Chx10 is required to block photoreceptor differentiation but is dispensable for progenitor proliferation in the postnatal retina

Abstract

In the Chx10-null ocular retardation (or J ) mouse, retinal progenitor cell (RPC) proliferation is impaired, and bipolar neurons, a late born cell type, fail to differentiate. It is unclear whether Chx10 is required to maintain proliferation throughout retinogenesis or whether the bipolar cell defect is an indirect effect of growth arrest. We show that Chx10 is dispensable for late-stage RPC proliferation but is essential to promote bipolar cell genesis in place of rods. Ectopic Chx10 expression drove bipolar instead of rod cell differentiation without affecting division. Converting Chx10 to an activator impaired bipolar cell differentiation, implying that repression is important for Chx10 activity. In the Chx10 null or J retina, only a small fraction of cells expressing mutated Chx10 mRNA were rods, but this fraction increased after p27 Kip1 inactivation, which partially rescues proliferation. Most significantly, acute Chx10 knockdown in the postnatal retina promoted rods in place of bipolar neurons without affecting division. Thus, Chx10 directly controls bipolar cell genesis by inhibiting rod differentiation independent of its temporally limited early effect on RPC proliferation.CVC domain ͉ homeobox ͉ homeodomain ͉ short-hairpin RNA

Suppressor of Fused Is Required to Maintain the Multipotency of Neural Progenitor Cells in the Retina

“…6O) (data not shown). The absence of Rax and Vsx2 expression, which are required for Müller glia (Furukawa et al, 2000) and bipolar cell (Burmeister et al, 1996;Livne-Bar et al, 2006) development, respectively, was also consistent with the absence of these differentiated cell types at later stages in the Sufu KO retina. The downregulation of these transcription factors in E14.5 Sufu CKO retinae was confirmed with RT-qPCR (Fig.…”

Mapping differentiation kinetics in the mouse retina reveals an extensive period of cell cycle protein expression in post‐mitotic newborn neurons

“…2A, B). Vsx2 is also expressed in progenitors and is required for proliferation of early but not late progenitors (Burmeister et al, 1996;Livne-Bar et al, 2006). In the post-natal retina, Vsx2 is also expressed in bipolar neurons and Mü ller glia; thus, this marker can be used as an unambiguous progenitor marker only in the embryonic retina (Burmeister et al, 1996;Rowan and Cepko, 2004;LivneBar et al, 2006).…”

Negative regulation of Vsx1 by its paralog Chx10/Vsx2 is conserved in the vertebrate retina

“…Chx10 overexpression inhibits photoreceptor differentiation and several phototransduction genes are candidate direct transcriptional targets of negative regulation by Chx10 (Dorval et al, 2006;Livne-Bar et al, 2006;Toy et al, 2002). These findings combined with the shared DNA binding characteristics and repressive activities of Chx10 and Vsx1 led to the proposal that these genes could function in bipolar cells to prevent inappropriate expression of photoreceptor genes (Dorval et al, 2006).…”

“…Mutations in Chx10 cause microphthalmia in humans (Bar-Yosef et al, 2004;Ferda Percin et al, 2000) and mice (Burmeister et al, 1996), and antisensechx10 RNA injected into zebrafish embryos causes a small eye phenotype (Barabino et al, 1997). Studies in ocular retardation J (orJ) mice, which carry a spontaneously-derived nonsense mutation in the HD (Y176stop) of Chx10 (Chx10 orJ ; Burmeister et al, 1996;Theiler et al, 1976), show that in addition to a lack of bipolar cells, the Chx10 orJ homozygote (Chx10 orJ/orJ ) retina exhibits a profound decrease in RPC proliferation, a propensity to transdifferentiate along a pigmentation pathway, delays in embryonic neurogenesis, persistent neurogenesis in the adult retina, and an enrichment of adult ciliary epithelium derived retinal stem cells (Bone-Larson et al, 2000;Burmeister et al, 1996;Coles et al, 2006;Dhomen et al, 2006;Green et al, 2003;Horsford et al, 2005;Livne-Bar et al, 2006;Rowan et al, 2004;Rutherford et al, 2004).…”