13. D I F F E R E N T I A T I O N
475
chick embryos, which pulsate in vitro for more than a day and respond
to pharmacological reagents in a fashion similar to that of adult
vertebrate heart. Harary and Farley (1960a, b) have presented similar
results with young rat heart and have gone on to confirm earlier reports
(Cavanaugh, 1955b) that isolated cells beat at different rates, but cells
in physical contact are coordinated so as to beat simultaneously. It is
worth noting that Harary and Farley describe their initial dispersate as
consisting of spherical cells which, upon settling to the glass, take on the
appearance of either fibroblasts or myofibrils. Both morphological types
show beating. There is evidence of up to a fourfold increase in cell
number, and on dilution and transfer of the population to a new vessel
all evidence of beating disappeared. These results with cardiac muscle
have their parallel with striated muscle. Lucy and Rinaldini (1959) have
studied amino-acid utilization of freshly isolated myoblasts from pectoral
muscle, and Stockdale and Holtzer (1961) and Bassleer (1962) have
followed the conversion of mononucleate myoblasts to multinucleate
myotubes in cultured cells from somite and thigh muscle. Stockdale and
Holtzer have combined autoradiographic and fluorescent-antibody
techniques to provide supporting evidence for the thesis that multinucleated myotubes are the product of fusion of myoblasts, and that
synthesis of D N A and contractile proteins do not go on simultaneously
in differentiating muscle cells. This important finding on the relation of
mitotic to differentiative events is in urgent need of confirmation and
extension to other cell types.
Konigsberg (1960, 1961) finds that suspensions of embryonic chick
leg-muscle cells can be used to initiate replicate monolayer cultures on
glass. The mononucleated cells, fibroblast-like in appearance, attach to
the glass and proliferate for several days. As the population approaches
the point of confluence of cells, multinuclearity and differentiation set
in. It is characterized by formation of myotubes; a positive tetrazolium
reaction for succinic dehydrogenase (Cooper and Konigsberg, 1961);
the appearance of striated fibers; and vigorous contraction. In connection with Konigsberg's finding it is of interest to recall the earlier result
of Rose, Pomerat, Shindler and Trunnell (1958) and the later report of
Capers (1960) employing a different technique and medium. Using a
multi-purpose chamber Rose et al. found that explants of chick-embryo
muscle on plasma clot gave rise to outgrowth of spindle cells, except
where the outgrowth occurred in the confined space under a cellophane
sheet. In the confined space muscle straps were present, with cross-striation and displaying contraction. This emphasizes again the possibility
that particular media or other factors may need alteration or conditioning before they can support differentiation, and that the alteration
may depend upon materials produced in too small quantity, or of such
475
chick embryos, which pulsate in vitro for more than a day and respond
to pharmacological reagents in a fashion similar to that of adult
vertebrate heart. Harary and Farley (1960a, b) have presented similar
results with young rat heart and have gone on to confirm earlier reports
(Cavanaugh, 1955b) that isolated cells beat at different rates, but cells
in physical contact are coordinated so as to beat simultaneously. It is
worth noting that Harary and Farley describe their initial dispersate as
consisting of spherical cells which, upon settling to the glass, take on the
appearance of either fibroblasts or myofibrils. Both morphological types
show beating. There is evidence of up to a fourfold increase in cell
number, and on dilution and transfer of the population to a new vessel
all evidence of beating disappeared. These results with cardiac muscle
have their parallel with striated muscle. Lucy and Rinaldini (1959) have
studied amino-acid utilization of freshly isolated myoblasts from pectoral
muscle, and Stockdale and Holtzer (1961) and Bassleer (1962) have
followed the conversion of mononucleate myoblasts to multinucleate
myotubes in cultured cells from somite and thigh muscle. Stockdale and
Holtzer have combined autoradiographic and fluorescent-antibody
techniques to provide supporting evidence for the thesis that multinucleated myotubes are the product of fusion of myoblasts, and that
synthesis of D N A and contractile proteins do not go on simultaneously
in differentiating muscle cells. This important finding on the relation of
mitotic to differentiative events is in urgent need of confirmation and
extension to other cell types.
Konigsberg (1960, 1961) finds that suspensions of embryonic chick
leg-muscle cells can be used to initiate replicate monolayer cultures on
glass. The mononucleated cells, fibroblast-like in appearance, attach to
the glass and proliferate for several days. As the population approaches
the point of confluence of cells, multinuclearity and differentiation set
in. It is characterized by formation of myotubes; a positive tetrazolium
reaction for succinic dehydrogenase (Cooper and Konigsberg, 1961);
the appearance of striated fibers; and vigorous contraction. In connection with Konigsberg's finding it is of interest to recall the earlier result
of Rose, Pomerat, Shindler and Trunnell (1958) and the later report of
Capers (1960) employing a different technique and medium. Using a
multi-purpose chamber Rose et al. found that explants of chick-embryo
muscle on plasma clot gave rise to outgrowth of spindle cells, except
where the outgrowth occurred in the confined space under a cellophane
sheet. In the confined space muscle straps were present, with cross-striation and displaying contraction. This emphasizes again the possibility
that particular media or other factors may need alteration or conditioning before they can support differentiation, and that the alteration
may depend upon materials produced in too small quantity, or of such