Narshi, Aruna (2011)
Ph.D. thesis, University of Birmingham.
I: Ambystoma mexicanum is a useful model for the study of heart development as it has a naturally occurring mutant, the cardiac (c/c) lethal, in which the embryos lack organised myofibrils and have low levels of tropomyosin. Antisense oligonucleotides specific to axolotl tropomyosin disrupted myofibril formation in normal heart, whereas sense oligonucleotides encouraged myofibrillogenesis in the mutant hearts, demonstrating the importance of tropomyosin in cardiac muscle development and the effectiveness of cationic liposome transfection system. A novel isoform of the human tropomyosin, TPM1κ, was discovered and found to be cardiac specific in humans. Ectopic expression of GFP.TPM1κ fusion protein promoted myofibrillogenesis in the cardiac mutant axolotl heart. Tropomyosin N- and C-termini modification did not affect its function.
II: The neotenous form had vagal preganglionic neurons (VPN) in the dorsal vagal nucleus (DVN) only. In the metamorphosed, VPN were found in the DVN but 18% were relocated in a ventro-lateral position. Neotenous ventilation rate followed heart rate. In the metamorphosed, ventilation caused heart rate variability. This may have been induced by the ventral-lateral VPN, which may be equivalent to a primitive nucleus ambiguus, an area that generates rhythmic sinus arrhythmia in mammals. Thus, ventrolateral VPN may be involved in cardiorespiratory control.
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