Epifluorescent image of transgenic animals expressing the Y37A1B.5::GFP reporter in the hypodermis. Original magnification, 600x. (Strain source: The Genome BC C. elegans gene expression consortium; McKay et al., 2004.)
A & B. L1 larvae.
A. Dorsal view. A thin layer of hypodermis continuous with the dorsal hypodermal ridge (white arrow) and lateral hypodermis covers the dorsal muscle quadrants (stars) on both sides.
B. Right lateral view. The nuclei of the hyp 6 and hyp 7 syncytia are located in the dorsal and ventral hypodermal ridges in the head (white arrows). However, along the body, hyp 7 nuclei are placed eccentrically and close to the seam cells as a result of the migration of dorsal cells during intercalation (arrowheads) (see HypFIG 2 and HypFIG 5A).
C. L1 larva and ongoing seam cell divisions (left lateral side). Anterior daughters of the V2 – V6 seam cells have joined the hyp 7 syncytium, separating P cells from one another and increasing the number of nuclei on the lateral side of hyp 7 (arrowheads). Anterior seam progenitors (e.g., V1) are still dividing.
D. Early-L2 larva, left lateral side. The number of hyp nuclei on the lateral sides has nearly doubled after H1-H2, V1-V6, and T seam divisions in L1. (Top left inset) Enlarged DIC image of the same animal. The large nuclei with prominent nucleoli of hyp7 (white arrowheads) are located close to the eye-shaped seam cells (black arrows). (Top right inset) Overlaid DIC and epifluorescent images of the same region. Seam cells do not express this GFP reporter gene. (Bottom inset) Epifluorescent image of a later-L2-stage animal showing duplicating seam cells at this time.
E. Late-L3 larva, left lateral side. Further divisions of seam cells at early L3 contribute 26 more nuclei to hyp 7 on the lateral side. Pnp divisions contribute more nuclei to the ventral hyp 7, increasing the nuclei number in the ventral hypodermal ridge (arrow).
F. Adult, graphic depiction of the medial and left lateral side nuclei of the hyp 7 syncytium. Medial nuclei are lighter colored while lateral nuclei are brighter beige. The seam syncytium (orange) is shown as labeled with each precursor. (e) embryonic origin; (L) larval origin; (P) P-cell derived. The number signs next to some of the nuclei correspond to those in HypFIG2 panel D.

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