Movie 1.

Imaging jump transcription over the length scale of the developmental niche. The time series progressively zooms out, showing transcriptional events in single cells, then zooming out to show the position and movement of individual cells in the context of the early developmental niche. The cells are a mixture of cafA transcriptional reporter cells and cells expressing the cAMP reporter, Flamindo2. The contrast has been optimised in this case to make the transcriptional reporter cells clearly visible. In the first frame, the arrow points to a cell with a bright nuclear spot corresponding to nascent cafA RNA, at the site of transcription. As the movie zooms out, the full niche becomes apparent, with the undifferentiated cells to the left and the differentiating cells further to the right, with the onset of cell aggregation (streaming) visible. The playback is at 7 frames per second, with each frame captured every 1 minute. When fully zoomed out, the field of view is 1.68mm along the long axis.