A multiphasic role for Pax7 in tectal development.

The optic tectum differentiates from the mesencephalic alar plate and matures into a characteristically laminated structure. Evidence presented here suggests a role for Pax7 in all stages of development of tectal architecture, from regionalisation to specification of neurons and tectal topography. Analysis of Pax7 expression profiles over a range of developmental stages (E2-E12) suggests a biphasic role for Pax7: initially Pax7 expressing cells in the proliferative neuroepithelial layer establish tectal polarity whereas later Pax7 is expressed in neurons of the retino-recipient precursor stratum griseum et fibrosum superficiale (sgfs) laminae where graded levels may establish tectal topography. Furthermore, co-localisation immunofluorescence confirmed that Pax7 is initially expressed in the majority of proliferative neuroepithelial cells and later in a subset of neurons of the sgfs laminae.