Expression of the Krüppel-type zinc finger protein rKr2 in the developing nervous system

Zinc finger transcription factors of the Krüppel-class figure prominently in cell fate specification and differentiation in the nervous system. One of the Krüppel-type genes that was originally cloned from an oligodendrocyte library by virtue of its homology with the prototypic Krüppel motif is the rat rKr2 gene (Pott et al., 1995). In primary cultures of rat glial cells, the rKr2 protein was only present in the oligodendrocyte lineage, predominantly in progenitors. Ninety percent of A2B5(+) oligodendrocyte progenitors displayed rKr2 immunoreactivity, while most MBP(+) oligodendrocytes lacked detectable rKr2. A similar pattern was found in vivo, in which the peak expression of rKr2 in the oligodendrocyte lineage of rats coincided with the wave of progenitor proliferation in early postnatal life. The subventricular zone, a source of neuronal and glial progenitors, displayed intense staining for rKr2 at late embryonic and postnatal stages. In the adult, cells within the remnants of this germinal zone continued to express rKr2 protein strongly. Some populations of mature neurons also displayed rKr2 immunostaining. Astrocytes and microglia were not labeled with the polyclonal anti-rKr2 antibody in vitro or in vivo. At all developmental stages, the rKr2 protein was localized to the nucleus. The stage-specific expression pattern and the subcellular localization of rKr2 recommend a role for this Krüppel-type gene in the progression of neural stem cells and in the early development of the oligodendrocyte lineage.