Choanocyte labelling and lineage-tracing in juvenile Amphimedon queenslandica. A, B: Choanocytes in chambers (ch) in juveniles are labelled with CM-DiI; note strong plasma membrane labelling in choanocytes (inset). C-F: Descendants of juveniles whose chambers were labelled with CM-DiI seven days earlier (as in A). Multiple other juvenile cell types are now labelled and spread through the sponge body. Note in (D) the limited number of CM-DiI-labelled choanocytes remaining in the choanocyte chambers (ch) seven days after labelling and the presence of labelled archeocytes with large nuclei (nu; inset), consistent with transdifferentiation of choanocytes into archeocytes. Note the presence of nuclear fragments (fr) presumably resulting from phagocytosis that has occurred during de-differentiation [see Additional file 5: Figure S5]. Arrowheads in E and F show a labelled exopinacocyte and a sclerocyte, respectively, indicating these cell types can also be produced from de-differentiating choanocytes. Nuclei are stained with DAPI. Scale bars: 100 μm (A, C), 10 μm (B, D-F). DAPI, 4',6-diamidino-2-phenylindole.