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. 2001 Aug 15;15(16):2161–2172. doi: 10.1101/gad.200601

Figure 1.

Figure 1

Summary of ventral epidermal cell fate specification in C. elegans (Cel) and P. pacificus (Ppa) and sequence comparison of Cel–LIN-39 and Ppa–LIN-39. (A) Schematic representation of the 12 ventral epidermal Pn.p cells in a C. elegans L1 stage larva. (B) In C. elegans (left panel), lin-39 activity defines the P(3–8).p cells as the vulval equivalence group. P6.p (black oval) has the 1° fate and forms the inner part of the vulva, whereas P(5,7).p (hatched ovals) have the 2° fate and form the outer part of the vulva. P(3,4,8).p (diagonally striped ovals) remain epidermal and have the 3° fate. P(5–7).p are induced by the anchor cell (AC) to undergo vulval differentiation. The inductive signal from the AC is encoded by an EGF-like molecule and is transmitted through an EGFR/RAS/MAPK signaling pathway, which modulates the activity of several transcription factors, including LIN-39. In the absence of lin-39 activity (Cel–lin-39), the P(3–8).p cells, like the other Pn.p cells, fuse with the surrounding hypodermis (white ovals). If lin-39 activity is provided during the early step but not during AC induction (Cel hs::lin39 early), the P(3–8).p cells take on the 3° fate. In P. pacificus (right panel), lin-39 defines P(5–8).p as the vulval equivalence group. P(5–7).p form the vulva with a 2°-1°-2° fate pattern. P8.p has a special fate designated as 4° (filled striped oval). Cells not receiving lin-39 activity (Ppa–lin-39) undergo programmed cell death (X). If programmed cell death is inhibited, a normal vulva is formed, indicating that lin-39 is dispensable for vulval formation (Ppa–lin-39; ced-3). It is not known if the EGF/RAS/MAPK pathway is involved in vulval induction by the gonad in P. pacificus. (C) Sequence alignment of Cel–LIN-39 and Ppa–LIN-39. The highly conserved homeodomain and hexapeptide motifs are overlined by a solid and a hatched bar, respectively. The putative phosphorylation site in Cel–LIN-39 is indicated by S/TP, and the motif similar to a MAPK docking site (Jacobs et al. 1999) is indicated by FXFP. Note that these motifs are absent in Ppa–LIN-39. (D) Schematic representation of the LIN-39 primary structure. (Hex) Hexapeptide motif, (HD) homeodomain. Solid and open arrowheads above the bar indicate the positions of all published nonsense and missense mutations, respectively, found in C. elegans lin-39 alleles (Clark et al. 1993; Wang et al. 1993). Arrows indicate nonsense mutations introduced in C. elegans rescue constructs. Solid arrowheads below the bar indicate all nonsense mutations found in P. pacificus lin-39 alleles (Eizinger and Sommer 1997).