Biology subjects

Dumollard, R.

Publications and source records attributed to Dumollard, R..

7 recordsLinked to original sources

bioRxiv2026

Spatiotemporal regulation of LGN/NuMA and astral microtubules generate mirror symmetric spindle rotations

The positioning of the mitotic spindle controls the size, content, and position of daughter cells within embryos and tissues. A major spindle positioning mechanism is cortical pulling whereby the membrane-bound complex LGN/NuMA/Dynein captures astral microtubules and pulls centrosomes toward the cell cortex. Cytoplasmic dynein and astral growth tend to counteract cortical pulling and position spindles at the cell center. It remains unclear how these opposing forces cooperate. Here we examine the ascidian embryo, where spindles of two germ line cells rotate toward one another causing divisions which are both mirror symmetric and unequal. We find that this spindle behavior is governed by transient enrichment of LGN and NuMA and enhanced cortical pulling at the shared cell contact. Inhibition of the LGN/NuMA complex disrupts spindle alignment, unequal cleavage, and mirror symmetry. Temporal analysis shows that cortical pulling force initates at anaphase when there is a sharp increase in astral microtubule length. These results point towards two phases of spindle positioning forces, with cytoplasmic pulling and cortical pulling operating sequentially during early and late mitosis.

cell biology↗

bioRxiv2026

The monoaminergic system in a bivalve larva: temporal deployment and spatial organization

Originating at the base of the bilaterian tree of life, the monoaminergic (MOA) system is a pivotal and evolutionarily conserved regulator of animal development and of responses to changing environmental conditions. Investigating the ontogeny of monoaminergic modulation in model systems such as marine bivalve molluscs is therefore particularly relevant, as their life cycle and developmental transitions are strongly influenced by environmental cues. Here, we characterized the spatio-temporal and tissue-specific expression of components of the MOA system during early larval development of the Mediterranean mussel Mytilus galloprovincialis using both time resolved transcriptomics and in situ Hybridization Chain Reaction (HCR). Our results identify serotonin and dopamine as the predominant and interconnected monoaminergic pathways deployed during early mussel development, with receptors, enzymes, and selective transporters broadly expressed across both neuronal and non-neuronal tissues. Notably, the expression of receptors preceding that of the corresponding biosynthetic enzymes indicates early, non-neuronal roles of monoaminergic signalling, supported by their localization in peripheral tissues such as ciliated epithelia. Altogether, These findings support the hypothesis that the MOA system acts as a pervasive and tightly regulated modulator of larval morphogenesis and could therefore play an evolutionary conserved role in mediating development and environmental plasticity in developing bilaterian organisms.

developmental biology↗

bioRxiv2023

The Mediterranean mussel, Mytilus galloprovincialis, a novel model for developmental studies of mollusks

A model organism in developmental biology is defined by its experimental amenability as well as by resources created for the model system by the scientific community. For the most powerful models, the combination of both has already yielded a thorough understanding of development. However, the number of developmental model systems is still very limited, and their phylogenetic distribution is heavily biased. Members of one of the largest animal phyla, the mollusks, for example, have long been neglected as developmental model organisms. To remedy this shortcoming, we produced a detailed developmental transcriptome for the Mediterranean mussel Mytilus galloprovincialis, a bivalve mollusk, and expanded the list of experimental protocols available for this species. Our high-quality transcriptome allowed us to identify transcriptomic signatures of developmental transitions and to perform a first comparison with the Pacific oyster Crassostrea gigas that can be used in future multi-species analyses. To allow co-labelling studies, we optimized protocols for immunohistochemistry and hybridization chain reaction and combined both techniques to create high-resolution co-expression maps of developmental genes. The resources and protocols we describe here thus represent an enormous boost for the establishment of the Mediterranean mussel as a laboratory model in developmental biology. Summary statementResources and techniques are described for the Mediterranean mussel Mytilus galloprovincialis, which, together, establish a novel model system for studying mollusk development and animal evolution.

developmental biology↗

bioRxiv2023

Reduction of cortical pulling at mitotic entry facilitates aster centration

Although it has been studied for more than a century, the question of how one cell divides into two equal parts is still not fully resolved. Zygotes have provided much of the mechanistic insight into how the mitotic apparatus finds the center of the cell since the centrally-located mitotic apparatus is created from a large sperm aster that forms at the cortex and thus far from the zygote center. Here we show that in ascidians, the sperm aster extends throughout the cytoplasm during interphase yet remains located near the cortex and does not migrate towards the zygote center. It is only at mitotic entry, when the sperm aster has duplicated and the mitotic apparatus is being assembled, that most of the migration and centration occurs. This temporal pattern of centration behavior is mirrored by primate zygotes (including human). The current mechanisms of aster centration include cytoplasmic pulling that scale with microtubule (MT) length, MT pushing against the proximal cortex or MT-based cortical pulling. However, it is not yet known whether and how these 3 mechanisms are coordinated to prevent aster migration during interphase and trigger migration at mitotic entry. By monitoring quantitatively all three mechanisms (cytoplasmic pulling, pushing and cortical pulling) we have discovered that cortical pulling is switched off as the zygote enters mitosis while both cytoplasmic pulling and proximal cortical pushing remain active. Physical simulations could recapitulate both the static and migratory aspects of sperm aster and mitotic apparatus behavior. We therefore surmise that the reduction in cortical pulling at mitotic entry represents a switch that allows proximal cortical pushing forces and cytoplasmic pulling forces to center the nascent mitotic apparatus. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=156 SRC="FIGDIR/small/533625v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@135189dorg.highwire.dtl.DTLVardef@e2ef1dorg.highwire.dtl.DTLVardef@c070f7org.highwire.dtl.DTLVardef@38832f_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LISperm aster/mitotic apparatus centration occurs at entry into first mitosis C_LIO_LIMT-based cortical pulling is active during interphase and switched off at mitotic entry C_LIO_LILoss of cortical pulling at mitosis entry facilitates centration of the aster C_LIO_LIMT-based cytoplasmic pulling is active during both interphase and mitosis C_LIO_LIAgent-based simulations advocate the need for cytoplasmic pulling, a switch in cortical pulling and a minor role of pushing for aster centration at mitotic entry. C_LI

cell biology↗

bioRxiv2021

Molecular basis of ocean acidification sensitivity and adaptation in Mytilus galloprovincialis

One challenge in global change biology is to identify the mechanisms underpinning physiological sensitivities to environmental change and to predict their potential to adapt to future conditions. Using ocean acidification as the representative stressor, molecular pathways associated with abnormal larval development of a globally distributed marine mussel are identified. The targeted developmental stage was the trochophore stage, which is, for a few hours, pH sensitive and is the main driver of developmental success. RNA sequencing and in situ RNA hybridization were used to identify processes associated with abnormal development, and DNA sequencing was used to identify which processes evolve when larvae are exposed to low pH for the full duration of their larval stage. Trochophores exposed to low pH exhibited 43 differentially expressed genes. Thirteen genes, none of which have previously been identified in mussel trochophores, including three unknown genes, were expressed in the shell field. Gene annotation and in situ hybridization point to two core processes associated with the response to low pH: development of the trochophore shell field and the cellular stress response. Encompassing both of these processes, five genes demonstrated changes in allele frequency that are indicative of rapid adaptation. Thus, genes underpinning the most pH-sensitive developmental processes also exhibit scope to adapt via genetic variation currently maintained in the mussel population. These results provide evidence that protecting species existing genetic diversity is a critical management action to maximize the potential for rapid adaptation under a changing environment.

ecology↗

bioRxiv2021

Combined effect of cell geometry and polarity domains determines the orientation of unequal division

Cell division orientation is thought to result from a competition between cell geometry and polarity domains controlling the position of the mitotic spindle during mitosis. Depending on the level of cell shape anisotropy or the strength of the polarity domain, one dominates the other and determines the orientation of the spindle. Whether and how such competition is also at work to determine unequal cell division (UCD), producing daughter cells of different size, remains unclear. Here, we show that cell geometry and polarity domains cooperate, rather than compete, in positioning the cleavage plane during UCDs in early ascidian embryos. We found that the UCDs and their orientation at the ascidian third cleavage rely on the spindle tilting in an anisotropic cell shape, and cortical polarity domains exerting different effects on spindle astral microtubules. By systematically varying mitotic cell shape, we could modulate the effect of attractive and repulsive polarity domains and consequently generate predicted daughter cell size asymmetries and position. We therefore propose that the spindle position during UCD is set by the combined activities of cell geometry and polarity domains, where cell geometry modulates the effect of cortical polarity domain(s). Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/442692v1_ufig1.gif" ALT="Figure 1"> View larger version (75K): org.highwire.dtl.DTLVardef@4b0e87org.highwire.dtl.DTLVardef@1a6fdbdorg.highwire.dtl.DTLVardef@5ca0ddorg.highwire.dtl.DTLVardef@1450e61_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightO_LISpindle tilting in anisotropic cell shape induces unequal cell division C_LIO_LICortical polarity domain can exert attractive or repulsive effect on spindle C_LIO_LICell geometry and polarity domain cooperate to position the spindle C_LIO_LICell geometry modulates the effect of polarity domain C_LI

cell biology↗

bioRxiv2017

Role of midbody remnant in meiosis II creating tethered polar bodies

Polar body (PB) formation is an extreme form of unequal cell division that occurs in oocytes due to the eccentric position of the small meiotic spindle near the oocyte cortex. Prior to PB formation, a chromatin-centered process causes the cortex overlying the meiotic chromosomes to become polarized. This polarized cortical subdomain marks the site where a cortical protrusion or outpocket forms at the oocyte surface creating the future PBs. We observed that PB1 becomes tethered to the egg via PB2, indicating that the site of PB1 cytokinesis directed the precise site for PB2 emission. We therefore studied whether the midbody remnant left behind following PB1 emission was involved, together with the egg chromatin, in defining the precise cortical site for PB2 emission. During outpocketing of PB2 in ascidians, we discovered that a small corps around 1m in diameter protruded from the center of the cortical outpocket that will form the future PB2, which we call the \"polar corps\". During emission of PB2, this small polar corps became localized between PB2 and PB1 and appeared to link PB2 to PB1. We tested the hypothesis that this small polar corps on the surface of the forming PB2 was the midbody remnant from the previous round of PB1 cytokinesis. We had previously discovered that Plk1::Ven labeled midbody remnants in ascidian embryos. We therefore used Plk1::Ven to follow the dynamics of the PB1 midbody remnant during meiosis II. Plk1::Ven strongly labeled the small polar corps that formed on the surface of the cortical outpocket that created PB2. Following emission of PB2, this polar corps was rich in Plk1::Ven and linked PB2 to PB1. By labelling actin (with LifeAct::mCherry/GFP or TRITC-Phalloidin) we also demonstrated that actin accumulates at the midbody remnant and also forms a cortical cap around the midbody remnant in meiosis II that prefigured the precise site of cortical outpocketing during PB2 emission. Phalloidin staining of actin and immunolabelling of anti-phospho aPKC during meiosis II in eggs that had PB1 removed showed that the midbody remnant remained within the egg following emission of PB1. Dynamic imaging of microtubules labelled with Ens::3GFP, MAP7::GFP or EB3::3GFP showed that one pole of the second meiotic spindle was located near the midbody remnant while the other pole rotated away from the cortex during outpocketing. Finally, we report that failure of the second meiotic spindle to rotate can lead to the formation of two cortical outpockets at anaphase II, one above each set of chromatids. It is not known whether the midbody remnant of PB1 is involved in directing the precise location of PB2 in other species as in ascidians. However, a review of the literature indicates that PB1 is tethered to the egg surface via PB2 in a number of species including members of the cnidarians, lophotrochozoa and echinoids, suggesting that the midbody remnant formed during PB1 emission may be involved in directing the precise site of PB2 emission throughout the invertebrates.

developmental biology↗