Cytogenetic evidence for diversity of two nuclei within a single diplomonad cell of Giardia

Abstract

Giardia intestinalis is an ancient protist that causes the most commonly reported human diarrheal disease of parasitic origin worldwide. An intriguing feature of the Giardia cell is the presence of two morphologically similar nuclei, generally considered equivalent, in spite of the fact that their karyotypes are unknown. We found that within a single cell, the two nuclei differ both in the number and the size of chromosomes and that representatives of two major genetic groups of G. intestinalis possess different karyotypes. Odd chromosome numbers indicate aneuploidy of Giardia nuclei, and their stable occurrence is suggestive of a long-term asexuality. A semi-open type of Giardia mitosis excludes a chromosome interfusion between the nuclei. Differences in karyotype and DNA content, and cell cycle-dependent asynchrony are indicative of diversity of the two Giardia nuclei.

Constitutive aneuploidy and genomic instability in the single‐celled eukaryote Giardia intestinalis

“…The slight asynchrony in chromosome condensation between the two nuclei was documented earlier; one of the two nuclei already had fully condensed chromosomes as defined particles, while in the other nucleus, the chromosome mass was still in the process of condensation (Tumova et al. 2007, 2015). …”

“…The two mother nuclei migrated one above the other and segregated laterally, as described previously (Tumova et al. 2007). The chromatin was counterstained with DAPI (blue).…”

“…We first described the aneuploidy and genetic diversity of the two nuclei in four Giardia lines (Tumova et al. 2007). In this study, more profound chromosome number changes were identified in additional Giardia lines, differing by up to seven chromosomes between lines.…”

“…For cytogenetic karyotyping, the chromosome suspensions were prepared, and the karyotypes were observed according to previously described protocols (Tumova et al. 2007, 2015). Briefly, hypotonization was achieved using 75 mmol/L KCl, and the time that was required for satisfactory chromosome separation varied from 15 to 45 min among Giardia lines, during which the cultures were kept at 37°C under anaerobic conditions.…”

“…In contrast, the imaging of chromosomes in individual nuclei indicated that the proposed diploid pattern per nucleus (2 n  = 10) can be modified to an aneuploid pattern and that the nuclei harbor different chromosome sets (Tumova et al. 2007). The structural organization of Giardia mitosis is unconventional and prone to chromatid missegregations (Tumova et al.…”