Fig. 4. Positional cloning of piranha. (A) Genomic organization of the piranha (tolloid-related 1, tlr1) locus. The 3' end of the tlr1 gene is less than 1 kb away from the 5' end of its paralog tolloid (tld), limiting the 5' regulatory region of tld to a minimum. (B) Domain structure of Drosophila Tlr1, Tld and their mouse homologs. The EMS-induced point mutations in the four piranha (tlr1) alleles are indicated (see text). (C-F) In situ hybridization using tlr1 antisense probes. tlr1 is expressed in the dorsal blastoderm at stage 5 (C), in progenitor cells of the visceral mesoderm at stage 10 (D), in somatic muscles at stage 13 (E) and in cells of the ventral nerve cord and ring gland (arrow) at stage 16 (F).