Heritability of cellular differentiation: clonal growth and expression of differentiation in retinal pigment cells in vitro.

Abstract

The electrical output of the lizard ear as a function of hair-cell population," Science, in press. 7Wever, E. G., "Structure and function of the lizard ear," to appear in J. Auditory Res.

SIMULTANEOUS SYNTHESIS OF HISTONE AND DNA IN SYNCHRONOUSLY DIVIDING TETRAHYMENA PYRIFORMIS

“…According to Scherbaum et al (28), the volume of such bodies represents 2.8% of the macronuclear volume during division, and these bodies occur in 55 % of the cells during the first synchronous division. In our experience, the loss of DNA from the macronuclear pellet into extrusion bodies during the first division is 28% of the DNA content of an average daughter macronucleus3 This value agrees closely with the corresponding value of 24 % calculated for division 1 of Shepard's data (31) for division of Tetrahymena, 4 Extrusion body DNA of the average cell is one-half of the DNA content before division minus the DNA strain W, which had accumulated excess DNA in response to ultraviolet irradiation. Decaying synchrony and probably also reduced amount of extruded macronuclear material (31) lead more closely to apparent halving of the DNA content at the second and third divisions.…”

“…teristically differentiated phenotype (4,7,13). These variously differentiated cells in a single metazoan are thought to express different portions of identical genomes.…”

Control of differentiation in heterokaryons and hybrids involving differentiation-defective myoblast variants.

“…Unfortunately, the expression of differentiated functions is frequently unstable under conditions of continuous cell culture (1)(2)(3)(4)(5)(6)(7). Although overgrowth ofthe differentiated cell type by "fibroblastoid cells" is often invoked as the cause in primary cultures, there is good evidence in some systems that differentiated diploid cells can "dedifferentiate" and reduce their synthesis of differentiated products (2,3,7). This loss of differentiated functions is also observed in cloned established cell lines where, if overgrowth is the cause, it is overgrowth by a dedifferentiated variant arising within the cloned population .…”

Protein nutrition in growth regulation during early development

“…Without attempting to review or summarize the extensive literature on cell culture, fractions of serum and embryo extract have been shown to influence such diverse phenomena as proliferation (Holley and Kiernan, 1968;Scher and Todaro, 1971;Paul et al, 1971), migration , survival Lipton et al, 1971) and the maintenance of the differentiated state (Coon, 1966;Cahn and Cahn, 1966;Spooner and Hilfer, 1971). Although the active components have not been rigorously defined, such observations as the ability to replace serum with insulin (Hershko e£ al., 1971), the importance of protein conformation in the serum growth promoting response (Tritsch et al, 1970), the selective utilization of serum proteins by different cell lines (Tritsch, 1967), and the ability to relate specific serum protein fractions with proliferation, survival, and migration suggest that proteins may indeed be involved.…”