Cytogenetic analysis of the neotropical spider Nephilengys cruentata (Araneomorphae, tetragnathidae): standard staining, NORs, C-bands and base-specific fluorochromes
Carregando...
Data
2005-05-01
Autores
Araújo, D. [UNESP]
Cella, D. M. [UNESP]
Brescovit, A. D.
Título da Revista
ISSN da Revista
Título de Volume
Editor
Instituto Internacional de Ecologia
Resumo
O objetivo deste trabalho é caracterizar Nephilengys cruentata em relação ao número diplóide, à morfologia cromossômica, ao tipo de sistema cromossômico de determinação sexual, aos cromossomos portadores de Regiões Organizadoras de Nucléolo (RONs), padrão de bandas C e seqüências AT ou GC repetitivas. As preparações cromossômicas foram submetidas à coloração convencional (Giemsa), à impregnação pelo nitrato de prata, técnica de obtenção de bandas C e à coloração com fluorocromos base-específicos. A análise das células mostrou 2n = 24 e 2n = 26 cromossomos nos embriões e 2n = 26 nas células ovarianas, sendo todos cromossomos acrocêntricos. O braço longo dos pares 1, 2 e 3 apresentou extensa região heteropicnótica negativa quando as metáfases mitóticas foram coradas com Giemsa. Os cromossomos sexuais não mostraram características diferenciais que permitissem distingui-los dos outros cromossomos do complemento. Considerando os números diplóides encontrados em N. cruentata e a predominância do sistema cromossômico de determinação sexual do tipo X1X2 em Tetragnathidae, N. cruentata parece contar com 2n = 24 = 22 + X1X2 nos machos e com 2n = 26 = 22 + X1X1X2X2 nas fêmeas. Os pares 1, 2 e 3 mostraram RONs coincidentes com as regiões heteropicnóticas negativas. Utilizando a técnica de obtenção de bandas C, a região pericentromérica dos cromossomos revelou pequena quantidade ou até mesmo ausência de heterocromatina constitutiva, diferindo do padrão de bandas C descrito em outras espécies de aranhas. em N. cruentata, os fluorocromos DAPI/DA, DAPI/MM e CMA3/DA revelaram que a heterocromatina constitutiva é rica em bases AT e as RONs apresentam seqüências repetidas de bases GC.
The aim of this work is to characterize Nephilengys cruentata in relation to the diploid number, chromosome morphology, type of sex determination chromosome system, chromosomes bearing the Nucleolar Organizer Regions (NORs), C-banding pattern, and AT or GC repetitive sequences. The chromosome preparations were submitted to standard staining (Giemsa), NOR silver impregnation, C-banding technique, and base-specific fluorochrome staining. The analysis of the cells showed 2n = 24 and 2n = 26 chromosomes in the embryos, and 2n = 26 in the ovarian cells, being all the chromosomes acrocentric. The long arm of the pairs 1, 2 and 3 showed an extensive negative heteropycnotic area when the mitotic metaphases were stained with Giemsa. The sexual chromosomes did not show differential characteristics that allowed to distinguish them from the other chromosomes of the complement. Considering the diploid numbers found in N. cruentata and the prevalence of X1X2 sex determination chromosome system in Tetragnathidae, N. cruentata seems to possess 2n = 24 = 22 + X1X2 in the males, and 2n = 26 = 22 + X1X1X2X2 in the females. The pairs 1, 2 and 3 showed NORs which are coincident with the negative heteropycnotic patterns. Using the C-banding technique, the pericentromeric region of the chromosomes revealed small quantity or even absence of constitutive heterochromatin, differing of the C-banding pattern described in other species of spiders. In N. cruentata the fluorochromes DAPI/DA, DAPI/MM and CMA3/DA revealed that the constitutive heterochromatin is rich in AT bases and the NORs possess repetitive sequences of GC bases.
The aim of this work is to characterize Nephilengys cruentata in relation to the diploid number, chromosome morphology, type of sex determination chromosome system, chromosomes bearing the Nucleolar Organizer Regions (NORs), C-banding pattern, and AT or GC repetitive sequences. The chromosome preparations were submitted to standard staining (Giemsa), NOR silver impregnation, C-banding technique, and base-specific fluorochrome staining. The analysis of the cells showed 2n = 24 and 2n = 26 chromosomes in the embryos, and 2n = 26 in the ovarian cells, being all the chromosomes acrocentric. The long arm of the pairs 1, 2 and 3 showed an extensive negative heteropycnotic area when the mitotic metaphases were stained with Giemsa. The sexual chromosomes did not show differential characteristics that allowed to distinguish them from the other chromosomes of the complement. Considering the diploid numbers found in N. cruentata and the prevalence of X1X2 sex determination chromosome system in Tetragnathidae, N. cruentata seems to possess 2n = 24 = 22 + X1X2 in the males, and 2n = 26 = 22 + X1X1X2X2 in the females. The pairs 1, 2 and 3 showed NORs which are coincident with the negative heteropycnotic patterns. Using the C-banding technique, the pericentromeric region of the chromosomes revealed small quantity or even absence of constitutive heterochromatin, differing of the C-banding pattern described in other species of spiders. In N. cruentata the fluorochromes DAPI/DA, DAPI/MM and CMA3/DA revealed that the constitutive heterochromatin is rich in AT bases and the NORs possess repetitive sequences of GC bases.
Descrição
Palavras-chave
cromossomo, Araneae, heterocromatina, constrição secundária, Cromomicina A3, chromosome, Araneae, heterochromatin, secondary constriction, Chromomycin A3
Como citar
Brazilian Journal of Biology. Instituto Internacional de Ecologia, v. 65, n. 2, p. 193-202, 2005.