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Biomedical subjects

D L Nanney

Publications and source records attributed to D L Nanney.

At least 19 recordsLinked to original sources
PubMed2000

Laboratory and evolutionary history of Tetrahymena thermophila.

An account is given of the early efforts to domesticate tetrahymenas as laboratory instruments for genetics. The rationale for developing a new organismic technology was the comparative leverage provided by a eukaryotic microorganism at a large evolutionary distance from both prokaryotic microbes and multicellular organisms. The tetrahymenine ciliates were considered more favorable materials than paramecia because of their ability to grow on simple media, though in fact their simpler nutritional needs have never been fully exploited. The first task was to sort the large set of phenotypically similar but evolutionarily and molecularly diverse ciliates referred to at the time as T. pyriformis. Then a species amenable to genetic manipulation was identified and its culture and cytogenetics were brought under control. Fortunately, the very first breeding system investigated--that in the species now called T. thermophila--has proved to be suitable for a wide range of studies. A large factor in the program's success was its use of the foundation previously established by studies on paramecia. However, serious unforeseen difficulties were encountered on the way to "domestication." These included inbreeding deterioration associated with their outbreeding life-style and germinal deterioration (mutational erosion) in the unexpressed micronuclear genome after long maintenance in vegetative culture. Cryogenic preservation was an important means of escaping these organismic limitations, and somatic (macronuclear) assortment has proved a valuable supplement to meiotic recombination.

Animals↗
PubMed1992

Crypthecodinium and Tetrahymena: an exercise in comparative evolution.

Nucleotide sequences have been determined for the highly variable D2 region of the large rRNA molecule for over 60 strains of dinoflagellates. These strains were selected from a worldwide collection that represents all the known sibling species (compatibility groups, Mendelian species) in the sibling swarm referred to as Crypthecodinium cohnii. A phylogenetic tree has been constructed from an analysis of the variations in a length of about 180 bases, using PHYLOGEN string analysis programs. The Crypthecodinium tree is compared with the previously published but here augmented tree constructed upon the same rRNA region for the sibling species of a worldwide collection of ciliated protozoa related to the genus Tetrahymena. The first reported sequence of Lambornella clarki, the parasite of tree-hole mosquitoes, is included. The dinoflagellate species complex is much more homogeneous with respect to ribosomal variation. The mean number of differences among sequences from different Crypthecodinium species is about 7, in comparison with 22 differences among the ciliate species examined. Moreover, all the diversity in the dinoflagellates can be explained by base substitutions, whereas insertions and deletions are common in the ciliates. The dinoflagellates are also much more uniform with respect to nutritional and genetic economies. The two complexes differ also in the relationship between molecular variations and breeding compatibility. All tetrahymenine sibling species thus far examined are monomorphic in the D2 region, but several dinoflagellate species are polymorphic. Several different dinoflagellate species, moreover, have identical D2 regions. This kind of ribosomal identity of incompatible strains is found in these ciliates only in one tight cluster of species--Group C. The tetrahymenine swarm is apparently much older than the Crypthecodinium swarm, and the dinoflagellate species produce incompatible progeny species much more readily than do the ciliates, perhaps by the acquisition of mutations that potentiate incompatibility in sympatric populations.

Animals↗
PubMed1991

Eukaryotic origins: string analysis of 5S ribosomal RNA sequences from some relevant organisms.

Using the PHYLOGEN tree-forming programs, we evaluate the published 5S rRNA sequences in certain of the files in the Berlin DataBank in an attempt to identify the connection between archaebacteria and the eukaryotic protists. These programs are based on methods of string analysis developed by Sankoff and others. Their discriminatory power is derived from their continuous realignment of sequences through repeated assessment of insertions and deletions as well as substitutions. The programs demonstrate that even these small molecules (ca. 120 bases) retain substantial records of evolutionary events that occurred over a billion years ago. The eukaryotes seem to have been derived from ancestors near the common origins of the halobacterial and Methanococcales groups. Identifying what might have been a primordial eukaryote is more difficult because several of the species considered as early derivatives from the common root are isolated species with large genetic differences from each other and from all other extant forms that have been sequenced. The ameboid, flagellated, and ciliated protists seem to have emerged nearly simultaneously from an ancient cluster, but the sarcodinid protozoa have preference as the group of most ancient origin. The euglenozoa and the ciliates are of later derivation. Our ability to tease plausible trees from such small molecules suggests that the mode of analysis rather than the size of the molecule is often a major limitation in the reconstruction of acceptable ancient phylogenics.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Ciliate evolution: the ribosomal phylogenies of the tetrahymenine ciliates.

We have assembled and analyzed nucleotide sequences for several different rRNA components from tetrahymenine ciliates. These include previously published and some new 5S and 5.8S rRNAs for a total of 18 species. We also report sequences for some 30 species obtained by primer extension analysis of a region near the 5' end of the 23S rRNAs (region 580). Phylogenetic trees have been constructed for these species, utilizing heuristics (shifting ditypic site analysis) described in a companion paper. The trees based on these sequences are consistent with each other and with those based on longer sequences of the 17S rRNA. They show the tetrahymenines to consist of a number of distinctive clusters of species. The clusters (ribosets) are homogeneous with respect to certain life history characteristics, especially the mode of mating type determination, but are inhomogeneous with respect to some morphological and life history features, such as cyst formation and adaptations to parasitism or carnivory. Using the same molecular data, we also begin to explore the relationships of the tetrahymenines to some other ciliate taxa and to some other protists.

Animals↗
PubMed1989

Shifting ditypic site analysis: heuristics for expanding the phylogenetic range of nucleotide sequences in Sankoff analyses.

We describe and illustrate a simple heuristic approach to the Sankoff methods for construction of parsimonious evolutionary trees from nucleotide sequence data. The procedure is intended to permit more valid inferences, particularly from relatively short sequences, concerning relationships among taxa separated for long time intervals. The procedure is based on the great variability of evolutionary plasticity among sites in the molecules and removes from consideration the more highly variable sites. Editing is accomplished after classifying sites in carefully aligned arrays of sequences. Only "ditypic sites," i.e., sites observed in only two evolutionary states within the array, are used in making phylogenetic inferences. This strategy makes possible the construction of good approximations to the most parsimonious Steiner trees, by means of efficient programs that require "dense species arrays," i.e., species sets that differ from each other by relatively small numbers of differences in conservative sites. The technique is illustrated with 5S and 5.8S rRNA sequence data from published catalogs.

Base Sequence↗
PubMed1980

Perturbance analysis of nuclear determination in Tetrahymena: effects of nutrition, cell extracts, and CaCl2 on A/B hybrids.

Mating type frequencies were ascertained among the progeny of crosses of strains A x B, Tetrahymena thermophila under a number of different circumstances. The frequencies are different if the parents are severely starved than if they are well-fed at the time of conjugation; severe starvation of the progeny before the first post-zygotic division has an effect similar to that of starving the parents. Mating type frequencies may also be modified by isolating conjugating pairs into cell extracts before the new macronuclei begin to develop; the changes do not appear to be related in a meaningful way to the mating type of the cells used as a source of the cell extracts. A third means of changing the mating type frequencies involves the exposure of conjugating pairs to CaCl2 solutions. Finally, changed frequency patterns may appear "spontaneously", and reflect either some as yet unsuspected environmental variable, or else an intrinsic metastable state that conditions the probabilities of mating type fixation. With the exception of the starvation effects, the pattern variations seem to fall into two groups. No satisfactory mechanism to account for these results is yet available.

Animals↗
PubMed1980

Perturbance analysis of nuclear determination in Tetrahymena: analysis of mating type frequency variations with reference to binary-switch models.

To test a 3-switch binary element model of mating type determination all possible assignments of the seven mating types of Tetrahymena thermophila to compound switch states have been examined, using a set of 77 experimentally obtained frequency patterns as a base. None of the assignments gives a satisfactory agreement with all the data. The result is similar whether the eighth switch state is considered forbidden or redundant. Moreover, further explorations of models in which the switches are not independent (as originally proposed), but coupled also fail to reveal a satisfactory agreement. Finally some 4-switch models are examined, again without discovering a satisfactory fit, though some evidence of structural relationship among the mating types is provided. The system is more complex than was assumed by the original models. To carry out this analysis certain statistical problems of a more general interest required solution. These include the management of samples from multinomial populations and the provision of efficient estimators for models of this sort.

Animals↗
PubMed1979

Germinal aging in Tetrahymena thermophila.

The manifestations of germinal aging in the ciliate Tetrahymena thermophila include death of the cells at conjugation and macronuclear retention in which the normal replacement of the old macronucleus by a new one fails to occur. Available data suggest that methods of routine maintenance that reduce the number of fissions may delay aging. Differences in breeding performance following maintenance for 1-5 years in axenic peptone broth vs. bacterized Cerophyl were not significant; those following maintenance at different temperatures were significant. The analysis of several hundred crosses is consistent with a random mutational basis for aging in the micronucleus and does not support the hypothesis of an age-correlated program in which the rate of deterioration increases with time. Following routine cultural maintenance for as long as 9-11 years, some lines show no deficiencies in their ability to produce viable progeny, and sublines of the same clone frequently differ significantly in their breeding performance. Moreover, breeding degeneration occurs at constant, but different, rates in different inbred strains.

Animals↗
PubMed1978

Scalar constraints in Tetrahymena evolution. Quantitative basal body variations within and between species.

Tetrahymenas of 17 species of the T. pyriformis complex have been stained with protargol and analyzed for numbers of basal bodies in half cells just before cell division. At this stage, cells of all strains manifest considerable variation in numbers of basal bodies; the coefficient of variation (sigma/m) is usually between 0.05 and 0.10. Much of this variability is observed in cells in the same nutritional state, at the same stage of the growth cycle, and in the same part of the life cycle. The basal body variability may be related to the variation in macronuclear DNA content that results from the imprecise amitotic macronuclear division. With a few exceptions, strains of different species are difficult to distinguish on the basis of basal body numbers. The species means in the samples examined show a range only from 234 (T. furgasoni) to 481 (T. capricornis), about a twofold difference. This limited variation in the means suggests that these organisms are constrained within narrow limited by some scalar function of their organismic design, which prevents an evolutionary size dispersion--even though molecular scrambling has occurred in the complex at an appreciable rate for a very long evolutionary interval.

Animals↗
PubMed1977

Perturbance analysis of nuclear determination in Tetrahymena I: background, rationale, and illustrative example, employing temperature responses.

A model based on comparative considerations, is presented for the nuclear determination of mating type in Tetrahymena thermophila. The model proposes a system of three binary control elements, each capable of stable persistence in one of two states. A general method is proposed for evaluating the model and for assigning particular mating types to particular compound states. Preliminary assignments of mating types are made from the responses of nuclei to temperature differentials.

Animals↗
PubMed1977

Cytogenetics of triplet conjugation in Tetrahymena: origin of haploid and triploid clones.

Triplet conjugation occurs frequently when three different mating types of T. thermophila are mixed under appropriate conditions. Genetic studies show that fertilization is usually tripolar, with each conjugant contributing a pronucleus to one mate and receiving a pronucleus from the other. Triplets are less common and less stable when only two mating types are mixed, and nuclear exchange is not always reciprocal. Some conjugants contribute a pronucleus but do not receive one in return. Others receive two pronuclei instead of one. Such triplets characteristically yield one haploid, one diploid and one triploid exconjugant, all of which are able to establish vigorous clones.

Animals↗
PubMed1977

Traumatic induction of early maturity in tetrahymena.

Exposure of conjugating pairs of Tetrahymena thermophila to high temperature (37 degrees) during macronuclear development causes an abortion of many macronuclei, but it also often induces an early appearance of sexual maturity in clones completing macronuclear development. Lines become mature after about 15 cell divisions rather than after 50 or more cell divisions in untreated pairs. The phenotype resembles that associated with Em (early maturity) mutants but, because it is not transmitted to the progeny in the next generation, it must be considered a phenocopy. The hypothesis is developed that an early genotype-environment incompatibiltiy, whether associated with an abnormal genotype or an unusual environment, activates a shunt mechanism permitting the organisms to undertake quickly an ordinarily forbidden sexual lottery.

Animals↗
PubMed1977

Molecules and morphologies: the perpetuation of pattern in the ciliated protozoa.

Three apparently conflicting generalizations concerning the relationships between molecules and cell structure may be derived from studies on cellular patterning in the ciliates. (A) Cells with identical genes and molecular composition may have different hereditary patterns. (B) Genes, through their prescribed molecular derivatives, constrain the modes of pattern permutation and define the states of greatest stability. (C) Cells with identical hereditary patterns may have entirely different genes and molecular compostitons. These priniciples may be reconciled through the recognition that they are characteristically applicable over different time intervals. Hereditary differences within a clone and without related molecular differences (principle A) may persist for hundreds of cell generations, but they are resolved eventually within a constant environment (principle B) as the configuration of minimal free energy is approached. On an even longer time scale, molecular substitutions have occurred for many or most components of the cell, but these have been constrained by selective pressures on an ancient design (principle C) that disallow substitutions affecting certain form-function relations which have been elevated to an adaptive peak.

Animals↗