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61.
The Saddle-billed Stork Ephippiorhynchus senegalensis exemplifies a case in conservation research in which a species is assessed as Least Concern on the IUCN Red List and the resulting consideration of low conservation priority has precluded proper scientific study. As a first step in understanding this stork’s true status, we collated all available data to develop a distribution map and then investigated range-wide patterns of occurrence. The updated map greatly improves on past knowledge of the stork’s distribution and helps to identify regions where range contractions have occurred, particularly in Central Africa and parts of West Africa. We found that the stork’s distribution closely overlaps with protected areas and that there has been an overall increase in surface water (largely manmade water bodies)—a proxy for habitat—across the species’ extent of occurrence in recent decades. While this research represents a valuable contribution to our understanding of the Saddle-billed Stork, it also highlights the need for unbiased empirical data, especially from areas that are poorly surveyed, for developing a science-based conservation status assessment. 相似文献
62.
We recently reported that bile salts play a role in the regulation of mucin
secretion by cultured dog gallbladder epithelial cells. In this study we
have examined whether bile salts also influence mucin secretion by the
human epithelial colon cell line LS174T. Solutions of bile salts were
applied to monolayers of LS174T cells. Mucin secretion was quantified by
measuring the secretion of [3H]GlcNAc labeled glycoproteins. Both
unconjugated bile salts as well as taurine conjugated bile salts stimulated
mucin secretion by the colon cells in a dose-dependent fashion. Hydrophobic
bile salts were more potent stimulators than hydrophilic bile salts. Free
(unconjugated) bile salts were more stimulatory compared with their taurine
conjugated counterparts. Stimulation of mucin secretion by LS174T cells was
found to occur at much lower bile salt concentrations than in the
experiments with the dog gallbladder epithelial cells. The protein kinase C
activators PMA and PDB had no stimulatory effect on mucin secretion. We
conclude that mucin secretion by the human colon epithelial cell line
LS174T is regulated by bile salts. We suggest that regulation of mucin
secretion by bile salts might be a common mechanism, by which different
epithelia protect themselves against the detergent action of bile salts, to
which they are exposed throughout the gastrointestinal tract.
相似文献
63.
We have determined the complete nucleotide sequence of the two nonallelic
adult beta-globin genes of the C57BL/10 mouse. These genes, designated beta
s and beta t, show a sequence similarity of 99.6% over the region bordered
by the translational start and stop codons. Both beta s and beta t encode
functional polypeptide chains that are identical. A comparison of the
C57BL/10 beta-globin haplotype, Hbbs, with that of the BALB/c mouse, Hbbd,
suggests that the two haplotypes have distinct evolutionary histories. The
two adult beta-globin genes of the Hbbd haplotype, beta dmaj and beta dmin,
are 16% divergent at the nucleotide level and encode distinct polypeptides
that are synthesized in differing amounts. Our analysis indicates that a
gene correction mechanism has been operating on the Hbbs chromosome to keep
beta s and beta t evolving in concert, whereas on the Hbbd chromosome, beta
dmin has diverged considerably from beta dmaj. We suggest that gene
conversion is responsible for the maintained similarity of the Hbbs genes.
Furthermore, we attribute the divergence of the Hbbd genes in part to the
absence of a region of simple-sequence DNA within the large intervening
sequence of beta dmin. We propose that this region of DNA plays a role in
facilitating gene conversion. The deletion of this area in beta dmin
introduced a block of nonhomology between the beta dmaj-beta dmin gene pair
and thus may have inhibited further gene correction within the Hbbd
haplotype.
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65.
Repeated epilation (Er) is a radiation-induced, autosomal, incomplete dominant mutation in mice which is expressed in heterozygotes but is lethal in the homozygous condition. Many effects of the mutation occur in skin: the epidermis in Er/Er mice is adhesive (oral and nasal orifices fuse, limbs adhere to the body wall), hyperplastic, and fails to undergo terminal differentiation. Skin from fetal +/+, Er/+ and Er/Er mice at ages pre- and postkeratinization examined by light, scanning, and transmission electron microscopy showed marked abnormalities in tissue architecture, differentiation, and cell structure; light and dark basal epidermal cells were separated by wide intercellular spaces, joined by few desmosomes, and contained phagolysomes. The numbers of spinous, granular, and superficial layers were highly variable within any given region and among various regions of the body. In some areas, 2-8 layers of granular cells, containing large or diminutive keratohyalin granules, extended to the epidermal surface; in others, the granular layers were covered by several layers of partially keratinized or nonkeratinized cells. In rare instances, a single or small group of cornified cells was present among the granular layers but was not associated with the epidermal surface. Both the granular and nonkeratinized/partially keratinized upper epidermal layers Er/Er skin gave positive immunofluorescence with antiserum to the histidine-rich, basic protein, filaggrin. Proteins in epidermal extracts from +/+, Er/+ and Er/Er mice were separated and identified by radio- and immunolabeling techniques. The Er/Er extract was missing a 26.5- kdalton protein and had an altered ratio of bands in the keratin region. The 26.5-kdalton band was histidine-rich and cross-reacted with the antiserum to rat filaggrin. Several high molecular weight bands present in both Er/Er and +/+ extracts also reacted with the antiserum. These are presumed to be the precursors of filaggrin and to account for the immunofluorescence om Er/Er epidermis even though the product protein is absent. The morphologic and biochemical data indicated that the genetic defect has a general and profound influence on epidermal differentiation, including alteration of two proteins (filaggrin and keratin) important in normal terminal differentiation, tissue architecture, and cytology. Identification of epidermal abnormalities at early stages of development (prekeratinization) and defective structure of other tissues and gross anatomy suggest that the mutation is responsible for a defect in same regulatory step important in many processes of differentiation and development. 相似文献
66.
While the potential for intermittent hydrostatic pressure to promote cartilaginous matrix synthesis is well established, its potential to influence chondroinduction remains poorly understood. This study examined the effects of relatively short- and long-duration cyclic hydrostatic compression on the chondroinduction of C3H/10T1/2 murine embryonic fibroblasts by recombinant human bone morphogenetic protein-2 (rhBMP-2). Cells were seeded at high density into round bottom wells of a 96-well plate and supplemented with 25 ng/ml rhBMP-2. Experimental cultures were subjected to either 1,800 cycles/day or 7,200 cycles/day of 1 Hz sinusoidal hydrostatic compression to 5 MPa (applied 10 min on/10 min off) for 3 days. Non-pressurized control and experimental cultures were maintained in static culture for an additional 5 days. Cultures were then analyzed for alcian blue staining intensity, DNA and sulfated glycosaminoglycan (sGAG) content, and for the rate of collagen synthesis. Whereas cultures subjected to 1,800 pressure cycles exhibited no significant differences (statistical or qualitative) compared to controls, those subjected to 7,200 cycles stained more intensely with alcian blue, contained nearly twice as much sGAG, and displayed twice the rate of collagen synthesis as non-pressurized controls. This study demonstrates the potential for cyclic hydrostatic compression to stimulate chondrogenic differentiation of the C3H/10T1/2 cell line in a duration-dependent manner. 相似文献
67.
The regulation of pig theca cell steroidogenesis was studied by the development of a physiological serum-free culture system, which was subsequently extended to investigate potential theca-granulosa cell interactions. Theca cells were isolated from antral follicles 6-9 mm in diameter and the effects of plating density (50-150x10(3) viable cells per well), LH (0.01-1.0 ng ml(-1)), Long R3 insulin-like growth factor I (IGF-I) (10, 100 ng ml(-1)) and insulin (1, 10 ng ml(-1)) on the number of cells and steroidogenesis were examined. The purity of the theca cell preparation was verified biochemically and histologically. Co-cultures contained 50x10(3) viable cells per well in granulosa to theca cell ratio of 4:1. Wells containing granulosa cells only were supplemented with 'physiological' doses of androstenedione or 100 ng ml(-1). Oestradiol production by co-cultures was compared with the sum of the oestradiol synthesized by granulosa and theca cells cultured separately. Oestradiol and androstenedione production continued throughout culture. High plating density decreased steroid production (P < 0.01). LH increased androstenedione (P < 0.001) and oestradiol (P < 0.05) synthesis and the sensitivity of the cells increased with time in culture. Oestradiol production was increased by 10 ng IGF-I ml(-1) (P < 0.001) but androstenedione required 100 ng ml(-1) (P < 0.001). Co-cultures produced more oestradiol than the sum of oestradiol synthesized by theca and granulosa cells cultured separately (P < 0. 001), irrespective of the androstenedione dose. This serum-free culture system for pig theca cells maintained in vivo steroidogenesis and gonadotrophin responsiveness. Thecal androstenedione and oestradiol production were differentially regulated and were primarily stimulated by LH and IGF-I, respectively. Theca-granulosa cell interactions stimulated oestradiol synthesis and this interaction was mediated by factors additional to the provision of thecal androgen substrate to granulosa cells. 相似文献
68.
69.
This commentary discusses and summarizes the key highlights of our recently reported work entitled “Neuronal Differentiation of Embryonic Stem Cell Derived Neuronal Progenitors Can Be Regulated by Stretchable Conducting Polymers.” The prospect of controlling the mechanical-rigidity and the surface conductance properties offers a unique combination for tailoring the growth and differentiation of neuronal cells. We emphasize the utility of transparent elastomeric substrates with coatings of electrically conducting polymer to realize the desired substrate-characteristics for cellular development processes. Our study showed that neuronal differentiation from ES cells is highly influenced by the specific substrates on which they are growing. Thus, our results provide a better strategy for regulated neuronal differentiation by using such functional conducting surfaces. 相似文献
70.