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. 2010 Oct 26;20(20):R875-6.
doi: 10.1016/j.cub.2010.09.014.

Multicellular development in a choanoflagellate

Stephen R Fairclough, Mark J Dayel, Nicole King

Multicellular development in a choanoflagellate

Stephen R Fairclough et al. Curr Biol. .

Abstract

Little is known about how the first animals evolved from their single celled ancestors. Over 120 years ago, Haeckel proposed that animals evolved through "repeated self-division of [a] primary cell,"[1] an idea supported by the observation that all animals develop from a single cell (the zygote) through successive rounds of cell division [2]. Nonetheless, there are multiple alternative hypotheses [3], including the formal possibility that multicellularity in the progenitor of animals occurred through cell aggregation, with embryogenesis by cell division being secondarily derived. The closest known relatives of animals, choanoflagellates, are emerging as a model system for testing specific hypotheses about animal origins [–7]. Studying colony formation in choanoflagellates may provide a context for reconstructing the evolution of animal multicellularity. We find that the transition from single cells to multicelled colonies in the choanoflagellate Salpingoeca rosetta occurs by cell division, with sister cells remaining stably attached.

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Figures

Figure 1
Figure 1. Salpingoeca rosetta colonies develop through cell division, not aggregation
(A) Still images from a time-lapse movie show S. rosetta cells dividing (arrows) during colony development. In each case, the sister cells (arrowheads) remain attached. Extra-colonial cells were never observed to join a colony through aggregation. Scale bar represents 10 µm. The founder cell and its progeny were marked 1 – 1.2.1.2 to generate the cell pedigree in panel B. Time since start of movie (hours:minutes) is indicated in lower right of each panel. (B) The mapping of cell pedigree as a function of time, based on the time-lapse movie in panel A, shows that cells divide asynchronously during colony formation. (C) The cell cycle inhibitor aphidicolin prevents S. rosetta cell proliferation and the effect is reversed by removal of the drug. Control cultures, whether induced to form colonies (filled square) or not (open square), proliferate at the same rate. Aphidicolin blocks cell proliferation in cultures induced to form colonies (filled triangle) relative to untreated cultures. Removal of aphidicolin (arrow) allows the resumption of proliferation (open triangle). (D) Cell cycle inhibition prevents S. rosetta colony development. Relative to untreated S. rosetta cultures (filled square) in which the number of cells in colonies increases steadily after induction of colony development, induced cultures treated with aphidicolin (filled triangle) lack colonies. After removal of aphidicolin (arrow), the number of cells in colonies increases (open triangle), demonstrating that colony formation is dependent on cell proliferation. Error bars represent the standard error of the mean for each time point from triplicate cultures.
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References

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