PRELIMINARY AND SHORT REPORT ELECTRON MICROSCOPIC STUDY OF KERATOHYALIN IN THE FORMATION OF KERATIN* EDWARD L. LADEN, M.D., PAUL GETHNER, M.D. AND JOHN 0. ERIcKsoN, PH.D.
Keratohyalin granules, first described more than seventy years ago, were believed by earlier investigators to be the precursors of keratin. In more recent years, biochemical research has east doubt on this apparent relationship. Thus keratohyalin granules do not stain with the new tecbnie of Barnett and Seligman for demonstrating protein-bound sulfhydryl groups (1, 2). Eisen, Montagna and Chase showed that the stratum eorneum is strongly reactive to this strain while the keratohyalin granules were unreaetive (3). However, the ground cytoplasm of the stratum granulosum cells did react to the strain. Barnett and Seligman feel that the failure of these granules to stain tends to disprove the impression that they are the immediate precursors of keratin. An additional argument against the association of keratohyalin and keratin is that the granules are supposedly not found in all types of keratin formation. Thus Leblond has stated that hard keratin such as occurs in nails and hair can he distinguished from soft keratin by the absence of keratohyalin (4). Eisen, ci el make these observations less certain by being unable to distinguish between hard and soft keratin. Evidence in favor of the existence of the relationship is the frequent observation that keratohyalin granules seem to occur exclusively in keratinizing epithelium. In general the more developed the granular layer, the stronger and harder is the resulting keratin structure. When cornification stops (as occurs in vitamin A deficiency or under the influence of estrogenic hormones) keratohyalin granules are not seen and when the epithelium regains its eornifying potentiality, keratohyalin granules reappear (5). Over the past several years, we have observed many sections of human epidermis with the electron microscope. Our impression of the phenomenon is in conformity with the earlier view, namely that keratohyalin granules appear to be precursors of keratin. Figure 1 is an electron micrograph of a stratum granulosum cell. In the right center of the picture, the nucleus is seen with most of its membrane visible. Around the nucleus and the cytoplasm which fills most of the picture lie the dense, irregular bodies which are the keratohyalin granules. The granules are elongated with jagged projections. They tend to line up in proximity to other granules forming strands or fibers. Figure 2 is an electron micrograph of the keratin layer at the site of its joining with the granular layer. The keratin fibers are irregular, variable in thickness and with jagged projections. In the lowermost border of the keratin are dark, dense, elongated bodies lined up with their long axes rnnning parallel to the lower border of the keratin. They appear to be keratohyalin granules being laid down to form keratin. It would, therefore, appear that keratohynlin granules have the general appearance of keratin fibers. They are seen in the lowermost border of the keratin, appearing to be transforming directly into kerntin fibers. * From the Medical Service, Radioisotope Laboratory, General Medical and Surgical Hospital, Veterans' Administration Center, Los Angeles 25, and the Division of Dermatology, Department of Medicine, University of California Medical Center, Los Angeles,
Calif. Reviewed by the Veterans' Administration and published with the approval of the Chief
Medical Director. The statements and conclusions of the authors are the result of their
own study and do not necessarily reflect the opinion or policy of the Veterans' Administration. Received for publication February 9, 1957 325
THE JOUENAL OF INVESTIGATIVE nEEMATOLOGY
FIG. 1 (Total magnification 7,940X) A cell of the stratum granulosum occupies most of the picture. The nucleus (N) has an almost intact nuclear membrane (N.M.). In the cytoplasm of the cell are the keratohyalin granules (K.H.). A portion of the stratum corneum (S.C.) is seen.
,y -t.. FIG. 2 (Total magnification 6,750X) The stratum corneum appears to be composed of wavy strands or fibers with sharp projections. At the lowermost border dense granules, presumably the keratohyalin granules, are seen.
KERATOHYALIN IN FORMATION OF KERATIN
REFERENCES 1. MESCON, H. AND FLESCH, P.: Modification of Bennett's method for histochemical demon-
stration of free sulfhydryl groups in skin. J. Invest. Dermat. 18: 261, 1952. 2. BARNETT, R. J. AND SELIGMAN, A. M.: Demonstration of protein-bound sulfhydryl and disulfide groups by two new histochemical methods. J. Nat. Cancer Inst., 13: 215, 1952.
3. Eis, A. Z., MONTAGNA, W. AND CHASE, H. B.: Sulfhydryl groups in the skin of the mouse and guinea pig. J. Nat. Cancer Inst., 14: 341, 1953. 4. LEBLOND, C. P.: Histological structure of hair with a brief comparison to other epidermal appendages and epidermis itself. Ann. New York Acad. Sc., 53: 464, 1951.
5. ROTHMAN, S.: Physiol. and Biochem. of the Skin, p. 375, Chicago, Ill., University of Chicago Press, 1954.