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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.     

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.     

Chronology of permethrin resistance in a southern Illinois population of the horn fly (Diptera: Muscidae) during and after selection by pyrethroid use

From 1985 through 1988, horn flies (Haematobia irritans (L)) collected at the Dixon Springs Agricultural Center (DSAC) in southern Illinois were tested in 22 h bioassays for permethrin resistance with residues on cotton cloths. The LC90 for a susceptible field population collected in June 1985 was 0.19 micrograms/cm2. In comparison, flies collected from pyrethroid-tagged cattle in 1985 and 1986 exhibited 25- to 116-fold resistance to permethrin. A 25-fold level of resistance allowed survival on treated cattle 8 wk after pyrethroid tag application. Flies representing the local background population were collected periodically from an untreated herd 2.4 km from the nearest cattle treated with a pyrethroid; these flies exhibited up to 18-fold resistance. Although pyrethroids were not used on DSAC animals after October 1986, all bioassays done in 1987 and 1988 indicated resistance levels of greater than or equal to 7-fold. The 95% confidence intervals for LC90s from all 1987 bioassays overlapped the confidence interval from the corresponding July 1986 estimate for resistant flies collected from pyrethroid-tagged cattle. Although some decline in resistance was evident in 1988, bioassays done at the end of the season produced resistance ratios of 7.4 and 15.3. Survivorship at a diagnostic dose indicated that resistance frequencies remained at 4-8% throughout 1988. Two years' abstinence from pyrethroid use was insufficient to allow an adequate decline in resistance levels.     

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.