Reflective densitometry of Western blots to quantitate the developmentally regulated accumulation of myosin light chain 3

Normal expression of myosin fast alkali light chain 3 in the hindlimb muscle of chick embryos paralyzed with curare

We have used a monoclonal antibody (Mab) raised against the fast alkali light chains of quail pectoral muscle myosin to study the expression of MLC1f and MLC3f in the hindlimb muscle of a staged series of control chick embryos and 16-day embryos that had been paralyzed with curare. The Mab (QBM-2) is highly specific for the fast myosin alkali light chains of chick, hamster, and human muscle myosin. On Western blots, MLC1f is detected in hindlimb actomyosin at all of the stages examined, whereas MLC3f cannot be detected until Embryonic Day 14 (E14). Most of the E16 embryos that had been paralyzed with curare since E4 express detectable levels of both MLC1f and MLC3f in their hindlimb muscles, even though embryos incubated under these conditions do not exhibit spontaneous limb movements. Contrary to other reports, our results demonstrate that muscle contraction is not required for the accumulation of MLC3f. In light of our previous finding that innervation is essential for MLC3f accumulation in limb buds grafted onto the chorioallantoic membrane of chick hosts, these results suggest that some neural influence other than contraction, possibly a trophic factor, may play a role in the developmentally regulated expression of MLC3f in avian limb muscle.

Effects of electrically induced contractile activity on cultured embryonic chick breast muscle cells

Development of chicken breast muscle is characterized by the sequential appearance of six electrophoretically distinct myosin heavy chain (HC) isoforms. Cultured secondary myotubes, derived from 12-day embryonic chick breast muscle, mainly express the early embryonic HC isoform HCemb/e, normally present in 8-day embryonic breast muscle, and the two fast light chain isoforms LC1f and LC2f. Direct low-frequency (2.5 Hz) stimulation of these myotubes via platinum electrodes leads to a shift in myosin HC expression with increases in the late embryonic HC isoform HCemb/l amounting to 35% of total HC in 19-day-stimulated cultures. Measurements of 35S-methionine incorporation and immunohistochemical analyses demonstrate increases in LC3f. This increase is also seen at the mRNA level. These results indicate that induced contractile activity promotes myotube maturation in vitro. The observation that chronic stimulation enhances the expression of the slow isoform LC2s at the RNA, as well as the protein level, suggests an additional effect consisting of a fast-to-slow change in phenotype expression. In view of the fact that muscle maturation and phenotype expression is under neural control during development in vivo, our results on directly stimulated, aneural myotubes indicate that neurally transmitted contractile activity may be an important factor in modulating phenotype expression of secondary myotubes.

Quantification of immunoglobulin on electrophoretic immunoblot strips as a tool for human immunodeficiency virus serodiagnosis

Electrophoretic immunoblotting (EIB [Western blotting]), the main method for verification of human immunodeficiency virus (HIV) seropositivity, needs thorough characterization and standardization. We explored the possibilities of quantifying immunoglobulin G (IgG) bound to EIB strips both by densitometry of the peroxidase-stained bands and by measurement of radioactivity with labeled anti-HIV IgG. The radioactivity method is inherently more exact but was more cumbersome. However, despite saturation phenomena at high IgG densities, the densitometric method was more convenient and yielded reproducible estimates of the amount of bound IgG. We found it useful primarily for documentation of changes in the relative abundance of antibodies to different HIV proteins from individual patients over time. To explore the potential usefulness of the method, we studied a small set of HIV-seropositive persons. The average p24/gp41 color yield ratios and standard deviations in 3 persons with recent seroconversion, 15 healthy subjects, and 6 diseased HIV-seropositive persons were 6.6 +/- 0.9, 2.3 +/- 1.9, and 1.3 +/- 0.5, respectively. These data are in accord with previous qualitative or semiquantitative observations but are too limited for any conclusions regarding the use of quantitative EIB for prognostic use with individual patients. Quantitative EIB is a valuable tool for comparative methodological studies and for research on the protective role of anti-HIV antibodies in acquired immunodeficiency syndrome pathogenesis. Its possible use in prognostication for individual patients must be evaluated in long-term studies.

Expression of myosin light chains during fetal development of human skeletal muscle

The expression of myosin light chains (MLCs) during the development of human skeletal muscle was investigated by using two different two-dimensional electrophoretic techniques. In both electrophoretic systems the predominant light chain 1 (LC1) expressed during the whole fetal period was found to co-migrate with the adult fast LC1 (LC1F). The main LC2 expressed during the whole fetal period was found to be different from the main fast LC2 (LC2F) and slow LC2 (LC2S) usually present in adult muscle, but co-migrated with a minor component often present in adult muscle. This fetal LC2 was phosphorylatable, and the phosphorylated form co-migrated with the main component of LC2F expressed in the adult. The adult fast LC3 appeared as early as week 20 of gestation, whereas the adult slow light chains (LC1S and LC2S) appeared only during the late fetal period. A minor component of LC1, previously described in humans as an 'embryonic LC' (LCemb.) [Strohman, Micou-Eastwood, Glass & Matsuda (1983) Science 221, 955-957], was only expressed in the early fetal period and was found to co-migrate with atrial LC1 (ALC1). We discuss the expression of these specific developmental forms of MLCs co-existing with immature myosin heavy chains during fetal life.