Differential expression of Hoxa-2 protein along the dorsal-ventral axis ofthe developing and adult mouse spinal cord

We have used synthetic oligopeptides derived from the coding sequence of th e murine Hoxa-2 protein to produce polyclonal antibodies that specifically recognize the Hoxa-2 recombinant protein. Immunohistochemical studies revea l a distinct pattern of spatial and temporal expression of Hoxa-2 protein w ithin the mouse spinal cord which is concomitant with the cytoarchitectural changes occurring in the developing cord. Hoxa-2 protein is predominantly detected in the nuclei of cells in the ventral mantle region of 10-day-old mouse embryos. Islet-l, a marker for motor neurons was also shown to be co- localized with Hoxa-2 in nuclei of cells in this region. As development pro gresses from 10-days to 14-days of gestation, Hoxa-2 protein expression gra dually extends to the dorsal regions of the mantle layer. The Hoxa-2 protei n expression pattern changes at 16-days of embryonic development with stron g expression visible throughout the dorsal mantle layer. In 18-day-old and adult mouse spinal cords, Hoxa-2 protein was expressed predominantly by cel ls of the dorsal horn and only by a few cells of the ventral horn. Double l abeling studies with an antibody against glial fibrillary acidic protein (G FAP, an astrocyte-specific intermediate filament protein) showed that withi n the adult spinal cord, astrocytes rarely expressed the Hoxa-2 protein. Ho wever, Hoxa-2 and GFAP double-labeled astrocytes were found in the neopalli al cultures, although not all astrocytes expressed Hoxa-2. Hoxa-2 expressin g oligodendrocyte progenitor cells were also identified after double-labeli ng with O4 and Hoxa-2 antibodies; although cells in this lineage that have begun to develop a more extensive array of cytoplasmic processes were less likely to be Hoxa-2 positive. The early pattern of Hoxa-2 protein expressio n across transverse sections of the neural tube is temporally and spatially modified as each major class of neuron is generated. This congruence in th e expression of the Hoxa-2 protein and the generation of neurons ia the cor d suggests that the Hoxa-2 protein may contribute to dorsal-ventral pattern ing and/or to the specification of neuronal phenotype. Dev Dyn 1999;216:201 -217. (C) 1999 Wiley-Liss, Inc.