The role of eggshell and underlying vitelline membrane for normal pattern formation in the early C. elegans embryo

Abstract

The embryo of the nematode Caenorhabditis elegans is surrounded by an inconspicuous inner vitelline membrane and a prominent outer chitinous eggshell proper. We demonstrate that the complete removal of the chitinous eggshell does not interfere with successful development to yield a normal worm. The same result can be obtained when the vitelline membrane is penetrated with laser microbeam irradiation of only the eggshell proper, gently enough to permit its resealing after a while. However, when large holes are made into the eggshell the concomitantly penetrated vitelline membrane does not reseal. While early development is quite normal under these conditions, gastrulation is defective in that gut precursor cells do not migrate in properly, eventually leading to embryonic arrest. This suggests a crucial role for pattern formation of the "micro-environment" around the embryo preserved by the intact vitelline membrane. Removing both eggshell and vitelline membrane results in a string-like arrangement of founder cells and subsequent grossly abnormal cell patterns. Our experiments support the idea that the prominent eggshell proper just functions as a mechanical protection while the thin vitelline membrane directly or indirectly serves as a necessary control element affecting the positions of cells which to begin with are determined by the orientation of the cleavage spindle.

Mechanisms of cell positioning during C. elegans gastrulation

“…It has previously been reported that gastrulation does not occur in devitellinized embryos, suggesting that the vitelline envelope might produce a micro-environment required for gastrulation (Schierenberg and Junkersdorf, 1992). However, half of the embryos cultured in that study did not make rhabditin/gut granules, a marker of endoderm differentiation in C. elegans embryos, suggesting that the embryonic culture medium used might not have supported development as well as EGM (see Materials and Methods).…”

Two cytochrome P450s in Caenorhabditis elegans are essential for the organization of eggshell, correct execution of meiosis and the polarization of embryo

“…The vitelline layer can be removed from the egg by brief bleaching with sodium hypochlorite without affecting the further development of the embryo (Schierenberg and Junkersdorf, 1992). Embryos after bleaching are neither osmotic sensitive nor permeable to dyes (Fig.…”

The C. elegans eggshell

“…Two additional layers have recently been observed and defined (Olson et al, 2012; Benenati et al, 2009)(Figure 1). These layers are defined visually through electron micrographs and also by diagnostic biochemical treatments that can remove individual layers from the embryo (Olson et al, 2012; Benenati et al, 2009; Rappleye et al, 1999; Schierenberg and Junkersdorf, 1992). The outermost layer is the vitelline layer (VL) and can be selectively removed by treatment with sodium hypochlorite, leaving the remainder of the eggshell intact.…”

“…Although there is a report of some lectin staining enriched in the VL (Bembenek et al, 2007), there is not, to our knowledge, a way to distinguish it from the plasma membrane of the oocyte. This layer can be removed from mitotic embryos using sodium hypochlorite (Schierenberg and Junkersdorf, 1992) without harming their development.…”