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S Pimpinelli

Publications and source records attributed to S Pimpinelli.

At least 37 records · Page 2Linked to original sources
PubMed1995

Developmental genetical analysis and molecular cloning of the abnormal oocyte gene of Drosophila melanogaster.

Studies of the abnormal oocyte (abo) gene of Drosophila melanogaster have previously been limited to the analysis of a single mutant allele, abnormal oocyte1 (abo1). The abo1 mutation causes a maternal-effect lethality that can be partially rescued zygotically by the abo+ allele and by increasing the dosage of specific regions of heterochromatin denoted ABO. This report describes the properties of abo2, a new P-element-induced allele that allowed us to reexamine the nature of maternal-effect defect. Comparisons of the phenotype of progeny of abo1/abo1 and abo1/abo2 females show that the preblastoderm lethality previously described as a component of the abo mutant maternal effect results from a recessive fertilization defect associated with the abo1 chromosome. We demonstrate here that the abo-induced maternal effect lethality occurs predominately late in embryogenesis after cuticle deposition but before hatching. The phenocritical period for zygotic rescue by heterochromatin coincides with this period of late embryogenesis. We have used the abo2 mutation to map and molecularly clone the gene. We show that the abo gene is located in the 32C cytogenetic interval and identify the putative abo transcript from mRNA isolated from adult females. Using germline transformation, we show that a 9-kb genomic fragment to which the transcript maps, partially fulfills requirement for maternal and zygotic abo+ function.

Animals↗
PubMed1994

Carnitine suppression of position-effect variegation in Drosophila melanogaster.

Carnitine is a well-known naturally occurring compound, very similar to butyrate, with an essential role in intermediary metabolism mainly at the mitochondrial level. Since butyrate inhibits the enzyme histone deacetylase and is capable of suppressing position-effect variegation in Drosophila melanogaster, we tested a further possible function of carnitine in the nucleus, using an assay for the suppression of position-effect variegation. We tested three physiological forms of carnitine (L-carnitine, L-propionylcarnitine, L-acetylcarnitine) for the ability to suppress two different chromosomal rearrangements, inducing variegation of the white+ and brown+ genes. The results show that the carnitine derivatives are capable of suppressing the position-effect variegation, albeit with different efficiencies. The carnitine derivatives interact lethally with Su-var(2-)1(01), a mutation that induces hyperacetylation of histones, whilst hyperacetylated histones accumulated in both the nuclei of HeLa cells and Drosophila polytene chromosomes treated with the same compounds. These results strongly suggest that the carnitine derivatives suppress position-effect variegation by a mechanism similar to that of butyrate. It is suggested that carnitines may have a functional role in the nucleus, probably at the chromatin level.

Alleles↗
PubMed1994

Interaction systems between heterochromatin and euchromatin in Drosophila melanogaster.

The constitutive heterochromatin is still one of the major unsolved problems in genetics. In Drosophila melanogaster three genetic systems involving specific interactions between heterochromatic and euchromatic genetic elements are known: the Segregation Distortion, the crystal-Stellate and the abo-ABO systems. The genetic and molecular analysis of each system will allow the identification of all the components and the elucidation of the mechanisms underlying their interactions. The results of this analysis should provide insights into the biological significance of heterochromatin and into the evolutionary forces that result in the maintainance and stability of this enigmatic genetic material.

Animals↗
PubMed1994

The genetic activity of 6-N-hydroxylaminopurine in Aspergillus nidulans.

The activity of a base analog (6-N-hydroxylaminopurine, HAP) has been tested on Aspergillus nidulans. In germinating haploid conidia HAP is a strong mutagen, while it does not have any activity in resting conidia. Moreover, HAP does not increase the frequency of recombination in germinating conidia. The mutagenic activity of this base analog has also been tested in diploid conidia of A. nidulans; in fact, it has been shown (Pavlov et al., 1991) that the HAP-induced frequency of heteroallelic recessive mutations in diploid cells of the yeast S. cerevisiae is higher than expected. In A. nidulans, we did not observe any increase in the frequency of recessive homozygous fpaA/fpaA (p-fluorophenylalanine-resistant) mutants over the expected one, which has been calculated on the basis of the observed mutation frequency in the haploid strain.

Adenine↗
PubMed1994

Looking at Drosophila mitotic chromosomes.

The repertoire of cytological procedures described in the present paper permits full analysis of brain neuroblast chromosomes. Moreover, if brains are cultured for 13 hr in the presence of 5-bromo-2'-deoxy-uridine, our fixation and Hoechst staining protocols allow visualization of sister chromatid differentiation and the scoring of sister chromatid exchanges (Gatti et al., 1979). Finally, we note that our cytological procedures can be successfully employed for preparation and staining of gonial cells of both sexes and male meiotic chromosomes (Ripoll et al., 1985; our unpublished results). Good chromosome preparations of female meiosis are obtained with the procedure described by Davring and Sunner (1977, 1979), Nokkala and Puro (1976), and Puro and Nokkala (1977). In this chapter, we have focused on the organization and behavior of Drosophila mitotic chromosomes, describing a repertoire of cytological techniques for neuroblast chromosome preparations. We have not considered the numerous excellent cytological procedures for embryonic chromosome preparations (for an example, see Foe and Alberts, 1985; Foe, 1989), because these chromosomes are usually less clearly defined than those of larval neuroblasts. In addition, we have not included the whole-mount and squashing techniques that allow chromosome visualization and spindle immunostaining of neuroblast cells (Axton et al., 1990; Gonzalez et al., 1990), male meiotic cells (Casal et al.. 1990; Cenci et al., 1994), and female meiotic cells (Theurkauf and Hawley. 1992), because the fixation methods used in these procedures alter chromosome morphology. Fixation methods for antibody staining result in poorly defined chromosomes, whereas the methanol/acetic acid fixation techniques, such as those described here, preserve very well chromosome morphology but remove a substantial fraction of chromosomal proteins. Thus, one of the major technical breakthroughs in Drosophila mitotic cytology will be the development of fixation procedures that maximize chromosomal quality with minimal removal of proteins. This will be particularly useful for precise immunolocalization of heterochromatic proteins, including those associated with the centromere.

Animals↗
PubMed1994

Chromosome damage and early developmental arrest caused by the Rex element of Drosophila melanogaster.

Rex (Ribosomal exchange) is a genetically identified repeated element within the ribosomal DNA (rDNA) of Drosophila melanogaster. Rex has a semidominant maternal effect that promotes exchange between and within rDNA arrays in the first few embryonic mitoses. Several of Rex's genetic properties suggest that its primary effect is rDNA-specific chromosome breakage that is resolved by recombination. We report here that rDNA crossovers are only a small, surviving minority of Rex-induced events. Cytology of embryos produced by Rex-homozygous females reveals obvious chromosome damage in at least a quarter of the embryos within the first three mitotic divisions. More than half of the embryos produced by Rex females die, and the developmental arrest is among the earliest reported for any maternal-effect lethal. The striking lethal phenotype suggests that embryos with early chromosome damage could be particularly fruitful subjects for analysis of the cell biology of early embryos.

Animals↗
PubMed1994

Genetic analysis of Stellate elements of Drosophila melanogaster.

Repeated elements are remarkably important for male meiosis and spermiogenesis in Drosophila melanogaster. Pairing of the X and Y chromosomes is mediated by the ribosomal RNA genes of the Y chromosome and X chromosome heterochromatin, spermiogenesis depends on the fertility factors of the Y chromosome. Intriguingly, a peculiar genetic system of interaction between the Y-linked crystal locus and the X-linked Stellate elements seem to be also involved in male meiosis and spermiogenesis. Deletion of the crystal element of the Y, via an interaction with the Stellate elements of the X, causes meiotic abnormalities, gamete-genotype dependent failure of sperm development (meiotic drive), and deposition of protein crystals in spermatocytes. The current hypothesis is that the meiotic abnormalities observed in cry- males is due to an induced overexpression of the normally repressed Ste elements. An implication of this hypothesis is that the strength of the abnormalities would depend on the amount of the Ste copies. To test this point we have genetically and cytologically examined the relationship of Ste copy number and organization to meiotic behavior in cry- males. We found that heterochromatic as well as euchromatic Ste repeats are functional and that the abnormality in chromosome condensation and the frequency of nondisjunction are related to Ste copy number. Moreover, we found that meiosis is disrupted after synapsis and that cry-induced meiotic drive is probably not mediated by Ste.

Animals↗
PubMed1993

The occurrence, role and evolution of chromatin diminution in nematodes.

Chromatin diminution takes place in presomatic cells of some parasitic nematodes during early development. This phenomenon may play an important role in somatic cell differentiation, since the somatic cells of these species undergo an extensive genome reorganization during development via chromatin diminution and polyploidization, as explained here by Clara Goday and Sergio Pimpinelli.

Journal Article↗
PubMed1993

Delays in anaphase initiation occur in individual nuclei of the syncytial Drosophila embryo.

The syncytial divisions of the Drosophila melanogaster embryo lack some of the well established cell-cycle checkpoints. It has been suggested that without these checkpoints the divisions would display a reduced fidelity. To test this idea, we examined division error frequencies in individuals bearing an abnormally long and rearranged second chromosome, designated C(2)EN. Relative to a normal chromosome, this chromosome imposes additional structural demands on the mitotic apparatus in both the early syncytial embryonic divisions and the later somatic divisions. We demonstrate that the C(2)EN chromosome does not increase the error frequency of the late larva neuroblast divisions. However, in the syncytial embryonic nuclear divisions, the C(2)EN chromosome produces a 10-fold increase in division errors relative to embryos with a normal karyotype. During late anaphase of the neuroblast divisions, the sister C(2)EN chromosomes cleanly separate from one another. In contrast, during late anaphase of the syncytial divisions in C(2)EN-bearing nuclei, large amounts of chromatin often lag on the metaphase plate. Live analysis of C(2)EN-bearing embryos demonstrates that individual nuclei in the syncytial population of dividing nuclei often delay in their initiation of anaphase. These delays frequently lead to division errors. Eventually the products of the nuclei delayed in anaphase sink inward and are removed from the dividing population of syncytial nuclei. These results suggest that the Drosophila embryo may be equipped with mechanisms that monitor the fidelity of the syncytial nuclear divisions. Unlike checkpoints that rely on cell cycle delays to identify and correct division errors, these embryonic mechanisms rely on cell cycle delays to identify and discard the products of division errors.

Anaphase↗
PubMed1993

Bari-1, a new transposon-like family in Drosophila melanogaster with a unique heterochromatic organization.

We have identified a new middle repetitive DNA family in Drosophila melanogaster. This family is composed of a 1.7-kb element, called Bari-1, that shows common characteristics with many transposable elements. Bari-1 is present in a few euchromatic sites that vary in different stocks. However, it is peculiar in that most copies are homogeneously clustered with a unique location in a specific heterochromatic region close to the centromere of the second chromosome. The molecular analysis of different copies coming from the euchromatin and the heterochromatin has revealed that, independent of their location, all possess the same open reading frame. The putative protein encoded by Bari-1 shares similarity with the transposase of the Tc1 transposon of Caenorhabditis elegans. We compare the Bari-1 organization with other mobile DNA families and discuss the possibility of some functional role for the heterochromatic cluster.

Amino Acid Sequence↗
PubMed1992

Kinetochores and chromatin diminution in early embryos of Parascaris univalens.

In Parascaris the mitotic chromosomes of gonial germline cells are holocentric and possess a continuous kinetochore along their entire length. By contrast, in meiotic cells, the centromeric activity is restricted to the heterochromatic tips where direct insertion of spindle microtubules into chromatin without any kinetochore plate is seen. In the presomatic cells of early embryos, which undergo heterochromatin elimination, only euchromatin shows kinetic activity. After developing a technique to separate the very resistant egg shell from the embryos, we studied the cell divisions during early embryogenesis by immunochemical and EM approaches. The results reported here show that in presomatic cells microtubules bind only the euchromatin where a continuous kinetochore plate is present. We also report observations suggesting that the binding of the long kinetochores to the mitotic spindle initiates to a limited number of sites and extends along the entire length, during chromosome condensation. The existence of different centromere stages in different cell types, rends Parascaris chromosomes a very good model to study centromere organization.

Animals↗
PubMed1991

Rescue from the abnormal oocyte maternal-effect lethality by ABO heterochromatin in Drosophila melanogaster.

The euchromatic maternal-effect mutation abnormal oocyte (abo), of Drosophila melanogaster interacts with regions of heterochromatin known as ABO, which reside on the X, Y and second chromosomes. Here, we show that survival of progeny from abo females depends in part upon the maternal dosage of ABO heterochromatin. A comparison was made of the recovery of genotypically identical progeny from abo mothers bearing sex chromosomes of various ABO contents. The results show that the recovery of daughters was decreased if mothers were ABO-/ABO-. However, no decrease was observed if mothers were ABO+/ABO-. In addition, the survival of daughters was greater when they received an ABO-X chromosome from an ABO-/ABO+ mother rather than the father. We suggest that these results reflect a complementation or interaction between the ABO-deficient X and the ABO heterochromatin in the maternal genome. This proposed interaction could occur early in oogenesis in the mother or prior to completion of meiosis I in the fertilized egg. To determine if zygotic dosage of ABO heterochromatin might also be important at very early stages of embryogenesis, we examined the timing of zygotic rescue by paternally donated ABO heterochromatin using a second mutation, paternal loss (pal). Homozygous pal males produce progeny which lose paternally derived chromosomes during the early zygotic divisions. Zygotes that have lost a paternal sex chromosome in a fraction of their nuclei will be mosaic for the amount of ABO heterochromatin. By monitoring the recovery of pal-induced mosaics from abo and abo+ females, we could determine the temporal and spatial requirements for ABO function. Results show that the survival of progeny from the abo maternal-effect lethality was increased if ABO heterochromatin was present prior to the pal-induced loss event. Analysis of mosaic patterns did not reveal a specific lethal focus. We conclude from these results that ABO heterochromatin serves its vital function prior to completion of the early cleavage divisions in progeny of abo mothers.

Animals↗
PubMed1989

Centromere organization in meiotic chromosomes of Parascaris univalens.

The chromosomes of Parascaris univalens possess a continuous centromeric structure spanning their entire length in gonial cells. A cytological and ultrastructural analysis of P. univalens meiotic chromosomes was performed. The results show that during meiosis the holocentric germline chromosomes of male P. univalens undergo restriction of kinetic activity to the heterochromatic terminal regions. These regions lack kinetochore structures and interact directly with spindle microtubules.

Animals↗
PubMed1989

Unusual kinetochores and chromatin diminution in Parascaris.

The first description of the cytogenetics of the horse parasitic nematode Ascaris megalocephala (Parascaris equorum) represented an important step in the history of genetics. The chromosomes of this organism possess a particular centromeric organization and undergo a process known as chromatin diminution in all presomatic cells during early development. Both these unusual features make Parascaris a good model to study general aspects of chromosome biology.

Animals↗
PubMed1989

Cytogenetic analysis of segregation distortion in Drosophila melanogaster: the cytological organization of the Responder (Rsp) locus.

The segregation distortion phenomenon occurs in Drosophila melanogaster males carrying an SD second chromosome and an SD+ homolog. In such males the SD chromosome is transmitted to the progeny more frequently than the expected 50% because of an abnormal differentiation of the SD+-bearing sperms. Three major loci are involved in this phenomenon: SD and Rsp, associated with the SD and SD+ chromosome, respectively, and E(SD). In the present work we performed a cytogenetic analysis of the Rsp locus which was known to map to the centromeric heterochromatin of the second chromosome. Hoechst- and N-banding techniques were used to characterize chromosomes carrying Responder insensitive (Rspi), Responder sensitive (Rsps) and Responder supersensitive (Rspss) alleles. Our results locate the Rsp locus to the h39 region of 2R heterochromatin. This region is a Hoechst-bright, N-banding negative heterochromatic block adjacent to the centromere. Quantitative variations of the h39 region were observed. The degree of sensitivity to Sd was found to be directly correlated with the physical size of that region, demonstrating that the Rsp locus is composed of repeated DNA.

Alleles↗
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↗
PubMed1986

The genetic factors altered in homozygous abo stocks of Drosophila melanogaster.

Females homozygous for the maternal-effect mutation abo (2-44.0) produce a large fraction of eggs which arrest during embryogenesis. Increasing doses of defined heterochromatic regions inherited by offspring of abo mothers from their fathers function zygotically to bring about a partial rescue of the abo-induced embryonic lethality. Another property of the abo mutation is that the severity of the maternal effect decreases when an abo stock is maintained in homozygous condition for a number of generations. Here, we show that the factors which change in homozygous abo stocks to result in the decrease in maternally induced embryonic lethality, act zygotically, dominantly and additively. More importantly, we show that the X and second chromosomes, but not the Y and third chromosomes, derived from homozygous abo stocks are, when inherited from males, more effective in promoting zygotic rescue of the abo-induced lethality than are the equivalent chromosomes derived from an abo stock maintained in heterozygous condition. The chromosomal locations of the factors maintained in the homozygous condition. The chromosomal locations of the factors altered in homozygous stock, as well as their behavior, strongly suggest that the same heterochromatic elements that are responsible for rescuing embryos from the abo-induced maternal effect are altered in homozygous abo flies in such a way that the maternal effect itself is less severe.

Animals↗