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Biomedical subjects

G Lyons

Publications and source records attributed to G Lyons.

At least 19 recordsLinked to original sources
PubMed1992

MyoD, myogenin independent differentiation of primordial myoblasts in mouse somites.

The accumulation of two myogenic regulatory proteins, MyoD and myogenin, was investigated by double-immunocytochemistry and correlated with myosin heavy chain expression in different classes of myoblasts in culture and during early myogenesis in vivo. During in vitro differentiation of fetal myoblasts, MyoD-positive cells were detected first, followed by the appearance of cells positive for both MyoD and myogenin and finally by the appearance of differentiated myocytes and myotubes expressing myosin heavy chain (MHC). A similar pattern of expression was observed in cultures of embryonic and satellite cells. In contrast, most myogenic cells isolated from newly formed somites, expressed MHC in the absence of detectable levels of myogenin or MyoD. In vivo, the appearance of both myogenin and MyoD proteins was only detected at 10.5 d postcoitum (d.p.c.), when terminally differentiated muscle cells could already be identified in the myotome. Parasagittal sections of the caudal myotomes of 10.5-d-old embryos showed that expression of contractile proteins preceded the expression of myogenin or MyoD and, when coexpressed, MHC and myogenin did not co-localize within all the cells of the myotome. In the limb bud, however, many myogenin (or MyoD) positive/MHC negative cells could be observed in the proximal region at day 11. During further embryonic development the expression of these proteins remained constant in all the muscle anlagens examined, decreasing to a low level during the late fetal period. Western and Northern analysis confirmed that the myogenin protein could only be detected after 10.5 d.p.c. while the corresponding message was clearly present at 9.5 d.p.c., strongly suggesting a posttranscriptional regulation of myogenin during this stage of embryonic development. These data show that the first myogenic cells which appear in the mouse myotome, and can be cultured from it, accumulate muscle structural proteins in their cytoplasm without expressing detectable levels of myogenin protein (although the message is clearly accumulated). Neither MyoD message or protein are detectable in these cells, which may represent a distinct myogenic population whose role in development remains to be established.

Animals↗
PubMed1992

Combined epidural/spinal anaesthesia for caesarean section. Through the needle or in separate spaces?

An evaluation of a 30 gauge spinal needle in a combined epidural/spinal anaesthetic technique for Caesarean section revealed a 25% failure rate of the spinal element. In this unit, no more than 4% of spinal anaesthetics might be expected to fail. One of the reasons for the higher failure rate was that, when using the Tuohy needle as an introducer, the dura was not identified. This prompted us to compare the 'through-the-Tuohy' or needle within needle approach for combined epidural/spinal anaesthesia, with a technique that involved siting the epidural and spinal sequentially in separate spaces. One hundred women requiring elective Caesarean section under spinal anaesthesia were randomised into single or double space groups. The technique failed in 16% of through-the-needle cases, and in 4% of sequential sitings. Combined spinal/epidural anaesthesia for Caesarean section is more successful if each procedure is performed using separate spaces.

Adult↗
PubMed1992

Diclofenac for analgesia after caesarean section.

The analgesic efficacy of a single intramuscular dose of 75 mg diclofenac given after elective Caesarean section was studied in 50 women in a double-blind randomised manner using a patient-controlled analgesia system. The mean 18 h papavaretum consumption of the placebo group was significantly greater (91.4 mg compared to 61.4 mg). Subjective experience of pain and observed sedation were significantly greater in the control group up to 6 h after operation.

Adult↗
PubMed1992

Apical ridge dependent and independent mesodermal domains of GHox-7 and GHox-8 expression in chick limb buds.

The homeobox-containing genes GHox-7 and GHox-8 have been proposed to play fundamental roles in limb development. The expression of GHox-8, by the apical ridge cells, and GHox-7, in the subridge mesoderm, suggests the involvement of these two genes in limb outgrowth and proximo-distal pattern formation. A straightforward way to test this is to remove the apical ridge. Here we report the relationship between the mesodermal expression of GHox-7 and GHox-8 and the apical ectodermal ridge in the chick limb bud. The data from ridge removal experiments indicate that there are at least two domains of GHox-7 expression in the apical limb bud mesoderm. The posterior subridge GHox-7 domain in the progress zone requires the influence of the apical ridge for continued expression, while the anterior GHox-7 domain continues expression after ridge removal. Posterior subridge mesoderm is exquisitely sensitive to the loss of the ridge in that GHox-7 expression by these cells is reduced in only two hours and undetectable by three hours after ridge removal. It would appear that one of the ways progress zone cells respond to the apical ridge signal is by expressing GHox-7. The loss of ridge influence whether by growth at the apex or by ridge removal is followed by an unusually rapid decline in detectable GHox-7 transcripts. Maintenance of GHox-8 expression by the anterior mesoderm appears to be independent of the presence of the apical ridge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Expression of muscle genes in the mouse embryo.

Using isogene specific probes and in situ hybridization on sections, we have examined the expression of structural and regulatory genes in the mouse embryo during the formation of cardiac and skeletal muscle. The temporal and spatial information thus obtained about the onset of expression of muscle genes provides insight into the regulation of myogenesis in vivo. Actin and myosin sequences present in different compartments of the adult heart are initially all co-expressed in the cardiac tube (between 7-8 days). The process of spatial restriction to atrial or ventricular compartments of the heart takes place asynchronously later. In contrast, the onset of expression of actin and myosin genes in the first skeletal muscle, the myotome, which corresponds to the central compartment of the somite, as well as their subsequent down-regulation in different skeletal muscle masses, takes place very asynchronously. One might predict that factor(s) responsible for the transcriptional activation of these genes are present in sufficient quantity in the cardiac tube, whereas in skeletal muscle individual genes are responding to variable levels of factor(s). In fact the four myogenic regulatory sequences present in the mouse - MyoD1, myogenin, myf-5 and myf-6 - do show distinct patterns of expression during the development of skeletal muscle. None of these sequences have been detected in the heart. In the myotome there is no general correlation between the appearance of a particular myogenic sequence and the activation of a particular structural gene. A striking example of this is provided by the muscle isoform of creatine phosphokinase. We would propose that each muscle structural gene has a different threshold of activation, depending on the quantity and nature of the myogenic factor present. We have also examined the onset of expression of the X-linked dystrophin gene known to be expressed in adult heart and skeletal muscle. In the myotome dystrophin transcripts are first detected at the time when myosin heavy chains first accumulate and muscular contraction is initiated. In contrast in the cardiac tube dystrophin transcripts are not detected initially, at a time (from 8 days) when the heart contracts. This observation can be correlated with the pathology of the disease which points to a more essential role of dystrophin in skeletal muscle. No muscle structural gene examined is expressed in the somite prior to myotome formation. If the myogenic regulatory sequences are implicated in muscle cell determination then they should be expressed in the dermomyotome of the immature somite which gives rise to muscle precursor cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1992

Carbonic anhydrase 3 (CA3), a mesodermal marker.

Carbonic anhydrase 3 (CA3) is an abundant muscle protein characteristic of adult type 1, slow-twitch, fibres. The protein plays an important role in facilitated CO2 diffusion and diverse processes involving H+ and HCO-3 transport. Nucleotide sequence comparisons have identified putative promoter and enhancer regions in the 5' flanking sequences of the CA3 gene. Functional assays show that 2.8kb of 5' flanking sequence efficiently promotes transcription of a reporter gene in a muscle specific manner. Removal of sequences 5' to -722bp leads to a major loss of activity and this result implies that the proximal promoter region which includes a GArG box and four potential MyoD1 binding sites is not adequate for maximal transcription. The longest CA3 promoter construct is also active in 10T1/2 cells, which are precursor mesodermal cells and do not normally express CA3. In situ hybridization to mRNA in developing mouse embryos reveals a pattern of expression in myotomes and pre-muscles masses of the limb buds which is consistent with the regulation of CA3 by myogenic determination factors. These studies also showed that CA3 expression is not confined to cells of the muscle lineage since it is expressed in primitive mesoderm prior to the onset of myogenesis. Later in embryogenesis CA3 defines a subset of mesodermal cell types which includes not only skeletal muscle but also notochord and adipocytes.

Animals↗
PubMed1991

The apical ectodermal ridge regulates Hox-7 and Hox-8 gene expression in developing chick limb buds.

We show that expression of the two related chicken homeo box genes, Hox-7 and Hox-8, which is widespread in the lateral mesoderm at early stages, becomes restricted to the mesoderm underlying the apical ectodermal ridge as limbs develop. Expression in the limb bud mesoderm is not maintained in the limbless mutant, which does not form an apical ridge. The mutant can be rescued by grafting normal ectoderm to the limb field. This leads to expression of the two homeo box genes in the mesoderm under the induced ridge. Phenocopies of eudiplopodia, which form an ectopic ridge on the limb bud, express the two genes under both ridges. When a quail ridge is grafted over nonexpressing mesoderm, a new site of expression is induced. Therefore, Hox-7 and Hox-8 depend on a functional ridge for their continued expression in the limb bud and can be induced by it.

Amino Acid Sequence↗
PubMed1991

Awareness during caesarean section.

Between 1982 and 1989 over 3000 patients were questioned about recall and dreaming after general anaesthesia for Caesarean section. Some 28 (0.9%) patients were able to recall something of their operation and 189 (6.1%) reported dreams. There was uniform adherence to a rigid anaesthetic protocol up to and including 1985, but a much publicized incident reported from the courtroom stimulated a relaxation of this regimen. Consequently the incidence of awareness decreased from 1.3% to 0.4%, and the incidence of dreaming was also reduced. Recollections of surgery were confined to manipulations, noises and voices. None of our patients complained of pain at the time of interview, although one since has. The inadequacies of the initial protocol and an approach to informed consent are discussed.

Adult↗
PubMed1991

Early expression of the myogenic regulatory gene, myf-5, in precursor cells of skeletal muscle in the mouse embryo.

We have analysed by in situ hybridization the expression of myf-5, the murine homologue of the human myogenic regulatory sequence myf5, during embryogenesis in the mouse. myf-5 sequences were first detected in the earliest somites (from about 8 days p.c.) in the dermomyotome, before formation of the dermatome, myotome and sclerotome. The dermomyotome is classically considered to give rise to the precursor muscle cells of body and limb skeletal muscle. myf-5-positive cells were also detected early in the visceral arches and limb buds. In this case, as in somites, myf-5 expression precedes that of the two related myogenic regulatory sequences, myogenin and MyoD1, and indeed any other skeletal muscle marker examined to date. myf-5 is not detected at any stage in developing cardiac muscle. From 11.5 days p.c., the level of myf-5 transcripts begins to decrease to become undetectable (by in situ hybridization) from 14 days p.c. Both the appearance and disappearance of myf-5 follow the anteroposterior gradient of somite formation and maturation in the embryo. The time and place of myf-5 expression are consistent with a role in the early events of myogenic differentiation, possibly during determination of the myogenic lineage.

Animals↗
PubMed1990

Doxorubicin selectively inhibits muscle gene expression in cardiac muscle cells in vivo and in vitro.

The anthracycline antibiotic doxorubicin produces a characteristic myopathy in cardiac muscle that limits its use in cancer therapy. We have shown in cultured neonatal rat cardiac muscle cells that doxorubicin treatment resulted in a rapid, selective decrease in the expression of muscle-specific genes, which preceded other changes characteristic of doxorubicin cardiomyopathy. Doxorubicin selectively and dramatically decreased the levels of mRNA for the sarcomeric genes, alpha-actin, troponin I, and myosin light chain 2, as well as the muscle-specific, but nonsarcomeric M isoform of creatine kinase. However, doxorubicin did not affect nonmuscle gene transcripts (pyruvate kinase, ferritin heavy chain, and beta-actin). Actinomycin D, an inhibitor of DNA-dependent RNA polymerase, did not show a similar selective decrease of muscle-specific mRNAs but, rather, produced a nonspecific, dose-dependent decrease of muscle and nonmuscle transcripts. The doxorubicin effect on muscle gene expression was limited to cardiac muscle; cultured skeletal myocytes were resistant to the effects of doxorubicin at 100-fold greater doses than those causing changes in mRNA levels in cardiac muscle cells. These effects of doxorubicin were reproduced in vivo; rats injected with doxorubicin showed a dose-dependent decrease in the levels of mRNAs for alpha-actin, troponin I, myosin light chain 2, and M isoform of creatine kinase in cardiac but not skeletal muscle. These selective changes in gene expression in cardiocyte cultures and cardiac muscle precede classical ultrastructural changes and may explain the myofibrillar loss that characterizes doxorubicin cardiac injury.

Actins↗
PubMed1990

Needlestick injuries in anaesthetists.

A survey of needlestick injuries among 42 anaesthetists at this university hospital was carried out over a 3-month period to ascertain the rate of occurrence and the extent to which a revised protocol for the management of such injuries was followed. There were nine reported incidents, of which six were with contaminated needles. Three were reported. Eight anaesthetists had not taken up immunisation against hepatitis B. The rationale behind the revised protocol, and possible reasons for poor compliance are discussed.

Accidents, Occupational↗
PubMed1990

An evaluation of a 30-gauge needle for spinal anaesthesia for caesarean section.

A 30-gauge spinal needle was evaluated for Caesarean section, using a combined epidural/spinal technique, in 50 mothers. Spinal anaesthesia failed in six mothers and was inadequate in another six. General anaesthesia was required on one occasion. A 25% overall failure rate suggests that a 30-gauge needle is not a practical proposition for routine clinical practice.

Adult↗
PubMed1989

Expression of two myogenic regulatory factors myogenin and MyoD1 during mouse embryogenesis.

MyoD1 and myogenin are muscle-specific proteins which can convert non-myogenic cells in culture to differentiated muscle fibres, implicating them in myogenic determination. The pattern of expression of MyoD1 and myogenin during the early stages of muscle formation in the mouse embryo in vivo and in limb-bud explants cultured in vitro, indicates that they may have different functions in different types of muscle during development.

Animals↗
PubMed1989

Caesarean section at 27 weeks gestation with removal of phaeochromocytoma.

We describe the anaesthetic management of a 31-yr-old woman undergoing combined Caesarean section and removal of phaeochromocytoma during the 27th week of pregnancy. The technique used (general anaesthesia with extradural block) provided good operating conditions and a relatively stable haemodynamic state.

Adrenal Gland Neoplasms↗