An Analysis of the Synthesis and Distribution of the Contractile Protein, Myosin, in the Development of the Heart

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Abstract
Cardiac and skeletal myosins were extracted from heart and hind limb muscle, respectively, of adult New Hampshire Red chickens of both sexes, using the method of Mommaerts and Parrish with minor modifications. The purity of the preparations was believed to be slightly below 85-90%. The titer and specificity of each serum were determined by the precipitin technique, using homologous or heterologous antigen. Fifty-four antisera from 22 rabbits were assayed, along with controls from sera of uninjected rabbits. The effective serum dilution titers of the antisera tested ranged from 164 to 1:8192, but only those sera with titers of at least 1:512 with homologous antigen were retained. In order to determine the antigenic specificity of cardiac myosin during development, hearts were removed from 60 18-day-old embryos and from 144 13-day-old embryos, and extracted by the technique described for adult hearts. The purified cardiac myosin from older embryos and the crude extract from younger embryos reacted positively with antisera against adult cardiac myosin using several methods. By employing repeated absorptions with embryonic cardiac antigens of any of the stages tested, all activity of antisera for adult cardiac myosin could be removed, indicating that the embryonic heart from 36 hours through 18 days contains antigens identical or similar to those in adult cardiac myosin. In order to detect the reactive groups of cardiac myosin in the early embryo, 1269 embryos in the pre-streak through head-process stages were extracted and the extract used as the test antigen in precipitin tests with antisera against adult cardiac myosin. Reactive groups were first detected at stage 3, the mid-streak blastoderm. The blastoderm at stage 4 or 5 was divided in the antero-posterior axis into 3 segments, anterior, mid and posterior, and the segments extracted. Tests indicated the presence of cardiac myosin in all 3 segments, with more in the mid and posterior segments than in the anterior segment of the stage 4 embryo. At stage 5 cardiac myosin was confined to the mid segment. In the medio-lateral axis the mid-piece was subdivided into left lateral, median and right lateral sections. At stage 4 of the embryo cardiac myosin was distributed almost equally among the 3 sections, but at stage 5 it was largely localized in the lateral areas, with traces in the median section containing the streak. At stages 6 and 7 (pooled data) the median region had no cardiac myosin.