Materials and Methods for Cdk1 cooperates with EGFR–MAPK signalling to coordinate the final mitosis with neuronal fate specification in Drosophila v1

Precise coordination between cell cycle progression and cellular differentiation isessential for tissue development, yet the mechanisms that couple theseprocesses remain poorly understood. Using the Drosophila eye imaginaldisc as a model for spatial and temporal integration of proliferation andneuronal specification, we performed a systematic RNA interference andoverexpression screen targeting cell cycle regulators. This screen identifiedthe universal mitotic kinase Cdk1 as a key link between intrinsic cell cyclecontrol and extrinsic EGFR–Ras–MAPK signalling. Loss of Cdk1 caused a selective block inEGFR-dependent R2/5 photoreceptor differentiation that could not be explainedby G2 arrest or apoptosis, revealing a non-canonical, differentiation-specificfunction for Cdk1. Mechanistically, Cdk1 cooperates with MAPK signalling byconverging on the ETS family transcription factor Pointed-P2 (PntP2),phosphorylating it at both shared and Cdk1-biased sites to regulate itstranscriptional activity and nuclear localisation. PntP2 is expressed duringthe final mitosis preceding differentiation, coinciding with high Cdk1 activityand transient repression of the proneural factor Atonal, which promotes R8fate. These findings support a model in which Cdk1 acts during the finalmitosis to prime MAPK-dependent transcription and bias subsequent fatedecisions, thereby coupling cell cycle progression to neuronal specification.Our study reveals a spatiotemporally orchestrated cooperation between core cellcycle machinery and developmental signalling pathways that synchronises proliferationwith differentiation, a principle likely conserved across metazoan development.