ZP2 and ZP3 traffic independently within oocytes prior to assembly into the extracellular zona pellucida

Mol Cell Biol. 2006 Nov;26(21):7991-8. doi: 10.1128/MCB.00904-06.


The extracellular zona pellucida surrounds mammalian eggs and mediates taxon-specific sperm-egg recognition at fertilization. In mice, the zona pellucida is composed of three glycoproteins, but the presence of ZP2 and ZP3 is sufficient to form a biologically functional structure. Each zona pellucida glycoprotein is synthesized in growing oocytes and traffics through the endomembrane system to the cell surface, where it is released from a transmembrane domain and assembled into the insoluble zona pellucida matrix. ZP2 and ZP3 colocalize in the endoplasmic reticulum and in 1- to 5-microm post-Golgi structures comprising multivesicular aggregates (MVA), but a coimmunoprecipitation assay does not detect physical interactions. In addition, ZP2 traffics normally in growing oocytes in the absence of ZP3 or if ZP3 has been mutated to prevent incorporation into the zona pellucida matrix, complementing earlier studies indicating the independence of ZP3 secretion in Zp2 null mice. N glycosylation has been implicated in correct protein folding and intracellular trafficking of secreted proteins. Although ZP3 contain five N-glycans, enhanced green fluorescent protein-tagged ZP3 lacking N glycosylation sites is present in MVA and is incorporated into the zona pellucida matrix of transgenic mice. Thus, ZP2 secretion is seemingly unaffected by ZP3 lacking N-glycans. Taken together, these observations indicate that ZP2 and ZP3 traffic independently through the oocyte prior to assembly into the zona pellucida.

Publication types

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

MeSH terms

  • Animals
  • Egg Proteins / genetics
  • Egg Proteins / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum / ultrastructure
  • Female
  • Fluorescent Dyes / metabolism
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Mice, Knockout
  • Mice, Transgenic
  • Oocytes / cytology
  • Oocytes / physiology*
  • Polysaccharides / chemistry
  • Polysaccharides / metabolism
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Zona Pellucida / chemistry
  • Zona Pellucida / metabolism*
  • Zona Pellucida Glycoproteins


  • Egg Proteins
  • Fluorescent Dyes
  • Membrane Glycoproteins
  • Polysaccharides
  • Receptors, Cell Surface
  • Recombinant Fusion Proteins
  • Zona Pellucida Glycoproteins
  • Zp2 protein, mouse
  • Zp3 protein, mouse