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PubMed2026

Costello Syndrome Associated With Somatic Mosaicism of Rare p.Gly13Asp HRAS Variant: Expanding the Phenotypic Spectrum.

BACKGROUND: Costello syndrome (CS) is a rare RASopathy, mostly caused by de novo heterozygous pathogenic variants in the HRAS gene. Over 80% of cases involve the germline p.Gly12Ser variant, resulting in a fairly uniform phenotype of neuro-cardio-facio-cutaneous involvement with an increased risk of malignancy. Consequences of other rare HRAS variants are less well understood due to the limited number of reported cases. METHODS: An adult, young woman was referred due to sparse, slow-growing scalp hair, Blaschko-linear hyperpigmentation, acanthosis nigricans, palmoplantar hyperkeratosis, and joint hyperlaxity. Molecular, imaging, and detailed laboratory studies were performed. RESULTS: Although initial clinical exome- and whole-exome sequencing (WES) were inconclusive, indicating possible mosaicism, subsequent WES from hair-derived DNA samples revealed somatic mosaicism for the rare HRAS p.Gly13Asp variant. Brain MRIs showed a cerebral cavernoma, while cardiological evaluation, urinalysis, abdominal, and pelvic ultrasound were unremarkable. Nevertheless, she remains under close follow-up. CONCLUSION: Among the ten reported individuals carrying the p.Gly13Asp variant, our patient is only the second with confirmed mosaicism and the fifth mosaic CS case described to date. This case expands the phenotypic spectrum of CS and highlights the need for multi-tissue analysis in attenuated or atypical presentations to ensure a correct diagnosis, oncological risk assessment, and informed genetic and reproductive counseling.

Humans↗
PubMed1994

Mating in the heterothallic haploid yeast Clavispora opuntiae, with special reference to mating type imbalances in local populations.

Mating was studied in the haploid, heterothallic yeast Clavispora opuntiae to assess the importance of nutritional, genetic, and other factors that may favour mating and recombination. Local populations of this yeast generally exhibit dramatic inequalities in mating type distributions, suggesting that mating is rare in nature even though most isolates mate freely in the laboratory. The absence of assimilable nitrogen is prerequisite to mating competence, presumably by causing G1 arrest. Maximum mating competence is found in cells entering stationary phase in nitrogen-limited media. Unlike the vast majority of mating yeasts, C. opuntiae does not appear to produce diffusible mating factors (sex pheromones), and mating-competent cells do not undergo sexual agglutination. Pairwise cell contact appears to be the only signal that triggers the sexual process in this case. In order to determine if mating type imbalances in nature are caused by reduced fertility of 'consanguine' crosses, meiotic recombination was measured in pairs of strains that varied in their genetic distances as indicated by restriction mapping. That hypothesis was rejected, as recombination efficiency decreased with increasing genetic distance. We conclude that the rarity of mating in local populations is exacerbated by the stringent physical (pairwise cell contact) and nutritional (nitrogen depletion) conditions that will allow mating to proceed. Parallels are drawn with mating patterns observed in Clavispora lusitaniae.

Crosses, Genetic↗
PubMed1997

A mutational analysis of conjugation in Tetrahymena thermophila. 1. Phenotypes affecting early development: meiosis to nuclear selection.

Conjugation in the freshwater ciliate Tetrahymena thermophila involves a developmental program that models meiosis, fertilization, and early developmental events characteristic of multicellular eukaryotes. We describe a gallery of five early-acting conjugation mutations. These mutants, cnj1-5, exhibit phenotypes in which specific steps in the conjugal pathway have been altered or eliminated. Specifically, cnj1 and cnj2 fail to condense their micronuclear chromatin prior to each of the three prezygotic nuclear divisions. This results in nuclear division failure, failure to replicate DNA, and failure to initiate postzygotic development. The cnj3 mutant appears to exhibit a defect in chromosome separation during anaphase of mitosis. cnj4 mutants successfully carry out meiosis I, yet are unable to execute the second meiotic division and abort all further development. cnj5 mutants are unable to initiate either meiosis I or meiosis II, yet proceed to execute all subsequent developmental events. These mutant phenotypes are used to draw inferences regarding developmental dependencies that exist within the conjugation program.

Animals↗
PubMed1997

A mutational analysis of conjugation in Tetrahymena thermophila. 2. Phenotypes affecting middle and late development: third prezygotic nuclear division, pronuclear exchange, pronuclear fusion, and postzygotic development.

Conjugation following pair formation in Tetrahymena can be divided into three distinct sequences of events: prezygotic development, postzygotic development, and exconjugant development. The decision to proceed with postzygotic development is governed by a developmental checkpoint occurring sometime during the middle stages of conjugation. A second developmental decision is made to initiate pair separation and exconjugant development. This paper examines the phenotypes of five newly isolated conjugation mutants (cnj6-cnj10) which affect middle and late events within the conjugation program. cnj6 mutants exhibit normal nuclear behavior throughout development up to and including differentiation of new macronuclear anlagen. Pairs arrest at this developmental endpoint, unable to dissociate. cnj7 and cnj8 eliminate the third prezygotic nuclear division and the first postzygotic nuclear division. All subsequent developmental events appear normal. cnj9 eliminates the second postzygotic nuclear division, and subsequently, new macronuclei fail to develop despite parental macronuclear degradation. cnj10 results in a pleiotropic phenotype characterized by failure of numerous events which all appear to involve nuclear-cytoskeletal interactions. These defects include nuclear selection (anchoring nuclei to the exchange junction), pronuclear exchange, pronuclear fusion, and anchoring postzygotic nuclear division products to the posterior cell cortex. These mutant phenotypes are used to draw inferences regarding developmental dependencies that govern a cell's entry into the postzygotic and exconjugant developmental programs.

Animals↗
PubMed2001

Analysis of mating-type genes in the chestnut blight fungus, Cryphonectria parasitica.

In nature, the chestnut blight fungus, Cryphonectria parasitica, has a mixed mating system; i.e., individuals in the same population have the ability to self and outcross. In the laboratory, C. parasitica appears to have a bipolar self-incompatibility system, typical of heterothallic ascomycetes; selfing is rare, although demonstrable. In this report we describe the cloning and sequencing of both mating-type idiomorphs and their flanking regions at the MAT locus in C. parasitica. The two idiomorphs, MAT1-1 and MAT1-2, are structurally similar to those of other pyrenomycetes described to date. MAT1-1 encodes three genes (MAT1-1-1, MAT1-1-2, and MAT1-1-3) and MAT1-2 encodes a single gene (MAT1-2-1). Unlike MAT idiomorphs in some ascomycetes, the sequences at both ends of the idiomorphs in C. parasitica show a relatively gradual, rather than abrupt, transition from identity in the flanking regions to almost complete dissimilarity in the coding regions. The flanking regions have repetitive polypyrimidine (T/C) and polypurine (A/G) tracts; the significance of these repetitive tracts is unknown. Although we found repetitive tracts in the flanks and gradual transition zones at the ends of the idiomorphs, we found no special features that would explain how selfing occurs in an otherwise self-incompatible fungus.

Alleles↗
PubMed1995

Origin of sex for error repair. I. Sex, diploidy, and haploidy.

Genetic damage is a fundamental problem for living systems. Recombination can repair a damaged gene, so long as there is an undamaged copy of the gene available in the cell. This requires that the cell be diploid for the damaged locus. During sex, outcrossing generates the diploid state by temporarily fusing two haploid cells (as in the case of meiosis) or by bringing DNA into the cell from outside (as in the case of bacterial transformation). But why should cells alternate between the haploid and diploid states in the first place? Why not just remain diploid, if damage repair is the only problem for a cell? The goal of our work is to understand if the problem of genetic damage would select for diploidy or for the alternation between diploid and haploid states--that is, sex--early in the history of life. Using mathematical models we study competition between asexual haploids (termed "haploids"), sexuals (termed "sexuals"), and asexual diploids (termed "diploids"). Haploid cells are efficient replicators, while diploid cells are resistant to damage. A sexual may combine the advantages of both: spending much of its life cycle in the haploid state, then temporarily fusing to become diploid, followed by splitting to the haploid state. During the diploid state DNA damage can be repaired, since there are two copies of the gene in the cell and one copy is presumed to be undamaged. We describe the competition in terms of mathematical models, employing five rate parameters which represent the life processes of cells most probably active at the time that sexuality arose: birth and death; genomic damage (for the haploids alone); and, for the sexual cell, fusion and splitting. Parameter space bifurcation diagrams for the equilibria are drawn in the three-dimensional space of damage, splitting, and fusion, and solutions of the equations (i.e., the outcomes of the competition) are described in terms of them. It turns out that those three parameters suffice to give an essentially complete description of the qualitative behavior possible, since one parameter can be scaled out of the equations we ultimately consider, and the other permits generic analysis, for the range of parameter values of interest, at a fixed value of that parameter. Each type of cell has a region of the parameter space that it occupies exclusively (given its initial presence in the competition). The haploid can win only in environments characterized by low damage (relative to mortality), while the diploid can win only in environments characterized by high damage (relative to mortality).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Production of fertile transgenic maize by electroporation of suspension culture cells.

Fertile, transgenic maize plants were generated by electroporation of suspension culture cells that were treated with a pectin-degrading enzyme. Electroporation of cells from two different suspension cultures, one derived from A188 X B73 and one derived from a B73-related inbred, with a plasmid containing the bar gene, resulted in high-frequency recovery of stably transformed callus lines. Plants were regenerated from thirteen transformed callus lines and transmission of bar to progeny was demonstrated.

Blotting, Southern↗
PubMed1992

The role of the transposable element hobo in the origin of endemic inversions in wild populations of Drosophila melanogaster.

Evidence from in situ hybridizations of DNA from the transposable element hobo to polytene salivary gland chromosome squashes reveals that hobo occupies both cytological breakpoints of three of four endemic inversions sampled from natural populations of Drosophila melanogaster in the Hawaiian islands. The fourth endemic inversion has a single hobo insert at one breakpoint. Cosmopolitan inversions on the same chromosomes do not show this association. Frequencies of both endemic and cosmopolitan inversions in Hawaiian populations fall in ranges typical for natural populations of D. melanogaster sampled worldwide, suggesting that these results may be typical of other regions besides Hawaii. This appears to be the first direct demonstration that transposable elements are responsible for causing specific rearrangements found in nature; consequently, it is also the first direct demonstration that chromosome rearrangements can arise in nature in a manner predicted by results of hybrid dysgenic crosses in the laboratory. Possible population genetic and evolutionary consequences are discussed.

Animals↗
PubMed1996

On the modification of recombination with sex-dependent fitnesses and linkage.

According to the Reduction Principle, when a recombination-reducing allele is introduced near an equilibrium that depends on recombination, that allele will increase in frequency. If the allele increases the recombination rate, it will be expelled from the population. There are known cases where this principle fails. In this respect, an interesting question is what kind of two-sex viability regimes support a general Reduction Principle. In this paper, we construct a model of viabilities, due to two autosomal linked genes, which differ between the sexes, such that recombination is different in the sexes. A complete analysis is provided for the case where recombination is absent in one sex. It is proved that the Reduction Principle is still valid for recombination in the other sex.

Alleles↗
PubMed1994

Norms of reaction and diversifying selection.

The numbers of progeny produced by comparable numbers of female Drosophila melanogaster of 26 geographic strains on nine different culture media are examined in the context of norms of reaction. Having emphasized that diversifying selection is seldom discussed simultaneously with its seemingly related topic, norms of reaction, I present the following argument: diversifying selection has generally been viewed as involving sub-populations inhabiting separate localities and subject to different patterns of selection, norms of reaction as variation whose weighted average determines the relative fitnesses of different genotypes within individual sub-populations. Should environmental challenges frequently involve life or death (including sterility) outcomes, norms of reaction involving components of fitness engender diversifying selection within local populations (demes).

Animals↗
PubMed1995

RAD58 (XRS4)--a new gene in the RAD52 epistasis group.

The RAD58 (XRS4) gene of Saccharomyces cerevisiae has been previously identified as a DNA repair gene. In this communication, we show that RAD58 also encodes an essential meiotic function. The spore inviability of rad58 strains is not rescued by a spo13 mutation. The rad50 mutation suppresses spore inviability of a spo13 rad58 strain suggesting that RAD58 acts after RAD50 in meiotic recombination. The rad58-4 mutation does not prevent mitotic recombination events. Haploid rad58 cells fail to carry out G2-repair of gamma-induced lesions, whereas rad58/rad58 diploids are able to perform some diploid-specific repair of these lesions.

DNA Damage↗
PubMed1991

Chimeric mitochondrial genes expressed in the C male-sterile cytoplasm of maize.

Aberrant recombinations involving the mitochondrial atp9, atp6 and coxII genes have created unique chimeric sequences in the C male-sterile cytoplasm (cms-C) of maize. An apparent consequence of the rearrangements is the interchanging of transcriptional and/or translational regulatory signals for these genes, and alterations in the reading frames encoding the atp6 and coxII genes in the C cytoplasm. Particularly unusual is the organization of the atp6 gene in cms-C mitochondria, designated atp6-C. The atp6-C sequence is a triple gene fusion product comprised of DNAs derived from atp9, atp6 and an open reading frame of unknown origin. Although there is no direct evidence indicating that these chimeric genes are responsible for the cytoplasmic male sterility (cms) trait, their novel arrangements and the strong correlation between these genes and the C type of male sterility suggest such a role.

Adenosine Triphosphatases↗
PubMed1990

Courtship behavior and control of reproductive isolation in Drosophila mojavensis: genetic analysis of population hybrids.

Drosophila mojavensis from the Sonora region and Baja California show asymmetrical sexual isolation in the laboratory: males from Sonora mate equally frequently with Sonora and Baja females, while the mating success of Baja males with Sonora females is reduced. This failure has been localized to three separate behavioral landmarks occurring during courtship. Genetic analysis was conducted using reciprocal F1 hybrids of Sonora and Baja strains to examine inheritance patterns of the responsible courtship behaviors. Mating success and propensity of F1 males were similar to Sonora males. F1 females mated with males of Sonora and Baja races equally, although mating propensity of F1 females was intermediate between that of Sonora and Baja females. Males of Baja strains presented with F1 females showed a relatively high level of failure at attempted intromission. Genes for mating behaviors are located in the autosomes, but different loci responsible for the sexual isolation appear to act in males and females.

Animals↗