Dinoflagellate nucleus contains an extensive endomembrane network, the nuclear net

Abstract

Dinoflagellates are some of the most common eukaryotic cells in the ocean, but have very unusual nuclei. Many exhibit a form of closed mitosis (dinomitosis) wherein the nuclear envelope (NE) invaginates to form one or more trans-nuclear tunnels. Rather than contact spindles directly, the chromatids then bind to membrane-based kinetochores on the NE. To better understand these unique mitotic features, we reconstructed the nuclear architecture of Polykrikos kofoidii in 3D using focused ion beam scanning electron microscopy (FIB-SEM) in conjunction with high-pressure freezing, freeze-substitution, TEM, and confocal microscopy. We found that P. kofoidii possessed six nuclear tunnels, which were continuous with a reticulating network of membranes that has thus far gone unnoticed. These membranous extensions interconnect the six tunnels while ramifying throughout the nucleus to form a “nuclear net.” To our knowledge, the nuclear net is the most elaborate endomembrane structure described within a nucleus. Our findings demonstrate the utility of tomographic approaches for detecting 3D membrane networks and show that nuclear complexity has been underestimated in Polykrikos kofoidii and, potentially, in other dinoflagellates.

In-cell quantitative structural imaging of phytoplankton using 3D electron microscopy

“…Here, we present a complete imaging workflow to access the cellular and subcellular features of phytoplankton at the nanometric scale based on Focused Ion Beam -Scanning Electron Microscopy (FIB-SEM) (Hawes and Hummel, 2015;Narayan and Subramaniam, 2015;Titze and Genoud, 2016). This technique has already been applied successfully to provide 3D models of eukaryotic cells (Decelle et al, 2019;Flori et al, 2017;Gavelis et al, 2019). Although the spatial resolution of FIB-SEM (4-8 nm) is lower than the resolution of transmission electron microscopy (Engel et al, 2015;Wietrzynski et al, 2020), it has the advantage of providing contextual 3D images of whole cells at a specific time.…”

First record of the spatial organization of the nucleosome‐less chromatin of dinoflagellates: The nonrandom distribution of microsatellites and bipolar arrangement of telomeres in the nucleus of Gambierdiscus australes (Dinophyceae)

“…In yeast (Bystricky et al 2005), Drosophila (Hochstrasser et al 1986), and many plants with larger genomes, such as wheat or barley, interphase chromosomes exhibit a Rabl organization, with the telomeres and centromeres at opposite poles of the nucleus (reviewed by Cremer et al 2006). Dinoflagellates are unique among eukaryotes, as their chromosomes lack centromeres and never directly contact the cytoplasmic spindles (Gavelis et al 2019). Instead, it is the ends of the chromosomes themselves that mediate chromosomal segregation.…”

“…Dinoflagellates are unique among eukaryotes, as their chromosomes lack centromeres and never directly contact the cytoplasmic spindles (Gavelis et al. 2019). Instead, it is the ends of the chromosomes themselves that mediate chromosomal segregation.…”

A Strategy for Gene Knockdown in Dinoflagellates

“…In previous studies, Endo-Porter sometimes results in unsuccessful endosomal acidification, and therefore no release of the MO into the cytoplasm from their vesicle, but these localization points are usually known to appear as punctate fluorescence throughout the cell [47]. The singular, large area of localization may signify MO aggregation in the nucleolus or an RNA-granule [55,[59][60][61][62]. Dinoflagellates are known to have very unusual nuclei, specially named the "dinokarya."…”

“…Dinoflagellates are known to have very unusual nuclei, specially named the "dinokarya." Among other peculiar features are recently discovered "nuclear tunnels" which extend from the nuclear envelope of Polykrikos kofoidii, specifically during mitosis [59]. These nuclear envelope tunnels are also connected with a membranous structure throughout the nucleus known as the "nuclear net".…”