Alan M. Kelly

Myogenic and neurogenic contributions to the development of fast and slow twitch muscles in rat

Abstract The histochemical ATPase activity and the myosin light chains of a rat fast muscle (extensor digitorum longus, EDL) and a rat slow muscle (soleus) during development have been investigated. Both muscles initially synthesize fast myosin light chains and show the intense histochemical ATPase activity characteristic of adult fast muscle fibers. After birth, the soleus begins to accumulate slow fibers with their characteristic low histochemical ATPase activity, and slow myosin light chains begin to appear. Sciatic neurectomy prevents the development of slow fibers and the synthesis of slow myosin light chains in the soleus, while the EDL is unaffected. Similarly, cordotomy of an adult rat results, in the soleus, in the appearance of fibers with more intense staining for ATPase and an increase in fast myosin light chains. The EDL is unchanged by cordotomy. As a result, we suggest that slow muscle development, but not fast muscle development, is dependent upon the functional activity of the nervous system.

THYROIDAL AND NEURAL CONTROL OF MYOSIN TRANSITIONS DURING DEVELOPMENT OF RAT FAST AND SLOW MUSCLES

Experiments with developing euthyroid, hypothyroid and hyperthyroid rats show that the transition from neonatal to adult fast myosin is orchestrated by thyroid hormones acting directly upon fast muscle cells. Denervation studies reveal the switch from neonatal to adult fast myosin synthesis is independent of the motoneuron. However the synthesis of slow myosin during development is critically dependent on innervation.

Satellite cells and myofiber growth in the rat soleus and extensor digitorum longus muscles

Abstract This study demonstrates a significantly lower incidence of satellite cells in the fast twitch extensor digitorum longus muscle (EDL) than in the slow twitch soleus muscles both in developing and mature rats. This distinction appears early in myogenesis, before histochemical differentiation is evident in the two muscles. Correlated with the differences in satellite cell population during development are greater rates of increase in myofiber nuclei per myofiber in the soleus than in the EDL. In addition, autoradiographic studies reveal there is more active [ 3 H]thymidine incorporation among satellite cells of the developing soleus than of the EDL. This is expected, as cell mitosis and fusion have previously been shown to be related events [ R. Bischoff (1970) . In “Regeneration of Striatal Muscle and Myogenesis.” Excerpta Medica Int. Congr. Ser. 19). Influence of the nervous system upon satellite cells in developing muscle is shown by a substantial decline in [ 3 H]thymidine incorporation by satellite cell nuclei within 24 hr of denervation in both the soleus and EDL of young rats. In view of the differences in myonuclear and satellite cell populations, growth of the histochemically distinct types of myofibers in the developing soleus and EDL has also been studied. The results indicate that increases in cross sectional area of myofibers in the soleus, particularly Type I fibers, is associated with satellite cell fusion and a progressive rise in the incidence of myonuclei. In contrast, increase in cross sectional area of myofibers in the EDL, particularly Type II glycolyte fibers, is less associated with myonuclear supplement and is more the product of pure muscle hypertrophy. There are thus substantial differences in the patterns of growth between the two muscles.

A rapid, inexpensive, quantitative, general-purpose densitometer and its application to one-dimensional gel electrophoretograms.

We describe the construction of a densitometer based on a TV camera linked to an IBM personal computer (PC) using commercially available components. We discuss some of the problems of accurate quantitative densitometry using low-cost video systems, and describe the manner in which absolute optical density values may be recorded. We describe a digital analysis routine designed to quantitate unresolved bands on noisy one-dimensional electrophoretograms.

Human embryonic myosin heavy chain cDNA. Interspecies sequence conservation of the myosin rod, chromosomal locus and isoform specific transcription of the gene.

Myosin heavy chain cDNA; Nucleotide sequence; Amino acid sequence; Myosin rod; Chromosomal mapping; Gene transcription; (Human embryo)

Myofibril organisation and mitosis in cultured cardiac muscle cells

Isolated cardiac muscle cells grown in vitro have been studied with respect to their ability to contract spontaneously and maintain myofibrillar organisation during division. These cells do not round up to undergo mitosis; division is achieved by the cell pinching itself in two in a selected area. This adaptation minimises disturbance to cell attachment sites and to myofibrils running between them. We correlated this with the persistence of beating during division and the maintenance of myofibrils with intact Z bands, even in close proximity to the nucleus, through division in many cells. Cessation of beating and disorganisation of myofibrils are therefore not prerequisites for division of cardiac muscle cells, as reported previously.

Selective expression of a ski transgene affects IIb fast muscles and skeletal structure

The expression of a ski transgene in the hind leg muscles of mice follows a spatial and temporal pattern reminiscent of the pattern of myogenic development. Anterior muscles, which are formed earliest during development, are also the first muscles to express ski mRNA. Muscles derived from the posterior muscle group, formed later during development, exhibit delayed expression of ski mRNA. In addition, there is regional variation in ski mRNA levels within a particular muscle. Superficial regions of fast muscles, which contain a large percentage of type IIb fibers and have a high ATPase activity, express a higher level of ski mRNA than the deep portions of the same muscles. The deep regions contain a lower percentage of type IIb fibers and lower ATPase activity. The soleus, a slow muscle composed predominantly of type I fibers, expresses low ATPase activity and contains much lower levels of ski mRNA. mRNA from the ski transgene is also expressed at high levels in the osteocytes of the leg bones of 15‐day and older transgenic mice. High levels of Ski protein is present in the osteocytes of the leg bones. ski expression appears to cause remodeling of the tibia and fibula. The cross‐sectional area of the tibia and fibula of ski transgenic mice is significantly decreased compared to controls. X‐rays of the skeletons of ski transgenic mice suggest that the bones of the entire skeleton are thinner than the bones in normal mice. Pathological stress fractures were found in several bones in the ski transgenic mice.

The induction of skeletal muscle hypertrophy by a ski transgene is promoter-dependent.

The chicken c-ski gene expresses at least three alternatively spliced messages. Transgenic mice expressing proteins from cDNA corresponding to two of these messages (FB27 and FB29) under the control of a murine sarcoma virus (MSV) long terminal repeat (LTR) express the transgene in skeletal muscle and develop a muscular phenotype. Both a biologically active form of c-ski and the MSV LTR are required for the development of the muscular phenotype. The normal c-ski gene linked to two other tissue-specific promoters failed to induce muscle growth in transgenic mice, as did an inactive mutant of c-ski expressed under the control of the MSV LTR.

Trends in gender, employment, salary, and debt of graduates of US veterinary medical schools and colleges

OBJECTIVE To characterize trends in gender, employment, starting salaries, and educational debt of graduates of US veterinary medical schools and colleges from 1988 to 2007. DESIGN Meta-analysis. Sample Population-Veterinary medical graduates from 26 or 27 of 27 US veterinary schools and colleges from 1988 through 2007. PROCEDURES Data were obtained from surveys published in the JAVMA. A chi2 test for trend was used to analyze trends in choices of employment and educational indebtedness for the veterinary graduate populations over time. RESULTS The greatest changes in employment occurred in predominantly large animal practice, which attracted 10.7% of new graduates in 1989 but only 2.2% in 2007, and in advanced study, which attracted 15.2% of new graduates in 1989 and 36.8% in 2007. In 2007, 75% of graduates were women, but this gender shift was not associated with the decline in the percentage of graduates entering rural practice. From 1989 through 2007, starting salaries in private practice increased at a rate of 4.60%/y. During the same period, educational debt increased at an annual rate of 7.36%, or 60% higher than the rate of increases for starting salaries. As a result, debt at graduation increased from 1.1 times the starting salary in 1989 to 2.0 times the starting salary in 2007. CONCLUSIONS AND CLINICAL RELEVANCE Veterinary students are now more in debt than they have ever been. This trend together with a substantial increase in the rate of interest charged for government-backed education loans create conditions for new graduates that appear unsustainable.

Influences of Testosterone on Contractile Proteins of the Guinea Pig Temporalis Muscle

The present study outlines the changes in contractile proteins which occur during sexual differentiation of the guinea pig temporalis muscle. This is an androgen sensitive muscle, which in the female progresses from a fetal phenotype to a muscle rich in IIa fibers, and in the male, undergoes a further switch to an almost pure IIb fiber phenotype. We show the IIa to IIb transition in the male involves a change in myosin heavy chain synthesis (Figure 39), a corresponding change in the mobility of native myosin isozymes run on pyrophosphate gels (Figure 43), and changes in the proportions of the alpha and beta subunits of tropomyosin (Figure 41). Myosin light chains appear to be unaltered in this transformation.