Pax6 Is Required for the Multipotent State of Retinal Progenitor Cells

Abstract

The molecular mechanisms mediating the retinogenic potential of multipotent retinal progenitor cells (RPCs) are poorly defined. Prior to initiating retinogenesis, RPCs express a limited set of transcription factors implicated in the evolutionary ancient genetic network that initiates eye development. We elucidated the function of one of these factors, Pax6, in the RPCs of the intact developing eye by conditional gene targeting. Upon Pax6 inactivation, the potential of RPCs becomes entirely restricted to only one of the cell fates normally available to RPCs, resulting in the exclusive generation of amacrine interneurons. Our findings demonstrate furthermore that Pax6 directly controls the transcriptional activation of retinogenic bHLH factors that bias subsets of RPCs toward the different retinal cell fates, thereby mediating the full retinogenic potential of RPCs.

Generation of structures formed by lens and retinal cells differentiating from embryonic stem cells

“…Pax6, a paired-type homeodomain protein, is a major regulator of eye development and is required for the formation of eye structures, the maintenance of lens competence, and the multipotency of retinal cells (Grindley et al, 1995;Marquardt et al, 2001). As shown in Figure 4A, Pax6 mRNA was detected from day 8 of the culture period, when no obvious eye-like structures had yet formed.…”

Conserved regulation of Math5 and Math1 revealed by Math5-GFP transgenes

“…Interestingly, all of these genes, except NeuroD, genetically require Pax6 (Marquardt et al, 2001;Blader et al, 2004). The activation of Ngn1 and Ngn2 is directly regulated by Pax6 binding to particular CNS enhancers (Marquardt et al, 2001;Scardigli et al, 2003;Blader et al, 2004).…”

“…Math5 requires the paired-domain transcription factor Pax6 for initial activation (Brown et al, 1998;Marquardt et al, 2001) and is repressed by the bHLH factor Hes1 (Lee et al, 2005). However, the cis-regulatory elements regulating Math5 expression are not yet well defined.…”

The homeobox geneXbh1cooperates with proneural genes to specify ganglion cell fate within theXenopusneural retina

“…RPCs differentiate according to an ordered spatiotemporal pattern, largely conserved among vertebrates: ganglion cells are born first, followed by cone photoreceptors, horizontal and amacrine cells, whereas rod photoreceptors, bipolar and Müller cells are born last (Cepko et al, 1996;Stiemke and Hollyfield, 1995). Recent evidence supports the hypothesis that the commitment towards specific cell types occurs very early in RPCs (Lillien, 1998;Marquardt and Gruss, 2002;Marquardt et al, 2001). At any given time of retinal development, each RPC expresses different repertoires of transcription factors (Perron et al, 1998), which are thought to provide the cell with the intrinsic competence to respond appropriately to external stimuli and to differentiate toward particular cell fates (reviewed by Livesey and Cepko, 2001).…”