PAX6 and microcephaly: In Hmmrtm1a/tm1amice, however, the predominant phenotype observed was microcephaly, which may be explained by a decreased mitotic rate for Pax6+ radial glial cells; consistent with the recent observations in Hmmrm/m brains, we did observe rare Hmmrtm1a/tm1a brains at E14.5 with cortex enlargement.