Inbreeding reveals interpopulation differences in inversion polymorphism of Drosophila subobscura

The adaptive significance of inversion polymorphism of Drosophila subobscura is well established. However, little is known about gene combinations within inversions which are coadapted because of population-specific effects. We studied this aspect of Dobzhansky's coadaptation hypothesis, using the systematic inbreeding method. Differences in magnitude and quality of inversion polymorphism in two ecologically and topologically distinct habitats were compared after several generations of continuous full-sib inbreeding. Populations from the two habitats differ in frequency of homokaryotypes after third and fifth generation of inbreeding and in the levels of homozygosity of different gene arrangements. The effect of homozygosity appears population and chromosome specific.     

Carotenoid synthesis in Streptomyces setonii ISP5395 is induced by the gene crtS, whose product is similar to a sigma factor

In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395.     

In vivo bone strain on the dog tibia during locomotion

Rosette and single-element strain gauges were implanted on the tibia in 2 dogs and recordings were made during locomotion on a treadmill. At foot contact and during the swing phase of locomotion, bone strains were low and directions of the principal strains were variable. There was a large shift in the directions of the principal strains at the beginning of the stance phase and bone strains were considerably higher. Peak strain occurred midway through the stance phase. At that time, the maximum principal strain (tension) was directed upwards and anteriorly between 30 and 60 degrees with respect to the long axis of the tibia. These bone strain patterns in the dog are similar to those found in sheep while both differ markedly from those found in humans.     

Enzyme distributions in subcellular fractions of BHK cells infected with Semliki forest virus: evidence for a major fraction of sphingomyelin synthase in the trans-golgi network.

BHK cells either untreated or infected with Semliki Forest virus have been fractionated on sucrose density gradients. Virus infection caused an increase in density of a membrane fraction enriched in sphingomyelin (SM), cholesterol, SM synthase and sialyltransferase activity. This increase in density was related to incorporation of viral proteins into this fraction, which is likely to contain trans-Golgi network (TGN) membranes. In contrast, glucosylceramide synthase and galactosyltransferase activities (markers for cis/medial and trans-Golgi respectively) underwent no density shift and alkaline phosphodiesterase, a plasma membrane marker, was only slightly density-shifted in infected cells. When cells were incubated with NBD-ceramide to enable them to synthesise NBD-SM and then washed with albumin to remove surface label, fluorescence in untreated cells was concentrated in a single juxtanuclear spot but in infected cells this region of bright fluorescence was larger and extended around the nucleus. After fractionation of these cells, NBD-SM (but only a small proportion of the NBD-ceramide) was found to be shifted into the higher density fraction in infected cells. This work provides further evidence that SM synthase is not mainly localised in the early Golgi cisternae as previously thought, but is associated more with a cholesterol-rich compartment which could be the TGN.     

Insulin receptor substrate-4 enhances insulin-like growth factor-I-induced cell proliferation.

The insulin receptor substrates (IRSs)-1-4 play important roles in signal transduction emanating from the insulin and insulin-like growth factor (IGF)-I receptors. IRS-4 is the most recently characterized member, which has been found primarily in human cells and tissues. It interacts with SH2-containing proteins such as phosphatidylinositol 3'-kinase (PI3K), Grb2, Crk-II, and CrkL. In this study, we transfected IRS-4 in mouse NIH-3T3 cells that overexpress IGF-I receptors. Clones expressing IRS-4 showed enhanced cellular proliferation when cells were cultured in 1% fetal bovine serum without added IGF-I. Addition of IGF-I enhanced cellular proliferation in cells overexpressing the IGF-I receptor alone but had an even greater proliferative effect in cells overexpressing both the IGF-I receptors and IRS-4. When etoposide and methylmethane sulfonate (MMS), both DNA damaging agents, were added to the cells, they uniformly induced cell cycle arrest. Fluorescence-activated cell sorter analysis demonstrated that the arrest of the cell cycle occurred at the G(1) checkpoint, and furthermore no significant degree of apoptosis was demonstrated with the use of either agent. In cells, overexpressing IGF-I receptors alone, IGF-I addition enhanced cellular proliferation, even in the presence of etoposide and MMS. In cells overexpressing IGF-I receptors and IRS-4, the effect of IGF-I in overcoming the cell cycle arrest was even more pronounced. These results suggest that IRS-4 is implicated in the IGF-I receptor mitogenic signaling pathway.