Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
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Oestradiol has been conjugated to allylamine-dUTP with an 11-atom spacer to allow enzymatic incorporation of the label into
DNA sequences. In a comparative DNA and mRNA FISH study we have used DNA probes that were either labelled with digoxigenin,
biotin or oestradiol. Results show that oestradiol-labelled probes can detect DNA and RNA sequences in FISH equally well as
digoxigenin- and biotin-labelled probes. Further, no crossreactivity between the various hapten-specific antibodies and the
three haptens were observed. Binding of the rabbit anti-oestradiol antibody to endogenous oestrogen in various tissues was
not observed under the conditions tested. In view of the increasing demands for multi-colour DNA and mRNA FISH applications,
oestradiol is a welcome addition to the collection of haptens employed in FISH.
Accepted 20 June 1997 相似文献
Summary The role of pyrimidine dimers in mutagenesis by ultraviolet light was examined by measuring the UV-induced reversion of six different bacteriophage M13 amber mutants for which the neighboring DNA sequences are known. The mutational response at amber (TAG) codons preceded by a guanine or adenine (where no pyrimidine dimer can be formed) were compared with those preceded by thymine or cytosine (where dimer formation is possible). Equivalent levels of UV-induced mutagenesis were observed at both kinds of sites. This observation demonstrates that there is no requirement for a pyrimidine dimer directly at the site of UV-induced mutation in this single-stranded DNA phage. UV irradiation of the phage was also performed in the presence of Ag+ ions, which specifically sensitize the DNA to dimer formation. The two methods of irradiation, when compared at equal survival levels (and presumably equal dimer frequencies), produced equivalent frequencies of reversion of the amber phage. We believe these results indicate that while the presence of pyrimidine dimers may be a prerequisite for UV mutagenesis, the actual mutagenic event can occur at a site some distance removed from a dimer. 相似文献
Summary Exposure of HTC cells to sodium butyrate caused inhibition of growth. The site of growth inhibition was studied by time-lapse
cinematography and [3H]thymidine incorporation studies. Evidence is presented that sodiunm butyrate affected the cell cycle at a specific point
immediately after mitosis. Inasmuch as it does not modify the interphase duration after its removal, butyrate may be used
for HTC synchronization.
This work was supported by l'Institut Nationale de la Santé et de la Recherche Médicale and la Centre Nationale de la Recherche
Scientifique (L. T. and J. K.). 相似文献
Summary A floating collagen matrix culture of neonatal rat heart myocardial cells shows rhythmic contractions which are dependent
on localization of cells, cell density, and collagen concentration. The rhythmic contractions of the collagen matrix can be
registered by a device scanning the optical density at the edge of the gel and have been observed over a temperature range
from 9° to 40° C. The results of the present study underline the usefulness of myocardial cell populated collagen matrixes
for studies on coherent contractions of heart cell cultures. 相似文献
The inbred strains GRS/A and LIS/A carry the haplotypeH-2dx, which had earlier been shown to have theKd,If,Sf, andGf alleles and a previously unknownD region allele,Ddx. We show here that theDdx allele determines a new private specificity, H-2.63, is H-2.28 negative, and determines at least one public specificity of the H-2.1 family. It is thus a second example (afterDk) of a H-2.1-positive H-2.28-negativeD region allele. Capping experiments show that the Ddx product comprises two molecules: H-2Ddx bearing the private specificity H-2.63, and H-2Ldx, which is H-2.63-negative but reacts with sera against the H-2.1 family of specificities. SDS gel electrophoresis of detergent-solubilized immunoprecipitated Ddx products shows that the H-2Ldx antigen has a molecular weight of approximately 45,000 daltons and is associated with a smaller polypeptide (mol. wt. 12,000). 相似文献
Brachyuran crabs are an important ecological and economical, yet often unstudied aspect of intertidal mudflats of the Arabian Peninsula. Here we provide baseline density estimates of crabs at the relatively pristine intertidal mudflats of Barr Al Hikman (Sultanate of Oman) and provide information on their life cycle and habitat preference. Across the winters of 2012–2015 crabs were sampled on a grid covering the entire intertidal depth gradient. 29 species were found and average densities varied between 12 and 54 crabs/m2. Deposit-feeding and herbivorous crabs were the most abundant species across all winters. Size frequency data and the presence of ovigerous females show that most crabs species reproduce in the intertidal area. P. segnis, the most important crab for local fisheries, was found to use the intertidal area as a nursery ground. We analysed the relationships between the two most abundant crab species, Macrophthalmus sulcatus and Thalamita poissonii and the environmental variables: seagrass density, tidal elevation, median grain size and sediment depth using Random Forest models. The predictive capacity of the models and the relative importance of the environmental predictors varied between years, but crab densities in general were positively associated with seagrass density, presumably because seagrass offers feeding habitat.
Two silicone coatings have been evaluated for barnacle adhesion. One coating is an unfilled hydrosilation cured polydimethylsiloxane (PDMS) network, while the other is a room temperature vulcanized (RTV), filled, ethoxysiloxane cured PDMS elastomer, RTV11?. The adhesion strength of one species of barnacle, Balanus eburneus, to the hydrosilation coatings is in the range of 0.37–0.60 kg cm‐2 while the corresponding range for RTV11 is 0.64–0.90 kg cm‐2. The easier release of B. eburneus from the hydrosilation cured network compared to RTV11 is discussed in relationship to differences in bulk and surface properties. Preliminary results suggest bulk modulus may be the most important parameter in determining barnacle adhesion strength. In light or mechanical property analysis, a re‐evaluation of surface properties and chemical stability is presented. 相似文献
Nitric oxide (NO) has been implicated in matrix metallopeptidase 9 (MMP9)-dependent mobilization of hematopoietic stem and progenitor cells from bone marrow (BM). However, direct measurement of NO in the BM remained elusive due to its low in situ concentration and short lifetime. Using NO spin trapping and electron paramagnetic resonance (EPR) spectroscopy we give the first experimental confirmation of free NO radicals in rodent BM. NO production was quantified and attributed to enzymatic activity of NO synthases (NOS). Although endothelial NOS (eNOS) accounts for most (66%) of basal NO, we identified a significant contribution (23%) from inducible NOS (iNOS). Basal NO levels closely correlate with MMP9 bioavailability in BM of both hypertensive and control rats. Our observations support the hypothesis that inadequate mobilization of BM-derived stem and progenitor cells in hypertension results from impaired NOS/NO/MMP9 signalling in BM, a condition that may be corrected with pharmacological intervention. 相似文献