Cytogenetic analysis of the 18S, 5S rDNA and B chromosome of Iheringichthys labrosus (Lütken, 1874) (Siluriformes, Pimelodidae) / Análise Citogenética de DNAr 18S, 5S e cromossomo B de Iheringichthys labrosus (Lütken, 1874) (Siluriformes, Pimelodidae)

Cytogenetic analyses of the location of 18S and 5S ribosomal DNAs, and the base composition of B chromosomes of Iheringichthys labrosus from Tibagi River, Paraná, Brazil, are provided. AgNORs were observed in the terminal position on the long arm of a subtelocentric chromosome pair. CMA3-positive staining was observed in some chromosomes, which besides being associated with NORs, were all DAPI-negative. Chromosome B showed a strong fluorescence with CMA3. The concomitant use of 18S and 5S rDNA probes using the FISH technique revealed 18S ribosomal cistrons in a pair of subtelocentric chromosomes, on the long arm in the terminal position, coinciding with the AgNOR. The 5S sites were found in another subtelocentric pair, on the long arm in the interstitial region, near the centromere. The findings of the present study suggest that, although there are some more conserved cytogenetic characteristics, populations of I. labrosus may show their own characteristics.

Foram realizadas análises citogenéticas em Iheringichthys labrosus do Rio Tibagi, Paraná, Brasil com a localização cromossômica dos DNAs ribossômicos 18S e 5S e a composição de bases de seus cromossomos B. As AgNORs foram observadas em posição terminal, no braço longo de um par de cromossomos subtelocêntricos. Marcações CMA3 positivas foram observadas em alguns cromossomos e associadas com as RONs. Porém, todas estas marcações apresentaram-se DAPI negativas. O cromossomo B mostrou-se fortemente fluorescente com CMA3. O uso concomitante das sondas de DNAr 18S e 5S, através da técnica de FISH, revelou os cístrons ribossômicos em um par de cromossomos subtelocêntricos, em posição terminal do braço longo, coincidindo com a AgNOR. Os sítios 5S foram observados em outro par subtelocêntrico, em posição intersticial do braço longo, próximo ao centrômero. Os resultados observados no presente estudo sugerem que, embora existam algumas características citogenéticas mais conservadas, as populações de I. labrosus podem mostrar suas próprias características.

Uses and limitations of two molecular cytogenetic techniques for the study of arrested embryos obtained through assisted reproduction technology

We studied chromosomal abnormalities in arrested embryos produced by assisted reproductive technology with fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) in order to determine the best technique for evaluating chromosomal aneusomies to be implemented in different situations. We examined individual blastomeres from arrested embryos by FISH and arrested whole embryos by CGH. All of the 10 FISH-analyzed embryos gave results, while only 7 of the 30 embryos analyzed by CGH were usable. Fifteen of the 17 embryos were chromosomally abnormal. CGH provided more accurate data for arrested embryos; however, FISH is the technique of choice for screening in preimplantation genetic diagnosis, because the results can be obtained within a day, while the embryos are still in culture.