Effects of EDTA treatment upon the protein subunit composition and mechanical properties of mammalian single skeletal muscle fibers

Considerable interest has been focused on the role of myosin light chain LC(2) in the contraction of vertebrate striated muscle. A study was undertaken to further our investigations (Moss, R.L., G.G. Giulian, and M.L. Greaser, 1981, J. Biol. Chem., 257:8588-8591) of the effects of LC(2) removal upon contraction in skinned fibers from rabbit psoas muscles. Isometric tension and maximum velocity of shortening, V(max), were measured in fiber segments prior to LC(2) removal. The segments were then bathed at 30 degrees C for up to 240 min in a buffer solution containing 20 mM EDTA in order to extract up to 60 percent of the LC(2). Troponin C (TnC) was also partially removed by this procedure. Mechanical measurements were done following the EDTA extraction and the readditions of first TnC and then LC(2) to the segments. The protein subunit compositions of the same fiber segments were determined following each of these procedures by SDS PAGE of small pieces of the fiber. V(max) was found to decrease as the LC(2) content of the fiber segments was reduced by increasing the duration of extraction. EDTA treatment also resulted in substantial reductions in tension due mainly to the loss of TnC, though smaller reductions due to the extraction of LC(2) were also observed. Reversal of the order of recombination of LC(2) and TnC indicated that the reduction in V(max) following EDTA treatment was a specific effect of LC(2) removal. These results strongly suggest that LC(2) may have roles in determining the kinetics and extent of interaction between myosin and actin.     

Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution

Lemur beta-related globin genes have been isolated and sequenced. Orthology of prosimian and human epsilon-, gamma-, and beta-related globin genes was established by dot-matrix analysis. All of these lemur globin genes potentially encode functional beta-related globin polypeptides, though precisely when the gamma-globin gene is expressed remains unknown. The organization of the 18-kb brown lemur beta-globin gene cluster (5' epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by contraction via unequal crossing-over from the putative ancestral mammalian beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf lemur nonadult globin genes are arranged as in the brown lemur. Similar levels of synonymous (silent) nucleotide substitutions and noncoding DNA sequence differences have accumulated between species in all of these genes, suggesting a uniform rate of noncoding DNA divergence throughout primate beta-globin gene clusters. These differences are comparable with those observed in the nonfunctional psi eta pseudogene and have therefore accumulated at the presumably maximal neutral rate. In contrast, nonsynonymous (replacement) nucleotide substitutions show a significant heterogeneity in distribution for both the same gene in different lineages and different genes in the same lineage. These major fluctuations in replacement but not silent substitution rates cannot be attributed to changes in mutation rate, suggesting that changes in the rate of globin polypeptide evolution in primates is not governed solely by variable mutation rates.      

Molecular population genetics of ref(2)P, a locus which confers viral resistance in Drosophila

The ref(2)P locus (2-54.2) is polymorphic for two allelic forms in natural populations of Drosophila melanogaster, ref(2)Po and ref(2)Pp. The latter allele confers resistance to the rhabdovirus sigma infecting wild populations. Previous work, based on a small sample of prescreened restrictive (resistant) and permissive (susceptible) alleles, identified a large number of amino acid replacement changes (7) relative to synonymous changes (1). Such protein variability could be the result of variation-enhancing selection. To further test the selection hypothesis, we have examined the DNA sequences of ten randomly chosen lines of D. melanogaster and one line of D. simulans. Nine of the ten lines are permissive; D. simulans does not harbor the virus. The melanogaster alleles contain 4 synonymous changes, 19 noncoding changes, and 13 amino acid replacement changes, indicating a relatively high level of polymorphism. Three sequenced restrictive alleles have nearly identical sequences, indicating that they are relatively young. Compared to the permissive alleles, they share only a complex deletion at codon 34, CAG-AAT to GGA, which our analysis indicates to be the site conferring the restrictive phenotype. Patterns of polymorphism and divergence differ from neutral predictions by several criteria for the amino terminal region, which contains the complex deletion (codons 1-91), but not the remainder of the protein (codons 92-599). We find a higher rate of evolution on the D. melanogaster lineage than on the D. simulans lineage. The relatively large amount of both replacement and silent polymorphism in the permissive alleles and the lack of divergence between permissive and restrictive alleles suggests that the sigma virus and ref(2)P may be engaged in an evolutionary race in which new restrictive alleles are continually arising but are relatively short-lived.      

Hip joint replacement surgery for idiopathic osteoarthritis aggregates in families

In order to determine whether there is a genetic component to hip or knee joint failure due to idiopathic osteoarthritis (OA), we invited patients (probands) undergoing hip or knee arthroplasty for management of idiopathic OA to provide detailed family histories regarding the prevalence of idiopathic OA requiring joint replacement in their siblings. We also invited their spouses to provide detailed family histories about their siblings to serve as a control group. In the probands, we confirmed the diagnosis of idiopathic OA using American College of Rheumatology criteria. The cohorts included the siblings of 635 probands undergoing total hip replacement, the siblings of 486 probands undergoing total knee replacement, and the siblings of 787 spouses. We compared the prevalence of arthroplasty for idiopathic OA among the siblings of the probands with that among the siblings of the spouses, and we used logistic regression to identify independent risk factors for hip and knee arthroplasty in the siblings. Familial aggregation for hip arthroplasty, but not for knee arthroplasty, was observed after controlling for age and sex, suggesting a genetic contribution to end-stage hip OA but not to end-stage knee OA. We conclude that attempts to identify genes that predispose to idiopathic OA resulting in joint failure are more likely to be successful in patients with hip OA than in those with knee OA.     

The early adaptive evolution of calmodulin

Interaction between gene duplication and natural selection in molecular evolution was investigated utilizing a phylogenetic tree constructed by the parsimony procedure from amino acid sequences of 50 calmodulin- family protein members. The 50 sequences, belonging to seven protein lineages related by gene duplication (calmodulin itself, troponin-C, alkali and regulatory light chains of myosin, parvalbumin, intestinal calcium-binding protein, and glial S-100 phenylalanine-rich protein), came from a wide range of eukaryotic taxa and yielded a denser tree (more branch points within each lineage) than in earlier studies. Evidence obtained from the reconstructed pattern of base substitutions and deletions in these ancestral loci suggests that, during the early history of the family, selection acted as a transforming force on expressed genes among the duplicates to encode molecular sites with new or modified functions. In later stages of descent, however, selection was a conserving force that preserved the structures of many coadapted functional sites. Each branch of the family was found to have a unique average tempo of evolutionary change, apparently regulated through functional constraints. Proteins whose functions dictate multiple interaction with several other macromolecules evolved more slowly than those which display fewer protein-protein and protein-ion interactions, e.g., calmodulin and next troponin-C evolved at the slowest average rates, whereas parvalbumin evolved at the fastest. The history of all lineages, however, appears to be characterized by rapid rates of evolutionary change in earlier periods, followed by slower rates in more recent periods. A particularly sharp contrast between such fast and slow rates is found in the evolution of calmodulin, whose rate of change in earlier eukaryotes was manyfold faster than the average rate over the past 1 billion years. In fact, the amino acid replacements in the nascent calmodulin lineage occurred at residue positions that in extant metazoans are largely invariable, lending further support to the Darwinian hypothesis that natural selection is both a creative and a conserving force in molecular evolution.      

Cultured endothelial cells produce heparinlike inhibitor of smooth muscle cell growth

Using cultured cells from bovine and rat aortas, we have examined the possibility that endothelial cells might regulate the growth of vascular smooth muscle cells. Conditioned medium from confluent bovine aortic endothelial cells inhibited the proliferation of growth-arrested smooth muscle cells. Conditioned medium from exponential endothelial cells, and from exponential or confluent smooth muscle cells and fibroblasts, did not inhibit smooth muscle cell growth. Conditioned medium from confluent endothelial cells did not inhibit the growth of endothelial cells or fibroblasts. In addition to the apparent specificity of both the producer and target cell, the inhibitory activity was heat stable and not affected by proteases. It was sensitive flavobacterium heparinase but not to hyaluronidase or chondroitin sulfate ABC lyase. It thus appears to be a heparinlike substance. Two other lines of evidence support this conclusion. First, a crude isolate of glycosaminoglycans (TCA-soluble, ethanol-precipitable material) from endothelial cell-conditioned medium reconstituted in 20 percent serum inhibited smooth muscle cell growth; glycosaminoglycans isolated from unconditioned medium (i.e., 0.4 percent serum) had no effect on smooth muscle cell growth. No inhibition was seen if the glycosaminoglycan preparation was treated with heparinase. Second, exogenous heparin, heparin sulfate, chondroitin sulfate B (dermatan sulfate), chondroitin sulfate ABC, and hyaluronic acid were added to 20 percent serum and tested for their ability to inhibit smooth muscle cell growth. Heparin inhibited growth at concentrations as low as 10 ng/ml. Other glycosaminoglycans had no effect at doses up to 10 μg/ml. Anticoagulant and non- anticoagulant heparin were equally effective at inhibiting smooth muscle cell growth, as they were in vivo following endothelial injury (Clowes and Karnovsk. Nature (Lond.). 265:625-626, 1977; Guyton et al. Circ. Res. 46:625-634, 1980), and in vitro following exposure of smooth muscle cells to platelet extract (Hoover et al. Circ. Res. 47:578-583, 1980). We suggest that vascular endothelial cells may secrete a heparinlike substance in vivo which may regulate the growth of underlying smooth muscle cells.