Figure 1.—

mrp-4 is required for the accumulation of birefringent material within embryonic gut granules. (A) mrp-4(−) embryos often lack birefringent, gut granule-associated material. Using polarization microscopy, birefringent contents of gut granules were visible in wild-type embryos (b, f, and j). In contrast, birefringent puncta were lacking in the intestinal primordium of all bean-stage (d), 1.5-fold-stage (h), and nearly all pretzel-stage (l) mrp-4(−) embryos. (B) mrp-4(−) embryos contain gut granules. Wild-type and mrp-4(−) 1.5-fold-stage embryos displayed acridine orange stained and FUS-1 (V-ATPase subunit) containing gut granules (a–h). Gut granules are additionally characterized by the presence of Nile Red stained fat (j), autofluorescence (n), and the ABC transporter PGP-2 (r). All of these markers were unaltered in mrp-4(−) embryos (l, p, and t). (C) Late-stage wild-type embryos always contained birefringent gut granule material. In contrast, the accumulation of birefringent material was delayed in mrp-4(−) embryos. The intestinal primordium is located between the solid arrowheads in A and B. C. elegans embryos are ∼50 μm long.