CHROMOSOME-STUDIES IN HYPOPTOPOMATINAE (PISCES, SILURIFORMES, LORICARIIDAE) .2. ZZ ZW SEX-CHROMOSOME SYSTEM, B-CHROMOSOMES, AND CONSTITUTIVE HETEROCHROMATIN DIFFERENTIATION IN MICROLEPIDOGASTER-LEUCOFRENATUS

Cytogenetic analysis of two local populations of microlepidogaster leucofrenatus showed a basic diploid chromosome number (2N) of 54 in both populations. Some fishes were found to have a 2N = 55 or 56 chromosomes due to the presence of one or two large heterochromatic B chromosomes. Specimens of M. leucofrenatus from the Poco Grande stream had 24 metacentrics, 24 submetacentrics, four subtelocentrics, and one submetacentric homomorphic pair in males and one submetacentric/subtelocentric heteromorphic pair in females, whereas individuals of this species from the Marumbi River had 22 metacentrics, 24 submetacentrics, four subtelocentrics, two acrocentrics, and one submetacentric/subtelocentric heteromorphic pair in females. The occurrence of the heteromorphic pair in the females was due to the presence of an extra C-banded segment on the W chromosome. Ag-NORs in both populations were located interstitially on the short arm of the largest metacentric pair. The Poco Grande population had less constitutive heterochromatin than did the Marumbi River population. The speciation process in this fish species is discussed on the basis of heterochromatin distribution.

A new locus for autosomal dominant amelogenesis imperfecta on chromosome 8q24.3

Amelogenesis imperfecta (AI) is a collective term used to describe phenotypically diverse forms of defective tooth enamel development. AI has been reported to exhibit a variety of inheritance patterns, and several loci have been identified that are associated with AI. We have performed a genome-wide scan in a large Brazilian family segregating an autosomal dominant form of AI and mapped a novel locus to 8q24.3. A maximum multipoint LOD score of 7.5 was obtained at marker D8S2334 (146,101,309 bp). The disease locus lies in a 1.9 cM (2.1 Mb) region according to the Rutgers Combined Linkage-Physical map, between a VNTR marker (at 143,988,705 bp) and the telomere (146,274,826 bp). Ten candidate genes were identified based on gene ontology and microarray-facilitated gene selection using the expression of murine orthologues in dental tissue, and examined for the presence of a mutation. However, no causative mutation was identified.

Ribosomal DNA ITS-1 intergenic spacer polymorphism in triatomines (Triatominae, Heteroptera)

The length polymorphism of ribosomal DNA ITS-1 intergenic spacer was analyzed in eight species of triatomines belonging to Triatoma, Rhodnius, and Panstrongylus genera. The analyzed species were Rhodnius domesticus, R. neivai, R. robustus, Triatoma brasiliensis, T. infestans, T. vitticeps, Panstrongylus megistus, and P. herreri. These insects are vectors of Chagas' disease, one of the most prominent public health problems among South American countries. This work allowed the differentiation between species of the Triatomini and Rhodniini tribes through the analysis of ITS-1 length polymorphism by PCR and RFLP techniques. The species of the Triatoma and Panstrongylus genera presented an amplified ITS-1 fragment between 600 and 1000 bp, whereas Rhodnius presented a less variable ITS-1 length fragment, around 300 bp, which could reflect the monophyletic origin of the Rhodniini tribe. Species belonging to this genus were further differentiated by RFLP with HaeIII and AluI endonucleases. Our results corroborate the hypothesis of polyphyletic origin in this group of insects and contribute to knowledge about evolutionary relationships in triatomines.

Origins of sequence diversity in the malaria vaccine candidate merozoite surface protein-2 (MSP-2) in Amazonian isolates of Plasmodium falciparum

The recent evolution of Plasmodium falciparum is at odds with the extensive polymorphism found in most genes coding for antigens. Here, we examined the patterns and putative mechanisms of sequence diversification in the merozoite surface protein-2 (MSP-2), a major malarial repetitive surface antigen. We compared the msp-2 gene sequences from closely related clones derived from sympatric parasite isolates from Brazilian Amazonia and used microsatellite typing to examine, in these same clones, the haplotype background of chromosome 2, where msp-2 is located. We found examples of msp-2 sequence rearrangements putatively created by nonreciprocal recombinational events, such as replication slippage and gene conversion, while maintaining the chromosome haplotype. We conclude that these nonreciprocal recombination events may represent a major source of antigenic diversity in MSP-2 in P falciparum populations with low rates of classical meiotic recombination. (c) 2006 Elsevier B.V. All rights reserved.

Predisposing genes and increased chromosome aberrations in lung cancer cigarette smokers

Genotoxic effects linking cigarette smoking with lung cancer have not been consistently demonstrated, therefore claims for the cause-effect relationships are vigorously contested. Using matched populations of 22 lung cancer patients who have been cigarette smokers (LCP), 22 non-cancerous cigarette smokers (SC) and 13 non-smokers (NSC), we have applied the fluorescence in situ hybridization (FISH) tandem probe assay to elucidate the frequency of chromosome breakage among the participants. Two probes were used, a classical satellite probe which hybridizes to the large heterochromatin region of chromosome 1, and an alpha-satellite probe which targets a small region adjacent to the heterochromatin probe. The highest frequency of structural aberrations was observed in LCP (1.4 +/- 0.1) followed by SC (1.25 +/- 0.1) and NSC (0.4 +/- 0.1). Aberration frequencies were not significantly different between LCP and SC (p > 0.05), however, a statistically significant difference was detected between the smoker populations combined (LCP and SC) and the NSC (p < 0.001). The breakage frequencies showed a positive correlation with duration of smoking for LCP (r = 0.5; p < 0.01), but not for SC (P > 0.05). In addition, the aberration frequencies were influenced by the inheritance of polymorphic glutathione S-transferase (GST) genes. LCPs missing one or the other GST (GSTM1 or GSTT1) genes were found to have significantly higher chromosome breaks compared to LCPs with both genes present (p < 0.05), Our data indicate that genetic predisposition and chromosome aberrations may be mechanistically related to the initiation of lung carcinogenesis; therefore, they may be useful biomarkers for lung cancer among cigarette smokers. (C) 1997 Elsevier B.V. B.V.

EFFECT OF PRETREATMENT WITH VENOM OF APIS-MELLIFERA BEES ON THE YIELD OF GAMMA-RAY INDUCED CHROMOSOME-ABERRATIONS IN HUMAN BLOOD-LYMPHOCYTES

Venom of the honey bee Apis mellifera induced a protective effect against the induction of dicentric chromosomes by gamma radiation (2.0 Gy) in human peripheral blood lymphocytes which the cultures were treated with 0.00015 mul venom/1 ml medium 6 h before irradiation. In cultures to which the venom was added immediately before irradiation with 0.25, 1.0 and 2.0 Gy, no significant differences in number of dicentric chromosomes induced was observed when compared to cultures submitted to irradiation only. The venom did not induce clastogenic effects nor did it increase the frequency of sister chromatid exchanges.

A natural triploid in Trichomycterus davisi (Siluriformes, Trichomycteridae): mitotic and meiotic characterization by chromosome banding and synaptonemal complex analyses

Within a total of 50 analyzed specimens a male individual of Trichomycterus davisi has been recorded with 81 chromosomes including 60 metacentric, 18 submetacentric and three subtelocentric chromosomes. When compared with diploid individuals (2n = 54) and the morphological standard of chromosomes, this male is a triploid with 3 = 81 chromosomes. Since staining with silver nitrate indicates three active nucleolar organizer regions (NORs), the three NOR- bearing chromosomes in this individual are genetically active. Analysis of the synaptonemal complex (SC) by electronic microscopy shows that there is an incomplete pairing of the third set of chromosomes in the triploid individual.

Polymorphism of the ITS-2 region of the ribosomal DNA of the Triatominae Rhodnius domesticus, R-pictipes, R-prolixus and R-stali

The polymerase chain reaction-restriction fragment length polymorphism technique (PCR-RFLP) was used to compare Rhodnius domesticus (Neiva & Pinto), R. pictipes (Stal), R. prolixus (Stal) and R. stali (Lent; Jurberg & Galvao) (Hemiptera: Reduviidae). The enzyme BstUI differentiated R. donzesticus, R. pictipes and R. prolixus, and HhaI differentiated R. domesticus, R. pictipes and R. stali. With the fingerprinting analysis generated by these two enzymes, it was possible to clearly identify all four species in the study.