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PubMed1999

Microsatellite retrieval in lettuce (Lactuca sativa L.).

By using enriched genomic libraries, microsatellite-containing sequences were isolated from lettuce (Lactuca sativa) with high efficiency. With this approach, a sizeable fraction (up to 55%) of the clones contained a microsatellite. In about half of these clones, primers could be designed for PCR amplification of the microsatellite. This yielded 28 primer sets amplifying unambiguously scorable products, of which 26 showed polymorphisms in a test set of six lettuce varieties. Practically all microsatellite-amplifying primer sets yielded products in lettuce's nearest relative, L. serriola, but only half of the primer sets yielded products in the more distant species L. saligna and L. virosa. An average polymorphism information content (PIC) value of 0.55 and an average number of 3.5 alleles per locus were in the normal range for a self-fertilizing species like lettuce. In addition, the incidental cloning of a microsatellite-containing repeat family, apparently specific for Lactuca, is reported and the implications for the efficient retrieval of single-locus microsatellite sequences are discussed. The microsatellite loci isolated will be useful for distinguishing lettuce cultivars and for screening diversity of genetic resources.

Alleles↗
PubMed1993

Analysis of ploidy and sexual characteristics of natural isolates of Cryptococcus neoformans.

We report here an extensive examination of the ploidy of a basidiomycetous yeast. The ploidy of 34 strains of Cryptococcus neoformans var. neoformans, isolated mostly from Japanese patients, was determined by means of quantitative fluorescence microscopy after DNA staining with propidium iodide. The sexual characteristics of the strains including the two tester strains were as follows. Twenty-four strains were of the heterothallic alpha type, 1 was of the heterothallic a type, and 2 were self fertile; the remaining 7 showed no sexual response. The following strains were found to be haploid: the heterothallic a strain, 20 of the 24 heterothallic alpha strains, and 3 of the 7 asexual strains. Thus, the C. neoformans strains were mostly haploid, as the sexual response of this organism suggests. Both of the self-fertile strains and four of the seven asexual strains were diploid. Unexpectedly, 4 of the 24 heterothallic alpha strains were diploid.

Cryptococcus neoformans↗
PubMed1995

A predicted membrane protein, TRA-2A, directs hermaphrodite development in Caenorhabditis elegans.

The nematode C. elegans naturally develops as either an XO male or XX hermaphrodite. The sex-determining gene, tra-2, promotes hermaphrodite development in XX animals. This gene encodes a predicted membrane protein, named TRA-2A, which has been proposed to provide the primary feminising activity of the tra-2 locus. Here, we show that transgenic TRA-2A driven from a heat shock promoter can fully feminise the somatic tissues of XX tra-2 loss-of-function mutants, which would otherwise develop as male. TRA-2A is thus likely to provide a component of the tra-2 locus that is both necessary and sufficient to promote female somatic development. Transgenic TRA-2A driven by the heat shock promoter can also transform XO animals from male to self-fertile hermaphrodite. This result establishes the role of tra-2 as a developmental switch that controls somatic sexual cell fate. We show that a carboxy-terminal region of TRA-2A, predicted to be intra-cellular, can partially feminise XX tra-2 loss-of-function mutants and XO tra-2(+) males. We suggest that this intra-cellular domain of TRA-2A promotes hermaphrodite development by negatively regulating the FEM proteins.

Animals↗
PubMed1983

Bioassay of genotoxic effects of environmental particles in a feeding ciliate.

The ciliated protozoan, Paramecium, can be used to quantitate cytotoxic and genotoxic effects of ingested complex environmental particles. Cytotoxicity is quantitated by the increased proportion of treated versus control cells which do not retain their capacity for normal cell replication. Genotoxic effects are assessed by the increased fraction of nonviable offspring from treated versus control parent cells after the self-fertilization process of autogamy. Since these cells ingest nonnutrient respirable-sized particles, biological activity of intracellular extraction of dusts and fly ash can be compared before and after extraction with polar and nonpolar solvents. Previous studies indicated that coal fly ash was mutagenic in these eukaryotic cells. Mutagenicity of coal fly ash was not detectable after extraction with a concentration of HCl known to remove nonmatrix trace elements. These results suggested that this ciliate bioassay might be a detector of mineral mutagens. Fine particles of the carcinogenic nickel compounds, alpha-nickel subsulfide, and beta-nickel sulfide were compared for their biological activity in this bioassay. Both nickel compounds were ingested by the ciliates and induced heritable damage in the progeny of the treated parent cells.

Animals↗
PubMedDate not supplied

Gamma (60)Co DL(50/30) of Biomphalaria glabrata (SAY, 1818).

The variation of resistance to (60)Co gamma-rays of Biomphalaria glabrata was studied. A population of 480 mollusks was observed during 30 days - distributed in 8 groups of snails isolated and 8 groups of snails in colonies - after exposure (30 snails per group per dose) to increasing doses of gamma radiation. Doses of 10, 20, 40, 60, 80, 160, 320 and 640 Gy from a Gamma-cell (60)Co irradiator, were applied to the test groups and two groups control (non-irradiated) of snails - isolated and colony - were kept apart. After have been exposed, the snails were drew back to the aquaria where they were maintained before. The survival was estimated on a daily score of the alive animals in each group-dose, starting after the irradiation exposure day. As a result, the survival self-fertilization forms (DL(50/30) = 218.2 Gy) was found greater than in cross-fecundation forms. These data point to a low radio-resistance on the cross-fertilization forms - the sexual reproductive form - which is most found in nature. The lower radio-resistance of the cross-fertilization forms suggests the presence of some sex-linked hormonal factor related to this phenomenon.

Animals↗
PubMed1999

Ploidy of serotype AD strains of Cryptococcus neoformans.

Twenty-four serotype AD strains of Cryptococcus neoformans were tested for ploidy and mating type. These included 13 natural isolates (1 from a patient, 1 from peach juice, 11 from pigeon droppings), 2 single clones from one of these natural isolates, 7 F1 progeny from a self-fertile strain and 2 F1 progeny of a cross between a strain from a patient (serotype A, alfa-mating type: MATalfa) and a tester strain (serotype D, a-mating type: MATa). Six strains (2 of natural isolates, 1 of single clone and 3 of F1 progeny) were MATalfa, 1 of F1 progeny was MATa, 4 (1 of natural isolate, 1 of single clone and 2 of F1 progeny) were a-alfa-mating type (MATa-alfa) and 13 (10 of natural isolates and 3 of F1 progeny) were untypable. Most strains, regardless of mating type, were diploid.

Cryptococcus neoformans↗
PubMed1999

Plasmodium falciparum parasites in French Guiana: limited genetic diversity and high selfing rate.

The genetic characteristics of Plasmodium falciparum isolates collected in French Guiana, where malaria transmission is low and occurs in isolated foci, were studied. Blood samples were collected from 142 patients with symptomatic malaria and typed using a polymerase chain reaction-based strategy for merozoite surface protein-(MSP-1) block 2, the MSP-2 central domain, and glutamate-rich protein (GLURP) repeat domain polymorphism. This showed that the parasite population circulating in French Guiana presented a limited number of allelic forms (4, 2, and 3 for MSP-1 block 2, MSP-1, and GLURP, respectively) and a small number of mixed infections, contrasting with the large genetic diversity of parasite populations and infection complexity reported for Africa, Asia, and other parts of South America. Two groups of isolates displaying identical 3 loci allele combinations were further studied for the Pf332 antigen, histidine-rich protein-1, thrombospondin-related anonymous protein, and Pf60 multigene family polymorphism. Within each group, most isolates were identical for all markers tested. This suggests a high rate of self-fertilization of P. falciparum parasites in French Guiana, resulting in homogenization of the population. The implications of these findings for malaria control in areas of low endemicity are discussed.

Animals↗
PubMed1999

Gene silencing-mediated resistance in transgenic tobacco plants carrying potato virus Y coat protein gene.

Unlike other pathogens, plant viruses are hardly controlled by chemical agents. Potato virus Y (PVY) is distributed around the world, and causes a great loss economically. In an attempt to minimize the damage by viruses, the PVY coat protein (CP) gene was introduced into tobacco by Agrobacterium-mediated transformation. A significant proportion of the transgenic plants displayed resistance to PVY and showed substantially decreased CP transgene expression at both protein and steady-state mRNA levels compared to susceptible transgenic or nontransgenic plants. A resistant plant was selected and self-fertilized for several generations until T4 progenitor lines were obtained. Most of these T4 plants accumulated extremely low levels of CP protein and steady-state mRNA, and exhibited almost complete resistance to PVY. DNA gel blot analysis revealed that the transgenic plants typically had two or three copies of the transgene. These results are characteristic of pathogen-derived resistance, in which the resistance against virus is the consequence of post-transcriptional gene silencing directed by homologous transgenes. To uncover factors that may play roles in gene silencing, sequences in the 3' part of the transcribed region of the CP gene were transcribed in vitro and the RNA fragments were incubated with cell extracts from transgenic plants. A ribonuclease activity was detected that appeared to be specific for this transcript in the PVY-resistant transgenic plants.

Capsid↗
PubMed1998

Reversible male sterility: a novel system for the production of hybrid corn.

Hybrid corn seed is traditionally produced using either mechanical/hand detasseling or cytoplasmic male sterility, or a combination of both. In recent years, the development of transgenic systems to produce hybrid seed in several crops has attracted much attention. Here we describe a transgenic mechanism for production of hybrid corn, reversible male sterility (RMS), in which the action of the cytotoxic gene used to introduce male sterility is suppressed by the application of a chemical to the plant. Reversion of the sterility allows the RMS parent to be self-fertilized, a step which overcomes the need to remove fertile sib plants prior to making the hybrid cross. The key enabling technology in RMS is the use of a plant gene promoter which is specifically induced by chemical application. We have exemplified RMS in transgenic corn plants and believe that it provides specific benefits in the production of hybrid corn seed.

Hybridization, Genetic↗
PubMed2000

Comparative pollen morphology and ultrastructure of the Callitrichaceae.

The Callitrichaceae are an aquatic family of dicots that include the single, geographically cosmopolitan genus Callitriche. Callitriche contains 40-50 terrestrial, amphibious, and obligately submersed species, and it is the only known genus in the plant kingdom with co-occurring aerial and hydrophilous pollination syndromes. Pollen morphology and ultrastructure were described for 13 Callitriche species using scanning electron and transmission electron microscopy. Representative taxa of each growth form were examined; these included three terrestrial species (C. deflexa, C. peploides, and C. nuttallii), nine amphibious species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis hybrid, C. cribrosa, C. hamulata, C. heterophylla var. heterophylla, C. lusitanica, C. marginata, and C. trochlearis), and one obligately submersed species (C. truncata). Of the amphibious taxa, C. heterophylla var. heterophylla and C. trochlearis had internal geitonogamy, a type of internal self-fertilization. Pollen from all taxa was spheroidal, small, intectate, and lacked well-defined apertures. Taxa primarily differed with respect to exine thickness, surface ornamentation, and the presence or absence of aperture-like regions. The pollen of terrestrial species, as well as that of C. marginata, had well-developed exines with thick sculptured and basal layers. In general, amphibious taxa produced pollen with distinct, but thinner, exines than that of terrestrial taxa. Pollen of the amphibious taxa with internal geitonogamy had a thicker basal layer than species without internal geitonogamy, whereas the overall exine was reduced in C. hamulata and absent in C. brutia and C. lusitanica. Pollen of the obligately submersed C. truncata also lacked an exine. These palynological data were correlated with growth habits and related pollination biologies, as well as with phylogenetic interpretations of Callitrichaceae. Exine reduction or loss has evolved at least twice in the family, and it is associated with aneuploid reduction in chromosome number.

Journal Article↗
PubMed2000

[Possibilities of selection with an increase in frequency of meiotic recombination (simulation and experiment)].

Polymorphism of rec genes, modifier genes of recombination frequency (rf), was analyzed. Genetic population analysis was used to estimate the efficiency of some schemes of direct and indirect selection for higher rf in a marked chromosomal region. A new modification of the cyclic selection scheme, based on selection of double recombinant marker genotypes in the offspring of self-fertilized plants, was found to be most effective in many cases. This indirect selection scheme was studied in more detail using deterministic and stochastic computer simulation. Effects of various factors on the efficiency of the modified scheme were analyzed. These factors were different degrees of cross-fertilization, differential adaptation of recombinant and non-recombinant gametes and zygotes, linkage between marker genes and rec genes, and environmental variation of rf. Sample sizes and the number of crosses required for a stable rf increase in experiment were estimated. Statistical properties of two new modified tests for comparison of rf values were studied. An experiment with marker forms of tomato were conducted taking into account the recommendations following from the results of simulation.

Genetic Linkage↗
PubMed2000

Outcrossing rate and inbreeding depression in the perennial yellow bush lupine, Lupinus arboreus (Fabaceae).

Little is known about the breeding systems of perennial Lupinus species. We provide information about the breeding system of the perennial yellow bush lupine, Lupinus arboreus, specifically determining self-compatibility, outcrossing rate, and level of inbreeding depression. Flowers are self-compatible, but autonomous self-fertilization rarely occurs; thus selfed seed are a product of facilitated selfing. Based on four isozyme loci from 34 maternal progeny arrays of seeds we estimated an outcrossing rate of 0.78. However, when we accounted for differential maturation of selfed seeds, the outcrossing rate at fertilization was lower, ∼0.64. Fitness and inbreeding depression of 11 selfed and outcrossed families were measured at four stages: seed maturation, seedling emergence, seedling survivorship, and growth at 12 wk. Cumulative inbreeding depression across all four life stages averaged 0.59, although variation existed between families for the magnitude of inbreeding depression. Inbreeding depression was not manifest uniformly across all four life stages. Outcrossed flowers produced twice as many seeds as selfed flowers, but the mean performance of selfed and outcrossed progeny was not different for emergence, seedling survivorship, and size at 12 wk. Counter to assumptions about this species, L. arboreus is both self-compatible and outcrosses ∼78% of the time.

Journal Article↗
PubMed1992

Mating behavior in the pulmonate small melampus: can regeneration restore function?

Previous anatomical observations have established that the penial complex of adult Melampus bidentatus is specifically reinnervated and that the penial complex itself can regenerate. This review describes experiments to determine whether a reinnervated penial complex and a regenerated penial complex can function in mating. The snails are not self-fertile, so the ability to transfer sperm, evaluated by production of fertile eggs, was the test of successful regeneration. Snails with nerve transections produced fertile eggs within the time-span expected for axonal regeneration to the target organ. Penial complex ablation interfered with sperm transfer for two egg-laying cycles but fertile eggs were laid within a time-span consistent with regeneration of a penial complex.

Animals↗
PubMed1990

Sexuality and hermaphroditism in fishes. I. Synchronous functional hermaphroditism in the serranid fish Serranus scriba L.

Anatomical and histological examination of Serranus scriba L. showed the existence of primary females (67%), hermaphrodites (31%) and primary males (2%). Synchronous functional hermaphroditism is described on the basis of an anatomical and histological study of the gonads. Although they function simultaneously, the testicular and ovarian parts of hermaphrodite gonads have completely separate ducts. Females and hermaphrodites have the same annual reproduction cycle. In hermaphrodites, the testicular part matures one month sooner than the ovarian part. Cross fertilization between primary females and hermaphrodite individuals and between two different hermaphrodites probably occurs, while self-fertilization is less likely. The testicular tissues of primary males are of the acinar type and those of hermaphrodites are of the radial type. It is possible that primary males do not take part in reproduction. Serranus scriba in Egyptian Mediterranean waters is a longperiod spawner, which spawns from June to the end of October, i.e. it is a summer-autumn spawner.

Animals↗
PubMed1986

Diethylnitrosamine-induced pancreatic neoplasms in the fish Rivulus ocellatus marmoratus.

Diethylnitrosamine [(DEN) CAS: 55-18-5] caused neoplasms of the exocrine pancreas in rivulus, Rivulus ocellatus marmoratus, a self-fertilizing hermaphroditic fish, after a single exposure to 810, 270, or 130 mg DEN/liter or after a continuous exposure to 50, 17, or 9 mg DEN/liter. Rivulus developed pancreatic adenomas after a single exposure. After continuous exposure, pancreatic adenomas, cystadenomas, and adenocarcinomas developed. Adenocarcinoma developed in fish first exposed as larvae but not in those first exposed as juveniles. Adenocarcinoma of pancreatic or biliary origin invaded the intestinal muscularis layer and mucosa. Dedifferentiation of acinar cells preceded the formation of adenomas, and atypical acinar cells formed parts of some of the ductlike structures in the pancreatic neoplasms.

Adenocarcinoma↗
PubMedDate not supplied

Population genetics of Biomphalaria straminea in Hong Kong. A neotropical schistosome-transmitting snail recently introduced into China.

Since its introduction in the early 1970s Biomphalaria straminea (Gastropoda: Planorbidae) has spread rapidly and is locally the most abundant fresh water snail in Hong Kong. Studies of 19 electrophoretically detected loci in four populations show that the colonists retain high levels of variability (P = 0.26, H = 0.056 - 0.097), comparable with those found in autochthonous samples of related species. Genotype frequencies at the five polymorphic loci, and a comparison of maternal and progeny genotypes of individual field-collected snails, revealed no evidence for self-fertilization in these functional hermaphrodites. F statistics indicated minimal genetic structuring, presumably because of outcrossing and recency of origin of the populations. Geographic distribution of various alleles and their frequencies suggest that two southern populations were derived from the original colonists by dispersal but that a northern population represents a second introduction in about 1982. This interpretation (based on genetics) is consistent with the known history of the various populations. The Asian populations of this South American snail are interpreted as being in the "flush" phase of the colonization process. Finally, the probability of the secondary spread of this snail from Hong Kong, and the probability of its parasite, the human blood fluke Schistosoma mansoni, being introduced to Asia are discussed.

Alleles↗
PubMed1984

Covariances of relatives stemming from a population undergoing mixed self and random mating.

We consider covariances of all parent and first-generation relatives from outcrossing or self-fertilization in a parent population that is in equilibrium with respect to these processes. The results, which are for any number of alleles and loci with additive and dominance effects, are phrased in terms of six quadratic genetic components whose coefficients are given by descent measures for equilibrium populations. Because of the variation in the inbreeding coefficients for this system of mating, the expressions include joint contributions of loci to the variances and covariances of relatives. By inclusion of the full complement of relatives, all quadratic components can be estimated. The findings of Ghai (1982, Biometrics 38, 87-92) for compound functions of the covariances with two alleles at a single locus are analyzed in terms of the more general model.

Alleles↗
PubMed1984

Usefulness of the hermaphroditic marine fish, Rivulus marmoratus, in carcinogenicity testing.

Hepatocellular carcinoma and other pathological changes were induced in the self-fertilizing hermaphroditic fish Rivulus marmoratus by aqueous exposure to 15, 30, and 45 ppm diethylnitrosamine (DENA). Fish exposed as larvae for 12 weeks and adults exposed for 5 weeks showed rates of hepatocellular carcinoma as high as 76.5 and 31.3%, respectively, when examined 1 year later. Fish exposed as embryos in various stages of development for 1 week to 10, 32, 100, 320, and 1,000 ppm DENA were without neoplasms when examined 1 year later. Other pathological changes of rivulus livers were cholangioma, adenofibrosis, and granuloma with incidences as high as 38.9, 88.9, and 61.1%, respectively. Simple rearing methods were developed and relevant biological data pertaining to reproduction, embryonic development, and subsequent growth of R. marmoratus are discussed. Advantages and disadvantages of the use of R. marmoratus as a carcinogenicity test animal are assessed.

Animals↗