Fig. 5. Perivitelline injection of heparin inhibits Dpp signaling and disrupts embryonic dorsoventral patterning. Heparin/PBS solution was injected into the perivitelline space of 1-2 hour embryos to achieve the specified final concentrations (see Materials and methods). Embryos were allowed to develop for 21 hours before fixation and staining. The dorsal-most embryonic tissue, the amnioserosa, is marked by the expression of a Kr-lacZ transgene (A-D), which provides a readout of alterations in DV patterning. Representative embryos are shown; the total sample size is indicated in parenthesis for each genotype. (A,B) Injection of heparin at 1.5 µg/ml (B) leads to a reduction in Kr-LacZ expression (A, n=136; B, n=114) and morphological defects typical of loss of dorsal cell fates, such as expansion of the cephalic furrow. (C,D) In dl embryos, ubiquitous dpp expression results in ventral expansion of reporter expression (C, n=40). Injected heparin (10.5 µg/ml) inhibits reporter expression in embryos lacking dl activity, demonstrating that heparin directly interferes with BMP signaling (D, n=37). (E,F) By contrast, embryonic morphology along the AP axis and segmental expression of a wg-lacZ reporter (E) are unaffected by heparin (1.5 µg/ml; F, n=121). This indicates that AP patterning and Wg/Hh activity are not compromised at heparin levels that disrupt BMP signaling, thus providing a control for specificity. Expansion of wg-lacZ stripes laterally (F) so that they encircle the embryo reflects cell fate changes resulting from ventralization.