Fig. 2. nXFPs as lineage tracers in Helobdella. (A) Photomontage made from stacks of confocal images (processed by Imaris, Bitplane) showing a ventral view (midline to left) of a stage 10 embryo, 140 hours after the left N teloblast had been injected with nGFP mRNA. nGFP labeled nuclei occupy the anterior and posterior lobes of N-derived ganglionic neurons and the three peripheral neurons lying just outside the posterior (nf-derived) lobe (arrows). (B) Higher magnification view of the boxed region in A. (C) Epifluorescence images of the germinal plate of a late stage 8 embryo (ventral midline towards the left) about 100 hours after the left N and P teloblasts were injected with nGFP mRNA. The N and P lineages can be distinguished by a difference in fluorescence intensity, reflecting differences in the amount of mRNA injected into the parent teloblasts. The temporal gradient of development is evident in the progress of migrating neurons (arrowheads) which originate from a single cell at the medial edge of the p blast cell clone (arrow). (D) Side view of an early stage 10 embryo, 150 hours after the left N teloblast had been injected with nGFP mRNA shows an anterior (arrowhead) to posterior gradient of GFP intensity. (E) Pseudocolored image (confocal stack) showing a ventral view of a live mid stage 8 embryo, 83 hours after one N teloblast had been injected at stage 7 with nCFP mRNA and the other with nYFP mRNA 3 hours later (nCFP, purple; nYFP, green). Scale bar: 20 µm.