 The ZLI was first discovered in the chick using explant and lineage-labeling experiments.In the explant experiments, cells in the region that will become the ZLI, the prethalamus, and the thalamus in the chick were removed and placed into separate cultures; the cells continued to grow and retained their identity (the ZLI began transcribing, whereas the prethalamus and thalamus did not).Necessity of the ZLI and its corresponding ' expression were evidenced by lack of thalamic and prethalamic genetic markers in culture (see Signaling).