Fig. 3. rnt-1 mutants have fewer seam cells. (A) Lineage diagram showing V and T lineage divisions in wild-type males. Seam cells are indicated by circles, hyp7 nuclei by squares, glial and neuronal cells by diamonds, and ray precursor cells by triangles. Proliferative divisions are in bold. The broken lines indicate parts of the lineage omitted for simplicity. The V and T lineages of the male are identical to those of the hermaphrodite until the end of L2. Divisions are asymmetric and stem cell like, with the anterior daughter adopting the syncytial fate (fusing with the hypodermal cell hyp7) and the posterior daughter adopting the proliferative fate (Sulston and Horvitz, 1977). An exception to this division pattern is at the beginning of L2, when an extra symmetrical division occurs in both sexes in V1-V4, V6 and T, resulting in an increase in seam cell number. In hermaphrodites, asymmetric divisions then continue, whereas in males V5-, V6- and T-derived cells undergo extra symmetrical, proliferative divisions at the beginning of L3 in order to generate nine ray precursor cells (R1-R9) (Sulston and Horvitz, 1977). Male-specific ray sub-lineages then give rise to nine similar sets of neuronal-like cells (including a structural cell) on each side of the animal, corresponding to the nine rays found on each side of the male tail, as well as nine hypodermal-like cells (Rn.p cells). The characteristic ray sensilla are formed by retraction of the hypodermis surrounding the ray cell groups, leaving finger-like protrusions embedded in the cuticular fan. (B,C) Seam cells in adult hermaphrodites visualised using the scm::GFP reporter. This reporter shows all seam cell nuclei (white arrows indicate one such nucleus in each panel) present along the length of the animal. (B) him-5(e1490). All 16 seam cells are present. (C) rnt-1(ok351); him-5(e1490) adult hermaphrodite. Fewer seam cells are present, 11 in this specimen. The most anterior seam cell is not visible in this photograph. Scale bar in B: 70 µm for B,C. (D) Graph showing a quantitative analysis of seam cell number in him-5(e1490) (n=30) and rnt-1(ok351); him-5(e1490) (n=32) adult hermaphrodites and males (n=30 for him-5(e1490) males; n=28 for rnt-1(ok351); him-5(e1490) males). There is a significant difference between wild-type and rnt-1 seam cell number in both hermaphrodites and males (P<0.0001). Error bars represent the s.e.m. The y-axis starts at 10 to reflect the number of seam cells present at hatching, as it is only post-embryonic divisions that are affected in rnt-1 mutants.