Cell death and survival alterations in Malpighian tubules of <i>Triatoma infestans</i> following heat shock

Abstract

In this study, we examined cell survival and cell death in response to heat shock in an insect organ composed of highly polyploid cells no longer capable of cell division. For this, the frequency of nuclear phenotypes in Feulgen-stained Malpighian tubules of the blood-sucking insect, Triatoma infestans, was analyzed at various times after a short heat shock with or without subsequent moderate fasting. Cell death DNA fragmentation was studied immunocytochemically. Normal phenotypes and phenotypes indicative of cell survival (heterochromatin decondensation, nuclear fusion) and death (apoptosis, necrosis) were observed, especially in heat-shocked specimens. While the number of total and normal nuclei decreased following heat shock, the frequency of apoptosis increased during a short period (7 days) after heat shock. During a 30-day period following heat shock, the frequency of necrosis in fasted but not in fully nourished nymphs increased simultaneously with a decrease in the frequency of apoptosis. This finding suggests that the stress promoted by heat shock, but not that associated with heat shock plus fasting, can be dealt with by the apoptosis program. When considering the forms of cell survival, heterochromatin decondensation was more relevant in fully nourished nymphs, whereas nuclear and cell fusions were more important in fasted specimens. The forms of cell survival and cell death reported here may have protected the organ from damage by the stressing agents. In cells with no induction or accumulation of heat-shock proteins, cell death and the forms of cell survival observed here were the probable consequence.

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.…”

“…The acid hydrolysis time used allowed for the maximal DNA depurination for this material as reported previously (Mello et al, 2001). The Feulgen-stained material was rinsed in three baths (5 min each) of sulfurous water and one bath of distilled water, air dried, cleared in xylene, and mounted in natural Canada balsam (n D = 1.54).…”

“…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.…”

“…The interphase cell nuclei of the blood-sucking insect Triatoma infestans, a reduviid hemipteran vector of the Chagas disease, contain conspicuous chromocenters that are composed of an aggregation of constitutive heterochromatin bodies (Mello, 1971(Mello, , 1978(Mello, , 1979Mello et al, 2001). Heterochromatinization in T. infestans has been shown to affect the A, B and C autosomes and the X and Y sex chromosomes (Schreiber et al, 1972;Solari, 1979), and has been suggested as a cytological mechanism that may contribute to the reproductive isolation of the species (Schreiber et al, 1972).…”

“…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).…”