Upregulation of the HLH Id gene family in neural progenitors and glial cells of the rat spinal cord following contusion injury

Spinal cord injury (SCI) leads to a complex sequence of cellular responses, including astrocyte activation, oligodendrocyte death, and ependymal cell proliferation. Inhibitors of DNA binding (Id1, Id2, ld3) belong to a helix- loop-helix (HLH) gene family. ld genes have been implicated in playing a vi tal role in the proliferation of many cell types, including astrocytes and myoblasts. In the present study, the expression of Id family members in spi nal cord after contusion injury was investigated by in situ hybridization. Id1, Id2, and ld3 mRNA expression was upregulated 5 mm rostral and caudal t o the lesion center, and reached maximal levels 3 days after SCI. In additi on, cell populations expressing Id1, Id2, and ld3 mRNA were maximally incre ased 3 days after SCI. The increase in Id2 and ld3 mRNA expression and Id2 and ld3 mRNA+ cells was still observed at 8 days. The Id mRNA expressing ce lls were phenotyped by combining immunostaining of cell-specific markers wi th in situ hybridization. Glial fibrillary acidic protein (GFAP)+ astrocyte s were found to express all three ld mRNA, whereas S-100 alpha+ astrocytes only expressed high levels of Id2 and ld3 mRNA. Cells having a neural proge nitor morphology and the marker nestin appeared after SCI and they expresse d Id1, Id2, and Id3 mRNA. Interestingly, some Rip+ oligodendrocytes located in the areas close to the central canal expressed Id3 mRNA after injury. I n conclusion, Id genes are upregulated in a time-dependent manner in astroc ytes, oligodendrocytes, and neural progenitor subpopulations after SCl, sug gesting that they play major roles in cellular responses following SCI. (C) 2001 Wiley-Liss, Inc.