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911.
Three polyhydroxylated sterol hemiacetals, pectinoacetals A-C (1–3) have been isolated as their acetyl derivatives (4–6) from the acetic anhydride treated organic extract of the Indo-Pacific gorgonianCtenocella pectinata. These natural products were found to undergo very rapid epimerization at the C-18 chiral center and thus exist only as an equilibrium mixture of two diastereomers. The structure assignments are based on spectral studies and chemical modifications of the natural products. 相似文献
912.
Treatment with the co-transport inhibitor, furosemide decreased36Cl– flux across perfused Malpighian tubules ofLocusta. However, exclusion of36Cl– from the bathing medium had not effect on22Na+ flux whereas substitution of bathing medium Na+ by K+ increased36Cl– flux. Diuretic extract of corpora cardiaca increased22Na+ (by 106%) and36Cl– (by 335%) fluxes differentially. 相似文献
913.
Sexual isolation betweenDrosophila melanogaster females andD. simulans males. Male mating propensities versus success in hybridization 总被引:1,自引:0,他引:1
J. A. Jamart M. C. Carracedo P. Casares 《Cellular and molecular life sciences : CMLS》1993,49(6-7):596-598
Genetic variation has been found in males of aD. simulans population for their eagerness to hybridize withD. melanogaster females. In a search for traits involved in this hybridization, males ofD. simulans were tested for mating speed and sexual vigour. Between-male differences were detected in both sexual traits, but no relationship was noticed between them, nor with the frequency of hybridization. Thus male mating propensities appear to be unrelated to the breakdown of sexual isolation between these sibling species. 相似文献
914.
There are many examples of patterned developing systems which are size invariant: if the total size of the system is reduced, then the pattern responds by changing its scale in such a way that the number of pattern elements remains constant. This phenomenon is one of the bases which underaly the formulation of the concept of positional information, one of the great unifying ideas in developmental biology. However, there are less common examples of patterns which are size dependent. In these, alterations of overall size lead to a reduction in pattern elements. Such size-dependent patterns are therefore of theoretical interest. Here we describe how the number of feather germs along the wing bud of the developing chick embryo responds to shortening of the limb, and consider the implications of these observations. 相似文献
915.
Flavins generate oxidants during metabolism and when exposed to light. Here we report that the photoreceptor layer of retinas from black-eyed rats is reduced in size by a dietary regime containing excess riboflavin. The effect of excess riboflavin was dose-dependent and was manifested by a decrease in photoreceptor length. This decrease was due in part to a reduction in the thickness of the outer nuclear layer, a structure formed from stacked photoreceptor nuclei. These changes were accompanied by an increase in photoreceptor outer segment autofluorescence following illumination at 328 nm, a wavelength that corresponds to the excitation maxima of oxidized lipopigments of the retinal pigment epithelium. 相似文献
916.
R. J. Capon K. Elsbury M. S. Butler C. C. Lu J. N. A. Hooper J. A. P. Rostas K. J. O'Brien L. -M. Mudge A. T. R. Sim 《Cellular and molecular life sciences : CMLS》1993,49(3):263-264
The Antarctic marine spongeTedania charcoti has been shown to contain extraordinarily high natural concentrations of cadmium and zinc, which have in turn been correlated to the ability of the crude ethanol extract to modulate protein phosphorylation in chicken forebrain and to inhibit the growth of several test bacteria. 相似文献
917.
C. Brugnara 《Cellular and molecular life sciences : CMLS》1993,49(2):100-109
The cellular concentration of Hb S plays a central role in the kinetic of Hb S polymerization and cell sickling. Blood of patients with homozygous sickle cell (SS) anemia contains a variable fraction of cells which are markedly dehydrated and have increased Hb S concentration. Since a decrease in cellular Hb S concentration reduces Hb S polymerization and sickling, the study of the processes leading to sickle cell dehydration has important pathophysiological and therapeutic implications. Sickle cell dehydration is due to cellular loss of K and Cl. K loss in sickle cells can take place via either the Ca2+-activated K+ channel, or the K?Cl cotransport, or the combined effect of oxidative damage and deformation of the red cell membrane. Inhibitors of K transport through these pathways could be used to prevent dehydration of sickle cells in vivo, provided that they can be administered safely. 相似文献
918.
Sex in Caenorhabditis elegans is determined by a regulatory cascade of seven interacting autosomal genes controlled by three X-linked genes in response to the X chromosome-to-autosome (X/A) ratio. XX animals (high X/A) develop as self-fertile hermaphrodites, and XO animals (low X/A) develop as males. The activity of the first gene in the sex-determining cascade, her-1, is required for male sexual development. XO her-1 loss-of-function mutants develop as self-fertile hermaphrodites, whereas XX her-1 gain-of-function mutants develop as masculinized intersexes. By genetic mosaic analysis using a fused free duplication linking her-1 to a cell-autonomous marker gene, we show here that her-1 expression in a sexually dimorphic cell is neither necessary nor sufficient for that cell to adopt a male fate. Our results suggest that her-1 is expressed in many, possibly all, cells and that its gene product can function non-autonomously through cell interactions to determine male sexual development. 相似文献
919.
Bazooka provides an apical cue for Inscuteable localization in Drosophila neuroblasts 总被引:1,自引:0,他引:1
Asymmetric cell division generates daughter cells with different developmental fates from progenitor cells that contain localized determinants. During this division, the asymmetric localization of cell-fate determinants and the orientation of the mitotic spindle must be precisely coordinated. In Drosophila neuroblasts, inscuteable controls both spindle orientation and the asymmetric localization of the cell-fate determinants Prospero and Numb. Inscuteable itself is localized in an apical cortical crescent and thus reflects the intrinsic asymmetry of the neuroblast. Here we show that localization of Inscuteable depends on Bazooka, a protein containing three PDZ domains with overall sequence similarity to Par-3 of Caenorhabditis elegans. Bazooka and Inscuteable form a complex that also contains Staufen, a protein responsible for the asymmetric localization of prospero messenger RNA. We propose that, after delamination of the neuroblast from the neuroepithelium, Bazooka provides an asymmetric cue in the apical cytocortex that is required to anchor Inscuteable. As Bazooka is also responsible for the maintenance of apical-basal polarity in epithelial tissues, it may be the missing link between epithelial polarity and neuroblast polarity. 相似文献
920.
The X-linked form of the human disease dyskeratosis congenita (DKC) is caused by mutations in the gene encoding dyskerin. Sufferers have defects in highly regenerative tissues such as skin and bone marrow, chromosome instability and a predisposition to develop certain types of malignancy. Dyskerin is a putative pseudouridine synthase, and it has been suggested that DKC may be caused by a defect in ribosomal RNA processing. Here we show that dyskerin is associated not only with H/ACA small nucleolar RNAs, but also with human telomerase RNA, which contains an H/ACA RNA motif. Telomerase adds simple sequence repeats to chromosome ends using an internal region of its RNA as a template, and is required for the indefinite proliferation of primary human cells. We find that primary fibroblasts and lymphoblasts from DKC-affected males are not detectably deficient in conventional H/ACA small nucleolar RNA accumulation or function; however, DKC cells have a lower level of telomerase RNA, produce lower levels of telomerase activity and have shorter telomeres than matched normal cells. The pathology of DKC is consistent with compromised telomerase function leading to a defect in telomere maintenance, which may limit the proliferative capacity of human somatic cells in epithelia and blood. 相似文献