LIM Homeobox 4 (lhx4) regulates retinal neural differentiation and visual function in zebrafish

Abstract

LIM homeobox 4 (LHX4) is expressed in the photoreceptors (PRs) of the outer nuclear layer (ONL) and bipolar cells (BCs) of the inner nuclear layer (INL) in mouse and chicken retina. It regulates the subtype-specific development of rod BCs and cone BCs in the mouse retina. However, no report has been published on its expression and function in the zebrafish retina. In this study, we assessed the expression of Lhx4 using in situ hybridization (ISH) technique and explored its role in zebrafish (Danio rerio) retinal development via morpholino (MO) technology. We found that the expression of lhx4 in the zebrafish retina begins 48 h post-fertilization (hpf) and is continuously expressed in the ONL and INL. A zebrafish model constructed with lhx4 knockdown in the eyes through vivo-MO revealed that: lhx4 knockdown inhibits the differentiation of Parvalbumin+ amacrine cells (ACs) and Rhodopsin+ rod photoreceptors (RPs), enhances the expression of visual system homeobox 2 (vsx2); and damages the responses of zebrafish to light stimulus, without affecting the differentiation of OFF-BCs and rod BCs, and apoptosis in the retina. These findings reveal that lhx4 regulates neural differentiation in the retina and visual function during zebrafish embryonic development.

Integrative Single‐Cell Transcriptomics and Epigenomics Mapping of the Fetal Retina Developmental Dynamics

“…UMAP embedding of SCENIC TF activity revealed four developmental branch endpoints derived from RPCs, which were demarcated and represented by respective TFs reported to affect the development of related lineages (Figure 2D ), such as SOX8 for the MGC lineage, POU4F3 for RGC lineage, TFAP2B for HC/AC lineage, and LHX4 and NEUROD1 for BC/PH lineage. [ 21 , 23 , 24 , 25 ]…”

“…UMAP embedding of SCENIC TF activity revealed four developmental branch endpoints derived from RPCs, which were demarcated and represented by respective TFs reported to affect the development of related lineages (Figure 2D), such as SOX8 for the MGC lineage, POU4F3 for RGC lineage, TFAP2B for HC/AC lineage, and LHX4 and NEUROD1 for BC/PH lineage. [21,[23][24][25] Next, we screened critical cell-type-specific TFs at the epigenetic level from the top predicted TFs; the 10 genes regulated by at least two key TFs, according to the weight value, were selected to depict the top GRNs of related TFs for each cell linage (Figure 2E; Figure S2B,C, Supporting Information). For instance, the Iroquois homeobox protein family TFs (IRX1 and IRX2) exhibited a marked influence on genes required for RGC development, such as EBF3, NRN1, and NEFL, [26,22] whereas ONECUT family members had regulatory effects on HC/AC lineage-specific factors, including PROX1 and BARHL2.…”