Fig. 5. (A) her4MO (1 µM) is sufficient to suppress Her4 synthesis in a radioactive in vitro translation assay without blocking her6 mRNA translation (left panel). her6MO (1 µM) reduces Her6 synthesis without affecting Her4 (right panel). (B-G') Somitogenesis is disrupted in Her6, Her4- and Her6+Her4-depleted embryos. Forty-eight hour embryos stained with anti-myosin heavy chain antibody. Anterior is towards the left. (B-G) Low-magnification images to compare the general morphology of control and experimental embryos. Details of somite and intersomitic boundary morphology are shown in the corresponding high-magnification images. Black arrows indicate complete intersomitic boundaries, white arrows indicate irregular and/or defective intersomitic boundaries, white arrowheads mark myosin fibrils crossing intersomitic boundaries. (B) Control embryo. (B') High magnification of the boxed area in B. (C-C''') In 3 ng her6MO-injected embryos, somitogenesis is initiated normally but somites and intersomitic boundaries become progressively more irregular. (C',C'',C''') High magnification of the anterior, intermediate and posterior boxed areas in C, respectively. (E) her4MO-injected (3 ng) embryos develop normally and only the tail tip is affected. (D,F) The effect of her6MO and her4MO on somitogenesis is dose dependent. her6MO- (D) and her4MO- (F) (6 ng) injected embryos have a bent body axis and the onset of somitic abnormalities is shifted rostrally. D',F' are magnified views of the boxed areas in D and F. In D', somites as anterior as number 16 have ill-defined boundaries. In F', the last normal intersomitic boundary occurs at somite 25. (G,G') Somitogenesis defects occur earlier in embryos co-injected with 3 ng each her6MO and her4MO than in embryos injected with 6 ng of either her6MO or her4MO. (G') High magnification of the boxed area in G: intersomitic boundaries are ill-defined (white arrows) and irregularly spaced (black ruler at the bottom of the picture). (G'') A high-magnification view of the boxed area in (G'): large myosin fibrils span several somites. The expression pattern of her6 in the PSM is not dependent on the function of the Her6 protein. 10 ss control (H) or her6MO-injected (I) embryos probed for the expression of her6. The levels of her6 transcript are higher in the somites, anterior PSM, notochord/ventral neural tube and ectoderm of her6MO-injected embryos (I) than in the corresponding tissues of control embryos (H). The segmental expression of her6 in the somites and the anterior PSM is not affected. (H',H'',I',I') sections of the embryos in H and I cut along the broken lines marked by the corresponding small letters. The her6 signal is stronger in the anterior PSM of her6MO-injected embryos than in control ones, but no accumulation of her6 transcript is detected in the intermediate/posterior PSM.