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排序方式: 共有133条查询结果,搜索用时 31 毫秒
81.
Electrophysiological and biochemical responses of mouse vomeronasal receptor cells to urine-derived compounds: possible mechanism of action 总被引:1,自引:1,他引:0
Receptor cells of the vomeronasal organ (VNO) are thought to detect
pheromone-like molecules important for reproductive physiology. Several
compounds derived from male mouse urine have been demonstrated to affect
endocrine events in female mice. In the present study, the ability of these
compounds to affect VNO activity was tested. In dissociated VNO cells held
under voltage clamp conditions, application of dehydro-exo-brevicomin (DHB)
evoked an outward current at negative holding potentials and an inward
current at positive holding potentials. Under current clamp, DHB reduced
action potential firing. Since DHB application caused a decrease in
membrane conductance, this compound appeared to act by reducing inward
current through closing an ion channel. Biochemical experiments tested the
effects of DHB and 2- (sec-butyl)-4,5-dihydrothiazole (SBT) on cAMP levels
in the VNO. A mixture of DHB and SBT decreased cAMP levels in VNO sensory
tissue and had no effect on VNO non-sensory tissue. The results suggest
that pheromones have an inhibitory influence on action potential generation
and on cAMP levels in receptor cells of the VNO.
相似文献
82.
83.
Walter RB; Rolig RL; Kozak KA; McEntire B; Morizot DC; Nairn RS 《Molecular biology and evolution》1993,10(6):1227-1238
Fishes represent the stem vertebrate condition and have maintained several
gene arrangements common to mammalian genomes throughout the 450 Myr of
divergence from a common ancestor. One such syntenic arrangement includes
the GPI-PEPD enzyme association on Xiphophorus linkage group IV and human
chromosome 19. Previously we assigned the Xiphophorus homologue of the
human ERCC2 gene to linkage group U5 in tight association with the CKM
locus. CKM is also tightly linked to the ERCC2 locus on human chromosome
19, leading to speculation that human chromosome 19 may have arisen by
fusion of two ancestral linkage groups which have been maintained in
fishes. To investigate this hypothesis further, we isolated and sequenced
Xiphophorus fish genomic regions exhibiting considerable sequence
similarity to the human DNA ligase 1 amino acid sequence. Comparison of the
fish DNA ligase sequence with those of other species suggests several modes
of amino acid conservation in this gene. A 2.2-kb restriction fragment
containing part of an X. maculatus DNA ligase 1 exon was used in backcross
hybrid mapping with 12 enzyme or RFLP loci. Significant linkage was
observed between the nucleoside phosphorylase (NP2) and the DNA ligase
(LIG1) loci on Xiphophorus linkage group VI. This assignment suggests that
the association of four DNA repair-related genes on human chromosome 19 may
be the result of chance chromosomal rearrangements.
相似文献
84.
A new model tissue (pseudoislet) is described for studies of pancreatic polypeptide (PP) secretion and biochemistry. It consists of islet-like aggregates of canine pancreatic endocrine cells which are formed and maintained on tissue culture. Immunocytochemical staining revealed that pseudoislets prepared from the duodenal end of the pancreas contained a predominance (40-60%) of F cells (the PP secreting cell). Also present were 10-25% exocrine cells and an equal proportion of A, B and D cells. Several studies were conducted to characterize the pseudoislets' capacity to secrete PP. Basal rates of PP release and the concentration of PP per pseudoislet remained constant during four weeks of culture. Stimulation at weekly intervals by carbachol (0.1 mM) resulted in a stable secretory rate for 2 weeks, that declined progressively at weeks 3 and 4. When studied in a perfusion system, carbachol-stimulated PP release occurred in a biphasic pattern, similar to the well-recognized biphasic release of insulin from perifused rat islets. Dose-response curves of four cholinergic agonists revealed clear differences in secretagogue activity. Acetylcholine and methacholine were found to be equipotent, followed in order of potency by carbachol and bethanechol. These histologic and secretory data show that canine pseudoislets are healthy tissues composed of a high proportion of F cells which secrete PP in response to cholinergic stimulation. The data suggest that the cultured canine pseudoislet model provides an excellent system useful in studies of PP secretion and biosynthesis. 相似文献
85.
Jan S. Fassler William Gray Jean Pyo Lee Guoying Yu Gregory Gingerich 《Molecular & general genetics : MGG》1991,230(1-2):310-320
86.
Restudy of virtually all of the important collections of European Eocene primates of the family Adapidae indicates that 28 valid species in 8 genera are now known, spanning a time period of nearly 20 million years. The biostratigraphic distribution of each species has been studied in the context of established reference levels, and a maximum of four evolutionary lineages are known from any one locality. Ten new species are proposed in the genera Pelycodus (1 sp.), Protoadapis (4 sp.), Periconodon (2 sp.), Anchomomys (1 sp.), and Adapis (2 sp.). Phylogenetic relationships among the species, based on stratophenetic linking, are indicated whenever possible. 相似文献
87.
Seegmiller A; Williams KR; Hammersmith RL; Doak TG; Witherspoon D; Messick T; Storjohann LL; Herrick G 《Molecular biology and evolution》1996,13(10):1351-1362
Internal eliminated sequences (IESs) often interrupt ciliate genes in the
silent germline nucleus but are exactly excised and eliminated from the
developing somatic nucleus from which genes are then expressed. Some long
IESs are transposons, supporting the hypothesis that short IESs are ancient
transposon relics. In light of that hypothesis and to explore the
evolutionary history of a collection of IESs, we have compared various
alleles of a particular locus (the 81 locus) of the ciliated protozoa
Oxytricha trifallax and O. fallax. Three short IESs that interrupt two
genes of the locus are found in alleles from both species, and thus must be
relatively ancient, consistent with the hypothesis that short IESs are
transposon relics. In contrast, TBE1 transposon interruptions of the locus
are allele-specific and probably the results of recent transpositions.
These IESs (and the TBE1s) are precisely excised from the DNA of the
developing somatic macronucleus. Each IES interrupts a highly conserved
sequence. A few nucleotides at the ends of each IES are also conserved,
suggesting that they interact critically with IES excision machinery.
However, most IES nucleotide positions have evolved at high rates, showing
little or no selective constraint for function. Nonetheless, the length of
each IES has been maintained (+/- 3 bp). While one IES is approximately 33
bp long, three other IESs have very similar sizes, approximately 70 bp
long. Two IESs are surrounded by direct repeats of the sequence TTCTT. No
other sequence similarities were found between any of the four IESs.
However, the ends of one IES do match the inverted terminal repeat
consensus sequence of the "TA" IESs of Paramecium. Three O. trifallax
alleles appear to have been recipients in recent conversion events that
could have been provoked by double-strand breaks associated with IES ends
subsequent to IES transposition. Our findings support the hypothesis that
short IESs evolved from ancient transposons that have lost most of their
sequences, except those necessary for precise excision during macronuclear
development.
相似文献
88.
Carbamoylphosphate synthetase (CPS) catalyzes the first committed step in
pyrimidine biosynthesis, arginine biosynthesis, or the urea cycle.
Organisms may contain either one generalized or two specific CPS enzymes,
and these enzymes may be heterodimeric (encoded by linked or unlinked
genes), monomeric, or part of a multifunctional protein. In order to help
elucidate the evolution of CPS, we have performed a comprehensive
phylogenetic analysis using the 21 available complete CPS sequences,
including a sequence from Sulfolobus solfataricus P2 which we report in
this paper. This is the first report of a complete CPS gene sequence from
an archaeon, and sequence analysis suggests that it encodes an enzyme
similar to heterodimeric CPSII. We confirm that internal similarity within
the synthetase domain of CPS is the result of an ancient gene duplication
that preceded the divergence of the Bacteria, Archaea, and Eukarya, and use
this internal duplication in phylogenetic tree construction to root the
tree of life. Our analysis indicates with high confidence that this
archaeal sequence is more closely related to those of Eukarya than to those
of Bacteria. In addition to this ancient duplication which created the
synthetase domain, our phylogenetic analysis reveals a complex history of
further gene duplications, fusions, and other events which have played an
integral part in the evolution of CPS.
相似文献
89.
90.
Philip D. Gingerich Kurt Heissig Ryan M. Bebej Wighart von Koenigswald 《Pal?ontologische Zeitschrift》2017,91(4):601-627
Richard Dehm and colleagues of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich made an important collection of early-to-middle Eocene mammals at Ganda Kas in Pakistan during the winter of 1955/56. The genera and species Ichthyolestes pinfoldi and Gandakasia potens were named from this collection. Both are now recognized as early and primitive archaeocete cetaceans. In addition, Dehm’s group collected 16 complete or partial astragali of archaeocetes that were misidentified as artiodactyls. These bring the total number of archaeocete astragali known from Ganda Kas to 28. They separate clearly into four species distinguished by size: from smallest to largest Ichthyolestes pinfoldi Dehm and Oettingen-Spielberg, Pakicetus attocki (West), Gandakasia potens Dehm and Oettingen-Spielberg, and Ambulocetus natans Thewissen et al. Ganda Kas artiodactyls are smaller and rare in comparison. Ichthyolestes and Pakicetus are pakicetid archaeocetes, Gandakasia is presently indeterminate to family, and Ambulocetus is an ambulocetid. Tooth size and astragalus size are highly correlated, corroborating reference of astragali to the first three archaeocete taxa based on teeth. Multivariate morphometric comparison (Auto3Dgm) shows that pakicetid astragali overlap almost completely in shape with those of early artiodactyls. Middle Eocene protocetid astragali are divergent from both. Retention of an astragalus indistinguishable from that of artiodactyls shows that pakicetids are closely related to artiodactyls phylogenetically, but does not make Ichthyolestes and Pakicetus terrestrial or cursorial. Other skeletal elements and bone microstructure indicate that pakicetids were semiaquatic like later protocetids. Tropical riverine and marginal marine facies of the Kuldana Formation are likely habitats for initial stages of the transition from terrestrial artiodactyls to semiaquatic and fully aquatic archaeocetes. 相似文献