CBD-1 organizes two independent complexes required for eggshell vitelline layer formation and egg activation in C. elegans

Dev Biol. 2018 Oct 15;442(2):288-300. doi: 10.1016/j.ydbio.2018.08.005. Epub 2018 Aug 16.


Metazoan eggs have a specialized coat of extracellular matrix that aids in sperm-egg recognition. The coat is rapidly remodeled after fertilization to prevent polyspermy and establish a more permanent barrier to protect the developing embryo. In nematodes, this coat is called the vitelline layer, which is remodeled into the outermost layer of a rigid and impermeable eggshell. We have identified three key components of the vitelline layer structural scaffold - PERM-2, PERM-4 and CBD-1, the first such proteins to be described in the nematode C. elegans. CBD-1 tethered PERM-2 and PERM-4 to the nascent vitelline layer via two N-terminal chitin-binding domains. After fertilization, all three proteins redistributed from the zygote surface to the outer eggshell. Depletion of PERM-2 and PERM-4 from the scaffold led to a porous vitelline layer that permitted soluble factors to leak through the eggshell and resulted in embryonic death. In addition to its role in vitelline layer assembly, CBD-1 is also known to anchor a protein complex required for fertilization and egg activation (EGG-1-5/CHS-1/MBK-2). We found the PERM complex and EGG complex to be functionally independent, and structurally organized through distinct domains of CBD-1. CBD-1 is thus a multifaceted regulator that promotes distinct aspects of vitelline layer assembly and egg activation. In sum, our findings characterize the first vitelline layer components in nematodes, and provide a foundation through which to explore both conserved and species-specific strategies used by animals to build protective barriers following fertilization.

Keywords: C. elegans eggshell; CBD-1; Fertilization; PERM-2 and PERM-4; Vitelline layer; Zona pellucida.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caenorhabditis elegans
  • Caenorhabditis elegans Proteins / metabolism*
  • Carrier Proteins / metabolism*
  • Egg Shell / metabolism*
  • Fertilization
  • Membrane Glycoproteins / metabolism
  • Oogenesis
  • Ovum / metabolism
  • Vitelline Membrane / metabolism*
  • Zygote / metabolism


  • CBD-1 protein, C elegans
  • Caenorhabditis elegans Proteins
  • Carrier Proteins
  • Membrane Glycoproteins