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Fig. 1. Seam cell lineages and expression patterns of selected heterochronic genes.
(A) The postembryonic cell division pattern of a generic seam cell (left),
with the divisions specific to each larval stage color coded. Horizontal bars
indicate the time of cell divisions. The triple horizontal bars at the bottom
represent alae, hallmark cuticular ridges that are specific to the adult
cuticle. Larval (L) stages are indicated on the left, with ticks denoting the
molts. Seam cell lineage patterns for several null (0) mutations are shown on
the right, together with that of lin-14 gain-of-function
(gf) alleles. The mutant lineages are color coded with respect to the
wild-type lineage. (B) The expression patterns of selected heterochronic
genes. Arrows indicate positive regulatory interactions and bars indicate
negative regulatory interactions (direct interactions are shown in blue).
(C-E) L3 molt animals identified by a characteristic just-reflexed gonad
indicated by the black arrow in C. The cuticle of L3 molt stage wild-type
animals is smooth (D), whereas in lin-14(lf) mutants it contains alae
(E), cuticular ridges normally synthesized during the L4 molt. (F,G) L3 stage
worms expressing scm:gfp, which marks seam cell nuclei. The nuclear
gfp signal has been pseudo-colored green to distinguish it from
background autofluorescence. The 11 seam blast cell nuclei in the left
mid-body (V cells) are shown in wild type (F). In lin-4 mutants at
the same stage, there are only six V cells (G), owing to the omission of the
L2 stage proliferative division (blue in A), which is normally executed by
five V cells. Scale bars: in C, 5 µm for C-E; in G, 50 µm for F,G.
lin-4 mutants are longer than wild type.
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