Apical cell extrusion is promoted by Mmp9 and loss of basement membrane integrity. (A and B) Laminin antibody staining (red) in the caudal fin fold revealing compromised basement membrane integrity in hai1a^hi2217 embryos at 48 hpf. (C) Genetic interaction between lama5 and hai1a. Sub-phenotypic/low doses of single morpholinos had no effect on the morphological phenotype, but combined injection of sub-phenotypic doses recapitulated the hai1a epidermal phenotype. n = 99 or 100 embryos per condition. (D) Genetic interaction between itga3 and hai1a. n = 100 embryos. (E–P) Representative bright field images of single and combined morpholino injections at 48 hpf. Note that the mat1a MO fully rescues the epidermal phenotype (H, L, and P). (Q–S) Quantification of cell extrusions at 48 hpf for the hai1a morphants (Q) and the genetic interaction between lama5 and hai1a (R) and itga3 and hai1a (S). The cell extrusion phenotype depends in part on Mmp9 and Mmp13, and is fully rescued upon coinjection of the mat1a morpholino. n = 40–178 embryos. (T) Q-RT-PCR demonstrating that levels of mmp9 in mutants are reduced upon treatment. n = 40 pooled embryo tails. For quantifications and statistical significances, see legend of Fig. 1. Scale bars in A and B, 20 µm; in E–P, 200 µm.