In vitro chamber specification during embryonic stem cell cardiogenesis. Expression of the ventricular myosin light chain-2 gene is independent of heart tube formation

The molecular cues that control patterning of the heart tube during early cardiogenesis are largely unknown. The present study has explored the embryonic stem (ES) cell differentiation system to determine if this in vitro model could be useful in studying the process of regional specification of cardiac muscle cells at the earliest possible stages. As assessed by polymerase chain reaction, ribonuclease protection, in situ hybridization, and immunohistochemical analyses, ES cell differentiation into embryoid bodies is characterized by the transcriptional and translational activation of the ventricular regulatory (phosphorylatable) myosin light chain gene, demonstrating that ventricular specification occurs during ES cell cardiogenesis. The finding of a ventricular-specific marker in an in vitro system in the absence of an intact heart tube provides evidence for cardiac regional specification independent of positional cues or physiologic stimuli. The temporal expression of the myogenic regulatory factors, myogenin and MyoD, suggests activation of the skeletal muscle program following cardiac myogenesis in vitro, indicating temporal fidelity to the progression of in vivo myogenesis. These data establish the mouse embryonic stem cell system as a model for cardiac chamber specification and suggest a promising approach in the study of regional specification in genetically engineered cardiac muscle cells.

Modulation of contractile protein gene expression in fetal murine crural muscles: emergence of muscle diversity

The modulation of contractile protein gene expression in mouse crural muscles (i.e., muscles located in the region between the knee and ankle) during the fetal period (defined as 15 days gestation to birth), resulting in diversity among and within these muscles, has been evaluated with in situ hybridization and correlated with morphogenetic events in the extensor digitorum longus and soleus muscles. During the fetal period extensive secondary myotube formation occurs in the crural muscles, and the myotubes become innervated (Ontell and Kozeka [1984a,b] Am. J. Anat. 171:133-148, 149-161; Ontell et al. [1988a,b] Am. J. Anat. 181:267-278, 181:278-288). At 15 days gestation, hybridization with 35S-labeled antisense cRNA probes demonstrates the accumulation of transcripts for alpha-cardiac and alpha-skeletal actin; MLC 1A, MLC 1F, and MLC 3F; and MHC emb, MHC pn, and MHC beta/slow. At 16 days gestation, accumulation of MHC emb transcripts is reduced (as compared with earlier developmental stages); intensity of signal following hybridization with the probe for alpha-skeletal actin is, for the first time, equal to that for the cardiac isoform; and MLC 1V mRNA accumulation is discernible. At this stage, variation in transcript accumulation for some mRNAs among and within crural muscles becomes evident. Two factors may play a role in the selective distribution of these transcripts: 1) the stage of muscle maturation; and 2) the future myofiber type. At 16 days gestation anterior crural muscles (which mature approximately 2 days before posterior crural muscles; Ontell and Kozeka [1984a,b], ibid., Ontell et al. [1988a,b], ibid.) exhibit a greater accumulation of transcripts for alpha-skeletal actin and for MLC 3F than is found in posterior crural muscles. In muscles that in the neonate are composed, in large part, of slow myofibers, MHC beta/slow and MLC 1V mRNAs accumulate in greater amounts, whereas MHC pn transcripts are less abundant in the soleus muscle than in other crural muscles. By 19 days gestation regionalization of transcript accumulation is more pronounced. The soleus muscle, a predominantly slow twitch muscle in the newborn mouse (Wirtz et al. [1983] J. Anat. 137:109-126) exhibits strong signal after hybridization with probes specific for MHC beta/slow and MLC 1V. While the level of transcript accumulation for the development isoforms, MHC emb, MLC 1A, and alpha-cardiac actin, is greatly reduced in most crural muscles at 19 days gestation, these transcripts persist in the soleus muscle at levels equal ot or exceeding their amount in limb muscles of 13 day gestation mouse embryos.(ABSTRACT TRUNCATED AT 400 WORDS)

Contractile protein gene expression in primary myotubes of embryonic mouse hindlimb muscles

The time course of contractile protein [actin, myosin heavy chain (MHC) and myosin light chain (MLC)] gene expression in the hindlimb muscles of the embryonic mouse (< 15 days gestation) has been correlated with the expression of genes for the myogenic regulatory factors, myogenin and MyoD, and with morphogenetic events. At 14 days gestation, secondary myotubes are not yet present in crural muscles (M. Ontell and K. Kozeka (1984) Am. J. Anat. 171, 133–148; M. Ontell, D. Bourke and D. Hughes (1988) Am. J. Anat. 181, 267–278); therefore, all transcripts for contractile proteins found in these muscles must be produced in primary myotubes. In situ hybridization, with 35S-labeled antisense cRNAs, demonstrates the versatility of primary myotubes in that transcripts for (1) alpha-cardiac and alpha-skeletal actin, (2) MHCembryonic, MHCperinatal and MHC beta/slow, and (3) MLC1A, MLC1F and MLC3F are detectable at 14 days gestation. While the general patterns of early activation of the cardiac genes and early activation of the genes for the developmental isoforms are preserved in both myotomal and limb muscles (D. Sassoon, I. Garner and M. Buckingham (1988) Development 104, 155–164 and G. E. Lyons, M. Ontell, R. Cox, D. Sassoon and M. Buckingham (1990) J. Cell Biol. 111, 1465–1476 for myotomal muscle), there are a number of differences in contractile protein gene expression. For example, in the myotome, when myosin light chain genes are initially transcribed, hybridization signal with probe for MLC1A mRNA is greater than that with probe for MLC1F transcripts, whereas the relative intensity of signal with these same probes is reversed in the hindlimb. The order in which myosin heavy chain genes are activated is also different, with MHCembryonic and MHCperinatal preceding the appearance of MHC beta/slow transcripts in limb muscles, while MHCembryonic and MHC beta/slow appear simultaneously in the myotomes prior to MHCperinatal. In the myotome, an intense hybridization signal for alpha-cardiac and a weak signal for alpha-skeletal actin transcripts are detectable prior to myosin mRNAs, whereas in the limb alpha-cardiac actin transcripts accumulate with myosin transcripts before alpha-skeletal actin mRNA is detectable. These differences indicate that there is no single coordinate pattern of expression of contractile protein genes during initial formation of the muscles of the mouse.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Synthesis and turnover of late H2B histone mRNA in developing embryos of the sea urchin, Strongylocentrotus purpuratus

In sea urchins, "early" histone proteins are synthesized during cleavage and blastula formation, "late" histone proteins in subsequent stages of development. To understand the molecular mechanisms responsible for this ontogenic switch in histone subtype synthesis, we determined the absolute amounts, rates of synthesis, and rates of turnover of late H2b histone mRNAs during development. We showed previously that late H2b mRNA comprises several mRNA isotypes. In this study, we used both a class-specific DNA probe to measure the amounts of the late H2b mRNA isotypes collectively, and a gene-specific probe to measure amounts of a particular late H2b mRNA encoded by a gene known as L1. We found that the amount of late H2b mRNA increased dramatically from 85,000 molecules per embryo in the 16-hr blastula to a peak of 670,000 molecules per embryo in the 24-hr mesenchyme blastula, and fell to 380,000 molecules per embryo in the 72-hr pluteus larva. The L1 late H2b mRNA achieved its maximum abundance earlier than the late H2b mRNA class as a whole, reaching a peak of 34% of total late H2b in the 14-hr blastula and declining to 7% in the pluteus larva. Measurements of the rate of incorporation of [3H]uridine into late class H2b mRNA, performed by a novel in vivo isotope incorporation method, enabled us to calculate both synthesis rates and half-lives of late H2b mRNA during development. These calculations showed (1) that the increase in late H2b mRNA level between 16 and 24 hr postfertilization is regulated primarily if not entirely at the level of mRNA synthesis; and (2) that the half-life of late H2b mRNA is comparatively short, around 20 min, at all stages examined.