A sticky problem: TheXenopus cement gland as a paradigm for anteroposterior patterning

Abstract

The cement gland is a mucus‐secreting organ found at the extreme anterior of frog embryos. It attaches the embryo to a solid support before swimming and feeding begin, and also serves a related sensory function that stops the embryo from moving once it is attached. Cement gland is an extremely useful anterior marker, whose study continues to yield fundamental information concerning vertebrate axial patterning. Cement gland arises from the outer layer of the embryonic ectoderm and, in Xenopus, forms a cone of columnar epithelium. It is the first ectodermal organ to differentiate, beginning to do so by late gastrula. A battery of genes expressed in the developing and mature cement gland serve as useful markers. Cement gland development can be influenced by both stimulatory and inhibitory cell interactions. Stimulatory signals arise from the anterior neural plate, head endoderm, and the dorsal mesoderm. Inhibitory signals are present in the posterior dorsal mesoderm and in ventral ectoderm and mesoderm. Further, signalling between the ectodermal layers may restrict cement gland differentiation to the outer ectodermal cells. Several secreted molecules are able to induce or repress cement gland formation: these include noggin, follistatin, hedgehog, chordin, retinoic acid, embryonic fibroblast growth factor (eFGF), Bone Morphogenetic Protein‐4 (BMP‐4), and Xwnt‐8. Several of these factors alter expression of the homeodomain gene Xotx2, which may be a transcriptional activator of cement gland differentiation genes. The significance of the cell interactions and factors described in positioning cement gland at the front of the embryo is explored. © 1996 Wiley‐Liss, Inc.

Xhairy2 functions in Xenopus lens development by regulating p27xic1 expression

“…In terms of expression layer, Xhairy2 is indeed expressed in the deep layer where PPE genes are expressed (Schlosser and Northcutt, 2000;Fig. 1c,c',f,f',i,i'), and not in the surface layer where genes marking the future cement gland region are expressed (Drysdale and Elinson, 1992;Sive and Bradley, 1996). This is consistent with the expression pattern of the PPE gene dlx5 (Fig.…”

Oriented cell divisions asymmetrically segregate aPKC and generate cell fate diversity in the earlyXenopusembryo

“…Apart from their role in shielding the embryo from the exterior, superficial cells differ from deep cells in many other ways. Superficial and deep cells do not mix until later in development (Keller, 1978;Smith and Malacinski, 1983;Hartenstein, 1989;Minsuk and Keller, 1997) and they follow different cell fates, express different genes and have different roles in gastrulation (Keller, 1975;Minsuk and Keller, 1997;Keller, 1976;Shih and Keller, 1992;Keller et al, 1985;Glinka et al, 1996;Smith et al, 1995;Sive and Bradley, 1996;Deblandre et al, 1999). Thus, the formation of an outer epithelial cell layer and one or more, internal non-epithelial cell layers, and the developmental distinction between them, is one of the fundamental differentiations in the early embryo.…”

Pitx1 and Pitx2c are required for ectopic cement gland formation in xenopus laevis

“…UV irradiation or retinoic acid treatment, reduce, or abolish cement gland formation (Kao and Elinson, 1988;Scharf and Gerhard, 1980). Many genes display a localized expression in the cement gland at all stages of development (Gammill and Sive, 1997Sive, , 2000Sive and Bradley, 1996). Some of these factors such as the homeobox genes otx2 and otx5 and the secreted factor Xag2 have been shown to induce ectopic cement glands in ectoderm of whole embryos and animal cap explants (Aberger et al, 1998;Blitz and Cho, 1995;Vignali et al, 2000).…”