Er81is a downstream target of Pax6 in cortical progenitors

Tran Cong Tuoc,Anastassia Stoykova

doi:10.1186/1471-213x-8-23

Abstract

BackgroundAlthough the transcription factor Pax6 plays an essential role in neurogenesis, layer formation and arealization in the developing mammalian cortex, the mechanisms by which it accomplishes these regulatory functions are largely unknown. Pax6 and the ETS family transcription factor Er81, which is presumed to play a role in the specification of a sublineage of layer 5 projection neurons, are expressed with a prominent rostrolateral-high to caudomedial-low gradient in cortical progenitors. In the absence of functional Pax6, progenitors do not express Er81 and the rostrolateral cortex lacks Er81-positive layer 5 neurons. In this study, we investigated the transcriptional regulation of Er81 and provide evidence that Er81 is a direct target of Pax6.ResultsWe identified and analyzed the regulatory function of an evolutionarily conserved upstream DNA sequence in the putative mouse Er81 promoter. Three potential Pax6 binding sites were identified in this region. We found that the presence of one of these sites is necessary and sufficient for full activation of the Er81 promoter in Pax6-transfected HeLa cells, while other still unknown factors appear to contribute to Er81 promoter activity in cortical progenitors and neuronal cells. The results suggest that endogenous Pax6, which is expressed at the highest level in progenitors of the rostrolateral cortex, exerts region-specific control of Er81 activity, thus specifying a subpopulation of layer 5 projection neurons.ConclusionWe conclude that the genetic interplay between the transcription factors, Pax6 and Er81, is responsible, in part, for the regional specification of a distinct sublineage of layer 5 projection neurons.

Highlights

The transcription factor Pax6 plays an essential role in neurogenesis, layer formation and arealization in the developing mammalian cortex, the mechanisms by which it accomplishes these regulatory functions are largely unknown
Using an electrophoretic mobility shift assay (EMSA) and in vitrotranslated Pax6 protein, we examined Pax6 binding to these three potential binding sites
The results indicate that Pax6 bound with low affinity to the Pax6 binding site at position -1190 to -1225, but not to any of the other putative sites (Fig. 1B, lanes 3 and 6 and data not shown)

Summary

Introduction

The transcription factor Pax plays an essential role in neurogenesis, layer formation and arealization in the developing mammalian cortex, the mechanisms by which it accomplishes these regulatory functions are largely unknown. Pax and the ETS family transcription factor Er81, which is presumed to play a role in the specification of a sublineage of layer 5 projection neurons, are expressed with a prominent rostrolateral-high to caudomedial-low gradient in cortical progenitors. The projection neurons of the lower (6 and 5) and upper (4–2) layers are generated predominantly from early (E12-E14) or late (E15-E18) progenitors in the two germinative zones, VZ and SVZ, respectively. Laminar fate is presumably determined by the timing of neuronal origin during distinct developmental stages, a process controlled by environmental cues [9], but is critically dependent on intrinsic mechanisms that control the molecular phenotype of the neuronal sublineages [5]. Ngn2- and Pax6-controlled genetic programs appear to and separately determine the neuronal fate of lower and upper neurons [14]. We have noted qualitatively similar mispatterning of Er81 expression in the rostrolateral cortex in the cortex-specific conditional Pax KO mice at juvenile and adult stages (T.C.T., A.S. unpublished observations), prompting us to examine possible genetic interactions between the two transcription factors, Pax and Er81

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