Differentiation of contractile proteins of smooth muscle

Tropomyosin was prepared from different developmental stages of embryonic chicken gizzard, and its differentiation was examined by one-and two-dimentional gel electrophoresis. There existed different four tropomyosin chains: two were the same as those of adult gizzard, f-chain and s-chain; another one was close to the f-chain; the last smallest one was very like to be non-muscle tropomyosin. Examination of the gels showed that the last two chains were gradually decreased in their amounts and finally disappeared just before hatching. These 4 chains, especially the last two abnormal chains were identified from their special behavior on IEF-SDS and urea-SDS-gel electrophoresis. The Mg2+-paracrystals prepared from 19 day tropomyosin showed two typical types of gizzard tropomyosin from the negatively stained image on electron microscopy, but that of 12 day tropomyosin gave another view like the non-muscle tropomyosin tactoid in addition to the two types of adult tropomyosin. Sectioned images of the fixed embryonic gizzard in the different stages showed relatively many non-muscle cells like fibroblasts in 12 day gizzard except for smooth muscle cells, and only smooth muscle cells were observed in 19 day gizzard. In conclusion, one chain of embryonic tropomyosin came from non-muscle cells in the early embryonic gizzard. Another chain exists which closely resembles the f-chain, and this might be the real embryonic tropomyosin.