Endogenous CLASP mRNA expression and the effect of exogenous CLASP overexpression on laminin in the primitive streak. (A and B) Whole-mount in situ hybridization of CLASP1 (A) and CLASP2 (B) transcripts. Both CLASP1 and CLASP2 are expressed in epiblast cells (epi) and absent in mesoderm cells (mes). Bars, 20 µm. (C–E) Effect of CLASP overexpression on laminin. (C) eGFP control overexpression. Normal laminin breakdown and normal ingression of expressing cells. (D and E) Electroporation with eGFP-CLASP1α (D) or eGFP-CLASP2γ (E) expression vectors. Arrowheads, streak midline; yellow arrows, laminin retention in CLASP-expressing cells. ps, primitive streak. Bars, 20 µm.