Integrin α subunit mRNAs are differentially expressed in early Xenopus embryos

Abstract

Adhesion of cells to extracellular matrix proteins is mediated, in large part, by transmembrane receptors of the integrin family. The identification of specific integrins expressed in early embryos is an important first step to understanding the roles of these receptors in developmental processes. We have used polymerase chain reaction methods and degenerate oligodeoxynucleotide primers to identify and clone Xenopus integrin alpha subunits from neurula-stage (stage 17) cDNA. Partial cDNAs encoding integrin subunits alpha 2, alpha 3, alpha 4, alpha 5, alpha 6 and an alpha IIb-related subunit were cloned and used to investigate integrin mRNA expression in early embryos by RNase protection assay and whole-mount in situ hybridization methods. Considerable integrin diversity is apparent early in development with integrins alpha 2, alpha 3, alpha 4, alpha 5 and alpha 6 each expressed by the end of gastrulation. Both alpha 3 and alpha 5 are expressed as maternal mRNAs. Zygotic expression of alpha 2, alpha 3, alpha 4 and alpha 6 transcripts begins during gastrulation. Integrin alpha 5 is expressed at relatively high levels during cleavage, blastula and gastrula stages suggesting that it may represent the major integrin expressed in the early embryo. We demonstrated previously that integrin beta 1 protein synthesis remains constant following induction of stage 8 animal cap cells with activin (Smith, J. C., Symes, K., Hynes, R. O. and DeSimone, D. W. (1990) Development 108, 289–298.). Here we report that integrin alpha 3, alpha 4 and alpha 6 mRNA levels increase following induction with 10 U/ml activin-A whereas alpha 5, beta 1 and beta 3 mRNA levels remain unchanged. Whole-mount in situ hybridization reveals that alpha 3 mRNAs are expressed by cells of the involuting mesoderm in the dorsal lip region of early gastrulae. As gastrulation proceeds, alpha 3 expression is localized to a stripe of presumptive notochordal cells along the dorsal midline. In neurulae, alpha 3 mRNA is highly expressed in the notochord but becomes progressively more restricted to the caudalmost portion of this tissue as development proceeds from tailbud to tadpole stages. In addition, alpha 3 is expressed in the forebrain region of later stage embryos. These data suggest that integrin-mediated adhesion may be involved in the process of mesoderm involution at gastrulation and the organization of tissues during embryogenesis.

Characteristic tetraspanin expression patterns mark various tissues during early Xenopus development

“…CD9 binds to the CD151–a3β1/a6β1 integrin complex or the CD81–a4β1 complex (Boucheix & Rubinstein, 2001). In a previous paper, Xenopus a3 integrin was reported to be expressed in the notochord from the gastrula to the neurula (Whittaker & DeSimone, 1993). While Xlcd9.S was expressed at the notochord and the dorsal tip (Figure 1k, arrowhead), Xlcd81.L expression was not observed in the notochord and looked complimentary to Xlcd9.S (Figure 1l, arrow).…”

Structural Characterization of the ADAM 16 Disintegrin Loop Active Site

“…The presence of integrins on the surfaces of X. laevis eggs is far less clear than for mice and sea urchins. The cloning and expression patterns of mRNA's for the integrin subunits α2, α3, α4, α5, α6, αIIb, and αv have been studied in X. laevis ( − ). Precursor and mature forms of the α5 () and αv () proteins have been detected in lysates from fertilized eggs (stage 1 embryos).…”