Fig. 3

C-terminal ttna truncations do not act as dominant negatives.

(A) Knockdown of ttnb by morpholino injection worsens skeletal muscle sarcomeric architecture in ttna^n/n mutants. Fixed skeletal muscle samples of 72 hpf ttna^n1/n1 mutant embryos were analyzed by immunostaining for α–actinin. (right) Cartoon representation of ttna and ttnb proteins, with a premature N-terminal stop codon in ttna (gold star). The purple lines indicate morpholino disruption of the ttnb transcript. Scale bar: 10 uµm. (B) Knockdown of ttna by morpholino injection does not rescue skeletal muscle architecture in ttna^c1/c1 mutants. ttna^c1/c1 embyros were injected with a ttna splice-site morpholino to the exon 4-intron 4 junction at the 1–2 cell stage and embryos were examined at 72 hpf. At this morpholino dose, knockdown efficacy was estimated at close to 80% and nearly complete cessation of cardiac contraction was achieved in >90% of wild-type embryos (data not shown). Immunostaining for α–actinin revealed no improvement in skeletal muscle architecture. (right) Cartoon representation of mutant ttna proteins, with a premature C-terminal stop codon (gold star). The purple lines indicate disruption of the ttna transcript using a morpholino that is expected to introduce an N-terminal truncation upstream of the C-terminal truncation.