I. The origin of animal multicellularity
II. Choanoflagellate colonies, bacterial signals and animal origins
Part I: The origin of animal multicellularity
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Animals, plants, green algae, fungi and slime molds are all forms of multicellular life, yet each evolved multicellularity independently. How did animals evolve from their single-celled ancestors? King addresses this question using a group of fascinating organisms called choanoflagellates. Choanoflagellates are the closest living relatives to animals; they are single-cell, flagellated, bacteria eating organisms found between fungi and animals on the phylogenetic tree of life. By sequencing the genomes of many choanoflagellate species, King and her colleagues have discovered that some genes required for multicellularity in animals, such as adhesion, signaling, and extracellular matrix genes, are found in choanoflagellates. This suggests that these genes may have evolved before the transition to multicellularity in animals.
The choanoflagellate S. rosetta can exist as a unicellular organism or it can switch to form multicellular colonies. In fact, its life cycle can be quite complex; it can form long chain colonies, spherical colonies called rosettes, or exist in different unicellular forms. In part 2 of her talk, King explains how she chose to use S. rosetta as a simple model for animal origins. After overcoming the technical difficulty of getting S. rosetta to form rosettes in the lab, she investigated how rosettes develop and how the cells within a rosette adhere to each other. She also asked the intriguing question “What regulates rosette development?”. It turns out that rosette formation is regulated by lipids produced by environmental bacteria that S. rosetta eat. This result adds to the growing interest in how bacteria may be influencing the behavior of diverse animals including humans.
While fossils sparked Nicole King’s childhood interest in evolution, she realized that the fossil record doesn’t explain fully how animals first evolved from their single celled ancestors. To answer this question, King decided to study modern day choanoflagellates. Choanoflagellates are single celled organisms that can also develop into multicellular assemblages.
King first learned about choanoflagellates while she was a graduate student with Richard Losick at Harvard University. She moved to the University of Wisconsin-Madison to do a post-doctoral fellowship focusing on choanoflagellates. In 2003, King joined the faculty at the University of California, Berkeley. Currently, she is a Professor of Molecular and Cell Biology at Berkeley and a Howard Hughes Medical Institute Investigator.
King’s innovative studies have been recognized with a MacArthur Foundation Fellowship and a Pew Scholarship. King is also a Senior Fellow of the Canadian Institute for Advanced Research.
- Marc Kirschner iBioSeminar: The Origin of Vertebrates
- Dianne Newman iBioSeminar: Microbial Diversity and Evolution
- Richard Losick iBioSeminar: New Research on Multicellularity
Levin TC, Greaney AJ, Wetzel L, King N: The rosetteless gene controls development in the choanoflagellate S. rosetta. eLife 2014, 3.
Alegado RA, King N: Bacterial Influences on Animal Origins. Cold Spring Harb Perspect Biol 2014.
Richter DJ, King N: The Genomic and Cellular Foundations of Animal Origins. Annu Rev Genet 2013, 47:527–555.
Levin TC, King N: Evidence for sex and recombination in the choanoflagellate Salpingoeca rosetta. Curr Biol 2013, 23:2176–2180.
Nichols SA, Roberts BW, Richter DJ, Fairclough SR, King N: Origin of metazoan cadherin diversity and the antiquity of the classical cadherin/β-catenin complex. Proc Natl Acad Sci USA 2012, 109:13046–13051.
Alegado RA, Brown LW, Cao S, Dermenjian RK, Zuzow R, Fairclough SR, Clardy J, King N: A bacterial sulfonolipid triggers multicellular development in the closest living relatives of animals. eLife 2012, 1:e00013.
King N, Westbrook MJ, Young SL, Kuo A, Abedin M, Chapman J, Fairclough S, Hellsten U, Isogai Y, Letunic I, Marr M, Pincus D, Putnam N, Rokas A, Wright KJ, Zuzow R, Dirks W, Good M, Goodstein D, Lemons D, Li W, Lyons JB, Morris A, Nichols S, Richter DJ, Salamov A, Sequencing JGI, Bork P, Lim WA, Manning G, et al.: The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans. Nature 2008, 451:783–788.
King N: The unicellular ancestry of animal development. Dev Cell 2004, 7:313–325.