Genetics of Male Sterility in Gynodioecious Plantago Coronopus. II. Nuclear Genetic Variation

Inheritance of male sterility was studied in the gynodioecious species Plantago coronopus using five plants and their descendants from an area of ~50 m(2) from each of four locations. In each location, crosses between these five plants yielded the entire array of possible sex phenotypes. Both nuclear and cytoplasmic genes were involved. Emphasis is placed on the nuclear (restorer) genetics of two cytoplasmic types. For both types, multiple interacting nuclear genes were demonstrated. These genes carried either dominant or recessive restorer alleles. The exact number of genes involved could not be determined, because different genetic models could be proposed for each location and no common genetic solution could be given. At least five genes, three with dominant and two with recessive restorer allele action, were involved with both cytoplasmic types. Segregation patterns of partially male sterile plants suggested that they are due to incomplete dominance at restorer loci. Restorer genes interact in different ways. In most instances models with independent restorer gene action were sufficient to explain the crossing results. However, for one case we propose a model with epistatic restorer gene action. There was a consistent difference in the segregation of male sterility between plants from the two cytoplasmic types. Hermaphrodites of cytoplasmic type 2 hardly segregated male steriles, in contrast to plants with cytoplasmic type 1.     

The spatial structure of sexual and cytonuclear polymorphism in the gynodioecious Beta vulgaris ssp. maritima: I/ at a local scale

We have analyzed the spatial distribution of the sex phenotypes and of mitochondrial, chloroplast, and nuclear markers within two gynodioecious populations of Beta vulgaris ssp. maritima. Within both populations, sexual phenotype variation is controlled mainly by the cytoplasmic genotype, although in one study population a joint polymorphism of cytonuclear factors is clearly involved. In spite of contrasts in the ecology (mainly due to different habitats), a clear common feature in both populations is the highly patchy distribution of cytoplasmic haplotypes, contrasting with the wide distribution of nuclear diversity. This high contrast between cytoplasmic vs. nuclear spatial structure may have important consequences for the maintenance of gynodioecy. It provides opportunities for differential selection since nuclear restorer alleles are expected to be selected for in the presence of their specific cytoplasmic male sterile (CMS) type, but to be neutral (or selected against if there is a cost of restoration) in the absence of their CMS type. Selective processes in such a cytonuclear landscape may explain the polymorphism we observed at restorer loci for two CMS types.     

A meta‐analysis of the strength and nature of cytoplasmic genetic effects

Genetic variation in cytoplasmic genomes (i.e. the mitochondrial genome in animals, and the combined mitochondrial and chloroplast genomes in plants) was traditionally assumed to accumulate under a neutral equilibrium model. This view has, however, come under increasing challenge from studies that have experimentally linked cytoplasmic genetic effects to the expression of life history phenotypes. Such results suggest that genetic variance located within the cytoplasm might be of evolutionary importance and potentially involved in shaping population evolutionary trajectories. As a step towards assessing this assertion, here we conduct a formal meta‐analytic review to quantitatively assess the extent to which cytoplasmic genetic effects contribute to phenotypic expression across animal and plant kingdoms. We report that cytoplasmic effect sizes are generally moderate in size and associated with variation across a range of factors. Specifically, cytoplasmic effects on morphological traits are generally larger than those on life history or metabolic traits. Cytoplasmic effect sizes estimated at the between‐species scale (via interspecies mix‐and‐matching of cytoplasmic and nuclear genomes) are larger than those at the within‐species scale. Furthermore, cytoplasmic effects tied to epistatic interactions with the nuclear genome tend to be stronger than additive cytoplasmic effects, at least when restricting the data set to gonochorous animal species. Our results thus confirm that cytoplasmic genetic variation is commonly tied to phenotypic expression across plants and animals, implicate the cytoplasmic–nuclear interaction as a key unit on which natural selection acts and generally suggest that the genetic variation that lies within the cytoplasm is likely to be entwined in adaptive evolutionary processes.     

Selection with Gene-Cytoplasm Interactions. II. Maintenance of Gynodioecy

Gynodioecy is apparently frequently inherited through gene-cytoplasm interactions. General conditions for the protectedness of gene-cytoplasm polymorphisms for a biallelic model with two cytoplasm types were obtained previously, and these are applied to seven special cases of gene-cytoplasm interactions controlling gynodioecy and involving dominance. It is assumed that nuclear polymorphisms cannot be maintained in one cytoplasm type only. It is held that pure cytoplasmic inheritance of gynodioecy without nuclear interactions is unlikely, and it is shown that gynodioecy with gene-cytoplasm interactions is easier to establish than purely nuclear gynodioecy, for monogenic biallelic dominant or recessive inheritance. For three special cases, a resource-allocation model with simple assumptions always leads to conditions for protectedness of gynodioecy.     

Selection with gene-cytoplasm interactions. I. Maintenance of cytoplasm polymorphisms

General conditions for the protectedness of gene-cytoplasm polymorphisms are considered for a biallelic model with two cytoplasm types and under the assumption that nuclear polymorphisms cannot be maintained in the presence of only one cytoplasm type. Analytical results involving male fertilities, female fertilities, viabilities and selfing rates are obtained, and numerical results show spiral and cyclic behavior of population trajectories. It is shown that a maternally inherited cytoplasmic polymorphism cannot be maintained in the absence of a nuclear polymorphism, and that a gene-cytoplasm polymorphism can only be maintained if the population shows sexual asymmetry, i.e. , if the ratio of male to female fertility varies among genotypes. Thus, the classical viability selection model does not allow gene-cytoplasm polymorphisms.     

A stochastic, molecular model of the fission yeast cell cycle: role of the nucleocytoplasmic ratio in cycle time regulation

We propose a stochastic version of a recently published, deterministic model of the molecular mechanism regulating the mitotic cell cycle of fission yeast, Schizosaccharomyces pombe. Stochasticity is introduced in two ways: (i) by considering the known asymmetry of cell division, which produces daughter cells of slightly different sizes; and (ii) by assuming that the nuclear volumes of the two newborn cells may also differ. In this model, the accumulation of cyclins in the nucleus is proportional to the ratio of cytoplasmic to nuclear volumes. We have simulated the cell-cycle statistics of populations of wild-type cells and of wee1(-) mutant cells. Our results are consistent with well known experimental observations.     

The maintenance of nucleocytoplasmic polymorphism in a metapopulation: the case of gynodioecy

In gynodioecious species, gender is generally determined by epistatic interactions between cytoplasmic and nuclear loci. However, theoretical studies suggest that, for a joint polymorphism at both cytoplasmic and nuclear loci to be maintained in a panmictic population, selection must act differently on the various genotypes that determine the same gender. Here we show that, in a metapopulation with local extinction and restricted gene flow, nucleocytoplasmic polymorphism can be maintained without these differences. We use deterministic simulations. We assume that gene flow occurred only at recolonization. Founder effects create genetic variance between populations in the metapopulation, and local population growth is faster when the local frequency of females is high. Group selection phenomena are involved in the maintenance of the joint polymorphism in the metapopulation. The frequency of females in the metapopulation at equilibrium is higher than in a panmictic population with the same genetic system. However, these conclusions hold only if nuclear alleles restoring male fertility are dominant.     

Crossing type variability associated with cytoplasmic incompatibility in Australian populations of the mosquito Culex quinquefasciatus Say

An analysis of cytoplasmic crossing type variation in Australian populations of Culex quinquefasciatus, a member of the Culex pipiens complex of mosquitoes, revealed high levels of variability causing partial incompatibility between natural populations. Segregating crossing types were commonly found together within sampled sites. No correlation was evident between similarity of crossing type and environmental parameters of the sites, nor distance between sites. The nature of the observed variation did not support the hypothesis of paternally expressed nuclear 'restorer' genes. Such high levels of crossing type variation would be likely to impede attempts to control populations of the Culex pipiens complex using cytoplasmic incompatibility.     

Host genotype determines cytoplasmic incompatibility type in the haplodiploid genus Nasonia

In haplodiploid species, Wolbachia-induced cytoplasmic incompatibility (CI) can be expressed in one of two ways: as a "conversion" of diploid fertilized eggs into haploid males or as embryonic mortality. Here we describe CI-type variation within the parasitic wasp genus Nasonia and genetically analyze the basis of this variation. We reach four main conclusions: (i) CI is expressed primarily as conversion in N. vitripennis, but as embryonic mortality in the sibling species N. giraulti and N. longicornis; (ii) the difference in CI type between N. giraulti (mortality) and N. vitripennis (conversion) is determined by host nuclear genotype rather than by Wolbachia differences; (iii) N. vitripennis "conversion genes" are recessive in hybrid females; and (iv) a difference in CI level between the sibling species N. giraulti and N. longicornis is due to the different Wolbachia infections in the species rather than to the host genotype. These results show that host nuclear genes can influence the type of CI present in a species. On the basis of these findings, we propose a model for how different CI types evolve in haplodiploids due to selection on nuclear genes modifying CI.     

Non-linear growth mechanics—I. Volterrahamilton systems

In this, the first of a series of papers on stochastic and deterministic non-linear allometric growth models, a deterministic model is proposed which generalizes the widely applicable classical linear model of Huxley and Needham. There aren types of producers, each type depositing a product which accumulates monotonically in the environment. Producers interact via a mass action law satisfying an optimality condition. Coefficients may be interpreted as competition between the various producer types in the usual Volterra sense. An ideal coral reef is studied in which then species of coral polyps lay down aragonite calcium carbonate in building the reef framework. This deterministic model predicts that younger reefs are strongly unstable relative to initial species abundance, while older reefs grow in the classical sense of Huxley and Needham, asymptotically, as time goes to infinity. This research has been partially supported by NSERC-A-7667     

The interaction of nuclear and cytoplasmic damage after treatments with toxic chemicals

An attempt is made to show how the interaction of different degrees of nuclear and cytoplasmic damage may contribute to the ultimate whole cell damage by a chemical. It suggests that cytoplasmic, as well as nuclear damage, may be important in the action of chemical carcinogens. Using Amoeba proteus as a single cell model where nuclear and cytoplasmic damage can be separated by micrurgy, the mortality curves for the nucleus, the cytoplasm and the whole cell are examined after four different treatments: exposure to N-methyl-N-nitroso urethane, a potent carcinogen in mammalian systems; exposure to ββ₁ (dichlorodiethyl) methyl amine, an alkylating agent used in chemotherapy; exposure to methylmercury chloride, a very toxic organo-metal; and irradiation with X-rays. These illustrate how different relative nuclear/cytoplasmic sensitivities contribute to the death of the cell. The evidence for nuclear and cytoplasmic damage after treatment with the N-methyl-N-nitroso urethane is detailed, and possibilities of nuclear repair after the four different types of treatment examined. Work on Amoeba proteus makes no attempt to assess separately changes in structure or activity of any one of the cells many enzyme systems, but looks at the balance between nuclear and cytoplasmic damage as a whole.     

Intracellular symbionts and the evolution of uniparental cytoplasmic inheritance.

Uniparental inheritance of cytoplasmic elements is widespread among eukaryotic organisms and is achieved by a diverse range of mechanisms. This paper shows that the cytoplasmic genetic system would be expected to evolve towards uniparental inheritance, given the existence of deleterious symbionts capable of invading the host cytoplasm together with nuclear genes that lead to the elimination of cytoplasmic elements from one of the gamete types. The reason for this is that, under biparental inheritance, foreign symbionts with strong deleterious effects are able to spread through host populations. A nuclear modifier gene which leads to the loss of cytoplasmic elements from one gamete type gains a net advantage as a symbiont spreads, because the modifier sometimes gives rise to a symbiont-free zygote. Insofar as small gametes reduce the rate of symbiont transmission to the zygote, modifier genes causing small gamete size would tend to accumulate, so that cytoplasmic inheritance would become associated with maternal rather than paternal gametes. Once uniparental inheritance predominates in the host population, the population is protected from invasions by a large class of harmful symbionts, but at the same time those symbionts that benefit their hosts are still able to increase in frequency.     

Genetics of Male Sterility in Gynodioecious Plantago Coronopus. I. Cytoplasmic Variation

Inheritance of male sterility was studied in the gynodioecious species Plantago coronopus using five plants and their descendants from an area of ~50 m(2) in each of six locations. The crosses were planned to test for cytoplasmic inheritance of male sterility. In four locations significant differences between reciprocal crosses were observed. The progenies of these reciprocal crosses were used in a crossing scheme designed to test whether these reciprocal differences were caused by different cytoplasmic types between the plants. In all four locations, the existence of at least two cytoplasmic types could be shown. Moreover, the results of the crosses between locations showed that the same two cytoplasmic types were present in all four locations. We therefore argue that there is only limited cytoplasmic variation in P. coronopus. In each cytoplasmic type a series of intermediate sex forms occurred. A marked difference in restoration level existed between the two cytoplasmic types. Plants with cytoplasmic type 2 hardly segregated male steriles, in contrast to plants with cytoplasmic type 1.     

Classification of Normal and Male-Sterile Cytoplasms in Maize. II. Electrophoretic Analysis of DNA Species in Mitochondria

Mitochondrial DNA preparations were made from 31 maize lines carrying different sources of cytoplasm in the same nuclear genetic background. The DNAs were analyzed by agarose gel electrophoresis. A number of discrete low molecular weight bands were present in all lines. However, only four different DNA banding patterns were observed. These were correlated with the N, T, S and C cytoplasms defined by nuclear fertility restorer genes. Of the 31 cytoplasmic sources examined, six possessed DNA species characteristic of N cytoplasms, four possessed DNA species characteristic of T cytoplasm, 19 possessed DNA species characteristic of S cytoplasm and two possessed DNA species characteristic of C cytoplasm. This classification is in complete agreement with that based on mitochondrial translation products reported in the accompanying paper. No within-group heterogeneity was observed in the DNA banding patterns, indicating a lack of cytoplasmic variation within the four cytoplasmic groups. Attributes of the various methods available for classifying maize cytoplasms are compared and discussed.     

Interactions between cytoplasmic and nuclear genomes confer sex‐specific effects on lifespan in Drosophila melanogaster

Genetic variation outside of the cell nucleus can affect the phenotype. The cytoplasm is home to the mitochondria, and in arthropods often hosts intracellular bacteria such as Wolbachia. Although numerous studies have implicated epistatic interactions between cytoplasmic and nuclear genetic variation as mediators of phenotypic expression, two questions remain. Firstly, it remains unclear whether outcomes of cyto‐nuclear interactions will manifest differently across the sexes, as might be predicted given that cytoplasmic genomes are screened by natural selection only through females as a consequence of their maternal inheritance. Secondly, the relative contribution of mitochondrial genetic variation to other cytoplasmic sources of variation, such as Wolbachia infection, in shaping phenotypic outcomes of cyto‐nuclear interactions remains unknown. Here, we address these questions, creating a fully crossed set of replicated cyto‐nuclear populations derived from three geographically distinct populations of Drosophila melanogaster, measuring the lifespan of males and females from each population. We observed that cyto‐nuclear interactions shape lifespan and that the outcomes of these interactions differ across the sexes. Yet, we found no evidence that placing the cytoplasms from one population alongside the nuclear background of others (generating putative cyto‐nuclear mismatches) leads to decreased lifespan in either sex. Although it was difficult to partition mitochondrial from Wolbachia effects, our results suggest at least some of the cytoplasmic genotypic contribution to lifespan was directly mediated by an effect of sequence variation in the mtDNA. Future work should explore the degree to which cyto‐nuclear interactions result in sex differences in the expression of other components of organismal life history.     

Purification and properties of NADP-dependent glutamate dehydrogenase from yeast nuclear fractions.

1. NADP-dependent glutamate dehydrogenase (EC 1.4.1.4) extracted from nuclear fractions of Saccharomyces cerevisiae was partially purified. The final purification achieved was over 100-fold over the initial extract. 2. Cellulose acetate electrophoresis shows that the preparation is close to homogeneity and that the enzyme is slightly more anionic than cytoplasmic glutamate dehydrogenase. 3. The response of the nuclear activity to variation of pH, of inorganic phosphate and other electrolyte concentration and of the concentration of the reaction substrates has been investigated. Several differences were detected in comparison with cytoplasmic glutamate dehydrogenase.     

A quantitative analysis of the human bone marrow granulocytic cell lineage using the SAMBA 200 cell image processor. II. The blast cells in refractory anemia with an excess of blasts

A quantitative image analysis of bone marrow blast cells from eight patients with refractory anemia with an excess of blast cells was performed using the SAMBA 200 cell image analyzer. A total of 33 parameters was computed on 665 cells visually classified as B1 blasts (agranular cells), B2 blasts (cells containing a few azurophilic granules) and B3 blasts (cells with numerous granules). The continuum of variation of some cytoplasmic parameters (area, hue and standard deviation of the luminance, hue and saturation histograms) and some nuclear parameters (area and convexity degree) from the B1 cells to the B3 cells indicated a concomitant cytoplasmic and nuclear maturation, with the B1 cells being the most immature. An attempt to automatically classify these cells using a stepwise linear discriminant analysis resulted in an average of 68% correctly classified cells at the fifth step. Among the B1 and B2 blast cells considered together, an unsupervised classification method distinguished seven subgroups of blasts, which were principally different in cytoplasmic area, cytoplasmic color and nuclear texture. The percentages of cells belonging to two of these subgroups were highly discriminatory with respect to the prognosis. These two cell types had morphologic, textural and color features that put them very near the normal immature myeloidlike progenitor cells and normal myeloblasts, as demonstrated by means of canonical analysis. All patients having a very low percentage of these two cells among their blast cells died from overt leukemia less than one year after the first diagnosis of their disease.     

A quantitative genetic analysis of nuclear-cytoplasmic male sterility in structured populations of Silene vulgaris

Gynodioecy, the coexistence of functionally female and hermaphroditic morphs within plant populations, often has a complicated genetic basis involving several cytoplasmic male-sterility factors and nuclear restorers. This complexity has made it difficult to study the genetics and evolution of gynodioecy in natural populations. We use a quantitative genetic analysis of crosses within and among populations of Silene vulgaris to partition genetic variance for sex expression into nuclear and cytoplasmic components. We also use mitochondrial markers to determine whether cytoplasmic effects on sex expression can be traced to mitochondrial variance. Cytoplasmic variation and epistatic interactions between nuclear and cytoplasmic loci accounted for a significant portion of the variation in sex expression among the crosses. Source population also accounted for a significant portion of the sex ratio variation. Crosses among populations greatly enhanced the dam (cytoplasmic) effect, indicating that most among-population variance was at cytoplasmic loci. This is supported by the large among-population variance in the frequency of mitochondrial haplotypes, which also accounted for a significant portion of the sex ratio variance in our data. We discuss the similarities between the population structure we observed at loci that influence sex expression and previous work on putatively neutral loci, as well as the implications this has for what mechanisms may create and maintain population structure at loci that are influenced by natural selection.