Dyrk1a gene dosage controls bipolar cell development and retinal connectivity.

Mammalian retina development is governed by a core set of eye-field transcription factors that orchestrate tissue lamination and neuronal connectivity through tightly regulated genetic hierarchies. The LIM homeodomain gene Lhx2 functions as a master eye-field regulator and this study identifies Dyrk1a as a previously unrecognised effector of Lhx2-dependent programs during mouse retinal development. Conditional deletion of Dyrk1a in retinal progenitor cells led to increased apoptosis within the inner retina demonstrating a requirement for Dyrk1a in cell survival and lineage maintenance. Adult heterozygous mice exhibited dorsoventral reductions in bipolar cell number and indicated a gene-dosage-sensitive control of interneuron survival. Bipolar cell loss disrupted their mosaic organisation and resulted in diminished activity across both scotopic and photopic retinal pathways. Dyrk1a haploinsufficient mice also displayed pronounced disruption of inner plexiform layer stratification consistent with defective laminar targeting and synaptic partner integration. This study defines a gene-dosage-dependent mechanism through which transcriptional hierarchies regulate neuronal connectivity and function during mammalian retinal development.