Biology subjects

Bellutti, L.

Publications and source records attributed to Bellutti, L..

3 recordsLinked to original sources

bioRxiv2024

An interkinetic envelope surrounds chromosomes between meiosis I and II in C. elegans oocytes

At the end of cell division, the nuclear envelope reassembles around the decondensing chromosomes. Female meiosis culminates in two consecutive cell divisions of the oocyte, meiosis I and II, which are separated by a brief transition phase known as interkinesis. Due to the absence of chromosome decondensation and the suppression of genome replication during interkinesis, it has been widely assumed that the nuclear envelope does not reassemble between meiosis I and II. By analyzing interkinesis in C. elegans oocytes, we instead show that an atypical structure made of two lipid bilayers, which we termed the interkinetic envelope, surrounds the surface of the segregating chromosomes. The interkinetic envelope shares common features with the nuclear envelope but also exhibits specific characteristics that distinguish it, including its lack of continuity with the endoplasmic reticulum, unique protein composition, assembly mechanism, and function in chromosome segregation. These distinct attributes collectively define the interkinetic envelope as a unique and specialized structure that has been previously overlooked.

cell biology↗

bioRxiv2024

Genome-wide transcriptional silencing and mRNA stabilization allow the coordinated expression of the meiotic program in mice

The transcriptional dynamic of mammalian cells when these transit from the ubiquitous mitotic to a meiotic specific program is key to understand this switch central to sexual reproduction. By quantifying active RNA polymerase II and nascent transcripts using single cell dataset and ethynyl-uridine pool-down with sorted cells from synchronised testes, we detailed the transcriptional activity of murine male germ cells. When spermatogonia differentiate, transcription slows down, reaching minimal activity at meiotic entry and resumes during pachytene stage. This event, we termed EMLT (for early meiotic low transcription), is distinct from the silencing of sex chromosomes as it is independent of Setdb1 though it is accompanied by the same chromatin mark, H3K9me3. EMLT is delayed in Stra8KO but occurs in mutants altering meiotic chromosome structure or DSB formation or repair. By comparing transcript abundance and neotranscription we unveil a massive event of mRNA stabilization that parallels EMLT. Altogether our data indicate that meiosis is initiated with a nearly silent genome and we propose that the stabilization of transcripts at that time facilitates the meiotic entry by synchronising the expression of several meiotic sub-programs.

cell biology↗

bioRxiv2022

Synergistic stabilization of microtubules by BUB-1, HCP-1 and CLS- 2 controls meiotic spindle assembly in C. elegans oocytes

During cell division, chromosome segregation is orchestrated by a microtubule-based spindle. Interaction between spindle microtubules and kinetochores is central to the bi-orientation of chromosomes. Initially dynamic to allow spindle assembly and kinetochore attachments, which is essential for chromosome alignment, microtubules are eventually stabilized for efficient segregation of sister chromatids and homologous chromosomes during mitosis and meiosis I respectively. Therefore, the precise control of microtubule dynamics is of utmost importance during mitosis and meiosis. Here, we study the assembly and role of a kinetochore module, comprised of the kinase BUB-1, the two redundant CENP-F orthologs HCP-1/2, and the CLASP family member CLS-2 (hereafter termed the BHC module), in the control of microtubule dynamics in Caenorhabditis elegans oocytes. Using a combination of in vivo structure-function analyses of BHC components and in vitro microtubule-based assays, we show that BHC components stabilize microtubules, which is essential for meiotic spindle formation and accurate chromosome segregation. Overall, our results show that BUB-1 and HCP-1/2 do not only act as targeting components for CLS-2 at kinetochores, but also synergistically control kinetochore-microtubule dynamics by promoting microtubule pause. Together, our results suggest that BUB-1 and HCP-1/2 actively participate in the control of kinetochore-microtubule dynamics in the context of the BHC module to promote accurate chromosome segregation in meiosis.

cell biology↗