Expression patterns of laminin receptor splice variants α6Aβ1 and α6Bβ1 suggest different roles in mouse development

Abstract

The a6pl integrin is a receptor for laminins and is present from early stages of mouse embryogenesis. In the present study we determined the temporal and spatial expression of the two cytoplasmic splice variants of the a6 integrin subunit, a6A and a6B, in the early-and midgestation mouse postimplantation embryo using RT-PCR, in situ hybridization, and immunofluorescence. Our results show that a6B is present in the embryo at all stages studied and is expressed before a6A. a6A expression begins in 8.5 day p.c. embryos and is initially exclusively localized to the developing heart. In 8.5 (and 9.5) day p.c. embryos a6A mRNA and protein are present in a gradient in the myocardium of the heart tube from strongest expression in the sinus venosus and in the common atrial chamber to a weakening expression along the ventricle and bulbus cordis. In 10.5 day p.c. embryos this gradient is less evident and in 12.5 day p.c. embryos a6A mRNA and protein are present in comparable amounts between atria and ventricles. Neither a6A nor a6B is present in endocardial cushion tissue. By day 12.5 p.c. (w6A expression is also present in the developing epidermis, dental primordia, lens, gonads, and in a few epithelia such as those of the digestive tract. a6B expression is always much more widespread than a6A expression. For example, only a6B is present in the myotome of the somites of 9.5 day p.c, embryos, in the developing central and peripheral nervous systems, and in the nephrogenic system at all stages studied, except after the differentiation of the gonads when a6A is also present. Furthermore, a6B is the only splice variant present on endothelial cells. We also examined the distribution of the f34 integrin subunit to determine whether the a6P4 integrin was present during these stages of development. p4 protein was absent in early postimplantation stages but was present in the epidermis and digestive tract of 12.5 day p.c. embryos. These results show a differential distribution of a6A and a6B during mouse development and thus strongly suggest a different function of these splice variants during embryogenesis. Our results point to a possible role for the 0 1995 WILEY-LISS, INC. a6Apl integrin in the development of the myocardium of the developing heart, but not in the migration of endocardial cushion cells, while a6Bp1 could be important in the developing nephrogenic and nervous systems. o l W 5 Wiley-Liss, Inc.

Differential expression of the integrins α6Aβ4 and α6Bβ4 along the crypt–villus axis in the human small intestine

“…Distinct patterns of expression for the two 6 variants have been reported in diVerent organs during development (de Curtis and Reichardt 1993;Segat et al 2002;Thorsteinsdottir et al 1995) suggesting a functional importance of the expression ratio of the two forms. The exclusive expression of 6A in a rapidly dividing cellular compartment is known from the epidermis .…”

“…The intestine was initially reported to express both variants . These patterns of expression for 6A and 6B as well as their dissimilar temporal expression during embryonic development (Thorsteinsdottir et al 1995) may imply that they serve diVerent biological functions.…”

Integrins in the mouse myotome: Developmental changes and differences between the epaxial and hypaxial lineage

“…Although the expression of the ␤1 (Pow and Hendrickx, 1995), ␣1 (Duband et al, 1992), ␣4 (Stepp et al, 1994), ␣6 (Bronner-Fraser et al, 1992Thorsteinsdó ttir et al, 1995;Pow and Hendrickx, 1995), and ␣7 (Velling et al, 1996) integrin subunits have been described in the myotome, it is not clear whether their expression patterns vary with the differentiation state of the myotomal cells and/or among the different regions of the myotome.…”

“…The ␣6 integrin subunit is present very early in development (Hierck et al, 1993;Thorsteinsdó ttir et al, 1995), and until E9.5, it is most strongly expressed in the paraxial mesoderm, heart, headfolds/head, and presumptive limb region (Fig. 1B,D).…”

“…Yang, and R.O. Hynes, respectively) and ␣6 (Thorsteinsdó ttir et al, 1995) were determined in whole-mount embryos from E9.0 to E10.5. To help interpret the patterns obtained, we used probes marking myogenic cells in different phases of differentiation, namely Myf-5, MLC1A, and ␣-cardiac actin (probes kindly provided by M. Buckingham).…”