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1.
The cave environment is consistently radically different than the surface environment because it lacks light, and animals adapting to cave life are subject to strong selective forces much different than those experienced by their ancestors who evolved in the presence of light. As such, their divergence from surface ancestors and eventual speciation is likely to be driven by the shift in ecology. We report here that hybrids between cave and surface Astyanax mexicanus fishes produce offspring with allelic frequencies that differ significantly from Mendelian expectations both for transmission ratios and for independent assortment of unlinked markers. Comparison of allelic content of DNA from fin clips and sperm pools show that the transmission ratio distortion likely occurs during spermatogenesis. Departures from expectations of independent assortment are essentially epistatic phenomena generating linkage disequilibrium. A novel analysis of the epistatic interactions reveals an apparent network of interactions among genes known or suspected to be involved in cave adaptation, implying that the epistasis arose as a “by product” of the divergence due to cave adaptation. 相似文献
2.
Dana M. Bergstrom George R. Stewart Patricia M. Selkirk Susanne Schmidt 《Oecologia》2002,130(2):309-314
'15N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '15N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '15N signatures of peat layers. At two sites 15N-enriched peat '15N signatures of up to +17 were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '15N. Less 15N enriched '15N signatures (e.g. -1.9 to +3.9) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that 15N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology. 相似文献
3.
JoAnne S. Richards Gerard J. Hickey Shiuan Chen John E. Shively Peter F. Hall Dana Gaddy-Kurten Richard Kurten 《Steroids》1987,50(4-6):393-409
To determine the molecular basis for changes in aromatase (P450arom) activity in rat ovarian follicles and corpora lutea, seven clones for rat P450arom cDNA have been identified and isolated from a rat granulosa cell λgtll cDNA expression library using a 62 mer deoxyoligonucleotide probe (derived from an amino acid sequence of purified human placental aromatase) and a human placental P450arom cDNA probe. One of the rat P450arom cDNA clones contained an insert 1.2 kb in size. Both the human 1.8 kb cDNA and the rat 1.2 kb cDNA probes hybridized to a single species of P450arom mRNA that was 2.6 kb in size. Northern blot analysis revealed that corpora lutea isolated on day 15 of pregnancy contained high amounts of P450arom mRNA, whereas granulosa cells of antral follicles of hormonally primed, hypophysectomized rats (i.e., those from which mRNA was isolated to construct the cDNA library) contained only low amounts of P450arom mRNA. The lower amounts of P450arom in granulosa cells of preovulatory follicles in the estradiol-follicle-stimulating hormone primed hypophysectomized rats were unexpected because follicles incubated in medium containing testosterone substrate produce more estradiol than do corpora lutea isolated on day 15 of pregnancy and incubated under similar conditions. Additional studies will determine the hormonal events responsible for the elevated amounts and constitutive maintenance of P450arom mRNA and aromatase activity in luteal cells in vivo and in vitro. 相似文献
4.
Summary Calcitonin gene-related peptide-immunoreactive cells were identified within the epithelium of distal conducting airways in the human fetus and infant. Several peptides and amines, including calcitonin, have been identified previously within a specific population of airway epithelial cells. These cells, referred to as pulmonary neuroendocrine cells, are postulated to be airway chemoreceptors responsible for changes in ventilation and perfusion in response to changes in airway gas composition. Calcitonin gene-related peptide immunoreactive cells could be identified throughout the period of development studies (20 weeks gestation to 3 months of age), but were present in only limited numbers in less than 50% of individuals (n=23). In contrast, large numbers of calcitonin gene-related peptide immunoreactive cells were identified in 100% of infants (1–3 months, n=5) with bronchopulmonary dysplasia. The differential processing of mRNA transcribed from the calcitonin gene in neural and non-neural tissue suggests that calcitonin, rather than calcitonin gene-related peptide, is the primary product of translation in pulmonary neuroendocrine cells. However, considering the potent vasodilatory and bronchoconstrictive effects of calcitonin gene-related peptide, its presence in pulmonary neuroendocrine cells, even in small amounts, may be important in controlling pulmonary vaso- and/or bronchomotor tone. The presence of large numbers of calcitonin gene-related peptide immunoreactive cells in infants with bronchopulmonary dysplasia suggests that calcitonin gene-related peptide may be one further agent contributing to the pulmonary pathophysiology seen in this disease. 相似文献
5.
Central administration of corticotropin releasing factor (CRF) in rats produces pituitary-adrenal activation and a variety of "anxiogenic-like" effects. The present study was designed to explore the contribution of the peripheral pituitary-adrenocortical axis in mediating these CRF responses. Intraventricularly administered CRF produced suppression of responding in the conflict test and a marked locomotor activation. Neither behavioral effect was altered by the prior administration of dexamethasone in a dose that blocked pituitary-adrenal activation to CRF. These results support the hypothesis that behavioral effects of CRF are mediated by its action at central sites and not via an action on the pituitary-adrenocortical system. 相似文献
6.
7.
Clare M. O'Connor Bonnie J. Germain Kathleen M. Guthrie Dana W. Aswad Clarke F. Millette 《Molecular reproduction and development》1989,22(3):307-319
An antiserum prepared against the purified protein carboxyl methltransferase (PCMT) from bovine brain has been used to compare testicular and ovarian levels of the enzyme and to study the regulation of PCMT concentrations during spermatogenesis. The PCMT, which specifically modifies age-damaged aspartyl residues, is present at a significantly higher concentration in mature mouse testis than in ovary. However, the PCMT is present at nearly equal concentrations in extracts of germ cell-deficient ovaries and testes obtained from mutant atrichosislatrichosis mice. In normal testis, the concentration of the PCMT increases severalfold during the first 4–5 weeks after birth, paralleling the appearance and maturation of testicular germ cells. Both immunochemical and enzymatic measurements of PCMT specific activities in purified spermatogenic cell preparations indicate that PCMT levels are twofold and 3.5-fold higher in round spermatids and residual bodies, respectively, than in pachytene spermatocytes. The results are consistent with the enhanced synthesis and/or stability of the PCMT in spermatogenic cells and with the continued translation of the PCMT during the haploid portion of spermatogenesis. The relatively high levels of PCMT in spermatogenic cells may be important for the extensive metabolism of proteins accompanying spermatid condensation or for the repair of damaged proteins in translationally inactive spermatozoa. 相似文献
8.
Dana Baron Yehuda G Assaraf Stavit Drori Ami Aronheim 《European journal of biochemistry》2003,270(22):4469-4477
Rogers syndrome is an autosomal recessive disorder resulting in megaloblastic anemia, diabetes mellitus, and sensorineural deafness. The gene associated with this disease encodes for thiamine transporter 1 (THTR1), a member of the SLC19 solute carrier family including THTR2 and the reduced folate carrier (RFC). Using transient transfections into NIH3T3 cells of a D93H mutant THTR1derived from a Rogers syndrome family, we determined the expression, post-translational modification, plasma membrane targeting and thiamine transport activity. We also explored the impact on methotrexate (MTX) transport activity of a homologous missense D88H mutation in the human RFC, a close homologue of THTR1. Western blot analysis revealed that the D93H mutant THTR1 was normally expressed and underwent a complete N-glycosylation. However, while this mutant THTR1 was targeted to the plasma membrane, it was completely devoid of thiamine transport activity. Consistently, introduction into MTX transport null cells of a homologous D88H mutation in the hRFC did not result in restoration of MTX transport activity, thereby suggesting that D88 is an essential residue for MTX transport activity. These results suggest that the D93H mutation does not interfere with transporter expression, glycosylation and plasma membrane targeting. However, the substitution of this negatively charged amino acid (Asp93) by a positively charged residue (His) in an extremely conserved region (the border of transmembrane domain 2/intracellular loop 2) in the SLC19 family, presumably inflicts deleterious structural alterations that abolish thiamine binding and/or translocation. Hence, this functional characterization of the D93H mutation provides a molecular basis for Rogers syndrome. 相似文献
9.
The linear-transfer and lag-Manly models of zooplankton cohortdevelopment were examined using data generated from a thirdmore realistic model. The more realistic multi-transfer modelincluded variance in development rate among individuals. Thelinear-transfer model produced highly biased estimates of developmentrate under conditions of rapidly changing recruitment. Althoughits performance was improved by increasing the number of modeledstages and thus decreasing the rate of change in recruitmentcompared to stage duration, a positive bias remained. The lag-Manlymodel also produced positively biased estimates of stage durationgiven non-zero variance in development rates. A comparison ofthe models' performances under different simulated samplingregimes recommended the multi-transfer model. Use of the multi-transfermodel was illustrated by determining the development and mortalityrates of the brine shrimp, Artemia monica reared under threedifferent conditions of food and temperature corresponding tonatural regimes in Mono Lake, California. The experimental conditionsand sampling regime resulted in high relative standard errors(mean, 33%) in stage abundance estimates not atypical of zooplanktonsampling regimes in lakes. A Monte Carlo analysis was used todetermine the uncertainty in estimated parameters and determinethe level of stage aggregation which maximized the amount ofinformation derived from the experiments. 相似文献
10.
Bilateral lesions of the ventromedial nucleus of the hypothalamus interfered with the estrogenic induction of sexual receptivity in the female rat, but seemingly did not affect the ability of female rats to show lordosis following combined stimulation with estrogen and progesterone. In addition, ventromedial hypothalamic lesions did not affect the ability of females to show male-like sexual activity in response to exogenous androgenic stimulation. 相似文献