Fig. 1. Loss of V and T rays in mab-2 mutants. (A) him-5(e1490) male tail, wild-type appearance. Lateral view. Nine sensory rays are visible on this side of the animal. Rays 1-6 are derived from the V lineage and rays 7-9 are T-lineage derived. Scale bar: 10 µm. (B) mab-2(e1241); him-5(e1490) male tail. Only three rays are present (white arrows). Scale bar: 10 µm. During execution of the ray sublineages, the ray precursor cells (R1-R9) divide to give a posterior hypodermal cell (R1.p-R9.p) and an anterior daughter that will go on to undergo two rounds of division to give rise to three cells (the fourth will die) that will make up the ray (two neuronal cells and a structural cell). R1.p-R5.p will make up the tail seam (set), whereas R6.p-R9.p will later fuse with hyp 7. At the stage shown, Rn.p cells are visible (labelled), as are cells from the anterior branch of each ray sublineage that will comprise each ray (white asterisks). Scale bar: 10 µm. (C,D) The arrangement of male tail hypodermal cells in L4 males visualised using the ajm-1::GFP reporter in him-5 and him-5; mab-2 animals. (C) him-5(e1490) male tail. Lateral view. R1.p-R8.p and associated ray cells are visible in this focal plane. (D) mab-2(e1241); him-5(e1490) male tail. Four Rn.p cells are present. These cells have enlarged to fill the gap left by the absence of other Rn.p cells. Scale bar: 10 µm. (E) mab-2(e1241); him-5(e1490) male showing a low penetrance (5-10%) ray fusion phenotype. Two white arrows indicate the fused rays. Scale bar: 10 µm. Posterior is towards the right in all panels.