differentiation and in protein transpor t is discussed. Moreover we consider Hsp90 function in cell signaling and t he role of Hsp25 in apoptosis protection.