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At least 469 records · Page 26Linked to original sources
PubMed1995

The Drosophila toll gene functions zygotically and is necessary for proper motoneuron and muscle development.

Toll is a maternally required Drosophila gene that encodes a transmembrane protein with an important function in embryonic dorsal-ventral patterning. The Toll protein is widely expressed zygotically, but its roles in late embryo-genesis have not been described in detail. We have examined the expression of Toll protein in the late embryonic central nervous system and somatic musculature. Toll is expressed in a dynamic pattern in teh musculature, initially in several muscle fibers in each hemisegment, with a later narrowing of expression to a single muscle fiber pair. Zygotic Toll mutants were used to investigate the development consequences of loss of Toll expression. We found that loss of one or both copies of the Toll gene leads to widespread defects in motoneuron number and muscle patterning. Loss of motoneurons prevents certain muscle fibers from receiving their wild-type innervation. Denervation in the mutants results in collateral sprouting from nearby nerve branches and leads to the appearance of ectopically placed motor endings. The limited expressivity observed suggests that Toll is only one of several genes required for proper motoneuron and muscle specification.

Animals↗
PubMedDate not supplied

Targeting of lysosomal enzymes: N-acetylglucosamine-1-phosphotransferase during muscle development.

It has been previously shown by morphological techniques and measurements of lysosomal enzyme levels that the I cell mutation is expressed in myoblasts but not in myotubes or mature muscle fibers. These findings suggested the possibility of developmental regulation of the affected enzyme, UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-phosphotransferase. In this article, we examine this possibility by measuring the phosphotransferase activity at various stages of muscle differentiation in three different animal species (human, chick, rat). Although activity of the enzyme is consistently higher in myoblasts than in myotubes or mature muscle, the difference in the levels of activity at these three states of muscle differentiation varies widely in the three species examined. We further found that the phosphotransferase activity was absent in the muscle of an I cell patient, in spite of normal muscle morphology. This indicates the presence of a mannose-6-phosphate-independent mechanism for lysosomal enzyme targeting in muscle and other unaffected tissues. The existence of such a pathway cannot be explained by lack of the necessary enzyme, as the phosphotransferase is present at a comparable level in normal muscle of three different species (human, chick, rat).

Animals↗
PubMedDate not supplied

Hoxa-11 and Hoxa-13 are involved in repression of MyoD during limb muscle development.

Under the influence of the limb mesenchyme, Hoxa-11 is expressed in migrating and proliferating premyoblasts in the limb field and Hoxa-13 is induced in subdomains of congregated limb muscle masses. To evaluate the roles of Hoxa-11 and Hoxa-13 in myogenesis of the limb, we performed electroporation in ovo to force expression of these Hox genes in limb muscle precursors. In the presence of ectopic Hoxa-11, expression of MyoD was blocked transiently. In C2C12 myoblasts, transfection of Hoxa-11 also repressed the expression of endogenous MyoD. Forced expression of Hoxa-13 resulted in more pronounced repression of MyoD in both limb and C2C12 myoblasts. In contrast, targeted disruption of Hoxa-13 gave rise to enhanced expression of MyoD in the flexor carpi radialis muscle, a forearm muscle that normally expressed Hoxa-13. These results suggest that Hoxa-11 and Hoxa-13 are involved in the negative regulation of MyoD expression in limb muscle precursors.

Animals↗
PubMed2004

HRC is a direct transcriptional target of MEF2 during cardiac, skeletal, and arterial smooth muscle development in vivo.

The HRC gene encodes the histidine-rich calcium-binding protein, which is found in the lumen of the junctional sarcoplasmic reticulum (SR) of cardiac and skeletal muscle and within calciosomes of arterial smooth muscle. The expression of HRC in cardiac, skeletal, and smooth muscle raises the possibility of a common transcriptional mechanism governing its expression in all three muscle cell types. In this study, we identified a transcriptional enhancer from the HRC gene that is sufficient to direct the expression of lacZ in the expression pattern of endogenous HRC in transgenic mice. The HRC enhancer contains a small, highly conserved sequence that is required for expression in all three muscle lineages. Within this conserved region is a consensus site for myocyte enhancer factor 2 (MEF2) proteins that we show is bound efficiently by MEF2 and is required for transgene expression in all three muscle lineages in vivo. Furthermore, the entire HRC enhancer sequence lacks any discernible CArG motifs, the binding site for serum response factor (SRF), and we show that the enhancer is not activated by SRF. Thus, these studies identify the HRC enhancer as the first MEF2-dependent, CArG-independent transcriptional target in smooth muscle and represent the first analysis of the transcriptional regulation of an SR gene in vivo.

Amino Acid Motifs↗
PubMed1993

A community effect in muscle development.

BACKGROUND: Most vertebrate tissues arise by embryonic induction, as a result of which new cell layers are formed. These are subsequently subdivided into discrete groups of homogeneous cell populations, each containing different cell-types with specific gene expression. There is preliminary evidence from previous work that the mesoderm-forming induction in amphibian development may be followed by a further interaction among some of the induced mesoderm cells, and that this could be required for muscle gene activation in uniform cell populations. RESULTS: We have established the existence, time and place of this further cell interaction by transplanting muscle progenitor cells from Xenopus mid-gastrulae into ectoderm sandwiches, and then culturing these constructs until the time of muscle gene activation. We find that cells implanted as reaggregates, but not those implanted as single cells, activate early myogenic genes and later muscle-specific genes. More than 100 cells must be near each other for muscle gene activation. These cells can induce non-muscle mesoderm cells to express muscle genes by emitting a signal that differs from the preceding mesoderm induction signal. Muscle gene activation under these conditions does not require gap junction communication. CONCLUSION: Cells within the muscle progenitor region of a Xenopus embryo need to interact with each other in order to activate muscle genes in homogeneous cell groups. This exemplifies the 'community effect', which may be a widespread developmental mechanism used to increase the homogeneity within, and demarkation between, embryonic tissues.

Journal Article↗
PubMed1988

Merosin, a protein specific for basement membranes of Schwann cells, striated muscle, and trophoblast, is expressed late in nerve and muscle development.

We have identified a tissue-specific basement membrane-associated protein by using monoclonal antibodies prepared against a protein fraction of human placenta. In immunofluorescence, the monoclonal antibodies stained basement membranes of Schwann cells, striated muscle, and trophoblast, whereas no reaction was seen with any other basement membrane or tissue structure. In antibody-affinity chromatography of proteolytic digests of human placenta, a 65-kDa polypeptide was bound by these monoclonal antibodies. Rabbit antisera and monoclonal antibodies raised against the isolated 65-kDa polypeptide stained human and monkey tissues identically to the original monoclonal antibodies and reacted with an 80-kDa polypeptide in tissue extracts prepared without proteolysis. The 65-kDa and 80-kDa polypeptides were shown to be immunologically distinct from laminin, type IV collagen, fibronectin, and major serum proteins. They presumably represent a novel basement membrane-associated protein, which we have named merosin. No merosin immunoreactivity could be detected in cultures of any of 28 established cell lines. In developing mouse tissues, merosin staining first appeared at the newborn stage. The restricted tissue distribution and late developmental appearance of merosin suggest that the protein has a tissue-specific function associated with a high level of differentiation.

Animals↗
PubMed1994

Early skeletal muscle development proceeds normally in parthenogenetic mouse embryos.

In mouse chimeras with parthenogenetic cell contribution, the skeletal musculature appears to be largely devoid of parthenogenetically derived cells. To analyze the appearance and early distribution of myotomal cells in parthenotes, we determined the expression of the muscle-specific transcription factors myogenin, MYF-5, and MYF-6 by in situ hybridization in somites of Day 10 and 11 embryos. Here, we report that these myogenic regulatory proteins are expressed in parthenogenetic animals together with desmin, one of the early muscle-specific structural proteins. We also show that parthenogenetic cells contribute equally to dermatome, sclerotome, and myotome in Day 10 and 11 chimeras. These results suggest that early myotomal cells expressing the myogenic control proteins develop and allocate normally in parthenogenetic embryos and in parthenogenetic<==>normal chimeras. The underrepresentation in older chimeras may therefore be due to selective elimination. These data also argue against imprinting of the myogenic factor genes myogenin, Myf-5, and Myf-6.

Animals↗
PubMedDate not supplied

An autopsy case of Pena-Shokeir syndrome: severe retardation of skeletal muscle development compared with neuronal abnormalities.

An infant with multiple joint ankyloses, facial anomalies, and pulmonary hypoplasia, features similar to the phenotype of Pena-Shokeir syndrome, was examined at autopsy. Histological examination of the skeletal muscles revealed many small muscle fibers in a mixed, not group, distribution, although the structure of them was normally arranged. Histochemical assessment of adenosine triphosphatase (ATPase) activity of the iliopsoas muscle demonstrated the failure of the differentiation into type I fibers and the retardation of the skeletal muscle. At the same time, severe pulmonary hypoplasia, which was the likely cause for the retardation of the respiratory system, was found. In contrast to these numerous pathologic changes in the skeletal muscles, no significant abnormalities were observed in the central nervous system except for a somewhat immature external appearance; however, an examination of the spinal cord could not be carried out. Overall, this pattern of pathology suggests the possibility that developmental disorders of the mesenchyme are the primary contributors to the pathogenesis of Pena-Shokeir syndrome, while the immaturity of the central nervous system is involved to a lesser degree.

Abnormalities, Multiple↗