Hierarchical assembly of the eggshell and permeability barrier in C. elegans.
In metazoans, fertilization triggers the assembly of an extracellular coat that constitutes the interface between the embryo and its environment. In nematodes, this coat is the eggshell, which provides mechanical rigidity, prevents polyspermy, and is impermeable to small molecules. Using immunoelectron microscopy, we found that the Caenorhabditis elegans eggshell was composed of an outer vitelline layer, a middle chitin layer, and an inner layer containing chondroitin proteoglycans. The switch between the chitin and proteoglycan layers was achieved by internalization of chitin synthase coincident with exocytosis of proteoglycan-containing cortical granules. Inner layer assembly did not make the zygote impermeable as previously proposed. Instead, correlative light and electron microscopy demonstrated that the permeability barrier was a distinct envelope that formed in a separate step that required fatty acid synthesis, the sugar-modifying enzyme PERM-1, and the acyl chain transfer enzyme DGTR-1. These findings delineate the hierarchy of eggshell assembly and define key molecular mechanisms at each step.
Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
Sara K
SK
Olson
Garrett
G
Greenan
Arshad
A
Desai
Thomas
T
Müller-Reichert
Karen
K
Oegema
D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000235:genetics / Q000502:physiology*; D004527:Egg Proteins / Q000235:genetics / Q000378:metabolism; D005306:Fertilization / Q000502:physiology*; D016253:Microscopy, Immunoelectron; D009865:Oocytes / Q000378:metabolism* / Q000648:ultrastructure; D015053:Zygote / Q000378:metabolism / Q000648:ultrastructure
D029742:Caenorhabditis elegans Proteins; D004527:Egg Proteins; C015753:chorion proteins