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PubMed1988

Genetic control of sex determination in the germ line of Caenorhabditis elegans.

The nematode Caenorhabditis elegans normally exists as one of two sexes: self-fertilizing hermaphrodite or male. Development as hermaphrodite or male requires the differentiation of each tissue in a sex-specific way. In this review, I discuss the genetic control of sex determination in a single tissue of C. elegans: the germ line. Sex determination in the germ line depends on the action of two types of genes:--those that act globally in all tissues to direct male or female development and those that act only in the germ line to specify either spermatogenesis or oogenesis. First, I consider a tissue-specific sex-determining gene, fog-1, which promotes spermatogenesis in the germ line. Second, I consider the regulation of the hermaphrodite pattern of germ-line gametogenesis where first sperm and then oocytes are produced.

Animals↗

PubMed1987

A genetic analysis of the sex-determining gene, tra-1, in the nematode Caenorhabditis elegans.

The normal sexes of Caenorhabditis elegans are the self-fertilizing hermaphrodite (XX) and the male (XO). The autosomal gene tra-1 is a major switch gene controlling sexual phenotype. Mutant phenotypes of 43 loss-of-function (lf) tra-1 alleles and 22 gain-of-function (gf) tra-1 alleles are described and discussed. The tra-1(lf) alleles are recessive and, in general, masculinizing. The most severe mutations (such as seven out of eight identified amber alleles) can transform XX animals into fertile males. These mutations have little effect on XO animals (which are male already) but lead to some abnormalities in XO gonadal development, indicating that tra-1 has functions in normal development of both sexes, although its major function is confined to the XX hermaphrodite. Weaker tra-1(lf) alleles lead to incomplete masculinization of XX animals, resulting in a variety of intersexual phenotypes. the tra-1(gf) alleles are dominant and have an opposite, feminizing effect. Six out of 22 can transform XO animals into fertile females or hermaphrodites, whereas the remainder cause partial feminization. All 22 transform XX animals into fertile females. Limited intragenic mapping indicates that the gene is large and that gf alleles map to a location different from lf alleles. The results suggest that the tra-1 gene has several roles in wild-type sexual development. First, tra-1 activity dictates female, as opposed to male, development in all nongonadal tissues of XX animals. Second, tra-1 activity dictates female development in the somatic gonad of XX animals. Third, a high level of tra-1 activity may act to inhibit spermatogenesis in the XX germ line, thereby assisting the switch from spermatogenesis to oogenesis in the hermaphrodite. These three functions are all feminizing and specific to the XX animal; the gene also has minor functions in the XO animal, which are to assist normal male somatic gonad development and to promote abundant spermatogenesis in males. A low level of both spermatogenesis and oogenesis can occur in the absence of tra-1 activity. Both the function and the regulation of this gene must be complex.

Alleles↗

PubMed2026

T2T genomes of Caenorhabditis nigoni and Caenorhabditis briggsae reveal divergence in satellite DNA abundance.

The two closely related nematode species, Caenorhabditis nigoni and Caenorhabditis briggsae, are commonly used to study the evolution of reproductive modes in animals, with the self-fertile C. briggsae and outcrossing C. nigoni sharing a common ancestor ∼3.5 million years ago. Earlier genomic analyses revealed that selfing Caenorhabditis species have smaller genomes and proposed that at least some gene loss in C. briggsae is adaptive. However, the incomplete C. nigoni reference genome has limited most comparative analyses to genic regions. Here, we leverage long-read sequencing to generate and annotate telomere-to-telomere (T2T) assemblies for the C. nigoni strain JU1422 and the C. briggsae strain AF16. This new 139 Mb C. nigoni genome resolves 57 gaps and 149 unassigned scaffolds from the previous genome assembly. A major driver of the size difference with the 107 Mb T2T C. briggsae genome is the abundance of satellite DNA, which accounts for 12.8 Mb (9.2%) in C. nigoni and only 3.2 Mb (3.0%) in C. briggsae Notably, the C. nigoni X Chromosome is 13.4 Mb larger than in the previous assembly, making it 60% larger than the C. briggsae X Chromosome compared with 18%-26% difference for the autosomes. We also document a surprising degree of plasticity in the ribosomal DNA, with the C. nigoni X Chromosome harboring a second 45S rDNA array that is absent in C. briggsae The hitherto undocumented divergence in the abundance of repetitive DNA elements makes the new genomes an invaluable resource for genomic analysis.

Journal Article↗

PubMed2025

Alternative splice acceptor site in MSH4 gene is responsible for male sterility conferred by ms5 in soybean.

In soybean breeding, using the recessive male-sterile ms5 gene, derived from fast neutron mutagenesis, for recurrent selection is advantageous because of the d2 locus, which controls cotyledon color in mature seeds and can be used as a phenotypic selection marker for ms5 male sterility. However, occasional self-fertilization occurs because of the elimination of d2 linkage and instability of male sterility. Elucidating the mechanism and the gene responsible for ms5 male sterility may resolve these problems. Using fine mapping with 15 simple sequence repeat (SSR) markers, we narrowed down the candidate ms5 locus to a 54-kbp region. Bulked-DNA analysis using next-generation sequencing revealed a deletion as a candidate variation in the region. This 15-bp deletion and a nucleotide substitution were identified in intron 1 of MutS homolog (GmMSH4), which modulates chromosomal recombination in meiosis. The ms5 transcript contained a novel exon with a premature termination codon. This exon originated from an alternative splice acceptor site caused by the deletion and nucleotide substitution, disrupting gene function. Co-segregation of male sterility with five independent mutations in GmMSH4 was confirmed using progeny of mutant lines. Mutations in GmMSH4 led to biased DNA partitioning during meiosis, resulting in collapsed or enlarged pollen and suggesting that ms5 male sterility is caused by the failure of pollen formation during meiosis due to the loss of function of GmMSH4. These findings could help explain the mechanism of instability of ms5 male sterility and improve the efficiency of recurrent selection using DNA markers in soybean breeding.

Glycine max↗

PubMed1967

Growth and sporulation of a pyrimidine spore color mutant of Sordaria fimicola.

A nonautonomous spore color mutant of Sordaria fimicola is a pyrimidine auxotroph that produces hyaline nonviable ascospores. Uracil, uridine, and cytidine are more effective growth factors than cytosine and thymine and, in high concentrations, render the mutant self-fertile by inducing the ascospores to resume development and maturation. Crosses with the unlinked arginine non-autonomus spore color mutant st-59 yielded the double mutant st-59 pyr that requires both arginine and a pyrimidine for growth, which indicates a lack of suppression of the pyrimidine requirement by the arginine locus.

Arginine↗

PubMed1970

Sexual reproduction on Geotrichum candidum.

A perfect state of Geotrichum candidum was isolated from soil in Puerto Rico. Wild-type cultures are self-fertile but give rise to self-sterile, cross-fertile mating types morphologically different in some respects from the wild type. This discovery of the perfect state of G. candidum and its unique pattern of sexuality may contribute to knowledge of its ecology, the origin of pathogenic races, and speciation.

Mitosporic Fungi↗

PubMed1988

DNAs of the two mating-type alleles of Neurospora crassa are highly dissimilar.

The mating-type alleles A and a of Neurospora crassa control mating in the sexual cycle and function in establishing heterokaryon incompatibility in the vegetative cycle. The A and a alleles were cloned, and they were shown to encode both the sexual functions and vegetative incompatibility. The mating-type clones contain nonhomologous DNA segments that are flanked by common DNA sequences. Neurospora crassa and all heterothallic and pseudohomothallic Neurospora species contain a single copy of one mating-type sequence or the other within each haploid genome. The six known self-fertile homothallic isolates contain an A homolog, but only one species also contains a homologous sequences. Homothallism in these species is not due to mating-type switching, as it is in Saccharomyces cerevisiae.

Chromosome Mapping↗

PubMed1986

Delay of disease development in transgenic plants that express the tobacco mosaic virus coat protein gene.

A chimeric gene containing a cloned cDNA of the coat protein (CP) gene of tobacco mosaic virus (TMV) was introduced into tobacco cells on a Ti plasmid of Agrobacterium tumefaciens from which tumor inducing genes had been removed. Plants regenerated from transformed cells expressed TMV mRNA and CP as a nuclear trait. Seedlings from self-fertilized transgenic plants were inoculated with TMV and observed for development of disease symptoms. The seedlings that expressed the CP gene were delayed in symptom development and 10 to 60 percent of the transgenic plants failed to develop symptoms for the duration of the experiments. Increasing the concentration of TMV in the inoculum shortened the delay in appearance of symptoms. The results of these experiments indicate that plants can be genetically transformed for resistance to virus disease development.

DNA↗

PubMed1979

Osmotic shock prevents nuclear exchange and produces whole-genome homozygotes in conjugating Tetrahymena.

Exposure of conjugating Tetrahymena to a hyperosmotic shock blocks the exchange of gametic nuclei and produces self-fertilized exconjugants that are homozygous for their whole genome. Cells are sensitive to this induction during a brief period after meiosis. The high efficiency of the treatment and the fertility of the progeny make this a useful method for the isolation of induced recessive mutations and enhances the value of Tetrahymena as an animal-cell model system in which genetic dissection is practical. The sharp peak of sensitivity is useful in the study of those cellular mechanisms responsible for the independent handling of several functionally distinct nuclei during conjugation.

Animals↗

PubMed1981

Mating types and macrocyst formation in Dictyostelium.

Macrocysts have been found among strains of Dictyostelium rosarium Raper and Cavender (K. B. Raper and J. C. Cavender, J. Elisha Mitchell Sci. Soc. 84:31-47, 1968). Strains that exhibit mating capabilities could be classified into one of three mating types: A1, A2, or A3. Each mating type was self-incompatible but cross-compatible with the other two types in most cases. No self-fertile strain was observed. Wet conditions, darkness, and moderate nutrient particularly favored macrocyst production; opposite conditions generally favored asexual sorocarp formation. Macrocyst development followed the same morphogenetic pattern reported previously for other species of Dictyostelium. Cultures exposed to light in stages prior to precyst appearance could be switched from macrocyst to sorocarp development. In contrast, precysts always developed into macrocysts despite the presence of light. There appeared to be an "all-or-none" phenomenon in macrocyst production, suggesting that transformation to macrocysts occurred once certain light-sensitive critical factors had reached a threshold level. Intimate association of cells of mating pairs appeared to be essential for macrocyst formation, and no mating hormones were detected.

Crosses, Genetic↗

PubMed1985

Direct and indirect gene replacements in Aspergillus nidulans.

We performed three sets of experiments to determine whether cloned DNA fragments can be substituted for homologous regions of the Aspergillus nidulans genome by DNA-mediated transformation. A linear DNA fragment containing a heteromorphic trpC+ allele was used to transform a trpC- strain to trpC+. Blot analysis of DNA from the transformants showed that the heteromorphic allele had replaced the trpC- allele in a minority of the strains. An A. nidulans trpC+ gene was inserted into the argB+ gene, and a linear DNA fragment containing the resultant null argB allele was used to transform a trpC- argB+ strain to trpC+. Approximately 30% of the transformants were simultaneously argB-. The null argB allele had replaced the wild-type allele in a majority of these strains. The A. nidulans SpoC1 C1-C gene was modified by removal of an internal restriction fragment and introduced into a trpC- strain by transformation with a circular plasmid. A transformant containing a tandem duplication of the C1-C region separated by plasmid DNA was self-fertilized, and trpC- progeny were selected. All of these had lost the introduced plasmid DNA sequences, whereas about half had retained the modified C1-C gene and lost the wild-type copy. Thus, it is possible with A. nidulans to replace chromosomal DNA sequences with DNA fragments that have been cloned and modified in vitro by using either one- or two-step procedures similar to those developed for Saccharomyces cerevisiae.

Aspergillus nidulans↗

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↗

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↗