CMTM4 is an adhesion modulator that regulates skeletal patterning and primary mesenchyme cell migration in sea urchin embryos

MARVEL proteins, including those of the CMTM gene family, are multi-pass transmembrane proteins that play important roles in vesicular trafficking and cell migration; however, little is understood about their role in development, and their role in skeletal patterning is unexplored. CMTM4 is the only CMTM family member found in the developmental transcriptome of the sea urchin Lytechinus variegatus . Here, we validate that LvCMTM4 is a transmembrane protein and show that perturbation of CMTM4 expression via zygotic morpholino or mRNA injection perturbs skeletal patterning, resulting in loss of secondary skeletal elements and rotational defects. We also demonstrate that normal levels of CMTM4 are required for normal PMC migration and filopodial organization, and that these effects are not due to gross mis-specification of the ectoderm. Finally, we show that CMTM4 is sufficient to mediate PMC cell-cell adhesion. Taken together, these data suggest that CMTM4 controls PMC migration and biomineralization via adhesive regulation during sea urchin skeletogenesis. This is the first discovery of a functionally required adhesive gene in this skeletal patterning system.