ANALYSIS OF THE 3-DIMENSIONAL DISTRIBUTIONS OF ALPHA-ACTININ, ANKYRIN, AND FILAMIN IN DEVELOPING HEARTS OF NORMAL AND CARDIAC MUTANT AXOLOTLS (AMBYSTOMA-MEXICANUM)

alpha-Actinin is an actin binding protein that assists in the stabiliz ation of the plasma membrane and helps to fix organelles in position i n a variety of cell types. In muscle, it is a major component of the Z -lines of organized myofibrils. Ankyrin binds to various elements of t he cytoskeletal system including microtubules, microfilaments, and int ermediate filaments and may help to anchor these structures to the cel l membrane. Filamin is a well-characterized actin-associated protein f irst isolated from chicken smooth muscle. In addition, filamin is a ge l-forming protein which aids in the formation of a loose, yet thick, n etwork of actin filaments. These proteins work together, in conjunctio n with other cytoskeletal proteins, to permit the contractions of hear t muscle cells in vertebrates. In a unique strain of the axolotls (Amb ystoma mexicanum) a simple recessive mutation, designated by gene c, r esults in an incomplete differentiation of the hearts of affected embr yos. Although the mutant (c/c) embryos form hearts, they do not beat b ecause of a failure in the formation of organized sarcomeric myofibril s. The current study was undertaken to examine the three-dimensional d istributions of three different contractile-cytoskeletal proteins (a-a ctinin, ankyrin, and filamin) during myofibrillogenesis in normal and mutant hearts from early heart-beat stage 37 through advanced embryoni c stage 42. Our results demonstrate that the contractile proteins beco me increasingly better organized in normal hearts as development progr esses. In mutant hearts, although the proteins are present in almost n ormal amounts, they fail to form normally organized myofibrils.