Effect of heavy metals on chromatin supraorganization, nuclear phenotypes, and survival of Triatoma infestans

Abstract

The nuclear phenotypes and survival of the hemipteran, Triatoma infestans (Hemiptera, Reduviidae), were studied in specimens treated with copper sulfate and methylmercury. The objective was to determine whether changes in chromatin supraorganization and insect survival similar to those promoted by other stressing agents could also be induced by heavy metals. At the concentrations used, copper sulfate and methylmercury were toxic to the cells, mainly inducing nuclear degeneration in the Malpighian tubules and being lethal to a large part of the insect population. Although some individual resistance was found, especially in fasted specimens, heavy metals were found to be much more lethal than was, for instance, a thermal shock at 0 °C for 12 h. The nuclear phenotypes detected after heavy metal treatment were similar to those reported under other stressing conditions. However, the frequency at which nuclei exhibited aspects of heterochromatin unraveling was much higher than that found in fasted and thermal‐shocked specimens, and was independent of the heavy metal type used. If this phenotype represents an attempt to improve opportunities for extensive cell and insect survival, it was not sufficiently effective. In 5th instar nymphs, the effect of CuSO4 on chromatin supraorganization was detected at early steps of spermatogenesis but not in the cells which were at late spermiogenesis when the metal was administered. This is probably due to changes in nuclear protein composition and to the tightly packed state of the DNA‐ protein complexes occurring at spermiogenesis, which may protect chromatin from damages. However, when CuSO4 was supplied to 4th instar nymphs, it slowed down the spermiogenesis process, possibly due to several factors including Cu2+ binding to DNA phosphates. Résumé L'effet des métaux lourds sur l'organisation supérieure de la chromatine, les phénotypes nucléaires et la survie de Triatoma infestans Klug (Hemiptera, Reduviidae) Les phénotypes nucléaires et la survie de l'hémiptère Triatoma infestans ont été étudiés sur des spécimens traités avec du sulfate de cuivre et du méthyle de mercure. L'objectif a été de déterminer si les changements provoqués par d'autres agents stressants sur l'organisation supérieure de la chromatine et la survie de l'insecte peuvent être induit aussi par les métaux lourds. Il est apparu qu'aux concentrations utilisées, le sulfate de cuivre et le méthyle de mercure sont toxiques pour les cellules, provoquent principalement une dégénération nucléaire dans des organes tels que les tubes de Malpighi, et sont léthaux pour une grande partie de la population. Bien qu'une certaine résistance individuelle ait été trouvée particulièrement chez les spécimens à jeun, les métaux lourds se sont révélés beaucoup plus léthaux que, par example, un choc thermique de 12 h à 0 °C. Les phénotypes nucléaires observés après traitement aux métaux lourds sont similaires à ceux décrits dans d'autres conditions stressantes. Toutefois, la fréquence avec laquelle les noyaux ont montré des asp...

Spatial distribution of AT- and GC-rich DNA within interphase cell nuclei of Triatoma infestans Klug

“…The unpackaging of heterochromatin, a phenomenon that was previously reported as a cellular survival response to stress factors in the Malpighian tubules of Triatomini (Mello et al, 1995(Mello et al, , 2001, was observed under all tested conditions. However, the frequency of nuclei with heterochromatin unpackaging one and 48 h following the 5-AZA treatment exceeded the frequency observed in the untreated controls or in DMSO-treated nymphs.…”

“…In addition, the T. infestans chromocenters are able to unpack under stressful conditions such as prolonged starvation, heat or cold shock, and the presence of heavy metals (Mello, 1989;Mello et al, 1990Mello et al, , 1995Mello et al, , 2001Campos et al, 2002). This finding may indicate activation of genes usually silent and contained in the chromocenter body (Mello et al, 1990).…”

“…Because heterochromatin decondensation in Triatomini is usually a response to stress (starvation, heavy metals and heat-shock) (Mello, 1989;Mello et al, 1995Mello et al, , 2001Campos et al, 2002), the effect of the 5-AZA demethylation was determined by quantifying the number of nuclei that displayed this phenotype above the baseline levels measured in the controls. Even for the nuclei that contained no visual change in the chromocenter packing state after a 48-h 5-AZA treatment, a slight chromocenter unpackaging was detected with scanning microspectrophotometry and agrees with the presence of methylcytidine in the euchromatin bordering the chromocenters or other non-heterochromatin nuclear areas.…”

Variation of the interphase heterochromatin in Artemia (Crustacea, Anostraca) of the Americas is related to changes in nuclear size and ionic composition of hipersaline habitats

“…Although the participation of these factors has not generally been demonstrated in Artemia, experimental data collected in other organisms reveals their existence. For instance, in NIH 3T3 mouse cells treated with valproic acid produce decondensation in the chromatin structure of the nucleus, including the heterochromatin areas (Felisbino et al, 2014); while in Malpighian tubule cells of the blood-sucking insect, Triatoma infestans, heterochromatin decondensation occurs either after treatments with heavy metals (copper and mercury) or heat shocks (Mello et al, 1995(Mello et al, , 2001). Moreover, heterochromatin decondensation after heat shock treatements in Malpighian tubule cells of a vector of Chagas' disease in Brazil, Panstrongylus megistus, infected and non-infected by Trypanosoma cruzi, has been also reported (Garcia et al, 2011).…”

Apoptosis in polyploid cells of the blood-sucking hemipteran,Triatoma infestansKlug

“…However, when examining responses of liver polyploid cells to in-flammatory cytokines such as interferon gamma (IFN-gamma), diploid, tetraploid, and octoploid hepatocytes are equally susceptible to IFNgamma-induced apoptosis (Martin et al 2002). No comparable data exist for invertebrate cell, although insect Malpighian tubules may also be involved with detoxifying mechanisms (layered "concretions" − Mello et al 1995).…”