Connexin-43 links Neuromesodermal progenitor states to segmentation clock robustness during vertebrate axis elongation

Neuromesodermal progenitors (NMPs) sustain vertebrate body-axis elongation by generating both neural and paraxial mesodermal tissues. Although signaling and metabolic pathways regulate NMP states, whether intercellular communication contributes to the coordination of progenitor behaviour and developmental timing remains unclear. Here, we identify GJA1, encoding connexin-43 (Cx43), as a gene dynamically enriched within the neuromesodermal competent domain of the chick embryo. Cx43-associated channels and hemichannels accumulate preferentially within the NMP population, and a photoactivatable tracer assay demonstrates enhanced connexin-mediated exchange within the posterior growth zone. Pharmacological inhibition of hemichannels or gap junctions revealed distinct contributions of these communication modes to transcriptional regulation across the NMP continuum. Gap-junction inhibition primarily altered SOX2 expression within progenitor populations, whereas hemichannel inhibition selectively affected TBXT expression in mesodermal cells. Connexin inhibition also reduced the relative size of the progenitor compartment and altered the spatial organization of newly formed somites. Strikingly, disruption of connexin-mediated communication impaired segmentation dynamics, leading to increased frequencies of off-pace segmentation events, accelerated segmentation timing and progressive deviation from the expected segmentation program. These defects emerged rapidly and accumulated over successive segmentation cycles, indicating a requirement for connexin activity in maintaining developmental robustness. Together, our findings identify connexin-43 as a regulator of neuromesodermal progenitor states and reveal a previously unrecognized link between intercellular communication and segmentation clock robustness during vertebrate axis elongation.