Critical electrolyte concentration of chromatin in polytene chromosomes of Trichosia pubescens (Diptera, Sciaridae)

Abstract

The binding of toluidine blue molecules to nucleic acid phosphates under conditions of competition with Mg2+ ions was studied in Trichosia pubescens polytene chromosome regions differing in composition and organization (RNA-rich areas and puffs, DNA puffs, heterochromatin). The aim was to find variability in the Mg2+ concentration at which metachromasy was completely prevented (= critical electrolyte concentration; CEC) and that could reflect differences at the level of nucleoprotein complexes in particular chromosome regions and developmental phases. Although high CEC values have been found in tightly packed chromatin such as that of heterochromatin zones, the CEC values for the other regions have proven to be affected not only by availability and proximity of DNA phosphates but also by RNA richness and other factors. Among these, changes in DNA geometry and packing state have been assumed for explaining increased values after RNA removal in DNA puffs and RNA-rich zones. Based on CEC values it has been suggested that alterations at the level of nucleoprotein complexes may occur in puffs before they are morphologically detectable. CEC results for polytene chromosomes were thus revealed to vary considerably with slight variations in nucleoprotein composition and organization. However, since a complex and apparently contradictory rationale has to be used for explaining part of the results, CEC is not recommended as a useful tool for extensive and comparative studies of this particular model.<br>A ligação de moléculas de azul de toluidina a grupamentos fosfatos de ácido nucléico em condições de competição com íons Mg2+ foi estudada em regiões de cromossomos politênicos de Trichosia pubescens que diferem em composição e organização (áreas ricas em RNA, pufes de RNA e DNA, heterocromatina). O objetivo foi encontrar variabilidade na concentração de Mg2+ na qual a metacromasia fosse completamente abolida (= concentração crítica de eletrólitos; CEC) e que refletisse diferenças ao nível dos complexos nucleoprotéicos em regiões cromossômicas e fases do desenvolvimento particulares. Embora valores altos de CEC tenham sido encontrados na cromatina altamente empacotada, como nas zonas heterocromáticas, os valores de CEC para outras regiões mostraram-se afetados não apenas pela disponibilidade e proximidade de fosfatos do DNA mas também pela riqueza em RNA e outros fatores. Entre estes, mudanças na geometria e no estado de empacotamento do DNA foram consideradas para explicar valores aumentados após remoção de RNA em pufes de DNA e zonas ricas em RNA. Baseando-se em valores de CEC foi sugerido que possam ocorrer alterações ao nível dos complexos nucleoprotéicos em pufes antes que estes sejam detectáveis morfologicamente como tal. Os valores de CEC nos cromossomos politênicos revelaram-se, pois, altamente variáveis com as variações em composição e organização nucleoprotéica do substrato. Contudo, uma vez que um raciocínio complexo e aparentemente contraditório tem que ser utilizado para a interpretação de parte dos resultados, ...

Critical Electrolyte Concentration of Chicken Erythrocyte Chromatin.

“…cells of the spermatheca and spermathecal glands in the honey bee [12], and most chromosome regions in polytene chromosomes of Trichosia pubescens [15]. The variability in CEC with different anticoagulants or with the same anticoagulant in acetic ethanol-fixed preparations may reflect the partial extraction of histones from the cell nuclei as well as changes in the histone H1 conformation induced by the fixative [3][4][5]10].…”

“…Chromatin types differing in DNA-protein complex composition and stereoarrangement, or in the presence of associated RNA exhibit different affinities for toluidine blue (TB) molecules in the presence of Mg2+, a competitive inhibitor [12,14,15,21]. In a manner analogous to Scott's concept of critical electrolyte concentration (CEC), proposed for the study of extracellular matrix polyanions [18], the inorganic cation (Mg2+) concentration at which TB metachromatic staining is completely prevented in chromatin has been considered to be the CEC value for the nucleoprotein complexes involved (DNA-protein, RNAprotein, or both) [11,21].…”

Critical electrolyte concentration of silk gland chromatin of the sugarcane borer Diatraea saccharalis, induced using agrochemicals

“…These proteins play an important role in protein interactions such as protein folding, assisting in establishing the proper conformation of proteins, and preventing unwanted protein aggregation (Qin et al, 2003;Sonoda et al, 2006;Sharma et al, 2012 The effect of fixation in acetic acid and ethanol on the results reported herein may be considered because the partial extraction of the core histones of the cells was reported after the action of fixatives, especially after long periods (Mello, 1979). However, it is assumed that most of the histones are not extracted during the short period of fixation that was used in this experiment because the recovery of nuclear metachromasia after reaching the CEC was observed in this and other studies (Mello and Falco, 1996;Monteiro and Mello, 1998).…”

Critical electrolyte concentration of spermatozoal chromatin containing histone H1 variants

“…The CEC of different DNA-protein complexes occurs at different Mg 2+ concentrations (Vidal and Mello, 1989;Amaral and Mello, 1989;Mello and Falco, 1996;Taboga et al, 1996;Monteiro and Mello, 1998).…”