Recessive cardiac mutant gene c in axolotls (salamanders) provides an excellent model for studying the molecular biology of heart induction. When homozygous, the gene results in a reduction of tropomyosin, an absence of myofibrils, and a failure of the cardiac muscle to initiate contractions. The gene appears to exert its effect via abnormal inductive processes from the anterior endoderm since mutant hearts can be """"""""rescued"""""""" by organ-culturing in the presence of normal endoderm, a known potent heart muscle inductor tissue in vertebrates. Furthermore, it has been determined that the addition of an RNA fraction obtained from normal anterior endoderm or from medium """"""""conditioned"""""""" by the normal endoderm can correct mutant hearts in vitro; these rescued mutant hearts have normal amounts of tropomyosin incorporated into myofibrils that contract normally. The present investigation is designed to elucidate the sequence of cellular and molecular events and mechanism(s) directing normal myofibrillogenesis and to identify, characterize and determine the role of inductive factors which regulate myocyte differentiation.
The specific aims are as follows: (1) we will purify and characterize the RNA produced by normal embryonic anterior endoderm that turns the quiescent mutant hearts into vigorously- contracting """"""""normal"""""""" organs. It is our hypothesis that the normal anterior endoderm in axolotl embryos produces a diffusible RNA which promotes (induces) differentiation of the heart; (2) The gene coding for the active heart inducing RNA will be cloned and sequenced. This will help us test our hypothesis that this single gene mutation alters the inductive capability of the anterior endoderm in mutant axolotls by affecting the production of a diffusible RNA; (3) Tropomyosin, whose expression is apparently modulated by the cardiac lethal mutation, will be analyzed in normal, mutant and rescued-mutant hearts by Northern blot studies, in situ hybridization, and in vitro translation experiments. This research will provide significant new information on the mechanism(s) of inductive interactions responsible for normal myocyte differentiation. The genetic abnormalities of the mutant axolotl system can be used as an important tool in these studies since there is a clearly-defined bioassay end point for the various experiments, namely, normally contracting mutant hearts. Thus, the proposed studies should provide significant insights into the regulation of heart muscle induction and normal myofibrillogenesis at the gene level. The health relevance of understanding the being able to turn a """"""""nonmuscle"""""""" cell into contracting muscle could be tremendous; if this could be applied in humans, people who have damaged tissue in their heart muscle due to myocardial infarcts might be able to have the tissue redifferentiate into functional muscle again. In a broader biological sense, this vertebrate """"""""birth defect"""""""" is potentially capable of providing answers to major unsolved problems in modern biology and medicine related to the control of gene expression during embryonic development.
|Zhang, C; Osinska, H E; Lemanski, S L et al. (2005) Changes in myofibrils and cytoskeleton of neonatal hamster myocardial cells in culture: an immunofluorescence study. Tissue Cell 37:435-45|
|Spinner, Belinda J; Zajdel, Robert W; McLean, Matthew D et al. (2002) Characterization of a TM-4 type tropomyosin that is essential for myofibrillogenesis and contractile activity in embryonic hearts of the Mexican axolotl. J Cell Biochem 85:747-61|
|Bhatia, R; Dube, D K; Gaur, A et al. (1999) Expression of axolotl RNA-binding protein during development of the Mexican axolotl. Cell Tissue Res 297:283-90|
|Gaur, A; Dube, D K; Lemanski, L F (1998) Cloning, sequencing and expression of a novel homeobox gene AxNox-1 from the Mexican axolotl. Gene 216:179-88|
|Gaur, A; Bhatia, R; Spring-Mills, E et al. (1998) The heart of metamorphosing Mexican axolotl but not that of the cardiac mutant is associated with the upregulation of Hox A5. Biochem Biophys Res Commun 245:746-51|
|Bhatia, R; Gaur, A; Lemanski, L F et al. (1998) Cloning and sequencing of the cDNA for an RNA-binding protein from the Mexican axolotl: binding affinity of the in vitro synthesized protein. Biochim Biophys Acta 1398:265-74|
|Zajdel, R W; McLean, M D; Lemanski, S L et al. (1998) Ectopic expression of tropomyosin promotes myofibrillogenesis in mutant axolotl hearts. Dev Dyn 213:412-20|
|Zajdel, R W; Zhu, Y; Fransen, M E et al. (1997) A primary cell culture model for defective cardiac myofibrillogenesis in Mexican axolotl embryos. In Vitro Cell Dev Biol Anim 33:677-80|
|Lemanski, S F; Kovacs, C P; Lemanski, L F (1997) Analysis of the three-dimensional distributions of alpha-actinin, ankyrin, and filamin in developing hearts of normal and cardiac mutant axolotls (Ambystoma mexicanum). Anat Embryol (Berl) 195:155-63|
|Luque, E A; Spinner, B J; Dube, S et al. (1997) Differential expression of a novel isoform of alpha-tropomyosin in cardiac and skeletal muscle of the Mexican axolotl (Ambystoma mexicanum). Gene 185:175-80|
Showing the most recent 10 out of 49 publications