Biology subjects

Le Bail, A.

Publications and source records attributed to Le Bail, A..

4 recordsLinked to original sources

bioRxiv2026

Cell position is more important than cell shape or age for the acquisition of cell identity in the brown alga Ectocarpus.

The brown alga Ectocarpus is a morphologically simple organism, with cells in the growing filament changing shape and position over time. In this study, we investigated the roles of cell shape, position, and age in establishing cell identity in Ectocarpus. Using laser capture microdissection, we isolated cells with different relative ages, shapes and positions from young sporophytes, and analysed their transcriptomes using differential RNA-seq to attribute a molecular signature to each cell. Five distinct cell transcriptomic signatures were found along the filament of WT Ectocarpus; the apical cell signature differed most from the others. To dissociate cell shape, age, and position, we analysed the transcriptomes of two mutants in which the relationships between these three parameters were disrupted. We found that the transcriptomic profile observed in the WT was significantly altered in these mutants. Overall, our data revealed that molecular cell signatures depend primarily on cell position along the filament and secondarily on cell shape.

developmental biology↗

bioRxiv2024

Processes essential for Physcomitrium patens protonemal development require distinct levels of total activity provided by functionally redundant PpROP GTPases

RHO GTPases are key regulators of cellular and developmental processes in most eukaryotic organisms. ROPs (RHO of plants) constitute a plant-specific RHO subfamily. ROP families expanded and functionally diversified during the evolution of structurally complex vascular plants, but generally contain few members in non-vascular plants with ancient features. In vascular and non-vascular plants, ROP proteins are required for cell polarization, directional cell expansion, and mitotic cell plate positioning. All these processes are impaired by the disruption of PpROP activity in the non-vascular moss Physcomitrium patens. The aim of the study presented here was to further characterize PpROP functions during P. patens protonemal development by a) knocking out individually or in all possible combinations each of the four RpROP genes, which encode nearly identical proteins, b) complementing knock-out mutants with WT or mutant PpROP isoforms, or with heterologous homologs, and c) performing overexpression experiments. PpROPs were found to have additional previously unknown functions in the regulation of cell proliferation, caulonema differentiation, and gametophore formation. Furthermore, different cellular and developmental processes were shown to require distinct levels of total PpROP activity, rather than individual PpROP isoforms. Implications of the remarkable sequence conservation and functional integration within the PpROP protein family are discussed. One-sentence summaryKnock-out, complementation, and overexpression experiments further defined PpROP functions in P. patens development, and demonstrated their dependence on distinct levels of total PpROP activity.

cell biology↗

bioRxiv2024

The longitudinal growth of the embryo of the kelp Saccharina depends on actin filaments that control the formation of an alginate corset in the cell wall

The initiation of embryogenesis in the kelp Saccharina latissima is accompanied by significant anisotropy in cell shape. Using monoclonal antibodies, we show that this anisotropy coincides with a spatio-temporal pattern of accumulation of alginates in the cell wall of the zygote and embryo. Alginates rich in guluronates as well as sulphated fucans show a homogeneous distribution in the embryo throughout Phase I of embryogenesis, but mannuronate alginates accumulate mainly on the sides of the zygote and embryo, disappearing as the embryo enlarges at the start of Phase II. This pattern depends on the presence of cortical actin filaments. In contrast, within the embryo lamina, the alginate composition of the walls newly formed by cytokinesis is not affected by the depolymerisation of actin filaments. Thus, in addition to revealing the existence of a mannuronate-rich alginate corset that may restrict the enlargement of the zygote and the embryo, thereby promoting the formation of the apico-basal growth axis, we demonstrate stage- and cytoskeleton-dependent differences in cell wall deposition in Saccharina embryos.

developmental biology↗

bioRxiv2021

Tip growth in the brown alga Ectocarpus is controlled by a RHO-GAP-BAR domain protein independently from F-actin organisation

The brown alga Ectocarpus is a filamentous seaweed that grows by tip growth and branching. In the morphometric mutant etoile, tip growth is slower than in the WT and eventually stops. In this paper, we show that the causal etoile mutation is a null mutation in a bi-domain BAR-RhoGAP gene. By quantitative RT-PCR, we showed that ETOILE is ubiquitously expressed in prostrate filaments of the Ectocarpus sporophyte, and is downregulated in the etoile mutant. We immunolocalised both domains of the protein in WT and etoile, as well as RAC1, the known target of Rho-GAP enzymes. Thus, ETOILE would be localised at the apical cell dome where it would control the localisation of EsRAC1 to the plasma membrane. Actin staining showed that the mutant is not affected in F-actin structures. Overall, these results suggest that in Ectocarpus, BAR-RhoGAP controls tip growth by controlling RAC1 localization and through an actin-independent mechanism.

developmental biology↗