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Analysis of karyotypic variability and chromosome behavior in meiosis of subgenus Tityus (Archaeotityus) (Buthidae) scorpions

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Author(s):
Viviane Fagundes de Mattos
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual Paulista (Unesp)
Defense date:
Advisor: Marielle Cristina Schneider
Abstract

The subgenus Tityus (Archaeotityus) comprises sedentary scorpions that live in the upper layers of the leaf litter. In this work, six Brazilian Archaeotityus species (Tityus clathratus, Tityus maranhensis, Tityus mattogrossensis, Tityus paraguayensis, Tityus pusillus and Tityus silvestris) were examined regarding to the diploid/haploid number, chromosome behavior during meiosis, repetitive DNA sequences (constitutive heterochromatin, 28S rDNA and telomeric (TTAGG)n), and epigenetic marks (H3K9ac, H4K5ac, H3S10f, H3K4m2, H3K9m2, H3K9m3). All analyzed species showed holocentric chromosomes, synaptic and achiasmatic meiosis, and chromosome chains in meiosis I. Intraespecific variation of diploid number and the presence of multivalent associations formed by a variable number of elements were visualized within and among populations of five species. Spermatogonial metaphase cells exhibited: 2n=16, 2n=17 and 2n=18 in T. paraguayensis; 2n=16 and 2n=24 in T. silvestris; 2n=20 in T. maranhensis, 2n=19 and 2n=20 in T. clathratus, T. mattogrossensis and T. pusillus. In postpachytene nuclei, a high variability in the number of bivalents and/or chromosomes involved in multivalent associations was verified. The most extreme variability occurred in T. clathratus, which showed 11 distinct chromosome configurations in meiosis, and T. pusillus, which exhibited polyploid cells. Metaphase II cells indicated that all chromosomes possess regular disjunction and balanced segregation. In all species, mitotic metaphase cells submitted to silver impregnation revealed two nucleolar organizer regions localized on terminal/subterminal chromosome sites. The constitutive heterochromatin was localized in the terminal region of the one chromosome pair. Meiotic cells submitted to FISH with 28S rDNA probe showed ribosomal cistrons in the terminal region of one bivalent-like element in T. clathratus, T. maranhensis, T. mattogrossensis, T. paraguayensis and T. pusillus, and in two chromosomes involved in a multivalent association in T. silvestris. FISH with (TTAGG)n probe exhibited typical telomeric signals in most chromosomes or at least in one chromosome ends. Taking into account all results obtained through the investigation of mitotic and meiotic cells, we determine the intraspecific and intrapopulational variability in species of Archaeotityus, which occurred due to fission/fusion and reciprocal translocation rearrangements. Thus, individuals with the same diploid number differed regarding to chromosomal structure organization, giving rise to distinct multivalent associations observed in meiotic cells. The six populations investigated of T. mattogrossensis revealed similar chromosome features, but showed differences related to the number of chromosomes involved in a quadrivalent association. This data may be an indicative of low gene flow among the populations. In scorpions, the study about epigenetic modifications is been accomplished for the first time here. The results revealed that all chromosomes were homogeneously phosphorylated during meiosis and with terminal regions hypertrimethylated. This later histone modification seems to be related to chromosome segregation during meiosis, and have function in anchorage of spindle microtubules. (AU)

FAPESP's process: 13/11840-0 - Analysis of the karyotype variability and chromosome behavior during meiosis of Tityus scorpions (Buthidae)
Grantee:Viviane Fagundes de Mattos
Support Opportunities: Scholarships in Brazil - Doctorate