Studying our unicellular cousins to understand the early ancestor of all animals. (A) Choanoflagellates are one of the closest living relatives of animals. (B) The choanoflagellate Salpingoeca rosetta forms rosette-like colonies, and Levin et al. have performed a random mutagenesis screen on S. rosetta (lightening bolt) and selected for strains that were unable to develop colonies. (C) One of the mutants identified (which Levin et al. named rosetteless) was affected in a protein with a signal peptide (red tip), ‘C-type lectin’ domains (green ovals) and two internal repeats (green rectangles). The red cross indicates where the mutation in the gene disrupts the normal processing (i.e. splicing) of the mRNA transcript. This introduces a premature stop into the transcript, which typically results in truncated versions of the protein being produced.
FIGURE CREDIT: 3D illustrations by Mark Dayel (CC BY-SA 3.0) www.dayel.com/blog/2010/10/07/choanoflagellate-illustrations.