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1.
Summary The inner ears of representatives of all six gymnophionan families, as well as an ontogenetic series of one species, were studied in order to understand the origin and changes of the amphibian and basilar papillae. The amphibian papilla is in close proximity to the papilla neglecta in some adult gymnophionans. During ontogeny, both epithelia are adherent before they are separated by the formation of the utriculosaccular foramen. The nerve fibers to both epithelia run together, and both epithelia show a comparable variation in size and position among amphibians (amphibian papilla) and among vertebrates (papilla neglecta). Based on these arguments we propose that the amphibian papilla is a translocation of a part of the papilla neglecta specific to amphibians. Present in all primitive gymnophionans, the basilar papilla is lost in all derived gymnophionans. In contrast to anurans, but similar to some urodeles, amniotes, and Latimeria, the basilar papilla rests partly on a basilar membrane. Because of similarities in structure, topology, and innervation, the basilar papilla is suggested to be homologous in Latimeria and tetrapods. The structural differences of most amphibian basilar papillae, compared to those of amniotes and Latimeria, may be due to the different course of the periotic system and the formation of a basilar papillar recess rather than to a separate evolution of this epithelium. In addition to loss of the basilar papilla, some derived gymnophionans have lost the lagena, presumably independently, and the amphibian papilla is extremely reduced in the only genus without a stapes (Scolecomorphus). The papilla neglecta is, for unknown functional reasons, relatively large in aquatic gymnophionans, whereas it is almost lost in some thoroughly terrestrial gymnophionans. The regressive changes in the inner ear are not reflected in obvious changes in the pattern of eighth nerve projection. However, there is a rearrangement of cell masses in the rhombencephalic alar plate of derived gymnophionans, which may be related to the partial or complete loss of lateral line afferents. We propose that the presence of a basilar papilla is a synapomorphy of tetrapods and Latimeria, that the translocation of the papilla neglecta is related to the unique course of the amphibian periotic canal, and that regressive changes in the inner ear are related to the primitive absence of a tympanic ear. 相似文献
2.
M H Wake 《Journal of morphology》1992,212(1):37-53
The innervation of the musculature of the tongue and the hyobranchial apparatus of caecilians has long been assumed to be simple and to exhibit little interspecific variation. A study of 14 genera representing all six families of caecilians demonstrates that general patterns of innervation by the trigeminal, facial, glossopharyngeal, and vagus nerves are similar across taxa but that the composition of the "hypoglossal" nerve is highly variable. Probably in all caecilians, spinal nerves 1 and 2 contribute to the hypoglossal. In addition, in certain taxa, an "occipital," the vagus, and/or spinal 3 appear to contribute fibers to the composition of the hypoglossal nerve. These patterns, the lengths of fusion of the contributing elements, and the branching patterns of the hypoglossal are assessed according to the currently accepted hypothesis of phylogenetic relationships of caecilians, and of amphibians. An hypothesis is proposed that limblessness and a simple tongue, with concomitant reduced complexity of innervation of muscles associated with limbs and the tongue, has released a constraint on pattern of innervation. As a consequence, a greater diversity and, in several taxa, greater complexity of neuroanatomical associations of nerve roots to form the hypoglossal are expressed. 相似文献
3.
An immobilized fork as a termination of replication intermediate in Bacillus subtilis 总被引:3,自引:0,他引:3
The structure of a DNA intermediate associated with termination of chromosome replication in Bacillus subtilis and derived from a unique BamHI 24.8 X 10(3) base-pair (bp) region of the chromosome has been investigated. The intermediate has properties expected for a forked structure. Gel electrophoresis followed by Southern transfer and hybridization to cloned DNA has shown it to comprise single strands of 15.4 X 10(3) bp and 24.8 X 10(3) bp, in approximately equimolar amounts. After purification away from the bulk of chromosomal DNA, electron microscopy of the intermediate established that 15% of the DNA was present as branched molecules and a significant proportion (11 of 31) of these contained two arms of matching length. The average dimensions (best estimates) of this unique class of Y-shaped molecule were 9.5(+/- 0.3) X 10(3), 15.1(+/- 0.4) X 10(3) and 24.6 24.6(+/- 0.6) X 10(3) bp for the stem, arms and end-to-end length, respectively. These values are consistent with the single strand composition of the intermediate as found. Furthermore, hybridization of the single strands to DNA from known locations within the BamHI 24.8 X 10(3) bp region has established the orientation of the forked intermediate relative to the genetic map. The intermediate presumably reflects the immobilization of the clockwise replication fork within the 24.8 X 10(3) bp region, at a location approximately 15.4 X 10(3) bp from the right end. 相似文献
4.
The endocytosis of latex particles (0.33, 0.46 and 0.80 micron in diameter) in the sinusoidal endothelial and Kupffer cells of the rat liver was studied electron microscopically. When the liver was perfused with serum-free oxygenated Krebs Ringer bicarbonate, latex particles of all three sizes were taken up by the endothelial cells. After a 10-min perfusion, particles were incorporated by the luminal cell surface of the perikarya or of the thick portion of the endothelial cells. A large patch of bristle coat was surrounding the ingested particle. The number of ingested particles in the endothelial cells, however, was much less than in the Kupffer cells. In in vivo experiments, no endocytosis of the latex particles was observed in the endothelial cells. In the Kupffer cells, particles were engulfed by the ruffled membranes or sank into the cytoplasm without a large patch of the bristle coat both in the perfusion system and in vivo. These observations show that at least 0.80 micron latex particles are taken up by the bristle-coated membranes in the sinusoidal endothelial cells of the perfused liver. The endocytic mechanism for latex particles in the endothelial cells is different from that of the Kupffer cells. 相似文献
5.
Induction of metallothionein mRNA in rat liver and kidney after copper chloride injection. 总被引:7,自引:4,他引:3
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The kinetics of the increase of metallothionein mRNA in rat liver and kidney after CuCl2 injection was determined by cell-free translation and dot-blot hybridization of total RNA isolated at various times after the injection. Both assay procedures gave essentially the same result: a 16-fold increase in hepatic metallothionein mRNA was observed 7h after CuCl2 injection, with a decline to basal values by 15 h. The response in the kidney was less dramatic, with a 6-fold increase in metallothionein mRNA 5 h after injection, and basal values were attained by 12h. The rise in Cu2+ concentration in both organs was closely correlated with the increase in metallothionein mRNA; hepatic Cu2+ was increased 5.9-fold by 5h after injection and renal Cu2+ was increased 4.3-fold 5h after injection. The Zn2+ concentration in the liver had not risen significantly within 5h of Cu2+ injection. Renal Zn2+ concentrations did not alter appreciably in the Cu2+-treated animals. These results support the conclusion that Cu2+ is acting as a primary inducer of metallothionein mRNA in the rat. 相似文献
6.
Timing and other features of the action of the ts1 division initiation gene product of Bacillus subtilis. 总被引:1,自引:0,他引:1
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The ts1 division initiation mutation of Bacillus subtilis 160 was transferred into a thymine-requiring strain of B. subtilis 168. Aspects of the role and timing of the action of the ts1 gene product in relation to septum formation were studied by comparing the behavior of this new strain with that of the isogenic wild type after outgrowth of germinated spores. The ts1 gene product was shown to be required for the asymmetric division which occurs in the absence of chromosome replication, in addition to normal division septation. The time interval between completion of the action of the ts1 gene product and initiation of the first central division septum was estimated to be less than 4 min at 34 degrees C, and it is possible that an active ts1 gene product is required until the commencement of septal growth. Recovery of septa after transfer of outgrown spores (filaments) from the nonpermissive to the permissive temperature was also examined. During recovery, septa formed at sites which were discrete fractional lengths of the filaments, with the first septum located at the most polar of these sites. The data have been interpreted in terms of the formation of potential division sites at the nonpermissive temperature and the preferred utilization, upon recovery, of the most recently formed site. Recovery of septa at the permissive temperature occurred in the absence of DNA synthesis but was blocked completely by inhibitors of RNA and protein synthesis. It is possible that the only protein synthesis required for recovery of septa is that of the ts1 gene product itself. 相似文献
7.
Basal tail constriction occurs in about two-thirds of the species of plethodontid salamanders. The constriction, which marks the site of tail autotomy, is a result of a reduction in length and diameter of the first caudal segment. Gross and microscopic anatomical studies reveal that many structural specializations are associated with basal constriction, and these are considered in detail. Areas of weakness in the skin at the posterior end of the first caudal segment, at the attachment of the musculature to the intermyotomal septum at the anterior end of the same segment, and between the last caudosacral and first caudal vertebrae precisely define the route of tail breakage. During autotomy the entire tail is shed, and a cylinder of skin one segment long closes over the wound at the end of the body. It is suggested that specializations described in this paper have evolved independently in three different groups of salamanders. Experiments and field observations reveal that, contrary to expectations, frequency of tail breakage is less in species with apparent provisions for tail autotomy than in less specialized species. The tail is a very important, highly functional organ in salamanders and it is suggested that selection has been for behavioral and structural adaptations for control of tail loss, rather than for tail loss per se. 相似文献
8.
Replication fork arrest at relocated replication terminators on the Bacillus subtilis chromosome.
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The replication terminus region of the Bacillus subtilis chromosome, comprising TerI and TerII plus the rtp gene (referred to as the terC region) was relocated to serC (257 degrees) and cym (10 degrees) on the anticlockwise- and clockwise-replicating segments of the chromosome, respectively. In both cases, it was found that only the orientation of the terC region that placed TerI in opposition to the approaching replication fork was functional in fork arrest. When TerII was opposed to the approaching fork, it was nonfunctional. These findings confirm and extend earlier work which involved relocations to only the clockwise-replicating segment, at metD (100 degrees) and pyr (139 degrees). In the present work, it was further shown that in the strain in which TerII was opposed to an approaching fork at metD, overproduction of the replication terminator protein (RTP) enabled TerII to function as an arrest site. Thus, chromosomal TerII is nonfunctional in arrest in vivo because of a limiting level of RTP. Marker frequency analysis showed that TerI at both cym and metD caused only transient arrest of a replication fork. Arrest appeared to be more severe in the latter situation and caused the two forks to meet at approximately 145 degrees (just outside or on the edge of the replication fork trap). The minimum pause time erected by TerI at metD was calculated to be approximately 40% of the time taken to complete a round of replication. This significant pause at metD caused the cells to become elongated, indicating that cell division was delayed. Further work is needed to establish the immediate cause of the delay in division. 相似文献
9.
Review: Hydrogels for cell immobilization 总被引:6,自引:0,他引:6
Hydrogels are being investigated for mammalian cell immobilization. Their material properties can be engineered for biocompatibility, selective permeability, mechanical and chemical stability, and other requirements as specified by the application including uniform cell distribution and a given membrane thickness or mechanical strength. These aqueous gels are attractive for analytical and tissue engineering applications and can be used with immobilization in therapies for various diseases as well as to generate bioartificial organs. Recent advances have broadened the use of hydrogel cell immobilization in biomedical fields. To provide an overview of available technology, this review surveys the current developments in immobilization of mammalian cells in hydrogels. Discussions cover hydrogel requirements for use in adhesion, matrix entrapment, and microencapsulation, the respective processing methods, as well as current applications. (c) 1996 John Wiley & Sons, Inc. 相似文献
10.
Subcutaneous infection withYersinia enterocolitica harboring plasmid responsible for Ca2+ dependence at 37°C induced cell-mediated protective immunity against a lethal challenge withYersinia pestis; the isogenic derivative strain cured from this plasmid subverted the immunity in mice. This is the first identification of the antigen(s) responsible for the induction of cell-mediated protective immunity against the facultatively intracellular bacteria. 相似文献