Evolutionary Patterns of Axial Muscle Systems in Some Invertebrates and Fish

SYNOPSIS. Axial muscles used for oscillatory swimming are foundnot only in fish and other vertebrates but also in some protochordatesand invertebrates. Chaetognaths have unsegmented locomotor musculaturewith some unusual features, but larvacean tunicates and thetadpole larvae of ascidians show the simplest variant of thechordate segmented axial muscle arrangement for flexing a notochordalcolumn, where all muscle cells along one side are electricallycoupled. With amphioxus, the basic fish myotomal layout is established,with two main fibre types probably used for different patternsof swimming (as in fish). There are, however, several uniquefeatures, including the flattened fibre shape and the paramyosinsystem of the notochord. Agnatha have two fibre types in themyotomes, a third type perhaps being a developmental stage inthe ontogeny of fast fibres. In lampreys, the central fibresof the characteristic fibre sandwiches in the myotomes are flattened(though less so than in amphioxus); they have a dual innervationof unknown function seen also in the fast fibre system of manyGnathostome fish groups. Hagfish fast fibres are not flattenednor do they have a dual innervation. Gnathostome fish axialmuscles are strikingly uniform in design with two possible exceptions:(1) higher teleost fast fibres which, unlike those of othergroups, are multiply-innervated and (2) tonic fibres in a fewfish, which seem not to be involved in locomotion.     

Muscarinic receptor reserve and beta-adrenergic sensitivity in tracheal smooth muscle

The possibility that differences in beta-adrenergic sensitivity among canine trachealis muscles contracted with different contractile agonists are related to differences in the receptor-occupancy characteristics of the contractile agonists was investigated. Relaxation to isoproterenol was compared in muscles contracted with the muscarinic agonists McN-A-343 and acetylcholine (ACh). The apparent dissociation constant (pKB) values for the M1-antagonist, pirenzepine, against ACh (6.96 +/- 0.18) and McN-A-343 (6.84 +/- 0.08) were similar. The pKB values for the M3-antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) against ACh (8.76 +/- 0.13) and McN-A-343 (8.71 +/- 0.10) were also similar, suggesting that these agonists were activating the same subtype of muscarinic receptor, probably M3. However, the contractile response to ACh was associated with a greater receptor reserve than that for McN-A-343. Isoproterenol relaxed muscles contracted with McN-A-343 much more effectively than those contracted with an equieffective concentration of ACh. The results suggest that the relative resistance of ACh-induced contractions to relaxation by isoproterenol may not be an inherent quality of muscarinic receptor stimulation. The large receptor reserve available to ACh may act to buffer the contractile response from the inhibitory effects of beta-adrenergic stimulation. Alternatively, ACh may be able to initiate subcellular mechanisms that are unavailable to agonists of lower efficacy.     

Cloning and characterization of a tandemly repeated DNA sequence in the crane family (Gruidae)

A tandemly repeated DNA sequence possessing a unique PstI site has been characterized in several species of the crane family. The "Pst family" comprises at least 8800 monomer units 187 base pairs (bp) in length and constitutes 0.14% of the genome of the sarus crane (Grus antigone). The array is located in the centromeric heterochromatin of chromosome 2 in the two species where in situ hybridizations of a cloned monomer to metaphase chromosome spreads were carried out. DNA sequence comparisons between five monomer units from G. antigone revealed a high degree of homology between four of the individual repeats, while the fifth was somewhat divergent. The G + C content deduced from the DNA sequence makes it likely that the Pst family constitutes part of a density satellite seen in profiles of crane DNA centrifuged to equilibrium in CsCl. The common occurrence of tandem arrays such as the Pst family, with repeat lengths close to 200 bp, leads us to an hypothesis implicating nucleosomes in the evolution of such families.     

The viral envelope gene is involved in macrophage tropism of a human immunodeficiency virus type 1 strain isolated from brain tissue.

Human immunodeficiency virus type 1 (HIV-1) strains isolated from the central nervous system (CNS) may represent a subgroup that displays a host cell tropism different from those isolated from peripheral blood and lymph nodes. One CNS-derived isolate, HIV-1SF128A, which can be propagated efficiently in primary macrophage culture but not in any T-cell lines, was molecularly cloned and characterized. Recombinant viruses between HIV-1SF128A and the peripheral blood isolate HIV-1SF2 were generated in order to map the viral gene(s) responsible for the macrophage tropism. The env gene sequences of the two isolates are about 91.1% homologous, with variations scattered mainly in the hypervariable regions of gp120. Recombinant viruses that have acquired the HIV-1SF128A env gene display HIV-1SF128A tropism for macrophages. Furthermore, the gp120 variable domains, V1, V2, V4, and V5, the CD4-binding domain, and the gp41 fusion domain are not directly involved in determining macrophage tropism.     

Identification of distinct T cell receptor (TCR)-gamma delta heterodimers using an anti-TCR-gamma variable region serum

T cell hybridomas were generated from CD3+, CD4-, CD8- splenocytes and fetal thymocytes. V gamma 1-expressing proteins present on these murine TCR-gamma delta hybridomas were identified by using an anti-TCR V gamma 1 peptide serum. This antiserum specifically immunoprecipitated 41-kDa TCR V gamma-C gamma 4 chains and 31-kDa TCR V gamma-C gamma 1/2 chains from distinct heterodimers expressed on the TCR-gamma delta T cell hybridomas. The RNA from a hybridoma with a 31-kDa TCR-gamma chain hybridized with a V gamma 1 probe but failed to hybridize with a V gamma 2 probe. In contrast, the RNA from a hybridoma with a 32-kDa TCR-gamma chain hybridized with a V gamma 2 probe. This 32-kDa TCR-gamma chain was not immunoprecipitated by the anti-V gamma 1 serum. These data were consistent with the conclusion that the 31-kDa protein was the product of a V gamma 1 to C gamma 2 rearrangement, whereas the 32-kDa protein was the product of a V gamma 2 to C gamma 1 rearrangement. Furthermore, Southern analyses confirmed that the 32-kDa protein was the product of a V gamma 1.2-J gamma 2 rearrangement, and all three of the 41-kDa TCR-gamma chains were the results of V gamma 1.1-J gamma 4 rearrangements. This was the first demonstration at the clonal level of TCR-gamma proteins which use members of the V gamma 1 gene family, as well as the C gamma 2 constant region. Additional biochemical analyses of the TCR-gamma and -delta proteins from three independently derived C gamma 4-bearing T cell hybridomas suggested that most of the molecular mass diversity observed in the bulk subpopulation of peripheral C gamma 4-containing heterodimers may be contributed by the TCR-delta chains.     

Otolith microstructure indicating growth and mortality among plaice, Pleuronectes platessa L., post-larval sub-cohorts

Growth and mortality of post-metamorphosed plaice were studied by means of daily increments in the sagittal otoliths. The Gompertz model was the best fit to length-at-age data and there were no significant differences between length-at-age and back-calculated lengths. The microstructure pattern of the otoliths at metamorphosis was also used to estimate hatching and settlement distributions. Differential growth and mortality occurred among sub-cohorts; growth rates and mortality were higher in fish that settled earlier. In 1986, the best survival was for a sub-cohort settling in late May to early June. In contrast, in the warmer season of 1987, survival was highest for the second and third sub-cohorts settling in late April and mid May.     

Unimpaired formation of hormone-stimulated inositol trisphosphate in human mesangial cells under hyperglycemic conditions.

The relationship between bulk cellular myo-inositol content and phosphatidylinositol metabolism was evaluated in a human mesangial cell line under euglycemic and hyperglycemic conditions. Mesangial cells maintained in high glucose medium displayed a concentration-dependent fall in myo-inositol as measured by gas-liquid chromatography. Measurements of phosphatidylinositol, phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-bisphosphate mass revealed slight but statistically insignificant increases in cells exposed to high glucose containing medium. CDP-diacylglycerol: myo-inositol 3-phosphatidylinositol transferase activity, measured in plasma membranes from mesangial cells grown under control and hyperglycemic conditions, was kinetically similar with Michaelis constants (Km values) for myo-inositol of 2.9 and 2.1 mM, respectively. Finally, hormone-stimulated intracellular calcium mobilization and myo-inositol 1,4,5-trisphosphate mass was measured from mesangial cells grown under normal and hyperglycemic conditions. Both intracellular calcium and inositol trisphosphate formation were unchanged in cells previously exposed to high glucose conditions (400 mg/dl) compared to cells grown under normal glucose concentration (100 mg/dl). These data indicate that bulk changes in myo-inositol induced by hyperglycemia are neither associated with alterations in basal levels of inositol containing glycerolipids nor with changes in hormone-stimulated calcium mobilization and inositol trisphosphate formation under conditions of short term changes in extracellular glucose.