Alteration of cardiac myofibrillogenesis by liposome-mediated delivery of exogenous proteins and nucleic acids into whole embryonic hearts

A precise organization of contractile proteins is essential for contraction of heart muscle. Without a necessary stoichiometry of proteins, beating is not possible. Disruption of this organization can be seen in diseases such as familial hypertrophic cardiomyopathy and also in acquired diseases. In addition, isoform diversity may affect contractile properties in such funct ional adaptations as cardiac hypertrophy. The Mexican axolotl provides an u ncommon model in which to examine specific proteins involved with myofibril formation in the heart. Cardiac mutant embryos lack organized myofibrils a nd have altered expression of contractile proteins. In order to replicate t he disruption of myofibril formation seen in mutant hearts, we have develop ed procedures for the introduction of contractile protein antibodies into n ormal hearts. Oligonucleotides specific to axolotl tropomyosin isoforms (AT mC-1 and ATmC-3), were also successfully introduced into the normal hearts. The antisense ATmC-3 oligonucleotide disrupted myofibril formation and bea ting, while the sense strands did not. A fluorescein-tagged sense oligonucl eotide clearly showed that the oligonucleotide is introduced within the cel ls of the intact hearts. In contrast, ATmC-1 anti-sense oligonucleotide did not cause a disruption of the myofibrillar organization. Specifically, tro pomyosin expression can be disrupted in normal hearts with a lack of organi zed myofibrils. In a broader approach, these procedures for whole hearts ar e important for studying myofibril formation in normal hearts at the DNA, R NA, and/or protein levels and can complement the studies of the cardiac mut ant phenotype. All of these tools taken together present a powerful approac h to the elucidation of myofibrillogenesis and show that embryonic heart ce lls can incorporate a wide variety of molecules with cationic liposomes.