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P Portin

Publications and source records attributed to P Portin.

At least 19 recordsLinked to original sources
PubMed2001

Numb suppresses the negative complementation at the Notch locus of Drosophila melanogaster, suggesting a putative mechanism for negative complementation.

The mutant form of the intracellular asymmetrically localized Numb membrane-bound protein of Drosophila melanogaster suppresses the negative complementation of certain Abruptex (Ax) mutations of the Notch (N) locus encoding a transmembrane receptor protein in which the Ax mutations are mutations in the epidermal growth factor (EGF)-like repeats of the extracellular domain of the receptor. One model for how Ax mutants affect N function is that they are refractory to an antagonistic signal generated by an excess of N ligands. Genetically numb (nb) is an antagonist of N. In the absence of nb, cells follow the same fate as they would in the presence of a gain-of-function N allele, such as Ax. Numb has been shown to interact with the cytoplasmic domain of Notch. It is therefore suggested that numb counteracts the effect of Abruptex on Notch ligand binding, i.e. that Numb is an antagonist to the activation of the Notch signal generated by Notch ligands. Numb might accomplish this by interfering with the proteolytic cleavage of the Notch intracellular domain at the cell membrane. Thus, it seems possible that the mechanism of negative complementation of certain Ax mutants is the failure of this cleavage. Other possible mechanisms for negative complementation are also discussed.

Animals↗
PubMed2000

The occurrence of double strand DNA breaks is not the sole condition for meiotic crossing over in Drosophila melanogaster.

Analysis of the interchromosomal effects of In(2L + 2R)Cy, In(3L + 3R)LVM and their joint effect on the frequencies of single and double crossovers in the cv-v-f region of the X chromosome as well as interference showed that both inversions, occurring separately, increased the frequency of single as well as double crossovers and the coefficient of coincidence. However, when the inversions occurred together the frequencies of single crossovers no longer increased, but the frequency of double crossovers, as well as the coefficient of coincidence did increase. These results indicate firstly that the interchromosomal effects influence some precondition of exchange, but that this precondition is not an occurrence of double strand DNA breaks. Thus, the occurrence of double strand DNA breaks is not the sole condition for crossing over in Drosophila melanogaster.

Animals↗
PubMed2000

Occurrence of double strand DNA breaks and pairing of homologous chromosomes are preconditions of crossing over in Drosophila melanogaster, and its timing.

Brood pattern analysis of the effect of a heat shock (35 degrees C 24h) given to the parental females in presence and absence of In (2L + 2R) Cy in heterozygous condition in the second chromosome on recombination and interference in the cv-v-f region of the X chromosome showed the following: (i) In the absence of the inversion recombination frequencies in both gene intervals increased in the daily broods, which represent oocytes in which premeiotic DNA synthesis was occurring during the heat shock treatment. (ii) In the presence of the inversion recombination frequencies did not increase in any of the daily broods. (iii) The frequencies of double crossovers did not increase in any broods either in the presence or in the absence of inversion. (iv) The coefficient of coincidence changed in virtually all broods both in the presence and absence of the inversion, indicating that the heat shock affects the distribution of single crossovers. (v) The results showed that the effect of the heat shock on the coefficient of coincidence was similar during premeiotic DNA synthesis both in the absence and presence of the inversion, but different in the broods representing oocytes which were undergoing the first meiotic division, suggesting that crossing over occurs during this division, probably during pachytene.

Animals↗
PubMed1998

Genetic evidence that Notch affects independently the development of machrochaeta and wing venation in Drosophila melanogaster.

Temperature sensitive experiments on the interaction of Abruptex mutations of the Notch locus and Enhancer of split indicate that the effect of temperature on the development of macrochaeta and wing venation is different. This suggest that Notch affects the development of macrochaeta and wing venation in different and independent ways being in accordance with the proposition that the signal pathway from the Notch receptor at the cell membrane to Enhancer of split complex in the nucleus is different in the case of the development of macrochaeta and wing venation. The Abruptex mutations as gain-of-function mutations of the Notch locus cannot rescue the Enhancer of split phenotype.

Animals↗
PubMed1997

A critical review of genetic studies of schizophrenia. I. Epidemiological and brain studies.

Family, twin and adoption studies suggest that susceptibility to schizophrenia is based at least to some extent on genes. The results of these studies vary and depend greatly on the diagnostic criteria used. When a broad definition of schizophrenia is employed, even high degrees of heritability are observed. However, when more narrow criteria are employed, the degrees of heritability decrease. According to a large Finnish adoption study, the patient-family interaction has an even more important role in the origin of schizophrenia than purely genetic factors. Interaction between the genetic factors on the one hand and physical, psychological and psychosocial factors on the other hand is emphasized.

Adoption↗
PubMed1997

A critical review of genetic studies of schizophrenia. II. Molecular genetic studies.

Recent molecular genetic studies of schizophrenia have, until now, been unable to demonstrate any specific major gene for schizophrenia. On the contrary, linkage and association studies have yielded almost exclusively negative or contradictory results. Such studies have involved certain candidate genes, such as the genes for dopamine receptors and other brain neurotransmitters. Some of these candidate genes have now actually been excluded as specific aetiological factors in schizophrenia. Similarly, studies searching for a major gene for susceptibility to schizophrenia involving the whole human genome or large parts of chromosomes have not yielded unambiguously positive results. However, the most recent empirical evidence suggests that many polygenes, acting together, could constitute a risk factor for schizophrenia. It is thus most probable that genetic susceptibility to schizophrenic psychoses is polygenic, and that their effects are dependent on interaction with physical and psychosocial environmental factors.

Gene Expression↗
PubMed1993

The concept of the gene: short history and present status.

The concept of the gene is and has always been a continuously evolving one. In order to provide a structure for understanding the concept, its history is divided into classical, neoclassical, and modern periods. The classical view prevailed into the 1930s, and conceived the gene as an indivisible unit of genetic transmission, recombination, mutation, and function. The discovery of intragenic recombination in the early 1940s and the establishment of DNA as the physical basis of inheritance led to the neoclassical concept of the gene, which prevailed until the 1970s. In this view the gene (or cistron, as it was called then) was subdivided into its constituent parts, mutons and recons, identified as nucleotides. Each cistron was believed to be responsible for the synthesis of a single mRNA and hence for one polypeptide. This colinearity hypothesis prevailed from 1955 to the 1970s. Starting from the early 1970s, DNA technologies have led to the modern period of gene conceptualization, wherein none of the classical or neoclassical criteria are sufficient to define a gene. Modern discoveries include those of repeated genes, split genes and alternative splicing, assembled genes, overlapping genes, transposable genes, complex promoters, multiple polyadenylation sites, polyprotein genes, editing of the primary transcript, and nested genes. We are currently left with a rather abstract, open, and generalized concept of the gene, even though our comprehension of the structure and organization of the genetic material has greatly increased.

Animals↗
PubMed1992

Partner choice in heterologous chromosome segregation of the Y chromosome in competitive situations in the oocyte of Drosophila melanogaster.

Heterologous segregation of the Y chromosome and secondary non-disjunction of the X chromosomes in female meiosis of Drosophila melanogaster was investigated in ten different crosses where different constellations of translocation/inversion or translocation/translocation systems of the large autosomes were present in the female parent. It appeared that the Y chromosome always segregates from the shortest of the possible heterologous pairing partners. This may be due to size-dependent mechanism of so-called 'distributive disjunction' or to the possibility that the shorter the chromosome element is, the more easily it moves in the nucleus of the oocyte. Secondary non-disjunction of the X chromosomes appeared to be lower the more possible autosomal pairing partners the Y chromosome had, suggesting that the autosomes effectively compete with the X chromosomes for pairing with the Y chromosome. An alternative explanation is that, due to interchromosomal effect on recombination, crossing over in the X chromosomes was different in different experiments.

Animals↗
PubMed1992

A selective method for studying primary sex chromosome non-disjunction in females and males and X-Y exchange in males of Drosophila melanogaster including a demonstration of euchromatic X-Y exchange.

A selective method was developed, based on negative complementation of the Abruptex alleles of the Notch locus, for studying primary sex chromosome non-disjunction in females and males of Drosophila melanogaster and X-Y exchange in males. The results show that the frequency of primary non-disjunction of structurally normal X chromosomes was lower than the frequency of X-derY non-disjunction in males. Double exchange between the X and the derY chromosome in the male occurs with a frequency of at least 0.091%. Single exchanges are naturally expected to occur with even higher frequency. Exchanges were interestingly at least partly of euchromatic nature. The origin of these exchanges is at least partly of gonial origin.

Animals↗
PubMed1991

Effect of extra Y chromosome on number and fluctuating asymmetry of sternopleural bristles in Drosophila melanogaster.

The effect of the extra Y chromosome on the number and fluctuating asymmetry of sternopleural bristles in Drosophila melanogaster was studied at two temperatures, 18 degrees C and 25 degrees C, in the stock In(l)wm4/y+Y. The extra Y chromosome significantly increased the number of sternopleural bristles especially in the lateral areas of the sternopleura, which hampered the analysis of the effect of the extra Y chromosome on fluctuating asymmetry. The formula used was one which assumes that the fluctuating asymmetry is dependent on the total number of bristles. It was found that the extra Y chromosome increased fluctuating asymmetry at 18 degrees C but decreased it at 25 degrees C. There was less fluctuating asymmetry in females than in males. It appears that the extra Y chromosome has an effect on the temperature which is most favourable to the development of the sternopleural bristles.

Aneuploidy↗
PubMed1990

Further studies on the interchromosomal effect on crossing over in Drosophila melanogaster affecting the preconditions of exchange.

The second chromosome inversion In (2L+2R) Cy in a heterozygous condition was studied for its effect on frequency and interference of crossing over in three different regions of the X chromosome of Drosophila melanogaster. A significant increase in crossing over frequency was observed in the proximal and distal regions of the X chromosome while in the middle of the chromosome crossing over frequency remained unaltered. The effect on interference remained unaltered at both ends of the X chromosome while a significant decrease was observed in the middle of the chromosome. These results suggest that the interchromosomal effect on crossing over affects the preconditions of exchange differently in different regions of the X chromosome, and possibly the duration of chromosome pairing.

Animals↗
PubMed1989

Interaction of hairless, delta, enhancer of split and notch genes of Drosophila melanogaster as expressed in adult morphology.

The interaction of three neurogenic loci viz. Delta, Enhancer of split and Notch, and a related gene, Hairless, of Drosophila melanogaster was investigated at the adult morphology level by measuring the effects of the mutations of the three other genes on the expression of the recessive lethal antimorphic Abruptex mutations of the Notch locus. The Abruptex mutations were also coupled in cis or trans with facet-glossy or split mutations of the Notch locus. In some of the experiments, the genotype of the fly was homozygous for either facet-glossy or split mutation or their wild type alleles but heterozygous for the Abruptex. Facet-glossy is located in a large intron of the locus, whereas split is located in the same exon as Abruptex. In all compounds studied, Delta suppressed the expression of Abruptex while Hairless and Enhancer of split enhanced it. The interactions of the four genes studied were allele specific, suggesting an interaction at the protein level. The comparison of the results presented in this study on the interaction of the neurogenic genes with other results on the same subject suggests that the interactions are similar in embryonic and imaginal development.

Alleles↗
PubMed1989

Gene dosage studies of a temperature sensitive Abruptex mutation of the Notch locus of Drosophila melanogaster.

Gene dosage studies of a temperature sensitive Abruptex mutation of the Notch locus of Drosophila melanogaster revealed, firstly, that hemizygous females were lethal at all temperatures studied, while hemizygous males were subvital at 18 degrees C, semilethal at 25 degrees C, and lethal at 29 degrees C. This is due to dosage compensation of the Notch locus. Secondly, it was observed that in general an increasing dose of the wild allele decreased the expression of Abruptex at all temperatures. An exception was the Axtsl/Axtsl/ + genotype, which was more expressed than Axtsl/Axtsl at low temperatures. This suggests antimorphism as the most likely mode of action of the temperature sensitive Abruptex mutation. Thirdly, it was observed that the expression of Abruptex phenotype increased from 18 degrees C to 25 degrees C but decreased from 25 degrees C to 29 degrees C if the wild type allele was involved in the genotype. This suggests that the gene product of the temperature sensitive Abruptex allele loses its function at high temperatures. The putative antimorphic mode of action of the temperature sensitive Abruptex mutation suggests that the Notch gene product interacts with products of other neurogenic loci or with itself.

Animals↗