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We aim to identify the list of factors which control how macroalgae build their body.

Brown algae display diverse body architectures with a wide range of morphological complexities involving specialised organs (stipe, holdfast, pneumatocysts), vascular tissue (kelp) and complex reproductive organs (receptacle).

Their vegetative cells are non-motile, photosynthetic and surrounded by a cell wall. Because of their marine environment, they experience high osmotic pressure variations, dehydration and strong mechanical forces.

Therefore, in addition to the endogenous factors (e.g. macroalgal gene products, cell-cell communication), the exogenous factors play important roles in macroalgal development and morphogenesis.

To identify these factors, we use a large pannel of cellular, molecular and genetic approaches and techniques (laser capture microdissection, genome-wide transcriptomics, mutant analysis, atomic force microscopy, cell immunolocalisation, electron microscopy).

We initiated our study in the filamentous brown alga Ectocarpus siliculosus, because its morphology is simple and basic: a string of cells, which ultimately branches. Re-iteration of this process leads to a bushy organism 1 cm wide.

Therefore, to encompass the overall developmental pattern, we study:

1- Tip growth: Early growth of the sporophyte filament is primarily ensured by apical cell elongation and division
2- Cell differentiation: Apical cylindrical cells progressively differentiate into spherical cells
3- Branching: primary filaments initiate branching at the ~ 10 cell stage. Re-iterative branching pattern on further filaments gives rise to the final body morphology

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Illustration: Time-lapse movie of young Ectocarpus sporophytes (movie speed approx. 1 image / h; 40000x real life speed).

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Ectocarpus Sporophyte Development

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Development of the parenchymatous seaweed Saccharina

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Saccharina sporophytes develop parenchymatous thallus. We aim to figure out how its large blade (several meters long) is produced, in regard to the patterns of cell division and cell differentiation, and the mechanisms of cell-cell communication within this tissue (local or large-range).

We used techniques such as time-lapse video to assess the growth dynamic of this alga in in vitro cultures.

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Presentation

Research Topics

Development of the filamentous brown alga Ectocarpus

Ectocarpus Sporophyte Development

Development of the parenchymatous seaweed Saccharina