ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02721.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.A satisfactory model of theTetrahymena thermophilamacronucleus must explain its genetic behavior in terms of its constituent molecules. Particular genetic phenomena requiring explanation are (a)phenotypic assortment, here interpreted as resulting from allelic disjunction rather than from differential gene expression; (b)unequal allelic input for some loci, interpreted as a consequence of unequal and selective replication of some alleles during early macronuclear development; (c)delayed assortment at some loci, interpreted as an effect of inequality of allelic input combined with a generalized elevation of DNA content during early clonal history; (d)linkage disruption, probably reflecting continuous somatic recombination rather than dissolution of chromosomes into small repliconic units; (e)assortment depression, brought about by the occasional association of homologous replicons (chromosomes) or else by a differential increase in some classes of replicons; (f)ploidy‐related developmental differences in macronuclear primordiaare interpreted on the basis of quantitative differences in DNA rather than in terms of an early perception of genic imbalance, (g)Ploidy independent macronuclear DNA contentis consistent with several models of size regulatio

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02722.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.The DNA of the macro‐ and the micronucleus ofTetrahymena thermophilahas been compared by various biochemical methods. It became evident from their thermal denaturation temperatures and buoyant densities that the 2 DNAs were very similar in overall composition. Small differences were detected when the sequence complexities of these DNAs were compared by DNA renaturation studies. The studies suggested that ˜ 10% of the micronuclear genome was lost or underrepresented in the macronucleus. Comparison of individual gene levels revealed further differences. By using the technic of gene cloning a micronuclear sequence was isolated which hybridized only with micronuclear, but not with macronuclear DNA. These results indicated the occurrence of elimination or underreplication of this sequence in the macronucleus. Gene amplification was also shown to occur. In the micronucleus only a single copy of rDNA was found integrated into the chromosome. During macro‐nuclear development, amplification was observed to occur, and the amount of rDNA to increase, until there were ˜ 200 copies per haploid genome in the mature macronucleus. all of them extrachromosomal and palindromic. The 3rd case of alteration involved a simple repeated sequence, (CCCCAA)n, present in the termini of rDNA and also in many other locations of the genome. Restriction endonuclease digestion studies revealed drastic differences in the organization of the repeats between macro‐and micronucleus. These differences may be interpreted as the results of chromosome fragmentation which occurs at every cluster of the repeats during macronuclear development. The relationship between this event and gene amplification and elimination is di

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02723.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.A considerable amount of evidence is now available to indicate that the DNA in the ciliatesOxytrichaandStylonychiaundergoes fragmentation when the micronucleus forms a macronucleus. Some evidence suggests that fragmentation may also occur inTetrahymenaand possibly inParamecium. It is shown that some regulatory or nonrandom segregational mechanism must operate during cell divisions to maintain genic balance inTetrahymena. Both the hypothesis of macronuclear subunits and also a new hypothesis based on replicative control of DNA are capable of explaining the currently know biochemical, cytological, and genetic facts.

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02724.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.The amitotic division of the macronucleus ofParamecium tetraureliaproduces daughter macronuclei which frequently differ in DNA content. In wild‐type cells these differences are small, but can be increased substantially by the action of mutant genes. The variance in macronuclear DNA content would increase continuously if there were no mechanism to regulate it.Parameciumhas a very effective regulatory mechanism—all cells synthesize similar amounts of macronuclear DNA, regardless of the number of macronuclei or their prereplication DNA content. DNA synthesis is controlled at the level of macronuclear subunits, and the postreplication macronucleus consists of a mosaic of subunits that have undergone different numbers of replication events during the previous cell cycle. It is evident from experimental results that the amount of DNA synthesized can be influenced by the total size or mass of the cell. Experimental modification of the initial DNA content leads to no change in the amount of DNA synthesized, or in the subsequent protein content of the cells, but modification of cell size causes corresponding changes in the amount of DNA synthesized and in the size of the macronucleus. The implications of these observations for cell growth and the cell cycle are discus

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02725.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.Unequal macronuclear division inTetrahymena thermophilaintroduces variance into G1 macronuclei; unless eliminated such variance would result in continuous variation in DNA content. Analysis of G1 and G2 macronuclear variances reveals that the added variance is eliminated by action on the extremes of macronuclear DNA content. In this model (Model II), macronuclei with small amounts of DNA have an additional complete S phase, while those with large amounts of DNA skip S. From available data, chromatin extrusion is shown not to contribute significantly, if at all, to the elimination of variance. Computer simulations utilizing haploid subunits indicate that model II predictions apply reasonably well to experimental data in terms of coefficients of variation, mean DNA content, and frequency of additional and skipped S phases. The simulations reveal also that within certain constraints, particularly the thresholds for additional and skipped S phases, macronuclear assortment is unaffected by Model II regulation. The relationships between Model II and other aspects of the cell cycle are briefly discussed.

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02726.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.Oocysts ofEimeria malabaricassp. n. andEimeria bandipurensisfrom the South Indian tree squirrelFunambulus tristriatuscollected in Kerala, India, are described. Sporulated oocysts ofE. malabaricaswere ellipsoid to subspherical measuring 39.8 (35–45) × 32.1 (29–37) m̈m, with a thick (2.5–3.0 m̈m), 2‐layered wall. The outer layer was yellow‐brown, striated, and rough. There was no micropyle. but a polar granule was present in 34% of oocysts. The sporocysts were ovoid, 16.0 (14.0–18.0) × 11.2 (11.0–12.0) m̈m, with a Stieda body and a granular residuum. Excysted sporozoites were 21.8 (19.0–23.0) × 3.4 (3.0–4.0) m̈m, with a large refractile body.The sporulated oocysts ofE. band

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02727.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.Hammondia pardalssp. n. (Eimeriorina: Sarcocystidae) from Panama Canal Zone is described as an obligate heteroxenous coccidian, with felids as the final host and laboratory mice as the experimental intermediate host. Ovoid oocysts. measuring 40.8 (36–46) × 28.5 (25–35) m̈m. are shed unsporulated. Oocysts were infective only for the intermediate host. the laboratory mouse,Mus musculus, and the intracellular cysts were infective only for felids. Attempted passage of tissue cysts from mouse to mouse was unsuccessful.Mice fed 5 × 104sporulated oocysts were found to harbor small intracellular cysts, 13–16 × 10–15 m̈m, in the mesenteric lymph nodes, lungs, and intestinal submucosa 15 days postinfection. The meronts in these early cysts were stubby and measured 3 × 6 m̈m. The prepatent period in the felids was 5 to 8 days and the patent period 5–13 days. Experimental infections of definitive hosts were successful with 6/6 domestic laboratory‐reared kittens,Felis catus; 5/5 ocelots,F. pardalis; and 1/1 jaguarundi,F. yagouaroundi.None of the exposed raccoons,Procyon l

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02728.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.A new species of Microsporida was observed in neurons of the marine molluscAplysia californicaand the ultrastructure of its spores was investigated. The spores were ˜ 1.3 m̈m long and had a thick 3‐layered coat. An anchoring disc and polar aperture were present. The polaroplast occupied most of the anterior half of the spore. The vesicular portion included lengths of loosely packed lamellar structures as well as the usual vesicular profiles embedded in fibrillar material; it was entirely surrounded by tightly packed, electron‐dense lamellae. The polar tube had 5 or 6 coils. In this stage of the life cycle (mature spores), the parasites did not appear to be disturbing the host cells. The organism was namedMicrosporidium aplysiae

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02729.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Synopsis.Facieplatycauda prattigen. n., sp. n. andMyxobolus kozloffisp. n., from the Klamath Lakesucker,Catostomus luxatus(Cope), are described. The new genus is placed in the family Myxobolidae betweenHenneguyaandMyxobolus.The spore valves beyond the sporoplasmic space are broad and long but not attenuated as an inverted triangle as in certain species ofMyxoboluswith tails, or ofHenneguyawith sometimes bifurcated tails. An organism resemblingMyxobolus insidiosus(Wyatt&Pratt) was found in the muscle of the body ofSalmo clarki(Richardson). Differences in spore structure and site of infection suggest this is a subspecies of the previous form which should be designatedMyxobolus insidiosus clarki.A previously unreported species ofMyxobolusfromCottus aleuticus(Gilbert) is also described.

ISSN:0022-3921    

DOI:10.1111/j.1550-7408.1979.tb02730.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY