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At least 325 records · Page 18Linked to original sources
PubMed1990

Functional implications of the unusual spatial distribution of a minor alpha-tubulin isotype in Drosophila: a common thread among chordotonal ligaments, developing muscle, and testis cyst cells.

Three of the four alpha-tubulin genes in Drosophila melanogaster are temporally regulated. mRNA from one of these genes, alpha 85E-tubulin, first appears in 6- to 8-hr embryos and persists, with marked fluctuations, through the end of pupal development. In adults, alpha 85E mRNA has been unequivocally identified only in testes. In the present study, isotype-specific antibodies have been used to localize alpha 85E tubulin protein in whole tissues. The results demonstrate a spatially restricted expression pattern of the alpha 85E gene that includes tissues of both ectodermal and mesodermal origins. Specifically, embryonic accumulation of alpha 85E tubulin is limited to support cells of chordotonal organs and the developing musculature of the viscera and body wall. In late third instar larvae, chordotonal organs and a subset of larval nerves, but not muscle, stain with anti-alpha 85E. The timing of protein accumulation during pupal development suggests that alpha 85E tubulin is involved in the construction of the adult as well as the larval musculature. In testis, only the somatically derived cyst cells that surround developing spermatid bundles accumulate alpha 85E-tubulin. The cell types that express alpha 85E share a requirement for extensive cell shape changes during development, suggesting that this minor alpha-tubulin may have distinct functional properties.

Animals↗
PubMed1990

Acetylcholinesterase activity of developing muscles in the lower limb of the rat.

A cytochemical study of acetylcholinesterase was done in the lower limb of the prenatal rat and in the gastrocnemius muscle of the postnatal rat. Between 15 and 17 days of gestation, mesenchymal cells constituting the muscle primordia are characterized by the presence of enzyme activity in their rough endoplasmic cisterns and nuclear envelopes, while those involved in the formation of the neocapillary and cartilage do not show enzyme activity. This suggests that mesenchymal cells destined to myogenic cells actively produce acetylcholinesterase in a limited period, which may play a role in cellular aggregation and fusion during the muscular morphogenesis. Cytochemical findings as to extensive networks of secondary synaptic folds of the neuromuscular junctions and invaginations of the sarcolemma in the extrasynaptic regions are also illustrated in the differentiating gastrocnemius muscles.

Acetylcholinesterase↗
PubMed1992

Activation of the gene encoding the glycolytic enzyme beta-enolase during early myogenesis precedes an increased expression during fetal muscle development.

We define the spatial and temporal patterns of expression of the gene encoding the glycolytic enzyme, beta-enolase, during mouse ontogenesis. Transcripts were detected by in situ hybridization using 35S labelled cRNA probes. The beta-enolase gene is expressed only in striated muscles. It is first detected in the embryo, in the cardiac tube and in newly formed myotomes. In the muscle masses of the limb, beta gene expression occurs at a low level in primary fibers, and subsequently greatly increases at a time which corresponds to the onset of innervation and secondary fiber formation. Later in development, it becomes undetectable in slow-twitch fibers. Our results demonstrate the multistep regulation of the beta-enolase gene. The regulation of this muscle-specific gene in somites is discussed in terms of the myogenic sequences of the MyoD family shown to be present when it is activated.

Animals↗
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↗
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↗
PubMed1987

Chick and quail limb bud myoblasts, isolated at different times during muscle development, express stage-specific phenotypes when differentiated in culture.

Evidence is presented which shows that myoblasts, isolated at different stages during chick and quail limb bud development, will form, in culture, myotubes which can be distinguished with a combination of morphological as well as biochemical criteria. Hind limb bud myoblasts isolated from 5-day-old embryos form very short myotubes which synthesize a myosin, the light chains of which are predominantly LC1F and LC2S. Myoblasts isolated from the limb buds of 7-8-day-old embryos form large myotubes which synthesize a myosin the light chains of which are predominantly LC1F, LC2S and LC2F. Myoblasts isolated from the thigh muscle of embryos older than 10 days form large myotubes which synthesize a myosin the light chains of which are predominantly LC1F and LC2F. These results have been confirmed by hybridization of the cellular mRNA with a molecular probe specific for LC2F. These results lead us to suggest the existence of at least two classes of myoblasts which appear at different times during limb bud development. The first class, or 'early' myoblasts, is present in the limb buds of 5-day-old embryos, whereas the second class, or 'late' myoblasts, is present in the muscles of embryos older than 8 days. This result, however, is also compatible with the hypothesis that all muscle cells are the same at all times during development, and that the different phenotypes simply reflect differences in the environmental conditions.

Animals↗
PubMed1987

Scanning electron microscopy of human prenatal muscle development.

A scanning electron microscopic study of the development of the human quadriceps was performed in 30 fetuses ranging from 6 to 40 weeks gestation. The results clearly illustrate the hyperplastic phase of myogenesis, showing the differentiation, multiplication and fusion of the myoblasts and the subsequent formation of different generations of myotubes. The myoblasts decrease relatively in number within the developing quadriceps until the 19th week of gestation, and remain afterwards as quiescent satellite cells. The maturation of the myotubes to myofibers and the metabolic differentiation of the fibers are not accompanied by significant changes in their external form in terms of scanning electron microscopy. The hypertrophic phase of myogenesis and general fetal growth can be followed with scanning electron microscopy by the increase in size of the fibers or bundles of fibers, as well as by the differentiation of the connective tissue components of the muscle.

Embryonic and Fetal Development↗