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P Ripoll

Publications and source records attributed to P Ripoll.

At least 19 recordsLinked to original sources
PubMed2000

A dicentric chromosome of Drosophila melanogaster showing alternate centromere inactivation.

Dicentric chromosomes are rarely found, because they interfere with normal cell division causing chromosome instability. By in situ hybridization of region-specific heterochromatic yeast artificial chromosomes we have found that the artificially generated C(1)A chromosome of Drosophila melanogaster has two potential centromeres: one carries all the sequences of the centromere of the Y chromosome and the other carries only a part of the Y centromeric region that is rich in telomere-related sequences. Immunostaining with anti-Bub1 (a kinetochore-specific marker) shows that, in spite of the differences in sequence, both centromeres can be active although as a rule only one at a time. In a small fraction of the chromosomes centromere inactivation is incomplete, giving rise to true dicentric chromosomes. The centromere inactivation is clonally inherited, providing a new example of epigenetic chromosome imprinting and the possibility of genetically dissecting this process. The involvement of telomere-related sequences in centromere function is discussed.

Animals↗
PubMed2000

Pericentromeric regions containing 1.688 satellite DNA sequences show anti-kinetochore antibody staining in prometaphase chromosomes of Drosophila melanogaster.

A striking characteristic of the centromeric heterochromatin of Drosophila melanogaster is that each chromosome carries different satellite DNA sequences. Here we show that while the major component of the 1.688 satellite DNA family expands across the centromere of the X chromosome the rest of the minor variants are located at pericentromeric positions in the large autosomes. Immunostaining of prometaphase chromosomes with the kinetocore-specific anti-BUB1 antibody reveals the transient presence of this centromeric protein in all the regions containing the 1.688 satellite.

Animals↗
PubMed1999

Centromeres from telomeres? The centromeric region of the Y chromosome of Drosophila melanogaster contains a tandem array of telomeric HeT-A- and TART-related sequences.

Cytological and cytogenetic studies have previously defined the region needed for centromeric function in the Y chromosome of Drosophila melanogaster. We have identified a YAC clone that originated from this region. Molecular analysis of the YAC and genomic DNAs has allowed the description of a satellite DNA made of telomeric HeT-A- and TART-derived sequences and the construction of a long-range physical map of the heterochromatic region h18. Sequences within the YAC clone are conserved in the centromeric region of the sibling species Drosophila simulans. That telomere-derived DNA now forms part of the centromeric region of the Y chromosome could indicate a telomeric origin of this centromere. The existence of common determinants for the function of both centromeres and telomeres is discussed.

Animals↗
PubMed1997

A chromatin-associated kinesin-related protein required for normal mitotic chromosome segregation in Drosophila.

The tiovivo (tio) gene of Drosophila encodes a kinesin-related protein, KLP38B, that colocalizes with condensed chromatin during cell division. Wild-type function of the tio gene product KLP38B is required for normal chromosome segregation during mitosis. Mitotic cells in tio larval brains displayed circular mitotic figures, increased ploidy, and abnormal anaphase figures. KLP38B mRNA is maternally provided and expressed in cells about to undergo division. We propose that KLP38B, perhaps redundantly with other chromosome-associated microtubule motor proteins, contributes to interactions between chromosome arms and microtubules important for establishing bipolar attachment of chromosomes and assembly of stable bipolar spindles.

Amino Acid Sequence↗
PubMed1991

The spindle is required for the process of sister chromatid separation in Drosophila neuroblasts.

We have studied two aspects of the process of sister chromatid separation in the Drosophila melanogaster neuroblasts. First, we analyzed the requirement of a functional spindle for sister chromatid separation to take place using microtubule depolymerizing drugs such as colchicine or a reversible analogue (MTC). Incubation of this tissue in colchicine causes the cells to block irreversibly at metaphase and no significant levels of sister chromatid separation were observed even after long periods of incubation. Exposure of neuroblasts to MTC also causes cells to block at metaphase, but after reversion most of the cells enter anaphase and are thus able to complete sister chromatid separation. These results imply that a functional spindle is required for sister chromatid separation. Second, we studied the role of heterochromatin during chromatid pairing and subsequent separation in chromosomes which carry either one or two extra pieces of heterochromatin. The results indicate that sister chromatids establish strong pairing along the translocated heterochromatin. During the early stages of anaphase, these chromosomes separate first the centromeric region and later the regions bearing extra heterochromatin. These results indicate that constitutive heterochromatin plays an important role for sister chromatid pairing and might be involved in the process of separation.

Animals↗
PubMed1991

Dosage dependence of maternal contribution to somatic cell division in Drosophila melanogaster.

Most mitotic mutants in Drosophila do not lead to lethality in early development despite the highly abnormal chromosome behaviour that they elicit. This has been explained as being the effect of maternally provided wild-type products. We have tested this hypothesis by studying cuticular clones derived from cells in which there has been loss of a marked Y chromosome due to chromosome nondisjunction in individuals homozygous for the mutation abnormal spindle who are progeny of heterozygous mothers. We have found that the size and frequency of these clones are higher than in control flies. Furthermore, by analysing flies whose female parents have different doses of the asp+ gene, we have found that there is a correlation between the amount of maternally contributed asp+ product and the frequency and size of cuticular clones. We have also estimated the time in development when the first mitotic mistakes take place, i.e. the time when maternal products are no longer sufficient to carry out normal cell division.

Alleles↗
PubMed1990

Abnormal meiotic spindles cause a cascade of defects during spermatogenesis in asp males of Drosophila.

Since spermatogenesis in Drosophila is a series of interconnected and interdependent steps and most of the spermatogenic events take place in the absence of transcription, failures in a given stage can give rise to a cascade of defects later on. The asp locus of Drosophila melanogaster codes for a non-tubulin component implicated in proper spindle structure and/or function (Ripoll et al. 1985). Homozygous asp males exhibit abnormal meiotic spindles giving rise to altered segregation of chromosomes and mitochondria and failures in cytokinesis. Postmeiotic spermatogenic stages of asp males show a series of alterations that we interpret as due to the previously occurring defective meiosis because meiotic spindles are the only microtubular structure altered in mutant testes. The most conspicuous alterations are: (i) variable size of nuclei and nebenkerns of early spermatids, which are also multinucleate instead of having single and uniformly sized nuclei; (ii) elongating spermatids in which abnormal-sized mitochondrial derivatives elongate alongside more than one axoneme; (iii) failures in the individualization process, where abnormal spermatids remain syncytial, and seem to be eliminated during the coiling stage.

Animals↗
PubMed1990

Mutations at the asp locus of Drosophila lead to multiple free centrosomes in syncytial embryos, but restrict centrosome duplication in larval neuroblasts.

Mutations at abnormal spindle result in abnormally long and wavy microtubules in the meiotic spindles of males. Some of these spindles have a single pole and take the form of unopposed hemi-spindles. Unfertilised eggs produced by homozygous asp females may have either no nuclei, or a small number of large nuclei, consistent with there also being an effect upon female meiosis. Such eggs also display free centrosomes and independent arrays of microtubules. Embryos that have this phenotype are also present among the progeny of fertilised homozygous asp females, together with embryos that undergo varying degrees of aberrant morphogenesis, developing a variety of abnormal cuticle patterns. This latter category shows asynchronous mitoses prior to cellularisation, and has abnormal arrays of spindle microtubules. Such embryos can develop large areas that are either devoid of or have a reduced number of nuclei, in which there are centrosomes that have dissociated from the mitotic spindles. Neuroblasts in the brains of homozygous asp larvae display a high mitotic index, and have condensed chromosomes aligned as if blocked at metaphase. Immunostaining reveals that many cells contain a single centrosome connected to the metaphase chromosomes by microtubules in a hemi-spindle-like structure.

Alleles↗
PubMed1990

Spindles and centrosomes during male meiosis in Drosophila melanogaster.

We have studied the spatial distribution of chromosomes, spindle fibers and centrosomes throughout the first meiotic division in males of Drosophila melanogaster. There seem to be two different types of spindle fibers: those which connect the poles to the chromosomes, and others arranged as cup-shaped hemispheres that reach from the poles to an unstained area on the equator of the cell. These pole-equator fibers could be responsible for positioning the nucleus and distributing cytoplasmic organelles around the nucleus during prophase, so that after meiosis, the daughter cells are provided with equal amounts of preorganized cytoplasmic organelles. These fibers remain until after the daughter nuclei have formed during telophase. An antigen associated with the centrosomes of mitotic spindles appears during meiosis as dispersed particles surrounding the nucleus; these particles might provide the developing spermatids with microtubule-organizing centers.

Animals↗
PubMed1989

Relationship between chromosome content and nuclear diameter in early spermatids of Drosophila melanogaster.

We have studied, using light microscopy, the relationship between chromosome content and nuclear diameter in early spermatids of males carrying different combinations of wild-type and compound chromosomes in Drosophila melanogaster. By using these genotypes we have been able to observe spermatid nuclei bearing various numbers of chromosomes ranging from only one sex chromosome and no major autosomes to almost twice the normal chromosome complement. We have found that variations in the chromosome content are accompanied by increasing the variance in early spermatid nuclear diameter; the more gametic classes produced, the higher the variance of nuclear diameters. These results indicate that measuring nuclear diameters in early spermatids represents a useful way to estimate the levels of meiotic non-disjunction and thereby to improve the characterization of lethal or male sterile mutants in which analysis of meiotic chromosome non-disjunction cannot be achieved by conventional genetic methods.

Animals↗
PubMed1989

Gross genetic dissection and interaction of the chromosomal region 95E;96F of Drosophila melanogaster.

Making use of deficiencies, inversions and translocations, we have genetically dissected the region 95E to 96F of Drosophila melanogaster. We localized cytologically the loci abnormal spindle (asp: 3-85.2: 96A20-25;96B1-10) and M(3)96C2 (96C1;96C5). We have also found several new phenotypes associated with lesions in the 95E to 97B region: (1) Minute(3)96A (M(3)96A) is a haplo-insufficient phenotype of thin and short bristles presented by individuals deficient for the region 95E6-8;96A1-5. (2) abdominal-one reduced (aor) shows two different phenotypes associated with the distal breakpoint of In(3R)Ubx7L (89E;96A1-7). One is the increase of the Ubx phenotype, but its effect requires the presence of lesions in Ubx. The other phenotype is a drastic reduction or disappearance of the first abdominal segment. Both phenotypes might be due to lesions in the same gene. (3) metaphase arrest (mar) is associated with the breakpoint of the T(Y;3)B197 (96B1-10) and produces a phenotype typical of mitotic mutants with arrest of the cell cycle during prometaphase or metaphase. There is another region localized in 97B which interacts with asp: in a background homozygous for asp, three doses of this region enhance the asp phenotype.

Animals↗
PubMed1988

Functional monopolar spindles caused by mutation in mgr, a cell division gene of Drosophila melanogaster.

Mutation in the gene merry-go-round (mgr) of Drosophila causes a variety of phenotypic traits in somatic and germinal tissues, such as polyploid cells, metaphasic arrest, postmeiotic cysts with 16 nuclei, and spermatids with four times the normal chromosome content. The most characteristic phenotype is the appearance of mitotic and meiotic figures where all chromosomes are arranged in a circle. Treatment with anti-mitotic drugs and the phenotype of double mutants mgr asp (asp being a mutation altering the spindle) show that these circular figures need a functional spindle for their formation. These abnormal figures are caused by monopolar spindles similar to those observed after different treatments in several organisms. All mutant traits indicate that mgr performs a function necessary for the correct behaviour of centrosomes, thus opening this organelle to genetic analysis.

Animals↗
PubMed1986

Nonrandom segregation of centromeres following mitotic recombination in Drosophila melanogaster.

Mitotic recombination is widely used in Drosophila as a technique to study genetic and developmental problems. It has been generally assumed that, following mitotic exchange between homologous chromatids during the G2 stage, the centromeres attached to the chromatids involved in the exchange segregate randomly. As a result, two equally frequent types of segregation, yielding genetically different products, are produced. However, when epidermal or enzymatic cell-marker mutants are used, only one type of segregation gives rise to marked cells. In the present work we test this assumption of random segregation using cytological markers. With cytological markers, larval neuroblast cells resulting from mitotic recombination exhibit recognizably all possible products from mitotic recombination. We find that one type of segregation is favored, in that, after mitotic recombination, the centromeres attached to the chromatids involved in the mitotic exchange preferentially migrate to opposite poles during anaphase. This favored segregation could be the result of exchange between previously oriented chromatids or could be due to the effect of the exchange upon subsequent orientation of homologous chromosomes. In either case, frequencies of mitotic recombination have been overestimated in the past.

Animals↗
PubMed1985

A cell division mutant of Drosophila with a functionally abnormal spindle.

Normal distribution of chromosomes to daughter cells is insured by the proper functioning of the spindle. Homozygosity for a semi-lethal mutation of Drosophila melanogaster (abnormal spindle) altering this structure has the following effects: the mitotic cycle is arrested in metaphase, leading to a high frequency of polyploid cells; sex chromosome disjunction during male meiosis is severely affected, as revealed by the resulting exceptional (diplo and nullo) gametes (microscopic examination of spermiogenesis confirms this aberrant segregation); meiotic spindles of living cells are morphologically abnormal; and tubulins extracted from mutant larvae are normal in amount, electrophoretic mobility, and ability to form microtubules in vitro. The results suggest that the mutant phenotype is due to an altered structural component of the spindle other than tubulins.

Animals↗
PubMed1981

Spontaneous mitotic recombination and evidence for an X-ray-inducible system for the repair of DNA damage in Drosophila melanogaster.

Spontaneous mitotic recombination in the left and of chromosome 3 was examined in both unirradiated control flies and sibs irradiated early in development by determining the sizes and frequencies of multiple-wing-hair (mwh) clones in the wing blade of heterozygous mwh/+ flies. Approximately 16% of the spontaneous mwh clones arise from events generating cells with normal division rates. The remaining 84% result from events generating cells with an average cell division rate one-third that of the surrounding cells; these are thought to result from events that generate aneuploid cells. Such clones probably arise from a failure correctly to repair spontaneous DNA damage. The frequency of spontaneous events late in development decreases significantly after irradiation as much as 150 hours earlier in development. The suppression of spontaneous events decreases with a longer period of time between irradiation and the final cell divisions in the wing blade. These results suggest the existence of a repair system for DNA damage in Drosophila that is induced by irradiation. The decrease in effect with time following irradiation could result from slow degradation or dilution by subsequent cell growth and division.

Animals↗