Mutations in the gene encoding laminin ␣2 chain cause congenital muscular dystrophy type 1A. In skeletal muscle, laminin ␣2 chain binds at least two receptor complexes: the dystrophinglycoprotein complex and integrin ␣7␤1. To gain insight into the molecular mechanisms underlying this disorder, we performed gene expression profiling of laminin ␣2 chain-deficient mouse limb muscle. One of the down-regulated genes encodes a protein called Cib2 (calcium-and integrin-binding protein 2) whose expression and function is unknown. However, the closely related Cib1 has been reported to bind integrin ␣IIb and may be involved in outside-in-signaling in platelets. Since Cib2 might be a novel integrin ␣7␤1-binding protein in muscle, we have studied Cib2 expression in the developing and adult mouse. Cib2 mRNA is mainly expressed in the developing central nervous system and in developing and adult skeletal muscle. In skeletal muscle, Cib2 colocalizes with the integrin ␣7B subunit at the sarcolemma and at the neuromuscular and myotendinous junctions. Finally, we demonstrate that Cib2 is a calcium-binding protein that interacts with integrin ␣7B␤1D. Thus, our data suggest a role for Cib2 as a cytoplasmic effector of integrin ␣7B␤1D signaling in skeletal muscle.

Embryonic stem (ES) cells are derived from the inner cell mass of the blastocyst and can be cultured as three-dimensional embryoid bodies (EBs) in which embryonic pregastrulation stages are faithfully mimicked. Fibroblast growth factor receptors (mainly FGFR2) are involved in the first differentiation events during early mammalian embryogenesis. It has been demonstrated that the presence of FGFR2 is a prerequisite for laminin-111 and collagen type IV synthesis and subsequently basement membrane formation in EBs. To identify genes that are influenced by FGFR signalling, we performed global gene expression profiling of differentiating EBs expressing dominant negative FGFR2 (dnFGFR2), acquiring an extensive catalogue of down-and up-regulated genes. We show a strong down-regulation of endodermal and basement membrane related genes, which strengthen the view that the FGFR signalling pathway is a main stimulator of basement membrane synthesis in EBs. We further present down-regulation of genes previously not linked to FGFR signalling, and in addition an active transcription of some mesodermal related genes in differentiating dnFGFR2 EBs.

We have recently identified 1110032E23Rik as a down-regulated target gene in Fgf receptor-signalling-deficient mouse embryoid bodies. Here, we present the expression pattern of this novel gene, designated Ened (Expressed in Nerve and Epithelium during Development), in mouse and Xenopus laevis embryos. Murine Ened transcripts were first seen at E9.5 in the heart and the gastrointestinal tract. At later stages of gestation, expression could be found in the floor plate, peripheral nervous system, lens epithelium, skin, midline dorsal aorta, lung, kidney and testis. In Xenopus, the expression of the Ened orthologue displayed common RNA distribution in several ectodermal and mesodermal tissues, but also distinct expression in locations including the brain, notochord and blood islands. We suggest that Ened might be a novel target gene of the Fgfr signalling pathway during embryonic development, and that its expression could be modulated by the basement membrane component laminin-111. KEY WORDS: Ened, embryonic development, epithelium, Fgf/Fgfr signalling, peripheral nerveFibroblast growth factors (Fgfs) and their receptors (Fgfrs) have been shown to play important roles in the regulation of cellular proliferation and of subsequent differentiation and tissue patterning during vertebrate embryogenesis (Böttcher and Niehrs, 2005). Embryoid bodies (EBs) are aggregates of in vitro-cultured embryonic stem cells and an established model to study the role of Fgfs in epithelial morphogenesis (Weitzer, 2006). It has previously been demonstrated that EBs, in which endogenous Fgfr signalling was attenuated by the over-expression of dominant-negative Fgfr2 (dnFgfr2), failed to produce the first epithelial layer of the EBs, i.e. the endoderm. In addition, expression of the networkforming basement membrane proteins laminin-111 and collagen type IV was abrogated in Fgfr signalling-deficient EBs, and as a consequence ectoderm differentiation failed . In a recent study, we conducted an extensive microarray-based gene expression analysis of dnFgfr2-transfected EBs and presented a catalogue of genes whose expression was significantly influenced by deficient Fgfr signalling. Among the strongly downregulated targets, a number of not yet annotated genes were identified, including the hitherto uncharacterized gene 1110032E23Rik (Meszaros et al., 2007). As confirmed by RTInt.