epithelial cell 



elongating 

 cells 



cortex fiber 

 cell region 



morphological 

 characteristics 



basophilic 



rough endoplasmic 



reticulum 

 cells replicate 



biochemical 

 characteristics 



a,P-crystallin synthesis 

 mhibited by actinomycin 



oxidotive metabolism is 

 efficient 



coif; LDH-5>LDH-| 



adult: LDH-I > LDH-5 



cell volume increases initiation of |f-crystallin 

 nuclei enlarge synthesis 



nucleoli enlarge o,3, j(-crystallin synthesis 

 increase in ribosomal inhibited by actinomycin 



population tronsition from LDH-5 to 

 cells no longer lDH-| enhanced 



replicate 



acidophilic 



smooth endoplasmic 

 reticulum 



ribosomes break down 

 m-RNA for crystallins is 

 stabilized 



nuclei decrease in size DNA is metabolically Inactive 

 nucleoli decrease in actinomycin stimulates 

 sue crystal! in synthesis 



LDH-I > LDH-5 

 active aerobic glycolysis 



Fig. 2. 



A dlagramatic presentation of the region of cellular elongation in the vertebrate lens. 

 The major morphological and biochemical characteristics associated with lens cell dif- 

 ferentiation are listed and are discussed in detail in the text. (Fig. 2, J. Papaconstantinou, 

 Science, in press; copyright 1966 by the American Association for the Advancement of 

 Science.) 



and y-crystallins from DEAE columns are 

 shown in Figs. 3B and 3C. The protein fractions 

 from the cortex fiber cells (Fig. 3B) and from 

 the nucleus fiber cells (Fig. 3C) of the adult 

 lens were precipitated and further character- 

 ized by free boundary electrophoresis. Their 

 electrophoretic mobilities are listed in Table I. 

 The mobility of these fractions was used as a 

 means of identification of the protein fractions 

 eluted from the column. 



At the time that these studies were initiated 

 I was impressed by the mechanism of lens 

 growth, especially, by the existence of many 

 layers of fiber cells which are systematically 

 laid down throughout the life of the animal. 

 Theoretically, therefore, by peeling away the 

 layers of fiber cells in an adult lens it should 

 be possible to recover the cells formed at 

 various ages. Actually, the fiber cells can be 

 peeled off when the decapsulated lenses are 

 placed in a buffered solution. The outer cortex 

 fiber cells, for example, continue to peel off 



until the central, nucleus region is reached. 

 The freed fiber cells can be separated from the 

 nucleus fiber cells by decanting, and using this 

 procedure for separating the fiber cells from 

 the different lens regions, one could look for 

 any chemical differences between cells that were 

 laid down throughout the growth periods of the 

 lens. Since the epithelial cells and elongating 

 cells from the equatorial zone could be removed 

 along with the lens capsule, we were now pro- 

 vided with a method for separating the lens 

 cells into three groups: (a) the epithelial 

 cells, (b) the newly formed cortex fiber cells 

 and (c) the fiber cells of the nucleus region 

 which had been laid down during the early life 

 of the animal. These cells were homogenized 

 in 0.005 M sodium phosphate buffer pH 7.0 and 

 fractionated on DEAE-cellulose columns. Char- 

 acteristic elution patterns for each of the regions 

 were obtained as is shown in Figs. 3A, 3B and 

 3C. These are not pure fractions as can be seen 

 from the electrophoresis data (Table I), but this 



49 



