# Chrdl1-mediated BMP4 inhibition disrupts the balance between retinal neurons and Müller Glia

## TL;DR

This study shows that inhibiting Bmp4 in the developing mouse retina shifts cell fate toward neurons and away from glial cells, affecting retinal function.

## Contribution

The study reveals how Bmp4 inhibition alters retinal cell differentiation and identifies specific genes involved in this process.

## Key findings

- Bmp4 inhibition disrupts both neuronal and Müller glial differentiation in the developing retina.
- Bmp4 inhibition leads to upregulation of Id1/2/3/4 and Hes1/5 and downregulation of Neurod1/2/4 and Bhlhe22/23.
- Bmp4 inhibition impairs retinal cell connectivity and visual function in mice.

## Abstract

Chordin-like 1 (CHRDL1) is a secreted protein that serves as an endogenous antagonist of bone morphogenetic proteins (BMPs). In the developing retina, Bmp4 has been demonstrated to be essential for sustaining the proliferation of progenitor cells and facilitating the differentiation of glial cells. Despite these efforts, the precise effects of Bmp4 inhibition on the developing retina are yet to be fully understood. We sought to address this question by overexpressing Chrdl1 in the developing retina. In this study, we explored the impact of Bmp4 inhibition on the developing mouse retina by conditionally overexpressing the Bmp4 inhibitor Chrdl1. Initially, we characterized the expression patterns of Bmp4 and Chrdl1 in the developing mouse retina from E10.5 to P12.5. Additionally, we utilized various molecular markers to demonstrate that Bmp4 inhibition disrupts both neuronal and Müller glial differentiation in the developing mouse retina. Moreover, through the application of RNA-seq analysis, distinctively expressed retinal genes under the modulation of Bmp4 signaling were discerned, encompassing the upregulation of Id1/2/3/4 and Hes1/5, as well as the downregulation of Neurod1/2/4 and Bhlhe22/23. Lastly, electroretinogram (ERG) and optomotor response (OMR) assays were conducted to illustrate that Bmp4 inhibition impairs the functional connectivity of various cells in the retina and consequently affects visual function. Collectively, this study demonstrates that inhibiting Bmp4 promotes the differentiation of retinal neurons over Müller glia by activating the expression of genes associated with neuron specification. These findings offer molecular insights into the role of Bmp4 signaling in mammalian retinal development.