The Adhesive Properties and Expansion of the Chick Blastoderm

Abstract

During the first 4 days of incubation the chick blastoderm expands to surround the yolk. Its expansion takes place over the inner surface of the vitelline membrane, and the edge of the blastoderm is firmly attached to this membrane. Little attention has been paid hitherto to the mechanism of this expansion, presumably because it lies outside the embryo proper. But many of the problems involved are of considerable interest, not only as they relate to development within cleidoic eggs, but also in connexion with more general questions affecting expansion of epithelia and the nature of cell surfaces. Blastoderm expansion has many points of similarity with the spreading of epithelia across wounds, and some of the factors involved may prove to be similar to those affecting the radiation of loose sheets of cells in tissue culture.

Computational and experimental study of the mechanics of embryonic wound healing

“…The chick embryo has been a popular model for studies of wound healing (Bortier et al, 1993;Brock et al, 1996;England and Cowper, 1977;Lawson and England, 1998;Mareel and Vakaet, 1977;Stanisstreet et al, 1980). The early embryo consists of a planar blastoderm, two to three cell layers thick, which is held under tension and attached to a substrate (the vitelline membrane) only at its periphery (Bellairs et al, 1967;Bortier et al, 1993;New, 1959). All forces required to close a wound are generated within the blastoderm itself.…”

The extra-embryonic area opaca plays a role in positioning the primitive streak of the early chick embryo

“…Based on a number of classical studies it had been generally thought that the peripheral region of the embryo, the area opaca, plays a role in providing nutrition to the embryo and in maintaining its tension, but that it does not have an instructive role in regulating cell fate or embryonic polarity ( Bellairs et al, 1967 ; Downie, 1976 ; Khaner et al, 1985 ; New, 1959 ; Spratt and Haas, 1960 ). Contrary to this conclusion, the present study uncovers three separable functions of the area opaca: induction of marginal zone properties, an influence on polarity of the marginal zone and determining the end of the period during which embryo fragments can ‘regulate’ (repolarise themselves and form a primitive streak from an isolated fragment lacking the primitive streak-forming region) ( Fig.…”

“…A second possibility is that tension generated by the expanding edges of the area opaca (the ‘margin of overgrowth’; Bellairs et al, 1967 ; Downie, 1976 ; New, 1959 ) plays a role. However, embryo fragments lacking the area opaca can regulate (albeit at reduced frequency) ( Spratt and Haas, 1960 , 1961 and results in the present paper) and, moreover, Spratt's experiments were performed by growing the embryo in the absence of the vitelline membrane and placing directly (in some cases with its ventral surface downwards) on a semi-soft agar substrate to which it cannot adhere and which promotes very limited expansion.…”

“…In contrast, the more peripheral region, area opaca, is generally believed to play a less active role in regulating embryonic patterning, its major functions at this early stage being providing a source of nutrition and maintaining the centrifugal tension of more central regions through adhesion of its edge to the vitelline membrane ( Bellairs et al, 1967 ; Downie, 1976 ; New, 1959 ). Indeed, the embryo can generate a primitive streak even when the area opaca is removed, which has been interpreted to imply that the area opaca has no role in embryonic polarity ( Spratt and Haas, 1960 ; Khaner et al, 1985 ).…”

Downregulation of Extraembryonic Tension Controls Body Axis Formation in Avian Embryos

“…The layers of the VM mainly consist of networks of glycoproteins, which provide structural integrity and share homologies to some components of the zona pellucida in mammals (Back et al, 1982; Mann, 2008; Rodler et al, 2012). In chicken embryos, the outer rim of the blastoderm stays attached to the VM during early development, allowing tension transmission between the VM and embryonic tissues (New 1959; Bellairs, Boyde, and Heaysman 1969). The disc-shaped blastoderm expands outwards prior to and during the first day after laying (D0, 0-24hrs) through extensive proliferation and cell movements at the blastoderm edge (epiboly, Figure 1A) (Eyal-Giladi and Kochav, 1976; New, 1959; Sheng, 2014).…”