Developmental tissue expression and phylogenetic conservation of stathmin, a phosphoprotein associated with cell regulations.

Stathmin is a 19-kDa phosphoprotein presumably involved in regulations of cell proliferation, differentiation, and functions as an intracellular relay for extracellular signals activating diverse second messenger pathways. Antisera prepared against the whole protein or against two peptides (residues 15-27 and 134-149) recognized the two isoforms (alpha and beta) of stathmin in their different phosphorylated states on immunoblots. Also, the possible existence of a family of stathmin-related proteins is suggested by the detection with some sera of proteins of 17, 21, and 60 kDa in brain. Stathmin and its diverse molecular forms were detected in all mouse tissues tested, in varying concentrations. Depending on the tissue, it is 2-100 times more abundant in the neonate than in the adult. It is most abundant in brain at both developmental stages, the protein levels being paralleled by the expression of the corresponding mRNA as detected with a specific cDNA probe. Antibodies directed against the rat protein also reacted with stathmin-like proteins in the brain of other mammals, birds, reptiles, amphibians, and some fish species, and the various isoforms could be recognized on immunoblots. In conclusion, our results suggest that stathmin is most likely involved in two distinct types of regulations: 1) "developmental" regulations, related to cell proliferation, differentiation, and maturation, and 2) "functional" regulations mostly at the adult stage, and typically in the nervous system. In addition, stathmin is also phylogenetically well conserved at least in vertebrates. Together, these observations support the proposed ubiquitous nature and general importance of stathmin in biological regulations.