Repurposing of the multiciliation gene regulatory network in fate specification of Cajal-Retzius neurons

Cajal-Retzius (CR) neurons are key players of cortical development that display a very unique transcriptomic identity. However, little is known about the mechanisms involved in their fate specification. Here we use scRNAseq to reconstruct the differentiation trajectory of hem-derived CR cells (CRs) and unravel the transient expression of a complete gene module previously known to control the cellular process of multiciliogenesis. However, we find that CRs do not undergo centriole amplification or multiciliation. We show that upon genetic disruption of Gmnc, the master regulator of the multiciliation cascade, CRs are initially produced but fail to reach their normal identity and lean towards an aberrant fate resulting in their massive apoptosis. We further dissect the contribution of multiciliation effector genes and identify Trp73 as a key determinant. Finally, we use in utero electroporation to demonstrate that the intrinsic competence of hem progenitors as well as the heterochronic expression of Gmnc prevent centriole amplification in the CR lineage. Our work exemplifies how the co-option of a complete gene module, repurposed to control a completely distinct process, may contribute to the emergence of novel cell identities.