(A) FISH was used to show that IF-1 is not coexpressed with prohormone convertase-2 (PC-2, 0/25 IF-1+ cells were PC-2+). (B) slc1a-5 and glutamine synthetase 1 (GS-1), genes required for glutamate uptake and conversion to glutamine are also expressed in an IF-1-like neuropil pattern. (C) IF-1 is co-expressed with slc1a-5 and GS-1 (46/62 IF-1+ cells were slc1a-5+ and 56/56 IF-1+ cells were GS-1+). IF-1+cells also express the solute carrier genes slc1a-3 (33/33), slc2a-1 (76/76), slc6a-2 (31/35), slc6a-8 (48/48) and slc7a-8 (63/63). Overlap was near perfect for some genes (all slc7a-8+ cells express IF-1), but other genes are more widely expressed (only 48/347 slc6a-8+ cells express IF-1). (D) Two genes from module 2 (a downregulated gene cluster) are also expressed in a neuropil-like pattern. jagged-like is expressed in puncta and a novel gene, estrella, is expressed strongly in the neuropil and in cells around the planarian body. (E) IF-1+ cells express jagged-like and estrella (48/48 and 61/61, respectively). (F–G) FISH with the estrella probe marks cells with extensive cytoplasmic projections in the neuropil, in the periphery of the animal body, near the brain branches, and in the eye, suggesting that estrella+ cells surround many components of the planarian nervous system. (H) An electron micrograph of a putative planarian glial cell in the neuropil of the ventral nerve cord. The cell membrane (determined by images acquired at higher magnification) is marked in magenta and the nuclear envelope is shown in cyan. The cytoplasm is more electron dense than that in surrounding axons. The nuclear morphology is elongated, with heterochromatin at the nuclear periphery; these features are not present in neurons visualized by EM. (I) A partial reconstruction of the cell in (H) through ten serial sections. The cell membrane and nuclear envelope are colored as above. Scale bars: 500 µm (B, D), 20 µm (A, C, E, G), 100 µm (F), 5 µm (H–I).