A confocal microscopic image shows a portion of an early embryo of the glossiphoniid leech, Helobdella triserialis. Leeches are segmented worms that generate segments sequentially from a posterior growth zone, via the stereotyped divisions of a set of ten embryonic stem cells (called teloblasts) and their progeny (primary blast cells).

In the image, one of the two mesodermal stem cells (the left hand M teloblast; the large red sphere) had been labeled by microinjection with a red-fluorescing lineage tracer, that was then passed on to the column of primary m blast cells arising by successive mitoses of the teloblast. Sometime later, an individual M-blast cell was injected with a green-fluorescing lineage tracer (the doubly labeled cell appears yellow) so that its individual contributions to the segmental mesoderm could be studied relative to the other M-teloblast derivatives.

This is part of a larger study on development in the laboratory of David Weisblat in the Department of Molecular and Cell Biology.

Photo submitted by Photo by Dr. Michael Leviten, when he was a postdoc in the Weisblat lab.