Asymmetrical cell division in brown algae: How far can we take the paradigm?

Asymmetrical cell division (ACD) is considered to be the major event leading to cellular differentiation, a crucial step in the development of multicellular organisms. However, when exactly a cell or tissue is considered differentiated is unclear. Focusing on brown algae, this review highlights the different cell division events during embryogenesis and in meristematic cells that establish symmetries or asymmetries in the resulting growing tissues. These examples show that global mechanisms at the embryo or stem cell level can act after and beyond the initial cell division event, which may therefore be less important. Therefore, this review suggests that the use of the term ACD should be restricted to cases where the different cellular functions 1) are characterised at the most comprehensive level possible and 2) are a direct consequence of cell division.