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First published online 3 January 2007
doi: 10.1242/dev.02764

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Controlled overexpression of Pax6 in vivo negatively autoregulates the Pax6 locus, causing cell-autonomous defects of late cortical progenitor proliferation with little effect on cortical arealization

¹ Genes and Development Group, Centres for Integrative Physiology and Neuroscience Research, Hugh Robson Building, George Square, University of Edinburgh, Edinburgh EH8 9XD, UK.
² Division of Reproductive and Developmental Sciences, Genes and Development Group, Centres for Integrative Physiology and Reproductive Biology, Hugh Robson Building, George Square, University of Edinburgh, Edinburgh EH8 9XD, UK.
³ MRC Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, UK.

^* Author for correspondence (e-mail: Martine.Manuel{at}ed.ac.uk)

Accepted 20 November 2006

Levels of expression of the transcription factor Pax6 vary throughout corticogenesis in a rostro-lateral^high to caudo-medial^low gradient across the cortical proliferative zone. Previous loss-of-function studies have indicated that Pax6 is required for normal cortical progenitor proliferation, neuronal differentiation, cortical lamination and cortical arealization, but whether and how its level of expression affects its function is unclear. We studied the developing cortex of PAX77 YAC transgenic mice carrying several copies of the human PAX6 locus with its full complement of regulatory regions. We found that PAX77 embryos express Pax6 in a normal spatial pattern, with levels up to three times higher than wild type. By crossing PAX77 mice with a new YAC transgenic line that reports Pax6 expression (DTy54), we showed that increased expression is limited by negative autoregulation. Increased expression reduces proliferation of late cortical progenitors specifically, and analysis of PAX77wild-type chimeras indicates that the defect is cell autonomous. We analyzed cortical arealization in PAX77 mice and found that, whereas the loss of Pax6 shifts caudal cortical areas rostrally, Pax6 overexpression at levels predicted to shift rostral areas caudally has very little effect. These findings indicate that Pax6 levels are stabilized by autoregulation, that the proliferation of cortical progenitors is sensitive to altered Pax6 levels and that cortical arealization is not.

Key words: Pax6, Cortex, Overexpression, Autoregulation, Proliferation, Neurogenesis, Lamination, Regionalization, Thalamocortical, Chimeras

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