Regulated extracellular matrix trafficking shapes cell growth during cartilage morphogenesis

Craniofacial malformations are present in more than one third of all congenital syndromes, but the pathogenesis of skeletal dysmorphology is poorly understood. Here, using an unbiased forward genetics approach in zebrafish, we identified a mutation in erc1b that leads to craniofacial defects, including micrognathia and hypertelorism caused by impaired cartilage and bone growth. To date, ERC1 has not been considered a candidate gene for craniofacial syndromes. Using live in vivo imaging, genetic depletion and replacement experiments, and transgenic approaches, we interrogated erc1b function. We found that Erc1b regulates extracellular matrix (ECM) trafficking required for the highly conserved "stack of coins" organization of chondrocytes in cartilage that is essential for skeletal growth and integrity. Erc1b functions cellautonomously at the chondrocyte cell cortex to regulate traffic of ECM and plasma membrane expansion in a microtubule dependent manner during isometric cell growth. Disruption of Erc1-Rab8-Kinesin-1 axis leads to failure of cartilage maturation, endochondral bone formation and ultimately chondrocyte cell death. Our study identifies Erc1b as a candidate genetic factor for craniofacial syndromes.