456' GENETICS OF SOMATIC CELLS 



tissue culturists, characterized by sluggish growth and loss of many cultures prior to the 

 establishment of vigorously growing strains of cells, sounds very much like an exercise 

 in selection. A recent interesting paper of Sato et al. 1158 reports experiments specifically 

 designed to illuminate this problem. They have found that tissue-culture populations 

 derived from liver of day-old rats differ markedly in antigenic structure from the liver 

 at this age. Furthermore, freshly prepared hepatic inocula are prevented from initiat- 

 ing growth in culture if pretreated with renal tissue-culture antiserum previously 

 absorbed with liver. On the other hand, the growth potential of hepatic inocula 

 remained unaffected by anti-liver antiserum containing demonstrable antibodies 

 against liver. Also, short-term cultures derived from liver possessed sharply reduced 

 ornithine-transcarbamylase activity and serum-albumin content; this residual activity 

 and content could be accounted for by the microscopically demonstrable persistence of 

 portions of the inoculum. It was concluded that the bulk of the tissue-culture popula- 

 tion derived from liver of day-old rats arose from a type of cell other than the paren- 

 chymal cell. This cellular type appeared to be a small minority of the total popula- 

 tion, since suspensions of day-old liver had a plating efficiency of about 10 _4 . 



Thus, the problem concerning the relationship between established strains of 

 cells in tissue culture and the normal or malignant tissue from which they had been 

 derived must be left entirely open at present. Existing strains of cells must be regarded 

 as interesting but completely artificial populations, useful as model systems, but by 

 no means informative with regard to somatic-cell genetics within the mammalian 

 organism. Intense efforts should be directed now toward the development of media 

 that can permit the survival and growth of many different types of cells in a state as 

 nearly approaching and representative of their condition in vivo as possible. The prob- 

 lem of representativeness will not be opened for serious investigation until it has become 

 possible to clone cells taken directly from the body with high efficiency. No cloning 

 of cells that have already passed the critical period of adaptation in culture can replace 

 this need. As far as the problem of malignancy and malignization in vitro is concerned, 

 a close passage-to-passage collaboration is necessary between culture in vitro and 

 transplantation tests in vivo, with appropriate isogenic animal recipients, as discussed 

 above. 



POSSIBLE APPROACHES TO GENETIC TRANSFER BETWEEN SOMATIC CELLS 



Among bacteria, three main forms of genetic transfer have been discovered: 

 sexual recombination, DNA-mediated transformation, and phage-mediated trans- 

 duction. Lysogenic conversion by which the phage particle itself controls a certain 

 phenotypic character of the host cell, and the field of episomes are also relevant. 



Sexual recombination between somatic cells is a rather remote possibility. It is 

 true that fusion and segregation have been observed in somatic cells, each by itself, 

 under particularly favorable and, as a rule, exceptional circumstances, 773, 774 but an 

 orderly sexual cycle of nuclear fusion followed by segregation appears rather unlikely. 



