Fig. 5. Peri-notochordal basement membrane. (A) The tri-laminar structure of the peri-notochordal basement membrane (between the arrowheads) shown using electron microscopy, from the sheath of a wild-type notochord cell. i, inner layer; m, medial layer; o, outer layer. (B) This structure is disrupted in the sheath of a dopey mutant notochord cell, where the outer and medial layers are missing. The inner layer is likely to consist of laminin as (C) wild-type levels of laminin immunoreactivity are clearly seen in (D) sneezy mutant embryos, but are abolished in (E) sleepy mutants.