Biology subjects

Castagnetti, S.

Publications and source records attributed to Castagnetti, S..

5 recordsLinked to original sources

bioRxiv2026

The extraordinary robustness of mitotic spindle assembly to microtubule dynamics plasticity revealed by end-binding proteins and tubulin tagging

Microtubules are dynamic, conserved cytoskeletal filaments that are essential for all eukaryotic cells. Microtubule dynamic properties are primarily characterized by measuring how fast they grow and shrink (growth and shrinkage rates) and how often they switch between assembly and disassembly (catastrophe and rescue frequencies). These four parameters measured for individual filaments can inform on the behavior of the entire microtubule network at the cell level. By comparing microtubule dynamics in Caenorhabditis elegans one-cell embryos using different genetically-encoded fluorescent probes, we observed an unexpected high variability in these parameters. Microtubule dynamics parameters were consistently higher in C. elegans strains expressing a fluorescently labelled microtubule end-binding protein than in strains relying on tubulin labelling, with microtubule growth rates differing by nearly a factor of two between the two conditions. This discrepancy was not limited to C. elegans, as we observed a similar effect in embryos of the tunicate Phallusia mammillata. Despite this, spindle size and assembly timing were only mildly affected. However, embryos expressing labelled end-binding protein exhibited higher frequency of mitotic defects and perturbed embryonic development upon exposure to various stresses such as elevated temperature or a compromised spindle assembly checkpoint. Thus, our work reveals both the remarkable robustness of mitotic spindle assembly in response to extreme microtubule dynamics plasticity, and the requirement for strict control of microtubule dynamics across successive early embryonic divisions. Our findings should also serve as a cautionary note when using tagged end-binding proteins to measure microtubule dynamics.

cell biology↗

bioRxiv2025

Embryonic development of the Mediterranean starfish Hacelia attenuata

Starfish play essential ecological roles as predators and ecosystem regulators, however detailed developmental descriptions exist for only a handful of species, none of which come from the Mediterranean. In this study we provide the first full account of the development of the Mediterranean starfish Hacelia attenuata, from oocyte maturation through embryogenesis and larval formation, showing that its development largely follows the canonical pattern known from other asteroids. Oocytes resume meiosis when exposed to 1-methyladenine, exhibiting conserved features such as formation of a nuclear actin shell for chromosome gathering prior to meiotic spindle assembly. Embryogenesis then proceeds through equal radial cleavages to form a ciliated blastula, followed by gastrulation via invagination and mesenchymal cell delamination. The larvae develop through typical bipinnaria and brachiolaria stages, displaying characteristic feeding structures and attachment organs. Importantly, developmental rate increases substantially at higher temperatures, consistent with the species distribution in warm Mediterranean waters. Together, these findings position H. attenuata as a promising new model for studying thermal adaptation, environmental resilience and conserved developmental mechanisms in starfish.

developmental biology↗

bioRxiv2023

Microtubule reorganization during mitotic cell division in the dinoflagellate Ostreospis cf. ovata

Dinoflagellates are marine organisms that undergo seasonal explosive proliferation events known as algal blooms. Vegetative cell proliferation is a main contributing factor in these events. However, mechanistical understanding of mitosis and cytokinesis in dinoflagellate remains rudimentary. Using an optimized immunofluorescence protocol, we analysed changes in microtubule organization occurring during the mitotic cycle of the toxic dinoflagellate Ostreopsis cf. ovata. This study revealed important features of dinoflagellate cell division. We find that the two flagella and the cortical microtubule array persist throughout the mitotic cycle. Two microtubule bundles are present in the cytoplasm originating from the ventral area, where the basal bodies are located: a cortical bundle and a cytoplasmic ventral bundle. The latter associates with the nucleus in the cell centre in preparation for mitosis and with the acentrosomal extranuclear spindle during mitosis. Analysis of tubulin post-translational modifications identifies two populations of spindle microtubules: polar acetylated microtubules whose length is stable throughout mitosis and central tyrosinated microtubules which elongate during chromosome segregation. During cell division a microtubule rich structure forms along the dorsal-ventral axis, associated with the site of cytokinesis, consistent with a cytokinetic mechanism independent of the actomyosin ring typical of animal and yeast cells. Summary statementOur study describes special features of mitosis and cytokinesis in dinoflagellates and uncovers a new alternative mechanism for cell division, highlighting the plasticity of cell biological process in eukaryotic cells.

cell biology↗

bioRxiv2022

Modulation of Spindle Assembly Checkpoint efficiency by cell fate in a chordate embryo

The spindle assembly checkpoint (SAC) is a surveillance system which preserves genome integrity by delaying anaphase onset until all chromosomes are correctly attached to spindle microtubules. Recruitment of SAC proteins to unattached kinetochores generates an inhibitory signal that prolongs mitotic duration. Chordate embryos are atypical in that spindle defects do not delay mitotic progression during early development, implying that either the SAC is inactive or the cell-cycle target machinery unresponsive. Here we show that in embryos of the chordate Phallusia mammillata the SAC delays mitotic progression from the 8th cleavage divisions. Unattached kinetochores are not recognized by the SAC machinery until the 7th cell cycle when the SAC is acquired. Following acquisition, SAC strength, manifest as the degree of mitotic lengthening induced by spindle perturbations, is specific to different cell types and is modulated by cell size showing similarity to SAC control in early Caenorhabditis elegans embryos. We conclude that SAC acquisition is a process likely specific to chordate embryos, while modulation of SAC efficiency in SAC proficient stages depends on cell fate and cell size similarly to non-chordate embryos.

cell biology↗

bioRxiv2019

The spindle assembly checkpoint functions during early development in non-chordate embryos.

In eukaryotic cells, a spindle assembly checkpoint (SAC) ensures accurate chromosome segregation. This control mechanism monitors proper attachment of chromosomes to spindle microtubules and delays mitotic progression if connections are erroneous or absent. The SAC operates in all eukaryotic cells tested so far, but is thought to be relaxed during early embryonic development in animals. Here, we evaluate the checkpoint response to lack of kinetochore-spindle microtubule interactions in early embryos of diverse animal species from the main metazoan groups. Our analysis shows that there are two classes of embryos, either proficient or deficient for SAC activation during cleavage. Sea urchins, mussels and jellyfish embryos show a prolonged mitotic block in the absence of spindle microtubules from the first cleavage division, while ascidian and amphioxus embryos, like those of Xenopus and zebrafish, continue mitotic cycling without delay. SAC competence during early development shows no correlation with cell size, chromosome number or kinetochore to cell volume ratio, ruling out the hypothesis that lack of checkpoint activity in early embryos is due to the large egg volume. Our results instead indicate that there is no inherent incompatibility between SAC activity and large fast-dividing embryonic cells. We suggest that SAC proficiency is the default situation of metazoan embryos, and that SAC activity is specifically silenced in chordate species with fast dividing embryos.

cell biology↗