Lhx1 in the proximal region of the optic vesicle permits neural retina development in the chicken

Abstract

SummaryHow the eye forms has been one of the fundamental issues in developmental biology. The retinal anlage first appears as the optic vesicle (OV) evaginating from the forebrain. Subsequently, its distal portion invaginates to form the two-walled optic cup, which develops into the outer pigmented and inner neurosensory layers of the retina. Recent work has shown that this optic-cup morphogenesis proceeds as a self-organizing activity without any extrinsic molecules. However, intrinsic factors that regulate this process have not been elucidated. Here we show that a LIM-homeobox gene, Lhx1, normally expressed in the proximal region of the nascent OV, induces a second neurosensory retina formation from the outer pigmented retina when overexpressed in the chicken OV. Lhx2, another LIM-homeobox gene supposed to be involved in early OV formation, could not substitute this function of Lhx1, while Lhx5, closely related to Lhx1, could replace it. Conversely, knockdown of Lhx1 expression by RNA interference resulted in the formation of a small or pigmented vesicle. These results suggest that the proximal region demarcated by Lhx1 expression permits OV development, eventually dividing the two retinal domains.

The expression of LIM‐homeobox genes, Lhx1 and Lhx5, in the forebrain is essential for neural retina differentiation

“…We previously reported that normal Lhx1 and Lhx5 expression is observed in the developing forebrain from HH stage 8 (Kawaue et al . ). We have also shown that overexpression of Lhx1 or Lhx5 induced the ectopic expression of NR differentiation markers (Kawaue et al .…”

“…We have also shown that overexpression of Lhx1 or Lhx5 induced the ectopic expression of NR differentiation markers (Kawaue et al . ). Therefore, it seemed likely that the activity of Lhx1 and Lhx5 in the forebrain might have a role in promoting NR identity.…”

“…TUNEL staining was performed using a Click‐iT TUNEL Assay (Life Technologies) as previously described (Kawaue et al . ).…”

The role of homeobox genes in retinal development and disease

“…In retinas lacking the Onecut transcription factor, Oc1, 80% of horizontal cells are lost with down-regulation of Lhx1 expression, demonstrating upstream regulation of Lhx1 by OC1 (Wu et al, 2013). An early role for Lhx1 in optic vesicle development has also been demonstrated in chick (Kawaue et al, 2012). Lhx1 expression is observed in the proximal optic vesicles.…”

Xenopus pitx3 target genes lhx1 and xnr5 are identified using a novel three‐fluor flow cytometry–based analysis of promoter activation and repression

“…Lhx1 directly targets and activates gsc expression and may be responsible for maintained gsc expression during late gastrulation within the prechordal plate (Mochizuki et al, ). In chicks, Lhx1 plays a critical role in retinal development (Kawaue et al, ; Inoue et al, ). In the present study, Xenopus lhx1 expression is identified as a pitx3 target (assessed by microarray, in situ hybridization), expression patterns overlap with pitx3 , and the gene contains multiple putative binding sites in its enhancer/promoter (Hooker et al, ).…”