Role of the imprinted allele of the p57Kip2 gene in mouse neocortical development

Imprinted genes are expressed from only one allele in a parent of origin–specific manner. The cyclin-dependent kinase inhibitor p57Kip2 (p57) is encoded by an imprinted gene, with the paternal allele being silenced. The possible expression and function of the paternal allele of p57 have remained little studied, however. We now show that the paternal allele of the p57 gene is expressed at a low level in the developing mouse neocortex. Surprisingly, the central nervous system-specific conditional deletion of the paternal allele ( pat cKO) at the p57 locus resulted in a marked reduction in brain size. Furthermore, pat cKO gradually reduced the number of neural stem-progenitor cells (NPCs) during neocortical development, and thus reduced the number of upper-layer neurons, which were derived from late-stage NPCs. Our results thus show that the paternal allele of the p57 locus plays a key role in maintenance of NPCs during neocortical development.