Septin 3 is a novel member of the
septin subfamily of
GTPase domain
proteins. Human
septin 3 was originally cloned during a screening of genes expressed in human
teratocarcinoma cells induced to differentiate with
retinoic acid. Alternative splicing of the
septin 3 gene transcript produces two
isoforms, A and B, in the human brain, though their regional expression and physiological function remain to be determined. The purpose of the present study was to identify the expression patterns of human
septin 3 isoforms in normal human brain and a human
neuroblastoma cell line, SH-SY5Y, after
retinoic acid-induced differentiation. The expression and distribution patterns of
septin 3 isoforms A and B were similar and resembled that of another
septin, CDCrel-1.
Septin 3A and 3B were expressed in normal human brain in a region-specific manner, with the highest level in the temporal cortex and hippocampus and the lowest level in the brainstem regions. Prominent immunoreactivity was observed diffusely in the neocortices in association with neuropils and punctate structures suggestive of synaptic junctions. Immunoprecipitation studies revealed that
septin 3A, 3B, and CDCrel-1 form a complex in the frontal cortex of human brain. These findings, taken together, suggest that
septin 3A and 3B, along with CDCrel-1, play some fundamental role(s) in synaptogenesis and neuronal development.