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1.
The evolution of the mouse immunoglobulin heavy chain variable region (Igh-V) locus was investigated by the comprehensive analysis of variable region (Vh) gene family content and restriction fragment polymorphism in the genusMus. The examination of naturalMus domesticus populations suggests an important role for recombination in the generation of the considerable restriction fragment polymorphism
found at theIgh-V locus. Although the sizes of individualVh gene families vary widely both within and between differentMus species, evolutionary trends ofVh gene family copy number are revealed by the analysis of homologues of mouseVh gene families inRattus andPeromyscus. Processes of duplication, deletion, and sequence divergence all contribute to the evolution ofVh gene copy number. CertainVh gene families have expanded or contracted differently in the various muroid lineages examined. Collectively, these findings
suggest that the evolution of individualVh family size is not driven by strong selective pressure but is relatively neutral, and that gene flow, rather than selection,
serves to maintain the high level of restriction fragment polymorphism seen inM. domesticus. 相似文献
2.
Adele Post 《Polar Biology》1990,10(4):241-245
Summary Variation in leaf pigmentation from green to ginger is observed for Ceratodon purpureus (Hedw.) Brid. in Antarctica. Electron microscopy of ginger and green leaves reveals less thylakoid stacking, a response to greater light exposure, in the ginger leaves. In extremely exposed sites C. purpureus has low chlorophyll a/b ratios which correlate with decreased 77K chlorophyll fluorescence, indicating damage to chlorophyll a. Pigment analysis of ginger moss shows that even when the chlorophyll a/b ratio has not decreased the pigment composition differs from green moss. The increase in anthocyanin and decrease in chlorophyll concentrations largely account for the visual change from green to ginger. The ratio of total carotenoid to chlorophyll varies from 0.35 in green moss to 0.55 in the ginger moss, with violaxanthin increased preferentially. Since these changes in pigmentation are consistent with photoprotection and they are linked to light dependent variations in chloroplast structure, it appears that photoprotective pigments are a useful adaptation for the bright Antarctic environment. 相似文献
3.
Helen Wendler Deane Sarah Wurzelmann Adele B. Kostellow 《Cell and tissue research》1966,75(1):166-177
Summary Mitochondria are frequently found to be closely associated with the plaques of desmosomes in a variety of columnar or cuboidal epithelia of fetal or early postnatal mammals (mouse, rat, human being). The organs in which mitochondrial-desmosome complexes were found include stomach, small intestine, pancreas, kidney, epididymis, seminal vesicle, coagulating gland, thyroid gland. The association has not been observed in simple squamous epithelium (vascular endothelium). Mitochondria lie quite close to desmosomes in the stratum spinosum of stratified squamous mucous epithelium of fetal animals and also to axo-dendritic synapses in still poorly differentiated central nervous system. Mitochondria have also been detected close to attachment sites in ectoderm of the early frog gastrulae. Here there is as yet no visible plaque material.We suggest that the mitochondria may provide energy or some chemical for the formation of the plaque. This hypothesis does not explain why the complexes are not found in poorly differentiated epithelia from older animals.Dedicated to Professor Berta V. Scharrer on her 60th birthday, with affection and admiration. — This study was supported by U.S.P.H.S. research grants NB-05219 and GM-10757 from the National Institutes of Health. 相似文献
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Based on similarities in basidial morphology and nucleotide sequences of the V3 variable region in the large sub-unit ribosomal RNA, the yeastLeucosporidium lari-marini is considered phylogenetically related to the genusCystofilobasidium. Therefore the new combinationCystofilobasidium lari-marini is proposed. 相似文献
6.
In this study we use dissociated cell cultures of the rat carotid body to investigate the adaptive capabilities of endogenous oxygen chemoreceptors, following chronic stimulation by various environmental factors. These oxygen chemoreceptors are catecholamine-containing glomus cells, which derive from the neural crest and resemble adrenal medullary chromaffin cells. Using double-label immunofluorescence, we found that chronic exposure of carotid body cultures to hypoxia (2% to 10% oxygen) caused a significant fraction of tyrosine hydroxylase-positive (TH+) glomus cells to acquire detectable immunoreactivity for growth-associated protein gap-43. The effect was dose-dependent and peaked around an oxygen tension of 6%, where approximately 30% of glomus cells were GAP-43 positive. Treatment with agents that elevate intracellular cyclic adenosine monophosphate (cAMP) (i.e., dibutyryl cAMP or forskolin) also markedly stimulated GAP-43 expression. Since hypoxia is known to increase cAMP levels in glomus cells, it is possible that the effect of hypoxia on GAP-43 expression was mediated, at least in part, by a cAMP-dependent pathway. Unlike hypoxia, however, cAMP analogs also stimulated neurofilament (NF 68 or NF 160 kD) expression and neurite outgrowth in glomus cells, and these properties were enhanced by retinoic acid. Nerve growth factor, which promotes neuronal differentiation in related crest-derived endocrine cells, and dibutyryl cGMP were ineffective. Thus, it appears that postnatal glomus cells are plastic and can express neuronal traits in vitro. However, since hypoxia stimulated GAP-43 expression, without promoting neurite outgrowth, it appears that the two processes can be uncoupled. We suggest that stimulation of GAP-43 by hypoxia may be important for other physiological processes, e.g., enhancing neurotransmitter release or sensitization of G-protein–coupled receptor transduction. © 1995 John Wiley & Sons, Inc. 相似文献
7.
To determine the influence of the inoculum age on the kinetics of hybridoma growth and metabolism, spinner flasks have been inoculated with cells previously propagated in T flasks for 43, 52, 62 and 71 hr respectively. Increasing the age of the inoculum is found to result in a longer lag phase, in a lower maximum specific growth rate and in a reduced maximal cell density. During the growth phase specific rates of glucose and glutamine uptake and of ammonia and lactate production are similar. However, with the older inoculum, much higher metabolic activities are observed during the lag phase. The production of antibodies is delayed with increasing inoculum age, but the final antibody concentrations are similar, which indicates a higher specific antibody production rate when inoculating with older cells. 相似文献
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Derek W. Hood Katherine Makepeace Mary E. Deadman Richard F. Rest Pierre Thibault Adele Martin James C. Richards & E. Richard Moxon 《Molecular microbiology》1999,33(4):679-692
A survey of Haemophilus influenzae strains indicated that around one-third of capsular strains and over two-thirds of non-typeable strains included sialic acid in their lipopolysaccharides (LPS). Mutation of the CMP-Neu5Ac synthetase gene (siaB) resulted in a sialylation-deficient phenotype. Isogenic pairs, wild type and siaB mutant of two non-typeable strains were used to demonstrate that sialic acid influences resistance to the killing effect of normal human serum but has little effect on attachment to, or invasion of, cultured human epithelial cells or neutrophils. We determine for the first time the site of attachment of sialic acid in the LPS of a non-typeable strain and report that a small proportion of glycoforms include two sialic acid residues in a disaccharide unit. 相似文献
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