Chromatin of Trypanosoma cruzi: In situ analysis revealed its unusual structure and nuclear organization

Abstract

Chromatin of Trypanosoma cruzi is known to be organized in classical nucleosomal filaments, but surprisingly, these filaments do not fold in visible chromosomes and the nuclear envelope is preserved during cell division. Our hypothesis about the role of chromatin structure in regulating gene expression and, more generally, cell functioning, pressed us to verify if chromatin organization is modulated during the parasite life-cycle. To this end, we analyzed in situ the fine structural organization of T. cruzi chromatin by means of an integrated biophysical approach, using differential scanning calorimetry and fluorescence microscopy. We observed that logarithmic forms exhibit a less condensed chromatin with respect to the stationary ones. Thermal analysis revealed that parasite chromatin is organized in three main levels of condensation, barring from the polynucleosomal filament till to superstructured fibers. Besides, the fluorescence images of nuclei showed a characteristic chromatin distribution, with defined domains localized near to the nuclear envelope. While in stationary parasites, these regions are highly condensed, in logarithmic forms they unfold by extending themselves toward the center of nucleus. These observations suggest that, in comparison with higher eukaryotes, in T. cruzi the nuclear envelope plays an unusual and pivotal role in interphase and in mitosis.

Widespread, focal copy number variations (CNV) and whole chromosome aneuploidies in Trypanosoma cruzi strains revealed by array comparative genomic hybridization

“…Normally, traditional cytological methods such as metaphase spreads would be used to resolve karyotypic differences between isolates. However, this approach is not possible in the case of T. cruzi because T. cruzi replicates via endodyogeny, where the nuclear membrane does not break down and chromosomes do not fully condense during replication [18]. Nevertheless it seems highly unlikely that sequence divergence alone could explain our observations of chromosomes with significantly decreased signal intensities in many of the test strains relative to the CL-Brener reference.…”

Chromosomal size conservation through the cell cycle supports karyotype stability in Trypanosoma cruzi

“…Thus, Trypanosoma chromatin shows a greater sensitivity to micrococcal nuclease and a lower compactness, when compared to mammalian chromatin [5]. Besides, proliferative epimastigote forms exhibit limited chromatin compaction with respect to the non‐proliferative epimastigotes and trypomastigotes (Go cells) [6,7]. Finally, Trypanosoma chromosomes are subjected both to dynamic spatial reorganization during DNA replication [8] and to traction forces by a mitotic spindle during chromosomal segregation [9].…”

SCN− binding to the charged lysines of histones end domains mimics acetylation and shows the major histone–DNA interactions involved in eu and heterochromatin stabilization

“…This correlation was established by exploiting the extraordinary capability of differential scanning calorimetry (DSC) to distinguish between the condensed and the unfolded state of the genome [Nicolini et al, 1983]. Using DSC, we and other groups were indeed able to characterize the thermodynamics of salt induces condensation [Cavazza et al, 1991;Labarbe et al, 1996], to elucidate the mechanism of binding of H1 to core chromatin [Russo et al, 1995], to describe the all-or-none structural transition which occurs inside the chromatin loop [Balbi et al, 1999] and to identify the role of histone acetylation [Gavazzo et al, 1997] and of the nuclear envelope [Spadiliero et al, 2002], respectively, in the modulation of chromatin higher order structure.…”