Muscular expressions: profiling genes in complex tissues

Gene-expression profiling has yielded important information about simple systems, but complex tissues have not yet been widely profiled. Four recent studies of mammalian skeletal muscles have added to the catalogs of their gene expression differences, but have yet to lead to better understanding of the molecular processes underlying their physiological differences.

Transduction of murine cerebellar neurons with recombinant FIV and AAV5 vectors

Our data demonstrate that vectors derived from recombinant feline immunodeficiency virus (rFIV) and adeno-associated virus type 5 (rAAV5) transduce cerebellar cells following direct injection into the cerebellar lobules of mice. Both recombinant viruses mediated gene transfer predominantly to neurons, with up to 2500 and 1500 Purkinje cells transduced for rAAV5 or rFIV-based vectors, respectively. The vectors also transduced stellate, basket and Golgi neurons, with occasional transduction of granule cells and deep cerebellar nuclei. rAAV5 also spread outside the cerebellum to the inferior colliculus and ventricular epithelium, while rFIV demonstrated the ability to undergo retrograde transport to the physically close lateral vestibular nuclei. Thus, AAV5 and FIV-based vectors show promise for targeting neurons affected in the hereditary spinocerebellar ataxias. These vectors could be important tools for unraveling the pathophysiology of these disorders, or in testing factors which may promote neuronal survival.

Evidence for differential post-translational modifications of slow myosin heavy chain during murine skeletal muscle development

The contractile properties of muscle fibres are, in part, determined by the myosin heavy chain (MyHC) isoforms they express. Using monoclonal antibodies, we show that at least three forms of slow twitch MyHC accumulate sequentially during mouse fetal development and that slow MyHC maturation in slow fibres occurs before expression of the adult fast MyHCs in fast fibres. Expression of deletion derivatives of beta-cardiac MyHC cDNA shows that the slow MyHC epitopes that are detected in adult but not in young animals are located near the N-terminus. The same N-terminal region of various fast MyHC molecules contains a conserved epitope that can, on occasions, be observed when slow MyHC cDNA is expressed in non-muscle cells. The results raise the possibility that the N-terminal epitopes result from post-translational modification of the MyHC and that a sequence of slow and fast MyHC isoform post-translational modifications plays a significant role during development of murine muscle fibres.

Modeling of biological processes using self-cycling fermentation and genetic algorithms

Self-cycling fermentation (SCF) was coupled with a genetic algorithm (GA) to provide a simple system for evaluating biological models. The SCF provided the necessary system excitation and data "richness" required to completely define the fitted biological models. The solution scheme based on the GA avoided the computational difficulties often associated with calculus-based nonlinear regression techniques, resulting in rapid and accurate convergence. After validating the mathematical approach, data from the SCF obtained under denitrifying conditions were fitted successfully to an established model using the GA. Finally, data obtained in the SCF for the removal of phenol were used to compare multiple models. This work suggests that the SCF, in conjunction with the GA, provides a coherent system that can facilitate the characterization of biological systems.

Control of muscle fibre size: a crucial factor in ageing

Force generation by skeletal muscle declines during ageing. This change contributes substantially to increased physical dependency in the aged. The decline in muscle mass is not entirely accounted for by a fall in muscle fibre number: fibres appear to lose volume. Here we review data that address the fundamental question of how muscle fibres regulate their size. In muscles, the problem has two elements because muscle fibres are syncitia formed by the fusion of mononucleate precursor cells. Thus, fibre size appears to be regulated both by the number of nuclei incorporated into each fibre and by a second variable, the volume of cytoplasm that each nucleus supports. We conclude that understanding of the regulation of muscle cell size is in its infancy and highlight directions that might productively be pursued.

Local signals in the chick limb bud can override myoblast lineage commitment: induction of slow myosin heavy chain in fast myoblasts

Patterning of fast and slow muscle fibres in limbs is regulated by signals from non-muscle cells. Myoblast lineage has, however, also been implicated in fibre type patterning. Here we test a founder cell hypothesis for the role of myoblast lineage, by implanting characterized fast and slow mouse myoblast clones into chick limb buds. In culture, late foetal mouse myoblast clones are committed to a probability (range 0-0.92) of slow myosin heavy chain (MyHC) expression. In contrast, when implanted into chick limbs, fast mouse myoblast clones express myosin characteristic of their new environment, without fusion to chick muscle cells and in the absence of innervation. Therefore, local signals exist within the chick limb bud during primary myogenesis that can override intrinsic commitment of at least some myoblasts, and induce slow MyHC.

Myogenin induces a shift of enzyme activity from glycolytic to oxidative metabolism in muscles of transgenic mice

Physical training regulates muscle metabolic and contractile properties by altering gene expression. Electrical activity evoked in muscle fiber membrane during physical activity is crucial for such regulation, but the subsequent intracellular pathway is virtually unmapped. Here we investigate the ability of myogenin, a muscle-specific transcription factor strongly regulated by electrical activity, to alter muscle phenotype. Myogenin was overexpressed in transgenic mice using regulatory elements that confer strong expression confined to differentiated post-mitotic fast muscle fibers. In fast muscles from such mice, the activity levels of oxidative mitochondrial enzymes were elevated two- to threefold, whereas levels of glycolytic enzymes were reduced to levels 0.3-0.6 times those found in wild-type mice. Histochemical analysis shows widespread increases in mitochondrial components and glycogen accumulation. The changes in enzyme content were accompanied by a reduction in fiber size, such that many fibers acquired a size typical of oxidative fibers. No change in fiber type-specific myosin heavy chain isoform expression was observed. Changes in metabolic properties without changes in myosins are observed after moderate endurance training in mammals, including humans. Our data suggest that myogenin regulated by electrical activity may mediate effects of physical training on metabolic capacity in muscle.

In vitro culture of neurons from sheep with Batten disease

Specific storage of mitochondrial ATP synthase subunit c occurs in most forms of Batten disease, including the ovine form, but its relationship to the characteristic neurodegeneration is not clear. Storage occurs in most cell types but only neurons are functionally affected. Neurons were cultured from control and affected sheep. Ewes were superovulated and inseminated, and embryos were collected, frozen, stored, and later transplanted into surrogate dams for gestation at times to suit experimental demands. The optimal fetal age for cultures was investigated, from 50 to 125 days. There were no differences between control and affected embryos in this period of rapid growth. At 50 days brains consist of smooth-surfaced hemispheres and cerebellum with no obvious demarcation between gray and white matter. At 90 days they are like miniature adult brains. From 200 to 600 million viable cells were recovered from each fetus, regardless of age. DMEM/F12 with B27 was the most practical medium tested. Cell viability was not as good in medium containing serum. Treatment of surfaces with polylysine aided neuron adhesion. No developmental or viability differences were observed between normal and affected neuron cultures. At plating out cells were rounded. A day later single process outgrowths began. After 4 days these were over 200 microm and by Day 6 had created a network. Most neurons were bipolar. Neurons from 50 to 90-day old fetuses persisted in culture for over 100 days.

Extrinsic influences on limb muscle organisation

Skeletal muscle within the vertebrate limb originates from the somite. Much work has focussed upon the role of secreted signalling molecules of the Hedgehog, fibroblast growth factor (FGF), bone morphogenetic protein (BMP), and Wnt families plus their associated antagonists in establishing somitic cell types, yet there is no consensus on how these signals combine to influence muscle patterning. When somitic cells migrate into the limb bud, they become subject to a new set of guidance and patterning cues. Here we discuss the possible roles played by signalling proteins, particularly Hedgehogs, in guiding the cells of the limb musculature to their fate.

Disease-specific pathology in neurons cultured from sheep affected with ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCL, Batten disease) are a group of inherited neurodegenerative storage diseases in children. Mutations in different genes underlie different forms. Subunit c of mitochondrial ATP synthase is specifically stored in autofluorescent bodies in most of them, including a form in sheep. Mature bodies are lysosomal but the initial site of storage is not known, nor is it known how this leads to the characteristic neurodegeneration. Neurons were cultured in serum-free medium from control and affected sheep fetuses at 90 days gestation. They showed positive microtubule-associated protein staining, developed neurites, and had typical neuron morphology. Time-dependent accumulation of subunit c and of fluorescent storage bodies was observed in affected cells by immunocytochemistry and confocal microscopy. A small number of autofluorescent bodies were apparent after 4 days in culture. After 10 days these bodies were more numerous, more intensely autofluorescent, and often larger in size. By 14 and 21 days many neurons were packed with autofluorescent material. These bodies were not seen in control cultures. Immunocytochemistry revealed subunit c-positive storage material only in affected neurons and not in affected glial cells. Confocal microscope analysis, using organelle-specific dyes, demonstrated colocalization of autofluorescent bodies with lysosomes, not with mitochondria. Survival rates of the affected cells were unaffected by the storage body accumulation over a 3-month period. These cultures can now be used to study the mechanism of subunit c accumulation and of neurodegeneration and to test therapeutic possibilities.

Fetal myoblast clones contribute to both fast and slow fibres in developing rat muscle

Retroviral cell lineage marking was used to investigate the role of cell lineage in fetal and neonatal rat muscle development. Clusters of infected cells, presumably myoblast clones, contribute cells to both slow primary and fast secondary fibres. Moreover, single clusters of marked cells contain both slow and fast primary fibres, suggesting that, at least during fetal life, single clones contribute nuclei to both fibres that are committed to remain slow and those that convert to a fast phenotype. The majority of fibres in individual fascicles of fetal muscle could be infected by a self-inactivating retroviral vector. Retroviral gene expression was markedly lower in non-muscle tissues, suggesting that fetal retroviral infection might target exogenous genes to mammalian muscle fibres during later life.

Control of muscle fibre and motoneuron diversification

Recent studies have elucidated both the mechanism of early formation of diverse muscle fibre types and the matching of diverse populations of motoneurons to their appropriate muscle targets. Highlights include the demonstration that distinct signals are necessary for the formation of several distinct myoblast populations in the vertebrate somite, the identification of motoneuron subtypes, studies of how motoneurons target appropriate muscles, and rapid progress on the Drosophila neuromuscular system. We propose a model in which four classes of decision control the patterning of both motoneurons and muscles.

Muscle development: electrical control of gene expression

The electrical activity resulting from stimulation by motor neurons regulates gene expression in skeletal muscle fibres. A recent study has suggested a mechanism by which distinct patterns of electrical stimulus might be integrated to control the contractile properties of these fibres.

n beta geo, a combined selection and reporter gene for retroviral and transgenic studies

Nuclear-targeted beta-galactosidase (beta-gal) is increasingly used as a genetic cell marker in vitro and in vivo. Nuclear sequestration concentrates beta-gal and permits sensitive identification of expressing cells and/or tissues without obscuring the cytoplasmic detail necessary for analysis of cell phenotype. Here, we report the construction and testing of a nuclear-targeted version of the beta geo fusion protein that combines nuclear localization with the ability to select expressing cells with the drug G418. This new marker gene functions efficiently in retroviral vectors and will be useful in identification and isolation of cells transfected in vitro and cells expressing transgenic or gene-targeted constructs in vivo.

Notochord induction of zebrafish slow muscle mediated by Sonic hedgehog

The patterning of vertebrate somitic muscle is regulated by signals from neighboring tissues. We examined the generation of slow and fast muscle in zebrafish embryos and show that Sonic hedgehog (Shh) secreted from the notochord can induce slow muscle from medial cells of the somite. Slow muscle derives from medial adaxial myoblasts that differentiate early, whereas fast muscle arises later from a separate myoblast pool. Mutant fish lacking shh expression fail to form slow muscle but do form fast muscle. Ectopic expression of shh, either in wild-type or mutant embryos, leads to ectopic slow muscle at the expense of fast. We suggest that Shh acts to induce myoblasts committed to slow muscle differentiation from uncommitted presomitic mesoderm.

MyoD protein is differentially accumulated in fast and slow skeletal muscle fibres and required for normal fibre type balance in rodents

MyoD is a muscle-specific transcription factor involved in commitment of cells to myogenesis. MyoD mRNA levels differ between fast and slow muscles, suggesting that MyoD may regulate aspects of fibre type. Here we show that detectable MyoD protein becomes restricted during development to the nuclei of the fastest classes of fibres in fast muscles. myoDm1 mice, in which the myoD gene has been disrupted, show subtle shifts in fibre type of fast muscles toward a slower character, suggesting that MyoD is involved in the maintenance of the fast IIB/IIX fibre type. In contrast, slow muscle shifts to a faster phenotype in myoDm1. Moreover, MD6.0-lacZ transgenic mice with the myoD promoter driving lacZ, show highest beta-galactosidase activity in the fastest fibres of fast muscles, but also express low levels in slow fibres of slow, but not fast, muscles, suggesting distinct regulation of gene expression in slow fibres of fast and slow muscles.

The distal limb environment regulates MyoD accumulation and muscle differentiation in mouse-chick chimaeric limbs

Differentiation of muscle and cartilage within developing vertebrate limbs occurs in a proximodistal progression. To investigate the cues responsible for regulating muscle pattern, mouse myoblasts were implanted into early chick wings prior to endogenous chick muscle differentiation. Fetal myogenic cells originating from transgenic mice carrying a lacZ reporter were readily detected in vivo after implantation and their state of differentiation determined with species-specific antibodies to MyoD and myosin heavy chain. When mouse myogenic cells are implanted at the growing tip of early stage 21 limbs MyoD expression is suppressed and little differentiation of the mouse cells is detected initially. At later stages ectopically implanted mouse cells come to lie within muscle masses, re-express MyoD and differentiate in parallel with differentiating chick myoblasts. However, if mouse cells are implanted either proximally at stage 21 or into the limb tip at stage 24, situations in which mouse cells encounter endogenous differentiating chick myoblasts earlier, MyoD suppression is not detected and a higher proportion of mouse cells differentiate. Mouse cells that remain distal to endogenous differentiating myogenic cells are more likely to remain undifferentiated than myoblasts that lie within differentiated chick muscle. Undifferentiated distal mouse cells are still capable of differentiating if explanted in vitro, suggesting that myoblast differentiation is inhibited in vivo. In vitro, MyoD is suppressed in primary mouse myoblasts by the addition of FGF2 and FGF4 to the culture media. Taken together, our data suggest that the inhibition of myogenic differentiation in the distal limb involves MyoD suppression in myoblasts, possibly through an FGF-like activity.

Comparative lipoprotein metabolism of myristate, palmitate, and stearate in normolipidemic men

This project was designed to test the hypothesis that long-chain saturated fatty acids (myristate, palmitate, and stearate) are metabolized differently in human subjects, and that these differences may therefore account for the changes in plasma lipoprotein composition when these fatty acids are altered in the diet. Ethyl esters of each of the stable-isotope-labeled fatty acids (2H3- or 2H4-myristate, 13C16-palmitate, and 13C18-stearate) were fed to five nonhyperlipidemic men. The concentration of each labeled fatty acid was monitored for up to 72 hours as the fatty acids were assimilated into the lipid components (phospholipid [PL], triglyceride [TG], and cholesteryl ester [CE]) of the plasma lipoproteins (TG-rich lipoproteins [TRL], intermediate-density [IDL], low-density [LDL], and high-density lipoprotein [HDL]). Over 95% of the myristate was incorporated into TG, whereas 33% and 9% of the stearate and 18% and 7% of the palmitate were incorporated into PL and CE, respectively. The mean residence times (MRTs) for myristate in TG (8.6 to 9.9 hours) and PL (6.7 to 10.9 hours) in the individual lipoprotein subfractions were significantly shorter than for either palmitate (TG, 12.7 to 15.3 hours; PL, 19.6 to 21.3 hours) or stearate (TG, 10.7 to 15.5 hours; PL, 17.8 to 19.9 hours). The MRTs for stearate were shorter than for palmitate in PL. These data indicate that TG fatty acid in general, and myristate TG in particular, is the most rapidly cleared of the saturated fatty acids. There was a rapid transfer of labeled TG and PL between the lipoproteins. We were unable to detect any significant amount of stearate desaturation or elongation. In conclusion, these data demonstrate that myristate, palmitate, and stearate are metabolized in unique ways, and that it may therefore be inappropriate to continue to regard all "saturated fatty acids" as metabolically similar in clinical studies. Rather, it is important that we elucidate more clearly the specific metabolic pathway of each fatty acid to understand the mechanisms by which it alters plasma lipoprotein concentrations and composition and influences atherogenesis.

Multiple mouse chromosomal loci for dynein-based motility

Dyneins are multisubunit mechanochemical enzymes capable of interacting with microtubules to generate force. Axonemal dyneins produce the motive force for ciliary and flagellar beating by inducing sliding between adjacent microtubules within the axoneme. Cytoplasmic dyneins translocate membranous organelles and chromosomes toward the minus ends of cytoplasmic microtubules. Dynactin is an accessory complex implicated in tethering cytoplasmic dynein to membranous organelles and mitotic kinetochores. In the studies described here, we have identified a number of new dynein genes and determined their mouse chromosomal locations by interspecific backcross analysis. We have also mapped several dynein and dynactin genes cloned previously. Our studies provide the first comprehensive attempt to map dynein and dynactin genes in mammals and provide a basis for the further analysis of dynein function in development and disease.

Thyroid hormone effects on contractility and myosin composition of soleus muscle and single fibres from young and old rats

1. Young (3-6 months) and old (20-24 months) male Wistar rat soleus muscles were examined for myosin isoform composition, fibre type, contractility and sarcoplasmic reticulum (SR) Ca2+ release properties either in control rats or in rats treated with thyroid hormone (3,5,3'-triiodothyronine, T3) for 4 weeks. 2. T3 treatment had a strong impact on myosin heavy chain (MyHC) and light chain (MyLC) isoform composition in both young and old rats. That is, all single fibres co-expressed type I and IIA (type I/IIA fibres) or type I, IIA and IIX MyHCs (type I/IIAX fibres) after treatment. Slow and fast MyLC isoforms, i.e. MyLC1s, MyLC1f, MyLC2s, MyLC2f and MyLC3, co-existed in each of the type I/IIA and I/IIAX fibres in variable proportions. 3. In old rats the maximum velocity of unloaded shortening (V0) was related to MyHC isoform composition: V0 for type I fibres was less than that for type I/IIA fibres which was less than that for type I/IIAX fibres. In young rats, on the other hand, V0 did not differ between pure type I fibres from controls and those co-expressing type I and type II MyHC isoforms from T3-treated rats. 4. Contraction and half-relaxation times of the isometric twitch were significantly longer in old than in young controls. This was paralleled by an age-related decrease in the caffeine threshold of the SR. Four weeks of T3 treatment eliminated the age-related differences in both speed of twitch contraction and caffeine thresholds. V0, on the other hand, was slower in old than in young animals, both control and T3-treated, when cells with a similar MyHC composition were compared. 5. In conclusion, thyroid hormone can substantially reverse at least some of the changes that occur in ageing muscle. Further, the age-related decline in V0 in soleus fibres from control and hyperthyroid rats suggests that: (1) the identification of beta/slow myosin isoforms is incomplete; or (2) the molecular characteristics of MyHC differ between young and old age; or (3) MyHC is not the only determinant of V0.

Kidney-pancreas transplantation. The effect of portal versus systemic venous drainage of the pancreas on the lipoprotein composition

We have previously shown that both kidney-alone and combined kidney-pancreas transplantation lower VLDL and IDL apoB while increasing LDL apoB, apoA-I, and HDL free cholesterol (FC). In this report, we analyze the lipoproteins of 31 patients who have undergone combined kidney-pancreas transplantation. Systemic venous drainage of the pancreas was utilized in 20 of these patients while 11 had portal venous drainage. Six lipoprotein subfractions (VLDL, IDL, LDL, HDL-L, HDL-M, HDL-D) were isolated by rapid gradient ultracentrifugation using a fixed-angle rotor. The apolipoprotein (by reverse-phase HPLC) and lipid (by enzymatic assays) composition of each subfraction was determined. After three months, there were few group differences. However, the portal group had substantial reductions in VLDL apoB at both six (-50% vs. +1%) and twelve months (-57% vs. +149%, P = .042) while the systemic group had increases in VLDL apoB. Similar differences were seen in IDL apoB (six months: -38% vs. +13%; twelve months: -61% vs. +56%, P = .008). LDL apoB increased in both groups at six months (portal: +7%; systemic: +30%) but fell in the portal group at twelve months (-17% vs. +41%, P = .0007). IDL triglyceride, cholesterol ester, phospholipids, and free cholesterol also fell by 19% to 47% in the portal group while they rose by 8% to 44% in the systemic patients, six and twelve months after surgery (P < .05). In addition, the VLDL and LDL free cholesterol to phospholipid ratios (FC/PL) fell (improved) by 16% to 26% in the portal patients while they rose by 9% to 28% in the systemic subjects during this time (P < .04). Finally, there were substantial improvements in the LDL composition of the portal patients compared to the systemic patients at six (PL/apoB: +23% vs. -16%, P = .005; CE/apoB: +14% vs. -14%, P = .037) and twelve months (PL/apoB: +39% vs. -13%, P = .011; CE/apoB: +41% vs. -15%, P = .011). These data indicate that portal drainage of the transplanted pancreas reduced the number of VLDL, IDL, and LDL particles, reduced the total mass of IDL (by 35%), and normalized the VLDL and LDL particle composition. These improvements were not seen in the patients who received systemic drainage of their pancreas. HDL-M also improved in the portal patients (TG: -29% vs. +12%, P = .025) (PL: +22% vs. -5%, P = .014) (total mass: +16% vs. +0.2%, P = .044) but not in the systemic patients six months after surgery. These results suggest that portal venous drainage of the pancreas leads to greater improvements in the lipoprotein composition of IDDM patients than does systemic drainage.

Postprandial lipoprotein responses in hypertriglyceridemic subjects with and without cardiovascular disease

Three groups of age- and weight-matched men (aged 40 to 70 years) without diabetes were studied: controls (n = 10), plasma triglycerides (TG) less than 180 mg/dL and no cardiovascular disease (CVD); HTG-CVD (n = 11), hypertriglyceridemic (HTG) (TG > 240 mg/dL) without CVD; and HTG+CVD (n = 10), HTG (TG > 240 mg/dL) with documented CVD. HTG+CVD subjects had higher fasting and post-oral glucose tolerance test insulin levels than the other two groups, respectively. Very-low-density lipoprotein (VLDL)+chylomicrons (CMs), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and three high-density lipoprotein (HDL) subfractions (HDL-L, HDL-M, and HDL-D, from least to most dense) were isolated by gradient ultracentrifugation. Fasting lipoproteins were similar in HTG groups, except for higher VLDL lipid to apolipoprotein (apo) B ratios (P < .04) in the HTG+CVD group. Subjects were fed a high-fat mixed meal, and lipoprotein composition was determined at 3, 6, 9, and 12 hours postprandially. Postprandial responses of the core lipids (TG and cholesterol esters [CE]) in all of the lipoprotein subfractions were similar in the two HTG groups at each time point. However, both controls and HTG-CVD subjects had increases in HDL-M phospholipid (PL) at 9 and 12 hours with no change in HDL-D PL. The HTG+CVD group, on the other hand, had no increase in HDL-M PL and had a substantial reduction in HDL-D PL. These changes resulted in significant increases in HDL-M and HDL-D PL to apo A-I ratios in both controls and HTG-CVD subjects between 6 and 12 hours, whereas there was no increase seen in the HTG+CVD group. The HTG-CVD group also had a significantly greater increase in the VLDL+CM PL to apo B ratio (P = .038) at 3 hours than the HTG+CVD group. This diminished amount of surface lipid per VLDL particle may account for the late decrease in the HDL-D PL to apo A-I ratio seen in HTG+CVD patients. There were no other postprandial lipid or apolipoprotein differences between the two HTG groups. We conclude therefore that the major postprandial lipoprotein abnormality in these HTG+CVD patients was a failure to increase the PL content per particle in VLDL+CM, HDL-M, and HDL-D. This abnormality could prevent the usual increase in reverse cholesterol transport seen in postprandial plasma and therefore contribute to their increased incidence of CVD. The greater insulin resistance seen in these patients also appears to contribute significantly to their CVD.

Molecular analysis of a cytoplasmic dynein light intermediate chain reveals homology to a family of ATPases

Cytoplasmic dynein is a multi-subunit complex involved in retrograde organelle transport and some aspects of mitosis. In previous work we have cloned and sequenced cDNAs encoding the rat cytoplasmic dynein heavy and intermediate chains. Here we report the cloning of the remaining class of cytoplasmic dynein subunits, which we refer to as the light intermediate chains (LICs: 53–59 kDa). Four LIC electrophoretic bands were resolved in purified bovine cytoplasmic dynein preparations by one-dimensional gel electrophoresis. These four bands were simplified to two bands (LIC53/55 and LIC57/59) by alkaline phosphatase treatment. N-terminal amino acid sequence was obtained from a total of 11 proteolytic peptides generated from both LIC53/55 and LIC57/59. Overlapping cDNA clones encoding LIC53/55 were isolated by oligonucleotide screening using probes based on the LIC53/55 peptide sequence. The cDNA sequence contained a 497 codon open reading frame encoding a polypeptide with a molecular mass of approximately 55 kDa. Each of the LIC53/55 peptides was found within the deduced amino acid sequence, as well as four of the LIC57/59 peptides. Analysis of the LIC53/55 primary sequence revealed homology with the ABC transporter family of ATPases in the region surrounding the P-loop sequence element. Together these data identify the LICs as a novel family of dynein subunits with potential ATPase activity. They also reveal that the complexity of the LICs is due to both post-translational modification and the existence of at least two LIC polypeptides for which we propose the names LIC-1a and LIC-2.

Fast myosin heavy chains expressed in secondary mammalian muscle fibers at the time of their inception

Mammalian skeletal muscle is generated by two waves of fiber formation, resulting in primary and secondary fibers. These fibers mature to give rise to several classes of adult muscle fibers with distinct contractile properties. Here we describe fast myosin heavy chain (MyHC) isoforms that are expressed in nascent secondary, but not primary, fibers in the early development of rat and human muscle. These fast MyHCs are distinct from previously described embryonic and neonatal fast MyHCs. To identify these MyHCs, monoclonal antibodies were used whose specificity was determined in western blots of MyHCs on denaturing gels and reactivity with muscle tissue at various stages of development. To facilitate a comparison of our results with those of others obtained using different antibodies or species, we have identified cDNAs that encode the epitopes recognized by our antibodies wherever possible. The results suggest that epitopes characteristic of adult fast MyHCs are expressed very early in muscle fiber development and distinguish newly formed secondary fibers from primary fibers. This marker of secondary fibers, which is detectable at the time of their inception, should prove useful in future studies of the derivation of primary and secondary fibers in mammalian muscle development.

Lipoprotein composition in insulin-dependent diabetes mellitus with chronic renal failure: effect of kidney and pancreas transplantation

Chronic renal failure (CRF) in nondiabetics is associated with a number of lipoprotein abnormalities that place these patients at high risk for atherosclerosis. This study compared the lipoprotein composition of nondiabetic controls (n = 68) with that of patients with insulin-dependent diabetes mellitus ([IDDM] n = 13) and of patients with IDDM and CRF ([IDDM + CRF] n = 74). Six lipoprotein subfractions (very-low-density lipoprotein [VLDL], intermediate-density lipoprotein [IDL], low-density lipoprotein [LDL], high-density lipoprotein-light [HDL-L], HDL-medium [HDL-M], and HDL-dense [HDL-D]) were isolated by rapid gradient ultracentrifugation using a fixed-angle rotor. The apolipoprotein (by reverse-phase high-performance liquid chromatography [HPLC]) and lipid (by enzymatic assays) composition of each subfraction was determined. The only abnormalities found in IDDM patients were increases in IDL and HDL-L triglyceride (TG) levels and an increase in the HDL-L free cholesterol (FC) level. The IDDM + CRF group had multiple abnormalities including (1) elevated TG, apolipoprotein (apo) C-II, and apo C-III levels in all lipid subfractions; (2) elevated VLDL and IDL apo B, TG, FC, cholesterol ester (CE), and phospholipid (PL) levels (with an increased CE/TG ratio in VLDL only); (3) decreased HDL-M apo A-I, apo A-II, CE, and PL levels, but an increased HDL-D apo A-I level; and (4) decreased lecithin:cholesterol acyltransferase (LCAT) activity. Twenty-five of the IDDM + CRF patients underwent combined pancreas and kidney (P + K) transplantation, and 12 patients received only a kidney transplant. Lipoprotein composition was determined at 3, 6, and 12 months posttransplant. Both types of transplantation resulted in similar alterations in lipoprotein composition, even though there was essential normalization of blood glucose levels in most of the patients who received a pancreas transplant (hemoglobin A1C [HbA1C], 9.1% +/- 1.1% v 5.7% +/- 0.3% at 12 months, P < .01). These posttransplant changes included (1) no improvement in the elevated TG level in any lipid subfraction even though there was some reduction in apo C-III levels in VLDL; (2) reductions in levels of VLDL and IDL apo B but increases in LDL apo B; (3) increases in HDL apo C-III and FC concentrations despite an increase in LCAT activity; and (4) increases in apo A-I levels in HDL-L and HDL-M. The addition of a pancreas to a kidney transplant had no obvious impact on the lipoproteins.(ABSTRACT TRUNCATED AT 400 WORDS)

A double-blind cross-over controlled study to evaluate the effect of human biosynthetic growth hormone on ovarian stimulation in previous poor responders to in-vitro fertilization

The effect of exogenous human biosynthetic growth hormone (HGH; 12 IU/day; Norditropin, Novo-Nordisk) on the response to ovarian stimulation using a buserelin/human menopausal gonadotrophin (HMG) regimen was assessed in women who had previously shown a 'poor response' in spite of increasing doses of HMG. Forty patients were recruited into a prospective double-blind placebo-controlled study. The serum follicle stimulating hormone (FSH) on day 2-5 of a menstrual cycle (< 10 IU/l) was used to exclude any peri-menopausal candidates. The urinary 24 h GH secretion was normal in all patients. Thirty-three patients completed the study with 21 patients having human chorionic gonadotrophin (HCG) in both arms, thus providing a complete set of placebo control data. Of these 21 patients, the administration of HGH compared to the placebo cycle resulted in increased serum concentrations of fasting insulin on the 8th (median 3.9 versus 5.8 mU/l; P < 0.0005) and 13th (median 4.4 versus 5.8 mU/l; P < 0.05) day of HMG in those cycles receiving HGH. After 8 days of co-treatment with HGH the number of cohort follicles (14-16.9 mm) was significantly increased, but this change was not sustained on the day of HCG administration. No statistical difference in the serum oestradiol on the 8th day of HMG or day of HCG, length of the follicular phase, total dose of HMG used, or the number of oocytes collected was seen between the placebo or HGH cycles. This study demonstrates that HGH does not improve the ovarian response to ovulation induction in previous poor responders.

Selective accumulation of MyoD and myogenin mRNAs in fast and slow adult skeletal muscle is controlled by innervation and hormones

Each of the myogenic helix-loop-helix transcription factors (MyoD, Myogenin, Myf-5, and MRF4) is capable of activating muscle-specific gene expression, yet distinct functions have not been ascribed to the individual proteins. We report here that MyoD and Myogenin mRNAs selectively accumulate in hindlimb muscles of the adult rat that differ in contractile properties: MyoD is prevalent in fast twitch and Myogenin in slow twitch muscles. The distribution of MyoD and Myogenin transcripts also differ within a single muscle and correlate with the proportions of fast glycolytic and slow oxidative muscle fibres, respectively. Furthermore, the expression of a transgene consisting of a muscle-specific cis-regulatory region from the myoD gene controlling lacZ was primarily associated with the fast glycolytic fibres. Alteration of the fast/slow fibre type distribution by thyroid hormone treatment or by cross-reinnervation resulted in a corresponding alteration in the MyoD/Myogenin mRNA expression pattern. These findings show that the expression of specific myogenic helix-loop-helix regulators is under the control of innervation and humoral factors and may mediate differential control of contractile protein gene expression in adult muscle.

Three slow myosin heavy chains sequentially expressed in developing mammalian skeletal muscle

Myosin heavy chain (MyHC) isoforms show a striking diversity of expression patterns during mammalian development. Using a set of monoclonal antibodies that recognize different epitopes on myosin heavy chain isoforms we show that there exist in human and rat skeletal muscle at least three isoforms of slow twitch myosin heavy chain. To facilitate a comparison of our results to others obtained using different antibodies or species, we have identified cDNAs encoding the epitopes recognized by the three slow antibodies. Using these reagents, we show that the onset of expression of three slow MyHC isoforms is temporally distinct during early gestation. This result suggests that a sequence of MyHC transitions plays an important role in determining muscle fiber function at fetal, neonatal, and adult stages.

Supplementary growth hormone treatment of women with poor ovarian response to exogenous gonadotrophins: changes in serum and follicular fluid insulin-like growth factor-1 (IGF-1) and IGF binding protein-3 (IGFBP-3)

The effects of supplementary growth hormone (GH) treatment upon insulin-like growth factor-1 (IGF-1), IGF binding protein-3 (IGFBP-3) concentrations in serum and ovarian follicular fluid were investigated in women undergoing buserelin human menopausal gonadotrophin (HMG) ovulation induction for in-vitro fertilization. Women (n = 40), aged 24-39 (mean 35 years), who showed poor ovarian responses to HMG, were recruited and randomly divided into two groups. Each patient received two cycles of ovulation induction, one with GH (12 IU/day x 12 days/HMG/buserelin) and another with placebo/HMG. Serum IGF-1 increased substantially during the GH treatment and remained significantly higher than the control 2 days after the last GH injection. Serum IGFBP-3 fell steadily during the placebo/HMG treatment and to a nadir on the day of oocyte retrieval (P < 0.05 compared to serum before any treatment). In contrast, IGFBP-3 was increased (P < 0.01) during the GH administration and returned to the control level 2 days after GH injection. Serum oestradiol concentrations on the eighth day of HMG and the day of human chorionic gonadotrophin (HCG) were not significantly different between the two groups. Serum IGF-1 was highly correlated with IGFBP-3 before any treatment (r = 0.433, P < 0.001). This correlation disappeared after buserelin, placebo/HMG treatment in the control group, but it was maintained during GH/HMG treatment (r = 0.343, P = 0.04). Follicular fluid concentrations of GH and IGF-1, not IGFBP-3 or oestradiol, were significantly elevated in the GH-treated women.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and endocrinological changes in women following ovulation induction using buserelin acetate/human menopausal gonadotrophin augmented with biosynthetic human growth hormone

Biosynthetic human growth hormone added to an ovarian stimulation regime of human menopausal gonadotrophin (HMG) for IVF treatment improves the response of women who were previously resistant. This study investigated the efficacy of growth hormone (GH)/buserelin/HMG treatment in women with a previous normal response to buserelin/HMG stimulation. Ten patients (28-36 years, mean 32.5 years) were treated with GH (6 IU/day) plus buserelin/HMG. A control group of 10 women (28-37 years mean 31.0 years) received buserelin/HMG alone. All were given buserelin 500 micrograms and 2 ampoules (150 IU) HMG daily once pituitary suppression had been confirmed. There was no improvement in the GH group as assessed by follicular growth rate or number, oocyte number per woman and pregnancy rate. There was no effect of GH upon the serum oestradiol level and the follicular fluid levels of oestradiol, GH and inhibin. Serum IGF-1 increased significantly during GH administration, returning to pre-treatment levels 2 days after the last dose of GH. Follicular IGF-1 was much higher in the GH-treated group than the controls. Significant correlations were found in the GH-treated group between follicular fluid GH and follicular fluid oestradiol concentrations and between follicular GH and follicular size. Follicular IGF-1 was correlated with the serum IGF-1 concentration on day 8 of the GH/HMG treatment. In conclusion GH/buserelin/HMG treatment in women with a previous normal response to buserelin/HMG stimulation increased their serum and follicular IGF-1 concentrations. However, it does not improve the clinical ovarian response or the follicular secretion of oestradiol or inhibin.

Muscle fiber pattern is independent of cell lineage in postnatal rodent development

Muscle fibers specialized for fast or slow contraction are arrayed in characteristic patterns within developing limbs. Clones of myoblasts analyzed in vitro express fast and slow myosin isoforms typical of the muscle from which they derive. As a result, it has been suggested that distinct myoblast lineages generate and maintain muscle fiber pattern. We tested this hypothesis in vivo by using a retrovirus to label myoblasts genetically so that the fate of individual clones could be monitored. Both myoblast clones labeled in muscle in situ and clones labeled in tissue culture and then injected into various muscles contribute progeny to all fiber types encountered. Thus, extrinsic signals override the intrinsic commitment of myoblast nuclei to particular programs of gene expression. We conclude that in postnatal development, pattern is not dictated by myoblast lineage.

MAP1B is encoded as a polyprotein that is processed to form a complex N-terminal microtubule-binding domain

Microtubule-associated protein 1B (MAP1B), an abundant developmentally regulated neuronal protein, is a stoichiometric complex of a heavy chain and two light chains (light chain 1 and light chain 3). We find that light chain 1 is encoded within the 3' end of a previously reported MAP1B heavy chain cDNA. Amino acid sequencing, epitope mapping, Northern blotting, and Southern blotting indicate that the light chain and heavy chain are encoded by the same mRNA within the same open reading frame. In addition, amino acid sequencing of a 120 kd microtubule-binding and light chain-binding fragment of the heavy chain reveals that light chain 1 binds near the heavy chain N-terminus. Together these data indicate that the heavy chain and light chain 1 are produced by proteolytic processing of a MAP1B polyprotein and form a complex microtubule-binding domain.

Modulation of MHC class II antigen expression in human myoblasts after treatment with IFN-gamma

Some investigators have proposed myoblast transfer as a potential therapy for the treatment of Duchenne muscular dystrophy. Little is known about the immunobiology of myoblast transplantation. Transplantation rejection is mediated to a large extent by CD8+ T cells, which recognize alloantigens encoded by class I HLA genes, and by CD4+ T cells, which recognize alloantigens encoded by class II HLA genes. Gamma interferon (IFN-gamma) is a potent inducer of HLA class II molecules as well as beta 2-microglobulin, which is co-expressed with HLA class I. IFN-gamma may be a critical cytokine involved in graft rejection. We purified human myoblasts by flow cytometry and incubated them in vitro for varying time periods with recombinant human IFN-gamma. The inducibility of HLA-DR and -DP molecules raises a note of caution concerning possible rejection phenomenon which might occur following myoblast transplantation.

Migration of myoblasts across basal lamina during skeletal muscle development

Basal lamina is a sheet of extracellular matrix that separates cells into topologically distinct groups during morphogenesis and is thought to form a barrier to cell migration. We have examined whether, during normal muscle development, myoblasts--mononucleate muscle precursor cells--can cross the basal lamina that surrounds each multinucleate muscle fibre. We marked myoblasts in vivo by injecting replication-defective retroviral vectors encoding LacZ into muscle tissue and analysed the fate of their progeny by the expression of beta-galactosidase. A dual labelling method with broad application to retroviral lineage-marking studies was developed to ensure that most clusters of labelled cells were clones derived from a single precursor cell. Most of the myoblasts that were infected at a late stage of rat hindlimb development, when each fibre with its satellite myoblasts is individually encased in a basal lamina sheath, gave rise to clones that contributed to several labelled fibres. Our results show that myoblasts from healthy fibres migrate across basal lamina during normal development and could contribute to the repair of fibres damaged by injury or disease.

Ciliary neurotrophic factor induces type-2 astrocyte differentiation in culture

We have been studying a population of bipotential glial progenitor cells in the perinatal rat optic nerve and brain in an attempt to understand how cells choose between alternative fates in the developing mammalian central nervous system (CNS). This cell population gives rise initially to oligodendrocytes and then to type-2 astrocytes, both of which apparently collaborate in sheathing axons in the CNS. In vitro studies suggest that oligodendrocyte differentiation is the constitutive pathway of development for the oligodendrocyte-type-2-astrocyte (O-2A) progenitor cell, whereas type-2 astrocyte differentiation depends on a specific inducing protein. This protein is present in the developing optic nerve when type-2 astrocytes are differentiating and can induce O-2A progenitor cells in vitro to express glial fibrillary acidic protein (GFAP), a marker of astrocyte differentiation. Here we show that the type-2-astrocyte-inducing protein is similar or identical to ciliary neutrotrophic factor (CNTF), which promotes the survival of some types of peripheral neurons in vitro, including ciliary ganglion neurons. This suggests that CNTF, in addition to its effect on neurons, may be responsible for triggering type-2 astrocyte differentiation in the developing CNS.

Type-2 astrocyte development in rat brain cultures is initiated by a CNTF-like protein produced by type-1 astrocytes

O-2A progenitor cells are bipotential glial precursors that give rise to both oligodendrocytes and type-2 astrocytes on a precise schedule in the rat CNS. Studies in culture suggest that oligodendrocyte differentiation occurs constitutively, while type-2 astrocyte differentiation requires an exogenous inducer such as fetal calf serum. Here we describe a rat brain cell culture system in which type-2 astrocytes develop on schedule in the absence of exogenous inducers. Coincident with type-2-astrocyte development, the cultures produce an approximately 20 kd type-2-astrocyte-inducing factor(s). Purified cultures of type-1 astrocytes can produce a similar factor(s). Under conditions where they produce type-2-astrocyte-inducing factor(s), both brain and type-1 astrocyte cultures produce a factor(s) with ciliary neurotrophic (CNTF)-like activity. Purified CNTF, like the inducers from brain and type-1 astrocyte cultures, prematurely induces type-2 astrocyte differentiation in brain cultures. These findings suggest that type-2 astrocyte development is initiated by a CNTF-like protein produced by type-1 astrocytes.

An inducer protein may control the timing of fate switching in a bipotential glial progenitor cell in rat optic nerve

In rat optic nerve, oligodendrocytes and type-2 astrocytes develop from a common (O-2A) progenitor cell. The first oligodendrocytes differentiate at birth, while the first type-2 astrocytes differentiate in the second postnatal week. We previously showed that the timing of oligodendrocyte differentiation depends on an intrinsic clock in the O-2A progenitor cell. Here we provide evidence that the timing of type-2 astrocyte differentiation, by contrast, may depend on an inducing protein that appears late in the developing nerve. We show that extracts of 3- to 4-week-old, but not 1-week-old, rat optic nerve contain a protein (apparent Mr approximately 25,000) that induces O-2A progenitor cells in culture to express glial fibrillary acidic protein (GFAP), an astrocyte-specific marker in the rat central nervous system.

Light changes the membrane potential and ion balances of retinal rod disks

Light stimulation of rod cells in vertebrate eyes may cause Ca2+ release from the intracellular disks. Radiolabelled tracers show that light causes a small hyperpolarization of intact disk stacks and redistribution of the ions Ca2+ and Cl-.

Lacrimal surgery in children

Of 142 children who underwent major lacrimal surgery (160 dacryocystorhinostomies, one congenital fistula excision, one dacryocystectomy, and one canaliculostomy), 49 had congenital nasolacrimal duct obstruction (34%). Lacrimal obstruction was also associated with canaliculitis, punctal agenesis, trauma, congenital fistula, dacryocystitis, craniofacial defects, and functional eyelid abnormalities. Although the timing and technique of the surgery varied according to the abnormalities, an overall functional success rate of 90% (144 of 160 procedures) was achieved.

Floppy eyelid with hyperglycinemia

A 31-year-old man with spastic paraparesis (diagnosed when he was 10 years old) and hyperglycinemia (diagnosed when he was 19 years old) had an intermittently swollen right eye and blurred vision. His right upper eyelid was S-shaped and edematous, the lateral canthal tendon was flaccid, and the eyelid everted easily. After the floppy eyelid syndrome was diagnosed, the patient underwent a tarsal strip procedure to shorten and tighten the lax upper eyelid. This relieved his symptoms, which have not recurred in the year since surgery.

Target size analysis of rhodopsin in retinal rod disk membranes

Radiation inactivation of rhodopsin in situ using high-energy electrons gave a value for Mr of 20,200 by spectral assay, but 47,100 by assay of rhodopsin regeneration from opsin and 11-cis-retinal (sequence Mr = 38,840). No light/dark differences were seen. We conclude: (a) radiation inactivation measures the size of the functional unit, and the single hit hypothesis does not hold in our experiments; (b) 500 nm absorbance requires only about half the rhodopsin molecule to be intact, but reconstitution of rhodopsin from opsin requires the whole molecule; (c) we find no evidence for functional interactions between rhodopsin monomers in darkness or light.

Are guanine nucleotide binding proteins a distinct class of regulatory proteins?

Proteins which bind guanine nucleotides are found in a diverse set of key regulatory positions. They are involved in hormone action, visual transduction, protein synthesis and microtubule assembly. In addition to their ability to bind guanine nucleotides these proteins possess several other common features. (i) They all have similar subunit composition, (ii) they can be ADP-ribosylated, (iii) their conformation changes depending on the nucleotide bound. These regulatory G-proteins have close functional homologies. Do they form a general class of regulatory proteins, like the protein kinases? Do they have a common evolutionary ancestry?