Spatial Distribution of Heterochromatin Bodies in the Nuclei of Triatoma infestans (Klug)

Abstract

Constitutive heterochromatin typically exhibits low gene density and is commonly found adjacent or close to the nuclear periphery, in contrast to transcriptionally active genes concentrated in the innermost nuclear region. In Triatoma infestans cells, conspicuous constitutive heterochromatin forms deeply stained structures named chromocenters. However, to the best of our knowledge, no information exists regarding whether these chromocenters acquire a precise topology in the cell nuclei or whether their 18S rDNA, which is important for ribosome function, faces the nuclear center preferentially. In this work, the spatial distribution of fluorescent Feulgen-stained chromocenters and the distribution of their 18S rDNA was analyzed in Malpighian tubule cells of T. infestans using confocal microscopy. The chromocenters were shown to be spatially positioned relatively close to the nuclear periphery, though not adjacent to it. The variable distance between the chromocenters and the nuclear periphery suggests mobility of these bodies within the cell nuclei. The distribution of 18S rDNA at the edge of the chromocenters was not found to face the nuclear interior exclusively. Because the genome regions containing 18S rDNA in the chromocenters also face the nuclear periphery, the proximity of the chromocenters to this nuclear region is not assumed to be associated with overall gene silencing.

Epigenetic studies in insects and the valproic acid perspective

“…Much longer exposition to VPA or the use of more concentrated doses of VPA leads Malpighian tubule cells to apoptosis and necrosis (Bassani et al, 2021). Regarding the response of the euchromatin of these cells to VPA treatment as assessed by H3K9ac immunofluorescence signals, it was slightly intensified under cultivation of the Malpighian tubules in the presence of 0.5 or 1.0 mM VPA for 4 h especially around the chromocenters, a nuclear area previously demonstrated to contain 18S rDNA (Imperador et al, 2020).…”

Nuclear Morphofunctional Organization and Epigenetic Characteristics in Somatic Cells of T. infestans (Klug, 1834)

“…Additionally, the hypothesis that heterochromatin acts as a gene-silencing compartment has been questioned [30]. Variability relative to the small distance between the edge of the chromocenters and the nuclear periphery raises the suspicion of the mobility of the heterochromatin body with respect to the nuclear envelope [25]. Unraveling of the chromocenter heterochromatin has been observed in a small number of nuclei in the Malpighian tubules of T. infestans under rearing conditions in the laboratory (Figure 1d) [10].…”

“…From the first to the third nymphal instar, only one chromocenter is present in the Malpighian tubules of T. infestans ; from this stage onward, a portion of the cells exhibit more than one chromocenter ( Figure 1 b–d) [ 7 , 8 ]. The process of formation of multi-chromocenters apparently involves budding or declustering from the single chromocenter body [ 25 ] and does not lead to the micronuclei production that results in cell death as reported for other cell systems [ 26 ]. The nuclear phenotype diversification and the size attained by chromocenters in the Malpighian tubules of nymphs and adults have not been identified in other species of the Reduviidae family studied till date [ 27 ].…”

“…T. infestans nuclei constitute an attractive model for studying the 3D position of chromocenters because of the large volume of these bodies inside the nuclei. Using confocal microscopy and quantitative measurement of the 3D position of the chromocenters in the Malpighian tubule cells of T. infestans , the proximity of these bodies to the nuclear periphery was demonstrated during the insect lifetime [ 25 ]. The spatial distribution of chromocenters in relation to the nuclear periphery was confirmed using electron microscopy [ 25 ].…”

“…The proximity of chromocenters to the nuclear periphery has been detected in the cells of several other organisms [ 29 , 30 , 31 , 32 ], including species of the Reduviidae family which exhibit very small chromocenters, as in the case of Panstrongylus megistus [ 33 ]; however, the reason for this phenomenon remains unclear [ 34 ]. The concept that proximity of a chromocenter to the nuclear periphery is associated with overall gene silencing [ 35 , 36 ] does not fully apply to T. infestans , because 18 active S rDNA sites were detected in the chromocenter surface including the region facing the nuclear periphery, according to videos obtained after 3D fluorescence in situ hybridization [ 25 ]. In T. infestans cells, the nucleolus was found to encircle chromocenters ( Figure 2 a,b) [ 37 ].…”