The developmental potentialities of regeneration blastema cell nuclei as determined by nuclear transplantation.

Formerly, many embryologists believed that the blastema cells in regenerating amphibian tails and limbs arose from a reserve of undifferentiated cells, but since the work of Hertwig (1927) and Butler (1935) few modern investigators would support this view. Others have suggested that blastema cells are of epidermal origin (Godlewski, 1928; Rose, 1948). However, this idea has largely fallen into disrepute following the investigations of Karczmar & Berg (1951), Chalkley (1954) and Hay & Fischman (1961). There is now abundant evidence that blastema cells arise by the dedifferentiation of some of the stump tissues, in particular the stump muscle and cartilage (Thornton, 1938 a, b; Hay, 1958,1959, 1962; Hay & Fischman, 1961), and that contributions may also arise from fibroblasts when they are present. Unfortunately, there has been a great deal of confusion concerning the exact meaning and implications of the term 'dedifferentiated'. The only definite evidence is that during the process of dedifferentiation there is a loss of specialized structural and functional characteristics. This evidence comes not only from the work already mentioned (Thornton, 1938 a, b; Hay, 1958, 1959, 1962; Hay & Fischman, 1961) but from many other investigators, notably Holtzer (1961), who studied the problem of dedifferentiation by using the technique of fluorescein-labelled antibodies (Coons & Kaplan, 1950) on regenerating salamander tails and limbs, and found that by 7 days the blastema cells no longer bind antimyosin. Perske, Parks & Walker (1957) have shown that liver cells which dedifferentiate in tissue culture lose several enzymes and Holtzer, Abbott, Lash & Holtzer (1960), using thionin to test for chondroitin sulphate, have shown that chondrocytes from 10-day chick vertebrae, which had undergone rapid mitosis in tissue culture, ceased to synthesize chondroitin sulphate and were unable to resynthesize it and so redifferentiate either in vitro or when grafted into the coelom of 4-day chick embryos or on to the chorioallantoic membrane.