Cadherins, a multigene family of transmembrane glycoproteins, mediate Ca2-dependent intercellular adhesion. They are thought to be essential for the control of morphogenetic processes, including myogenesis. Here we report the identification and characterization of the cDNA of another member of the cadherin family, M-cadheria (M for muscle), from differentiating muscle cells. The longest open reading frame of the cDNAs isolated contains almost the entire coding region of the mature M-cadherin as determined by sequence homology to the known cadherins. M-cadherin mRNA is present at low levels in myoblasts and is upregulated in myotube-forming cells. In mouse L cells (fibroblasts), M-cadherin mRNA is undetectable. This expression pattern indicates that M-cadherin is part of the myogenic program and may provide a trigger for terminal muscle differentiation.

No abstract

During zebrafish development, the thyroid primordium initiates expression of molecular markers such as hhex and nk2.1a in the endoderm prior to pharynx formation. As expected for an endodermally derived organ, initiation of thyroid development depends on Nodal signalling. We find that it also depends on three downstream effectors of Nodal activity, casanova (cas), bonnie and clyde (bon), and faust (fau)/gata5. Despite their early Nodal-dependent expression in the endoderm, both hhex and nk2.1a are only required relatively late during thyroid development. In hhex and nk2.1a loss-of-function phenotypes, thyroid development is initiated and arrests only after the primordium has evaginated from the pharyngeal epithelium. Thus, like pax2.1, both hhex and nk2.1a have similarly late roles in differentiation or growth of thyroid follicular cells, and here, we show that all three genes act in parallel rather than in a single pathway. Our functional analysis suggests that these genes have similar roles as in mammalian thyroid development, albeit in a different temporal mode of organogenesis.

To identify genes that are differentially expressed during self-repair processes in mouse brain, we screened a subtracted cDNA library enriched for brain-specific clones. One of these clones, H74, detected a 4.4-kb mRNA predominantly expressed in brain and dorsal root ganglia neurons. Expression increased continuously during the lifespan and the state of differentiation, but decreased after entorhinal-cortex lesion. A full-length cDNA clone was isolated from a cerebellum cDNA library and characterized. Sequence analysis and database search revealed high sequence similarity to FAP52, a protein expressed in focal-adhesion contacts, and uncharacterized Echinococcus and Caenorhabditis elegans gene products. Furthermore, peptide sequences derived from human cDNA fragments showed up to 65% sequence identity at the amino acid level. The presence of a C-terminal src homology 3 (SH3) domain and its phosphorylation by casein kinase 2 (CK2) and protein kinase C (PKC) imply a role in signaling. Here we demonstrate that the gene encodes a phosphoprotein, referred to as PACSIN, with a restricted spatial and temporal expression pattern.Keywords : signal transduction; neuron; SH3 domain; phosphorylation; brain protein.Partial deafferentation in selected areas of the adult rodent brain induces a sequence of compensatory events in both the remaining afferent fibers and the denervated dendrites, resulting in reorganization of the circuitry in the denervated area. The regeneration events include sprouting of the remaining afferent fibers, restoration of spine density and length, as well as replacement of vacated synaptic contacts [1]. One of the most carefully examined mammalian brain structures is the hippocampus, which is known for its role in learning and memory and which appears to maintain a high degree of anatomical plasticity even in adult animals. This phenomenon has been studied particularly for changes in the dentate gyrus in response to the loss of input after unilateral entorhinal cortex lesion (ECL).Relatively little is known regarding the molecular and biochemical events that underlie regeneration or self-repair proCorrespondence to M. Plomann,

The zinc finger protein RE-1-silencing transcription factor (REST) 1 is a transcriptional repressor that represses neuronal genes in nonneuronal tissues. Transfection experiments of neuroblastoma cells using a REST expression vector revealed that synapsin I promoter activity is controlled by REST. The biological activity of REST was further investigated using a battery of model promoters containing strong promoters/enhancers and REST binding sites. REST functioned as a transcriptional repressor when REST binding motifs derived from the genes encoding synapsin I, SCG10, ␣ 1 -glycine receptor, the ␤2-subunit of the neuronal nicotinic acetylcholine receptor, and the m4-subunit of the muscarinic acetylcholine receptor were present in the promoter region. No differences in the biological activity of these REST binding motifs tested were detected. Moreover, we found that REST functioned very effectively as a transcriptional repressor at a distance. Thus, REST represents a general transcriptional repressor that blocks transcription regardless of the location or orientation of its binding site relative to the enhancer and promoter. This biological activity could also be attributed to isolated domains of REST. Both repressor domains identified at the N and C termini of REST were transferable to a heterologous DNA binding domain and functioned from proximal and distal positions, similar to the REST protein. RE-1-silencing transcription factor (REST)1 , also known as neuron-restrictive silencer factor, functions as a transcriptional repressor of neuronal genes in nonneuronal tissues (1, 2). Target genes of REST are the genes encoding choline acetyltransferase, the type II sodium channel, SCG10, the m4 muscarinic acetylcholine receptor, and the adhesion proteins L1 and NgCAM (1-6). We have shown recently that the REST binding motif within the synapsin I promoter is responsible for restricting the expression of synapsin I to neuronal cells (7). Deletion of the REST binding site abolished neuron-specific expression of the reporter gene entirely, allowing constitutively acting elements of the promoter to direct expression in a nontissue specific manner.The REST binding motif termed the neural-restrictive silencer element (NRSE) was identified at various positions in those genes regulated by REST. NRSEs were found in the promoter region as shown for the synapsin I and the muscarinic acetylcholine receptor m4-subunit genes (7-9). In the SCG10 gene, an NRSE is located farther upstream at position Ϫ1472 to Ϫ1452 (10), whereas in the NgCAM gene, five NRSEs have been discovered within the first intron (3). Furthermore, genes encoding the ␣ 1 -glycine receptor and the ␤2-subunit of the neuronal nicotinic acetylcholine receptor contain NRSEs in the 5Ј-untranslated region downstream of the transcriptional start site (11,12). It has been proposed that REST switches its activity from repressing to activating transcription when REST binds to an NRSE located in the 5Ј-untranslated region or less than 50 base pairs upstream from the TATA bo...

Antigen Leu-19 (Leul9-Ag), a 200-to 220-kDa surface glycoprotein, was originally identified on a subset of human peripheral lymphocytes exhibiting non-major histocompatibility complex-restricted cytotoxicity. Here we report that monoclonal antibody Leu-19 (mAb-Leu19) labels structures in human skeletal muscle: (i) satellite cells, which form the stem cell pool of muscle fiber regeneration, both in normal and diseased muscle; (ii) myotubes and myotube projections in regions of muscle fiber repair; (iii) periodically organized fibrillar structures in areas of regeneration; (iv) the surface of myoblasts and developing myotubes in culture. mAb-Leul19 precipitated a protein of -200 kDa from cultured muscle cells. Our data show that Leul9-Ag is expressed on muscle-specific components of myosegments in repair and thus represents a molecular marker of muscle regeneration. On the basis of this molecular marker and using laser scan microscopy, it is possible to visualize at the light microscopic level hitherto undetectable details of muscle regeneration in routine cryostat sections.

Molecules regulating morphogenesis by cell‐cell interactions are the cadherins, a class of calcium‐dependent adhesion molecules. One of its members, M‐cadherin, has been isolated from a myoblast cell line (Donalies et al. [1991] Proc. Natl. Acad. Sci. U.S.A. 88:8024—8028). In mouse development, expression of M‐cadherin mRNA first appears at day 8.5 of gestation (E8.5) in somites and has been postulated to be down‐regulated in developing muscle masses (Moore and Walsh [1993] Development 117:1409—1420). Affinity‐purified polyclonal M‐cadherin antibodies, detecting a protein of approximately 120 kDa, were used to study the cell expression pattern of M‐cadherin protein. It was first visualized in somites at E10 1/3 and could be confined to desmin positive, myotomal cells. At all subsequent prenatal stages, M‐cadherin was only found in myogenic cells of somitic origin. The detection of the protein at E10 1/3 suggests a translational delay of M‐cadherin mRNA of 1 to 2 days (E8.5 vs. E10 1/3). This was further supported by the finding that during differentiation of ES cell line BLC6 into skeletal muscle cells in culture, expression of M‐cadherin mRNA can be detected 2 days prior to M‐cadherin protein. During prenatal development, the pattern of M‐cadherin expression changes: In E10 1/3 embryos and also in myotomal cells of later stages, M‐cadherin is evenly distributed on the cell surface. In developing muscle masses (tested at E16 to E18), however, M‐cadherin protein becomes clustered most likely at sites of cell‐cell contact as indicated by double‐labelling experiments: M‐cadherin‐staining is the positive image of laminin negative areas excluding the presence of a basal lamina at M‐cadherin positive sites. Furthermore, M‐cadherin is coexpressed with the neuronal cell adhesion molecule N‐CAM which has been shown to mediate cell‐cell contact in myogenic cells. In summary, our results are in line with the idea that M‐cadherin might play a central role in myogenic morphogenesis. © 1994 Wiley‐Liss, Inc.

Isolated hapten-binding receptors of sensitized lymphocytes Receptors from nylon wool-enriched mouse T lymphocyte lack serological markers of immunoglobulin constant domain but express heavy chain variable portions*Hapten-binding receptor material was isolated from hapten-sensitized mouse lymphocytestas .described previously (Eur. J. ImmunoL 1976. 6 : 529; Cold Spring Harbor Symp. Quant. Biol. 1977.41: 285). The material was separated into a fraction expressing immunoglobulin determinants (anti-lg+ fraction) and a fraction lacking determinants of the known Ig constant domains (anti-lgfraction). We present further evidence in support of the notion that the anti-lg+ fraction is B cell-derived, whereas the anti-lg-fraction originates from T lymphocytes. Receptors derived from C57BL/6 mice of-the anti-lg-phenotype with specificity for the hapten (4-hydroxy-3-nitropheny1)acetyl (NP) are found t o express markers which are characteristic for the variable portion of primary anti-NP antibodies. One of these markers relates t o the fine specificity of hapten binding [6,24], the other is defined by anti-idiotypic antibodies. Genetic studies show that the expression of these markers both in antibodies and the anti-lgreceptor fraction is controlled by genes in the heavy chain linkage group.The results demonstrate that in this system, humoral antibodies and receptor molecules of both the anti-lg+ and anti-Ig-phenotype bind the hapten with strikingly similar affinity and fine specificity. More specifically, they suggest that the molecules in the anti-Ig-receptor fraction carry the variable region (and in fact the en tire variable region) of the Ig heavy chain.