Figure 9

The eggshell in development of the one-cell C. elegans embryo. (A) cej-1, B0280.5 and gna-2 are released from GLD-1 translational repression in the proximal germline (indicated by 'x' superimposed on 'GLD-1'). GNA-2 supports synthesis of UDP-GlcNAc. GNA-1 expression is suppressed by SUP-46. '-1 oocyte' indicates the oocyte adjacent to the spermatheca. (B) CHS-1 synthesizes chitin (black) from UDP-GlcNAc. Chitin is deposited into the eggshell immediately after fertilization. (C) The chitin-binding proteins, CEJ-1 and/or B0280.5, bind chitin and water, resulting in the development of a hydrated matrix (pale blue), which is required for faithful chromosome segregation at meiosis I and for (D) extrusion of the first polar body. (E) Chitin and CEJ-1 and/or B0280.5 are also needed for extrusion of the osmotic/permeability barrier, for faithful meiosis II chromosome segregation and for extrusion of the second polar body. (F) The eggshell is required for association of the SPCC with the cortex, which (G) is associated with the initiation of polarization.