Expression of the transcription factor Pax6 in the adult rat dentate gyrus

The transcription factor Pax6 is expressed in precursor cells during embryonic CNS development, and it plays an important role in the regulation of cell proliferation and neuronal fate determination. Pax6-expressing cells are also present in the adult hippocampal dentate gyrus and subventricular zone/rostral migratory stream, regions in which nepronal precursors exist during adult life. In the adult dentate gyrus, precursor cells are located in the innermost portion of the granule cell layer, and Pax6-expressing nuclei are most abundant in this region. To examine the putative role of Pax6 in adult hippocampal neurogenesis, we have studied the proliferative activity, distribution, and phenotype of Pax6-expressing cells by using immunohistochemistry. Our results indicate that Pax6 is intensely expressed in proliferating precursors of the adult dentate gyrus. Pax6 is also expressed in nonproliferating cells, which may correspond to resting progenitor cells and to granule neurons in their very early developmental stages, because this transcription factor is strongly down-regulated during granule neuron differentiation. However, a small subpopulation of hilar mature neurons and certain astrocytes of the adult hippocampus also express Pax6. Although the precise roles of this transcription factor in the adult brain remain to be determined, our findings support the idea that its function in the control of cell proliferation and neuronal fate determination during embryogenesis is also operative in the adult hippo-campus. However, the expression of Pax6 in astrocytes and certain mature neurons may indicate the existence of other roles for this transcription factor in this telencephalic region. (c) 2005 Wiley-Liss, Inc.