Fluorescence started to be visible in two cells of young embryos at around the 64 AB cell stage. Towards the end of gastrulation expression was visible in about 40 cells throughout the embryo including neuronal precursors, ventral hypodermal cells, and pharyngeal precursor cells. At the 1 to 2 fold stages fluorescence was observed in IL1 neurons (the identity was determined post-embryonically), the nine buccal epidermal cells, and additional cells in the head, most likely arcade cells. Transient expression was also observed in embryonic motoneurons (no longer visible in 3 fold stage embryos) and in a few apoptotic cells in the head. Based on their position they could be the sister cells of some of the IL1 neurons, which are known to undergo programmed cell death at this developmental stage. At the 3 fold stage expression was restricted to the buccal epidermal cells, most of the arcade cells (3 anterior and the DL and DR posterior arcade cells), and the six IL1 neurons. The two lateral IL1 neurons expressed the marker only weakly also in the L1 larval stage (but not later during development), whereas the dorsal and ventral IL1 neurons expressed GFP strongly throughout all larval stages and in the adults. Starting from the L1 larval stage expression could also be observed in the posterior cells of the gut. Starting from the L2 stage, when gonad development and migration begins, fluorescence became also visible in the distal tip cells of the gonad.