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An extremely unorthodox method of chromosome segregation is found in sciarid flies (Diptera, Sciaridae), where at male meiosis, the whole paternal complement is eliminated and the maternal X chromosome undergoes non-disjunction. At meiosis I, a monopolar spindle directs the segregation of maternal chromosomes to the single pole, whereas paternal chromosomes are discarded. At meiosis II, although maternal autosomes segregate normally, the X chromosome remains undivided. A cis-acting locus within the heterochromatin proximal to the centromere is known to regulate X centromere activity. By immunofluorescence analysis in spermatocytes from Sciara ocellaris and Sciara coprophila, we investigated histone H3 phosphorylation at Ser10, Ser28, Thr3 and Thr11 during male meiosis. We found that chromosome condensation and H3 phosphorylation patterns differ between chromosomes of different parental origin at the time of paternal set elimination. Importantly, at meiosis II, the maternal X chromosome differs from the rest of the chromosomes in that its centromeric region does not become phosphorylated at the four histone H3 sites. We provide here the first evidence linking the under-phosphorylated H3 status of the X chromosome centromeric region with its meiotic non-disjunction in sciarid flies. Our findings strongly support the idea that the deficiency in local H3 phosphorylation inactivates the X centromere at the transition from meiosis I to meiosis II., This work was supported by grant BFU2008-02947-C02-02/BMC to C.G. and FPI BES-2006-12492 to M.C.E.

11 páginas, 8 figuras -- PAGS nros. 387-397, Sciara coprophila (Diptera, Nematocera) constitutes a classic model to analyze unusual chromosome behavior such as the somatic elimination of paternal X chromosomes, the elimination of the whole paternal, plus non-disjunction of the maternal X chromosome at male meiosis. The molecular organization of the heterochromatin in S. coprophila is mostly unknown except for the ribosomal DNA located in the X chromosome pericentromeric heterochromatin. The characterization of the centromeric regions, thus, is an essential and required step for the establishment of S. coprophila as a model system to study fundamental mechanisms of chromosome segregation. To accomplish such a study, heterochromatic sections of the X chromosome centromeric region from salivary glands polytene chromosomes were microdissected and microcloned. Here, we report the identification and characterization of two tandem repeated DNA sequences from the pericentromeric region of the X chromosome, a pericentromeric RTE element and an AT-rich centromeric satellite. These sequences will be important tools for the cloning of S. coprophila centromeric heterochromatin using libraries of large genomic clones, This work was supported by grants BFU2008-02947-C02-02/BMC to C.G. and BFU2008-02947-C02-01/BMC to A.V. from the Ministerio de Ciencia e Innovación, an institutional grant from the Fundación Ramón Areces to the Centro de Biología Molecular “Severo Ochoa” and a grant supporting the Cambridge Resource Centre from the Wellcome Trust to M.A.FS; M.C.Escribá was supported by the FPI fellowship BES-2006-12492 from the Ministerio de Ciencia e Innovación

We report here the molecular and cytological characterization of two proteins, ScoHET1 and ScoHET2 (for Sciara coprophila heterochromatin), which associate to constitutive heterochromatin in the dipteran S. coprophila. Both proteins, ScoHET1 of 37 kDa and ScoHET2 of 44 kDa, display two chromodomain motifs that contain the conserved residues essential for the recognition of methylated histone H3 at lysine 9. We raised antibodies to analyze the chromosomal location of ScoHET1 and ScoHET2 in somatic and germline cells. In S. coprophila polytene chromosomes, both proteins associate to the pericentromeric regions and to the heterochromatic subterminal bands of the chromosomes. In germinal nuclei, ScoHET1 and ScoHET2 proteins distribute to the heterochromatic regions of the regular chromosome complement and are abundantly present along the heterochromatic germline-limited >L> chromosomes. We investigated histone methylation modifications and found that all heterochromatic regions enriched in ScoHET1/ScoHET2 proteins exhibit high levels of di- and tri-methylated histone H3 at lysine 9. Taken together, our results support that the association of ScoHET1/ScoHET2 to heterochromatin is mediated by histone H3K9 methylation. Using 5-methylcytosine antibodies, we proved the cytological detection of DNA methylation in S. coprophila. From our observations in L germline chromosomes, heterochromatin in S. coprophila is highly enriched in DNA 5-methylcytosine residues.

This paper reports a comparative analysis of heterochromatin organization in the sex chromosomes of the fruit fly Anastrepha. Mitotic chromosomes of eight Anastrepha species from different taxonomic groups were stained with DAPI and chromomycin A3 fluorochromes followed by C-banding. A specific sex-chromosome banding pattern was obtained for each of the analyzed species. Fluorescence in situ hybridization (FISH) was performed to investigate the chromosomal location of rDNA loci. In all cases the rDNA sequences were found to localize exclusively to the sex chromosomes. The results further extend the chromosomal knowledge of Anastrepha and allow a precise species identification.

This article reports the cloning and characterization of the gene homologous to Sex-lethal (Sxl) of Drosophila melanogaster from Sciara coprophila, Rhynchosciara americana, and Trichosia pubescens. This gene plays the key role in controlling sex determination and dosage compensation in D. melanogaster. The Sxl gene of the three species studied produces a single transcript encoding a single protein in both males and females. Comparison of the Sxl proteins of these Nematocera insects with those of the Brachycera showed their two RNA-binding domains (RBD) to be highly conserved, whereas significant variation was observed in both the N- and C-terminal domains. The great majority of nucleotide changes in the RBDs were synonymous, indicating that purifying selection is acting on them. In both sexes of the three Nematocera insects, the Sxl protein colocalized with transcription-active regions dependent on RNA polymerase II but not on RNA polymerase I. Together, these results indicate that Sxl does not appear to play a discriminatory role in the control of sex determination and dosage compensation in nematocerans. Thus, in the phylogenetic lineage that gave rise to the drosophilids, evolution coopted for the Sxl gene, modified it, and converted it into the key gene controlling sex determination and dosage compensation. At the same time, however, certain properties of the recruited ancestral Sxl gene were beneficial, and these are maintained in the evolved Sxl gene, allowing it to exert its sex-determining and dose compensation functions in Drosophila.

The equine ascarid parasite Parascaris equorum is well known as a ubiquitous parasite infecting foals. A sibling species, Parascaris univalens, was first described over 130 years ago, but very little attention has been given to its existence and possible implications for anthelmintic resistance, clinical disease, or host age spectrum. P. univalens only possesses one germ line chromosome pair as opposed to two for P. equorum, but the two species are otherwise considered morphologically identical. For the present study, live worms obtained from the University of Kentucky parasitology horse herd were dissected and identified using karyotyping techniques. With no exception, all specimens (n = 30) were identified to be P. univalens. Further, the karyotyping technique was adapted to ascarid eggs derived from fecal samples and carried out on samples collected from 25 Thoroughbred foals from three farms in Central Kentucky. P. equorum was not identified among these, whereas P. univalens was found in 17 samples, with the remaining being inconclusive. The mitochondrial genome was sequenced, assembled, and annotated from one male worm identified as P. univalens, and comparison with available sequence reads labeled as P. equorum revealed only 0.16 % nucleotide differences. However, it is unlikely that the sequences available in public databases have been unequivocally identified to species level by karyotyping. Taken together, these data suggest that P. univalens is likely the main species now observed in equines and that perhaps the designation Parascaris spp. should be used unless cytological characterization has confirmed the species.

The programmed elimination of part of the genome through chromosome loss or chromatin diminution constitutes an exceptional biological process found to be present in several diverse groups of organisms. The occurrence of this phenomenon during early embryogenesis is generally correlated to somatic versus germ-line differentiation. A most outstanding example of chromosome elimination and genomic imprinting is found in sciarid flies, where whole chromosomes of exclusive parental origin are selectively eliminated at different developmental stages. Three types of tissue-specific chromosome elimination events occur in sciarids. During early cleavages, one or two X paternal chromosomes is/are discarded from somatic cells of embryos which then develop as females or males respectively. Thus, the sex of the embryo is determined by the number of eliminated paternal X chromosomes. In germ cells, instead, a single paternal X chromosome is eliminated in embryos of both sexes. In addition, while female meiosis is orthodox, male meiosis is highly unusual as the whole paternal chromosome set is discarded from spermatocytes. As a consequence, only maternally derived chromosomes are included in the functional sperm. This paper reviews current cytological and molecular knowledge on the tissue-specific cell mechanisms evolved to achieve chromosome elimination in sciarids.

Spindle formation and chromosome elimination during male meiosis in Sciara ocellaris (Diptera, Sciaridae) has been studied by immunofluorescence techniques. During meiosis I a monopolar spindle is formed from a single polar complex (centrosome-like structure). This single centrosomal structure persists during meiosis II and is responsible for the non-disjunction of the maternal X chromatids. During meiosis I and II non-spindle microtubules are assembled in the cytoplasmic bud regions of the spermatocytes. The chromosomes undergoing elimination during both meiotic divisions are segregated to the bud region where they associate with bundles of microtubules. The presence and distribution of centrosomal antigens in S. ocellaris meiotic spindles and bud regions has been investigated using different antibodies. gamma-Tubulin and centrin are present in the bud as well as in the single polar complex of first meiotic spindle. The results suggest that spermatocyte bud regions contain microtubule-organizing centres (MTOCs) that nucleate cytoplasmic microtubules that are involved in capturing chromosomes in the bud regions. The distribution of actin and myosin in the spermatocytes during meiosis is also reported., This work has been supported by a UE project C11*-CT94-0071.

In sciarid flies (Diptera, Sciaridae), one or two paternally derived X chromosomes are discarded from the soma at early cleavages to determine the sex of the embryo (XX, females; X0, males). X chromosome(s) elimination is achieved by an abnormal anaphase segregation so that X sister chromatids do not reach the poles and are not included in the daughter nuclei. A cis-acting locus (CE) within the heterochromatin proximal to the centromere is known to regulate X chromosome elimination. By immunofluorescence analysis in early embryos from Sciara ocellaris and Sciara coprophila, we investigated histone H3 phosphorylation at Ser10, Ser28 and Thr3 prior to, and during, the X elimination process. We found that the regular syncytial nuclear divisions are characterized by a gradual loss of H3S10 phosphorylation along the chromosome arms at anaphase. Importantly, the eliminating X chromosomes show a retardation in anaphase chromatid segregation and high levels of H3S10 phosphorylation in the chromosome arms. In the present study, we provide the first evidence linking the hyper-phosphorylated H3 status of the X chromosome with a delay in sister chromatid separation at anaphase. Our findings support the idea that the CE induces a deficiency in H3 dephosphorylation in the paternal X chromosomes to be eliminated., This work was supported by Ministerio de Ciencia e Innovación [grant number BFU2008-02947-C02-02/BMC to C.G. and M.C.E.]

We have studied the relationship between the occurrence of chromatin diminution and the developmental behavior of somatic blastomeres in early development of the nematode Parascaris univalens. A cytological and immunocytochemical analysis of chromatin diminution was performed in P. univalens embryos exposed to ‘vegetalizing’ (LiCl) and ‘animalizing’ (NaSCN) substances during early developmental stages. We have also analyzed chromatin diminution in embryos displaying only symmetrical ‘somatic-like’ divisions due to a brief cytochalasin B treatment at the pronuclear stage. The results show that LiCl treatment induces chromatin diminution in P0-P4 pregerminal blastomeres while NaSCN treatment prevents it. Pregerminal cells undergoing chromatin diminution in ‘vegetalized’ embryos behaved like somatic cells with respect to division and cleavage patterns. NaSCN treatment results in undiminuted polynucleated embryos that are not capable of cleavage. In cytochalasin B-pulsed embryos, chromatin diminution occurs in all blastomeres. From our results we conclude that chromatin diminution and somatic cell behavior are not separable and constitute strictly correlated events in Parascaris. Moreover, the results indicate that the segregation of the cytoplasmic factors involved in chromatin diminution in early Parascaris development are microfilament-mediated. Here, we also report the formation of a latter pregerminal cell precursor (P5) not susceptible to LiCl-induced chromatin diminution., We acknowledge the support of DGICYT (grant PB90-0073).

In the zebra finch (Taeniopygia guttata) a germline-restricted chromosome (GRC) is regularly present in males and females. While the GRC is euchromatic in oocytes, in spermatocytes this chromosome is cytologically seen as entirely heterochromatic and presumably inactive. At the end of male meiosis, the GRC is eliminated from the nucleus. By immunofluorescence on microspreads, we investigated HP1 proteins and histone modifications throughout male meiotic prophase, as well as in young spermatid stages after the GRC elimination. We found that in prophase spermatocytes the GRC chromatin differs from that of the regular chromosome complement. The GRC is highly enriched in HP1β and exhibits high levels of di- and tri-methylated histone H3 at lysine 9 and tri- and di-methylated histone H4 at lysine 20. The GRC does not exhibit neither detectable levels of di- and tri-methylated histone H3 at lysine 4 nor acetylated histone H4 at lysine 5 and 8. The results prove the heterochromatic organization of the GRC in male germline and strongly suggest its transcriptional inactive state during male prophase. Following elimination, in young spermatids the GRC lacks HP1β signals but maintains high levels of methylated histone H3 at lysine 9 and methylated histone H4 at lysine 20. The release of HP1 from the GRC with respect to its elimination is discussed., This work was supported with grant PIP 124 from the National Research Council (CONICET) and UBACyT M429 from the University of Buenos Aires to MIP and with grant BFU2008- 02947-C02-02/BMC to CG from M.E.C of Spain.

An outstanding example of programmed chromosome elimination and genomic imprinting is found in sciarid flies (Diptera, Sciaridae), where whole chromosomes of paternal origin are selectively discarded from the genome during development. In early germ cells a single paternal X chromosome is eliminated in embryos of both sexes and in male meiotic cells the whole paternal complement is discarded. In sciarids, differential acetylation of histones H3 and H4 occurs between chromosomes of different parental origin, both in early germ nuclei and in male meiotic cells (Goday and Ruiz, 2002). We here investigated histone methylation modifications between chromosomes in germline cells of Sciara ocellaris. In early germ nuclei, maternal chromosomes show high levels of di- and trimethylated histone H3 at Lys4, whereas this histone modification is not detected in paternal chromosomes. In male meiosis, only the eliminated paternal chromosomes exhibit high levels of di- and trimethylated histones H3 at Lys4 and dimethylated H4 at Lys20. In early germ nuclei, RNA polymerase II associates to maternally-derived chromosomes but lacks phosphorylation of the C-terminal domain on Ser2. We found that histone H3 methylation at Lys4 does not correlate with transcriptional activity in early Sciara germline nuclei. The results support the conclusion that specific covalent chromatin modifications are involved in the imprinted behaviour of germline chromosomes in Sciara., This work was supported with grant BFU2005-00769-C02-02 to C.G. from D.G.I.C.Y.T., Ministerio de Educación y Ciencia of Spain.

Ageing is a phenomenon related to mammalian female infertility. One cause of ageing-induced infertility is the abnormal meiotic maturation from germinal vesicle stage oocytes (GVs). GVs are immature oocytes, which stay arrested in the ovaries during the life span. The abnormal oocyte maturation in aged animals is partially originated from molecular changes, not well defined, such as chromatin modifications and differential gene expression. Here, we analyze chromatin modifications such as histone acetylation and the corresponding gene expression changes induced by ageing in mouse GVs. We measured by immunofluorescence histone H4 acetylation at lysine residues 5 (H4-K5), 8 (H4-K8), and 12 (H4-K12) in GVs collected from young (1 month old) and aged (12–18 months old) CDC1 female mice. Immunofluorescence was analyzed with a microscope (Leica TCS SP2 AOBS) and its image analysis software. Whereas H4-K5 and H4-K8 show similar acetylation levels in both young and old mice, significant lower acetylation of H4-K12 is detected in GVs from old mice. Since H4-K12 acetylation has been related to Cdc2a expression during oocyte maturation (Akiyama et al. 2004 Mol. Reprod. Dev. 69, 222–227; Minuzzo et al. 2005 Mol. Pharmacol. 68, 1496–1503), we investigated whether Cdc2a mRNA levels change in aged mice. Cdc2a expression was measured by RT-PCR and quantified with a densitometer (BioRad GS800). We observed a decrease of Cdc2a expression in GVs of old mice. This result is further confirmed by an immunofluorescence analysis where lower levels of Cdc2a protein in old mouse GVs was observed. In conclusion, we find that the levels of H4-K12 acetylation and Cdc2a mRNA are lower in old compared to young mouse GVs. Our observations suggest that ageing affects histone modifications such as H4-K12, which might induce chromatin remodelling and gene expression changes like that of Cdc2a.

Chromosome elimination is a widespread developmental phenomenon in insects. The main types of chromosome elimination take place at early embryonic somatic cleavages and at the first male meiotic division. The cellular mechanisms responsible for both elimination types are different but show common aspects in Diptera, notably unusual anaphase behavior of the chromosomes to be eliminated. Chromosome elimination can be parent-of-origin specific, highlighting this phenomenon as an example of genomic imprinting. Keywords: chromosome elimination; Diptera; Sciaridae; Cecidomyiidae; Chironomidae; imprinting

This paper reports the cloning and characterization in Sciara ocellaris of the gene homologous to Sex-lethal (Sxl) of Drosophila melanogaster. This gene plays the key role controlling sex determination and dosage compensation in the latter species. The Sciara Sxl gene produces a single transcript encoding a single protein in both males and females. This protein, found inside the nucleus, is expressed in all tissues. Both Sciara and Drosophila Sxl proteins are highly conserved at their two RNA-binding domains. In both Sciara sexes, the Sxl protein co-localizes with transcription-active regions dependent on RNA polymerase II but not on RNA polymerase I. It would appear that in Sciara, Sxl does not appear to play the key discriminative role in controlling sex determination and dosage compensation that it plays in Drosophila., This work was financed by grant PB98-0466 awarded to L.S. and grant BMC2000-0901 to C.G. by the DGICYT. M.F.R. and P.G. were supported by a postdoctoral and a predoctoral fellowship, respectively, from the Comunidad Autónoma de Madrid.

A classic example of chromosome elimination and genomic imprinting is found in sciarid flies (Diptera. Sciaridae), where whole chromosomes of exclusively paternal origin are discarded from the genome at different developmental stages. Two types of chromosome elimination event occur in the germline. In embryos of both sexes, the extrusion of a single paternal X chromosome occurs in early germ nuclei and in male meiotic cells the whole paternal complement is discarded. In sciarids, early germ nuclei remain undivided for a long time and exhibit a high degree of chromatin compaction,so that chromosomes are cytologically individualized. We investigated chromatin differences between parental chromosomes in Sciara ocellaris and S. coprophila by analyzing histone acetylation modifications in early germ nuclei. We examined germ nuclei from early embryonic stages to premeiotic larval stages, male meiotic cell and early somatic nuclei following fertilization. In early germ cells, only half of the regular chromosome complement is highly acetylated for histones H4 and H3. The chromosomes that are highly acetylated are paternally derived. An exception is the paternal X chromosome that is eliminated from germ nuclei. At later stages preceding the initiation of mitotic gonial divisions, all chromosomes of the germline complement show similar high levels of histone H4/H3 acetylation. In male meiosis, maternal chromosomes are highly acetylated for histones H4 and H3, whereas the entire paternal chromosome set undergoing elimination appears under-acetylated. The results suggest that histone acetylation contributes towards specifying the imprinted behavior of germline chromosomes in sciarids., This work was supported with grant BMC2000-0901 to C.G. from D.G.I.C.Y.T.,Ministerio de Ciencia y Tecnología of Spain.

In Drosophila melanogaster and in Sciara ocellaris dosage compensation occurs by hypertranscription of the single male X chromosome. This article reports the cloning and characterization in S. ocellaris of the gene homologous to maleless (mle) of D. melanogaster, which implements dosage compensation. The Sciara mle gene produces a single transcript, encoding a helicase, which is present in both male and female larvae and adults and in testes and ovaries. Both Sciara and Drosophila MLE proteins are highly conserved. The affinity-purified antibody to D. melanogaster MLE recognizes the S. ocellaris MLE protein. In contrast to Drosophila polytene chromosomes, where MLE is preferentially associated with the male X chromosome, in Sciara MLE is found associated with all chromosomes. Anti-MLE staining of Drosophila postblastoderm male embryos revealed a single nuclear dot, whereas Sciara male and female embryos present multiple intranuclear staining spots. This expression pattern in Sciara is also observed before blastoderm stage, when dosage compensation is not yet set up. The affinity-purified antibodies against D. melanogaster MSL1, MSL3, and MOF proteins involved in dosage compensation also revealed no differences in the staining pattern between the X chromosome and the autosomes in both Sciara males and females. These results lead us to propose that different proteins in Drosophila and Sciara would implement dosage compensation., This work was supported by grants UE95-0035 and PB95-1236 to L. Sánchez and PB96-0810 to C. Goday from D.G.I.C.Y.T., Ministerio de Educación y Cultura of Spain, and CI1*-CT 94-0071 BR from European Union to L. Sánchez and C. Goday.

The distribution of antigens to two antibodies (Bx63 and Rb188) that associate to Drosophila melanogaster centrosomes has been investigated in the nematode Parascaris. By western blot analysis both antibodies identify in Parascaris polypeptides of the same molecular mass as in Drosophila (Rb188 a 185 kDa antigen and Bx63 185 kDa and 66 kDa antigens). By immunocytochemistry we show that the centrosomes of Parascaris contain the 185 kDa antigen recognized by polyclonal Rb188 and monoclonal Bx63 antibodies. In addition, Bx63 reveals cytoplasmic midzone structures, not found in Drosophila, that display a cell cycle-dependent organization in embryos. These structures, which most probably contain the 66 kDa antigen revealed by Bx63, appear at the onset of anaphase as fibrillar-like structures that during anaphase form a ring-like structure encircling the equatorial plane of the blastomere. Before furrowing, the antigen participates in the formation of the midbody and associates with convergent polar microtubules. After blastomere division, Bx63 signal persists as a single body between the daughter cells. The analysis of chilled and nocodazole-treated embryos suggests that the localization of the midzone Bx63 antigen is dependent on non-kinetochore microtubules. Inhibition of furrowing by cytochalasin B shows that the antigen persists after the disassembly of microfilaments. Cytological observations of contractile ring and Bx63 ring assembly indicate that both structures do not simultaneously colocalize at the equatorial zone. The data suggest a spindle-dependent distribution of the Bx63 antigen during cytokinesis. We discuss the participation of this antigen in the organization of the midbody before furrowing, and consider the possible relevance of the midbody with respect to cell to cell communication during early development in nematodes.

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.

A study of the Q (quinacrine fluorescence) and G (Giemsa) banding patterns of the chromosomes of Pan troglodytes and Gorilla gorilla gorilla shows that they are almost identical. The differences include a pericentric inversion in pairs 5, 9, 19 and the X-chromosome, a possible translocation between pairs 7 and 17 of gorilla and a deletion of part of the long arms of the Y-chromosome in the chimpanzee. Several species of the genera Macaca, Papio and Cercocebus have the same karyotype and identical banding patterns. This suggests that speciation in this group may have taken place on purely genic grounds, without, involving any karyological changes.

Ultrastructural analysis of the centromere in germ-line mitotic chromosomes of Parascaris univalens and Parascaris equorum revealed that these chromosomes are holocentric. In thin longitudinal sections of both species the kinetochore appeared as a continuous plate (up to 3.8 μm long) and displayed a layered structure. This structure consisted of electron-dense inner and outer layers (average width 10 nm) separated by a less dense middle layer (25 nm wide), which had transverse electron-dense bars (10 nm wide) regularly spaced every 25–30 nm. Thus the ladderlike kinetochore profile observed in Parascaris gonial mitotic chromosomes represents a different type of organization from that of the classical trilaminar kinetochore found in both holocentric and monocentric chromosomes., This work was supported in part by Euroatom grant BI0-E-450

The case of a 21/2-month-old male child with intrauterine distrophy features and multiple congenital malformations is presented. Cytogenetic studies of the child and his parents, completed with Q- and G-banding techniques led us to conclude that it is a case of 22 trisomy inherited from his mother.

A cytological analysis by modern banding techniques of gonial metaphases in two Parascaris forms that have been considered varieties but now seem to be two species [P. univalens (karyotype 2n = 2) and P. equorum (karyotype 2n = 4)] reveals a different chromosome organization in each. Parascaris univalens chromosomes contain only terminal heterochromatin, while P. equorum chromosomes also contain intercalary heterochromatin. In the somatic cells of both species during early embryogenesis, chromatin diminution occurs in and consists of the elimination of all heterochromatin independent of its localization in the chromosomes.

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.

Quinacrine and Giemsa banding studies of the chromosomes of Ateles geoffroyi permitted to establish a pattern for the species and revealed the presence of a pericentric inversion in two of the animals studied.

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.

The cytogenetic study is reported of a female infant affected with several malformations and presenting a mosaicism of the type 47,XX,+8/46,XX in her karyotype. G band analysis and the distribution curves of these bands were studied in order to obtain a more objective identification of trisomy 8. Results of Q banding, X chromatin and dermatoglyphic studies are given and compared with previous reports.

Chromosome organization and the phenomenon of “chromatin diminution” in the two species Parascaris univalens (2n=2) and P. equorum (2n=4) were cytologically analysed by a variety of staining techniques (Quinacrine, Hoechst 33258, Chromomycin A3 and C-banding). The results show that: (1) the chromosomes of the two species differ markedly in both the location and the type of heterochromatin they contain; (2) in both species there is a strong chromosome polymorphism which, however, ranges within a basic species-specific phenotype; (3) the heterochromatin can be eliminated in presomatic cells during early embryogenesis at two different stages and in both cases the consequence of this process is the generation of somatic cells with a 2n=60 karyotype. Moreover, evidence suggesting the sterility of hybrids between the two species is provided., This work was supported by a grant from Grandi Progetti di Ateneo of the University of Rome "La Sapienza", Euratom Grants B10-E-400 and BI0-E-450, and a Consejo Superior de Investigaciones Cientificas fellowship (to C.G.).

[EN]: A comparison of the banding patterns of the chromosomes of man (Homo sapiens) and the chimpanzee (Pan troglodytes) using G (Giemsa) and Q (quinacrine) banding techniques shows that the differences between the karyotypes of the two species are the result of a few simple structural rearrangements, which include one centric fusion, five pericentric inversions, one paracentric inversion and the absence of one secondary constriction., [DE]: Ein Vergleich der Bandenmuster der Chromosomen des Menschen (Homo sapiens) und des Schimpansen (Pan troglodytes) bei Anwendung der G(Giemsa)- und Q(Quinacrin)-Bandentechnik zeigt, daß die Unterschiede zwischen den Karyotypen beider Species das Ergebnis einiger weniger einfacher Umstrukturierungen sind, nämlich einer zentrischen Fusion, 5 perizentrischen Inversionen, einer parazentrischen Inversion und des Fehlens einer sekundären Konstriktion.