Role of the Otx1 gene in cell differentiation of mammalian cortex

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Abstract
This study analyses by immunohistochemical methods the effects of the deletion of the Otx1 gene on 12 areas of the cerebral cortex and on neurons expressing Ca-binding proteins (CaBP), such as parvalbumin (Pv) and calbindin-D28K (Cb). We found that the deletion of the Otx1 gene modified differently the various cortical areas. The decrease in cortical thickness ranged from 29.35 to 9.85% and the reduction in cellular population from 35.90 to 3.65% in the different cortical areas. The influence of the Otx1 gene concerns all cortical layers with variable effects on different cortical areas. The cellular population of cerebral cortex considered as a whole was reduced by 20.67%, Pv-positive (Pv+) cells by 58.01% and Cb-positive (Cb+) cells by 51.54%. The quantitative distribution of Pv+ and Cb+ cells varied independently in the different cortical areas. Topographic analysis of CaBP cells in Otx1-null mice (Otx1(-/-)) showed that Pv+ cells were principally distributed in layers IV and V and Cb+ cells in layers V and VI. Given that in the development of wild-type mice both cell types first appear in deep layers and later spread to superficial ones, the segregation of CaBP neurons in inner layers of Otx1(-/-) animals is an index of the immaturity of the cerebral cortex of these animals. This study showed that the Otx1 gene has a more complex role than previously reported, as it is involved in the maturation and differentiation of various cerebral cortices, and, specifically, in the development of CaBP cells.