264 KERATIN AND KERATINIZATION 



the acid and base-binding capacity of nuclei accompanied by a decrease in 

 nuclear volume. It is supposed that the basic proteins (histones) normally 

 combined with the DNA become dissociated from it, each then becoming 

 more easily stainable, and that there is also a loss in water-binding power. 

 The total DNA content remains more or less constant. 



According to Bern et al. (1954 and 1957) the nuclear changes during 

 keratinization are, however, different from this and are not simply de- 

 generative. The nuclear volume at first increases to be followed by a 

 collapse in the final stages of cell condensation. During the swelling stage 

 the nuclei are less stainable and the DNA content decreases. This fall in 

 DNA continues during the phase of active keratin synthesis. The histone 

 content seems to remain constant and these proteins in an altered form 

 may represent in part the "nuclear remnants" found in the keratinized cell. 



A production of masses of keratohyalin by the nucleus or even the actual 

 dissolution of that body has been envisaged by Hinglais-Guillard (1959) 

 as a result of her study of keratinization in the cervical epithelium of 

 women. This tissue undergoes a cyclic change of functional activity in 

 phase with the other sexual tissues (see p. 144), the cells oscillating 

 between a keratinizing condition and one in which glycogen is accumulated. 

 In the keratinizing phase the nuclei of the superficial cells reveal a curious 

 clumping of their contents and rather similar lumps of material are to be 

 seen in the adjacent cytoplasm. 



These observations are not incompatible with the possibility that the 

 nucleus is playing a different synthetic role in the later stages of keratin 

 formation. Evidence, given below (p. 268), suggests that a peculiar 

 cystine-rich protein may be formed at this stage and its formation may 

 involve the nucleus. The observation of Fell and Pelc, already referred to 

 (pp. 63 and 220), that radioactive sulphur compounds on injection appear 

 first in nuclei may also mean that sulphur-containing amino acids are built 

 into protein precursors in the nucleus. It is known that a small amount of 

 protein synthesis occurs in nuclei in other sites and that it involves energy 

 transfers following pathways not involving the enzymes normally partici- 

 pating in the cytoplasm (Allfrey et al., 1953 and 1957). The situation in the 

 keratinizing cell is admittedly peculiar — it is largely cut off from supplies of 

 metabolites and its life as a synthetic unit is drawing to a close — it would 

 not be surprising then if special mechanisms were called into play. For 

 example, it is compatible with the little evidence we have to suppose that 

 here the DNA molecules participate at first-hand (i.e. not through the 

 intermediary of RNA) in the synthesis of proteins and are themselves 

 consumed in the process. 



The RNA granules of the cytoplasm persist into the keratinization zone 

 and are lost from view between the masses of condensing fibrils. Histo- 

 chemically also the cells of the bulb are strongly RNA positive, and the 



