Somite formation, muscle specification, and muscle differentiation proceed in embryos deficient for both Hh signaling and laminin gamma1. A-J: Side views, anterior left, dorsal top. A-F3: Twenty-two-somite-stage embryos. A-D: DIC images. A1-D1: Stained for β-catenin (white) to outline cells. White arrowheads point to somite boundaries. Note that somite boundaries form in the absence of both laminin and Hh signaling (D, D1). E-F3: In situ hybridizations showing MyoD and myogenin expression in wild-type and lam gamma1 mutant embryos treated with EtOH or CyA. Segmental expression of MyoD and myogenin persists. G-J: Laminin and Hh signaling are required for proper anterior-posterior myosin distribution. Lettered panels: MF20 (light meromyosin) in green. Panels numbered 1 show F310 (myosin light chain) in blue. Panels numbered 2 are histograms that correlate with the images above. The posterior expression domains are indicated by white arrows for EtOH-treated embryos and white arrowheads for CyA-treated embryos. G-G2: EtOH-treated wild-type embryos. MF20 is expressed more posteriorly than F310. H-H2: CyA-treated wild-type embryos. MF20 is not expressed more posteriorly than F310. I-I2: Similar to EtOH-treated wild-type embryos, MF20 is expressed in younger somites than F310 in EtOH-treated lam gamma1 mutant embryos. J-J2: The same shift in myosin chain expression as seen in CyA-treated wild-type embryos is observed in CyA-treated lam gamma1 mutant embryos. K: Graph showing the average posterior limits of MF20 and F310 expression (error bars reflect standard error). L-N3: The lateral-medial pattern of MF20 expression is preserved in CyA-treated embryos. Lettered panels (lateral focal planes) and panels numbered 1 (medial focal planes) are side views, anterior left, dorsal top. Panels numbered 2 and 3 are 3-D reconstructed, transverse views, medial left, lateral right. MF20 expression (white *) is strongest laterally in all embryos (note the lateral peak of MF20 expression in histograms numbered 4).
|
