Organizing Principles

What am I looking at?

This is a side-by-side time-lapse video of the same developing fruit fly embryo. In the view on the left, all its cells are visible, and in the view on the right, just the nervous system can be seen.

On the left, you can see the movement of the cells within the embryo as it develops. These early cell migrations establish the body plan for the eventual larva, in the fly’s next stage of development, including the location of its various tissues and organs.

Then about 15 seconds into the video, you can see the ghostly outline of the ventral nerve cord, a chain of nerve centers; watch as this develops into segmental ganglia connected by horizontal junctions called commissures. And about 20 seconds in, you can see the brain start forming at the top of the embryo. The jerky movements visible toward the end of the video are a result of the larva developing its musculature and trying to move.

And on the right, you can see in more detail the development of the organism’s nervous system.

Biology in the background

As organisms develop and grow, the cells in their bodies move and reorganize to satisfy changing developmental needs. As you can see in the embryo on the right, specific systems, like the nervous system, tend to begin development with their cells relatively loosely organized and widely distributed throughout the organism. However, as development progresses, the cells start to concentrate in specific areas and refine their organization, moving toward their location in the adult organism.

Analyzing how organisms develop from a fertilized egg to their complex adult form reveals how genetic information is translated into phenotypic traits – that is, an organism’s physical and behavioral characteristics.

A fruit fly embryo is about half a millimeter long, or roughly seven times larger than the width of a human hair.

Technique

This image was created using Simultaneous Multi-View (SiMView) light-sheet microscopy, a technology that allows fast, high-resolution microscopic imaging and is gentle enough for prolonged recording of living specimens.