<i>Emx1</i> and <i>Emx2</i> Show Different Patterns of Expression During Proliferation and Differentiation of the Developing Cerebral Cortex in the Mouse

<jats:title>Abstract</jats:title><jats:p>Insights into the complex structure of the forebrain and its regulation have recently come from the analysis of the expression of genes that are likely to be involved in regionalization of this structure. We cloned four new homeo box genes, <jats:italic>Emx1, Emx2, Otx1</jats:italic> and <jats:italic>Otx2</jats:italic>, and we showed that in day 10 mouse embryos their expression domains are continuous regions of the developing brain contained within each other in the sequence <jats:italic>Emx1 < Emx2 < Otx1 < Otx2.</jats:italic> Recently <jats:italic>Otx1</jats:italic> has been found to be specifically expressed during neurogenesis of layers 5 and 6 in the developing cerebral cortex. In order to better understand the role of <jats:italic>Emx1</jats:italic> and <jats:italic>Emx2</jats:italic> in the maturation of the cortex we analysed by <jats:italic>in situ</jats:italic> hybridization their expression patterns in the developing mouse cerebral cortex, from embryonic day 12.5 to adulthood. We found that <jats:italic>Emx2</jats:italic> is expressed exclusively in proliferating cells of the ventricular zone whereas <jats:italic>Emx1</jats:italic> is expressed in both proliferating and differentiated neurons, throughout the cortical layers and during all the developmental stages examined. Therefore, <jats:italic>Emx2</jats:italic> gene products might control some biological parameters of the proliferation of cortical neuroblasts or of the subsequent cell migration of postmitotic neurons, leaving the cortical germinal zone. Conversely, <jats:italic>Emx1</jats:italic> expression, which is confined exclusively to the dorsal telencephalon, characterizes most cortical neurons during proliferation, differentiation, migration and postnatal development and maturation.</jats:p>