Figure 6. The EFN-2::GFP Expression Pattern. Anterior is to the left in all panels. (A-F) are ventral views, and (G-L) are lateral views. At the beginning of epiboly, epidermal cells cover the dorsal part of the embryo and begin to migrate ventralward led by cells at the ventral epidermal margin (four anterior leader cells and 17 pocket cells).(A and B) Early during ventral enclosure, EFN-2::GFP is expressed in a small number of lateral putative neuroblasts underneath and anterior to the posterior epidermal pocket cells.(C-F) As enclosure proceeds and the ventral pocket (opening to the gastrulation cleft) narrows, additional anterior (red arrow) as well as posterior (white arrow) neuroblasts within the pocket express the reporter. The pattern of neuroblast expression reflects the approximate shape of the ring of leading pocket cells that line the pocket opening at this stage.(G and H) In a lateral view of an embryo that has just completed epiboly, the GFP-expressing cells are underneath the surface layer of epidermal pocket cells. Posterior and anterior neuroblasts, probably corresponding to those seen in (C) and (E), are indicated with conserved symbols (white and red arrows, respectively). The anterior part of the EFN-2::GFP-expressing neuroblast ring appears as a line of fluorescing cells (red arrow) just underneath the epidermal surface in the ventral region of the head. At this stage, a large number of more anterior cells in the head, including pharyngeal cells, expresses the reporter.(I and J) Embryos at the 2-fold stage of development continue to express in the head and also express in ventral cord motorneurons (white arrow).(K and L) In late embryonic (data not shown) and early postembryonic development, the reporter expresses in epidermal cells
hyp8,
hyp9,
hyp10, and
hyp11 (white arrows) in the tip of the tail. At this stage,
hyp7 does not express high levels of EFN-2::GFP, but the
hyp7 cell that flanks
hyp8 reportedly expresses VAB-1::GFP during epiboly (George et al. 1998). Also indicated is the anal sphincter muscle (red arrow). Expression is prominent in the tail body muscles between the anal sphincter and the tail epidermal cells (unmarked), but not other body wall muscles. Expression persists in the tail and pharynx after hatching (data not shown).