arkWD40 mutants contain additional midline glia (MG) cells and produce detectable proteins. (a) Stage 17 wild-type embryos contain on average 3 MG per segment. (b) Stage 17 arkH16 embryos contain on average 10.7 MG per segment (N = 7). (c) Stage 17 arkE4 embryos contain on average 9.1 MG per segment (N = 7). (d) Stage 17 arkJ7 embryos contain on average 8.3 MG per segment (N = 7). (e) Immunoblot analysis of head extracts probed with anti-ARK antibody.29 Relative molecular weight (Mr) in kDa is indicated on the left. Note P35 does not denote an ark allele, but encodes a caspase inhibitor. An unspecific band indicated by * serves as loading control. The genotypes of the head extracts are as follows: lane 1, FRT42D P[y+] (wild-type); lane 2, GheF; FRT42D arkP56/FRT42D P[w+]; lane 3, GheF; FRT42D arkD3/FRT42D P[w+]; lane 4, GheF; FRT42D arkE4/FRT42D P[w+]; lane 5, Ghef; GMR-P35