ELECTRON MICROSCOPIC STUDY OF EPIDERMAL PRICKLE CELLS*

Transcription

1 ELECTRON MCROSCOPC STUDY OF EPDERMAL PRCKLE CELLS* EDWARD L. LADEN, M.D., JOHN 0. ERCKSON, Pn.D., AND DOROTHY ARMEN The introduction of the electron microscope by Knoll and Rnska (1) in 1931 has led to the development of new technics for the examination of biological material with this instrument. The preparation of very thin tissue sections of the thickness of io micron and thinner has been one such recent development. The usual commercial electron microscope operates at a potential of 50,000 volts. The electron beam does not have sufficient power to penetrate a tissue specimen of four to five microns thickness. n the ast four years Pease and Baker (2, 6) and others (3, 4, 5, 7) have modified and refined technics of fixing, imbedding and cutting sections so that it is now possible to prepare sections of J4o micron thickness. With such sections, satisfactory visualization of tissue cells can be made. t is the purpose of this paper to demonstrate and describe the appearance of normal epidermal prickle cells as seen with the electron microscope. METHOD The procedure that we have followed in the preparation of our sections is exactly as that described by M. L. Watson (8). Briefly this involves fixation of the tissue in 2% osmic acid and embedding in butyl methacrylate monomer. Cutting is done with a Spencer Model 820 microtome modified with a wedge as described by Pease and Baker (2). The sections are picked up on one hundred mesh, silica-coated, collodion covered screens and are evaporated by a heated tungsten coil in a 0.1 M vacuum which removed nearly all the embedding material by sublimation (8). OB5ERVATON5 Many prickle cells have now been examined. n no instance has it been possible for us to distinguish a structure which we can call a cell membrane. Cell boundaries can be readily recognized because of the presence of intercellular bridges and intercellular spaces. However, in many areas the cytoplasm of adjoining cells is so intimate that no cell boundaries can be seen. The nuclei have distinct membranes. The nucleoli appear in most instances to be compact homogeneous masses. However nucleoli as shown in Figure 2 are not unusual. Here the nucleolus appears to be composed of a fine network. * 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 24. 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 April 26,

2 r. fi 4 '.P :' ;,4 '' A '1 a " 'a :cvc.: H.. ''t;: Fm. 1. Group of prickle cells n upper third of epidermis. )C1600 ' L' -o '.' 1\ "f' F,_.,;. -, fl'. ;.< ':.:.,0 : ' ' lr... flo.2. Prickle cell showing nucleus with nucleolus, intracellular fibrils and intercellular bridges. X401X). 212

3 ,'... -, 4t'. 4. ' r. - ' ( j -7,t t_ -., i.1-4 Fin. 3. ntercellular bridges and boundaries of two adjoining prickle cells. X1O,400 FG. 4. ntercellular bridges. X26,

4 214 TlE JOURNAL OF NVESTGATVE DERMATOLOGY Figure 1 is an electron micrograph of the upper third of the epidermis. The magnification was X The cells appear to be well defined as individual structures which are held together by dense intercellular bridges. Although cell boundaries are easily recognized no cellular membranes can be seen. Figure 2 is of a cell ia the same areas as Figure 1 taken at a magnification of X4000. Much greater detail is now evident. Many fine fibrils can be seen to traverse the cytoplasm. ntracellular fibrils appear to leave the cell and become continuous with the intercellular fibrils or bridges which join the cells together. The nuclear membrane is evident as a definite structure but no cellular membrane can be seen. No fibrils are present in the nucleus. The nuclear structure appears granular. The nucleolus looks to be composed of a delicate network of granular material. Figure 3 is a micrograph of the intercellular bridges and the boundaries of two adjoining cells. The magnification is X10,400. t is readily apparent that the bridges are formed of the cytoplasm of the adjoining cells. The visual impression is that cytoplasm of one cell joins with the cytoplasm of its neighbors by these bridges. Figure 4 taken at X26,400 magnification reveals the same finding. D5CUSSON Cytoplnsmic fibrils in epidermal cells were first described by Rio Hortego in Chambers and subsequent workers have failed to demonstrate fibrils by micro dissection and examination of living cells. The cytoplasm of a healthy living cell of a generalized type appears optically structureless. t is a homogeneous watery fluid containing in colloidal solution a number of chemical substances such as proteins, lipoids and crystalloids in true molecular solution (9). However, certain specialized cells are known to show visible defined cytoplasmic structure. Thus, the striations of voluntary muscle fibers, flbrillne of nerve cells and spindle forms of cell division are examples of such visible definition. Whether the fibrils seen in the cytoplasm of fixed malphigian cells actually exist in the living cell is still not determined. Adolph, Baker and Leihy (10) have recently reported their observations of prickle cells as seen with the electron microscope. They state that the intercellular fibrils appear to terminate at the cell boundaries. The precipitated cytoplasm appeared to them to consist of a fine felt work of fibers which were of a different order of size than the intracellular fibers which have been described. They could see no apparent relationship between the intracellular fibers and intercellular bridges and postulated that the intracellular fibers which have been described in the past are artifacts, produced by intercellular bridges lying just above and below the plane of focus of these cells. We do not know whether intracellular fibrils are present in the living cells. n the fixed cells that we have studied these fibrils appear to become part of the intercellular bridges. The bridges under high magnification can be seen to consist of tubes of cytoplasm formed by and joining neighboring cells. Gessler, et al. (11) have published electron micrographs of normal human breast skin in which they demonstrate well defined cellular membranes in the

5 EPDEEMAL PRCKLE CELLS 215 Cells of the stratum germiaativum. We cannot explain this discrepancy with our results except to point out that the technic used by these authors, particularly in regard to embedding and cutting of their tissues, is different from ours. t is our impression from examining these published pictures that their sections may have been cut thicker than ours and that the cell membranes they demonstrate are artefacts due to this difference. The important conclusion we wonld draw from our studies is that the malphigian cell layer appears to be a syncitium. CONCLU5ONS 1. Electron micrographs of normal prickle cells are shown. 2. The presence of cell membranes cannot be seen at magnifications up to X26, The intercellular bridges appear to be tubes of cytoplasm connecting the cytoplasm of adjoining cells. 4. The prickle cell layer of the epidermis appears to be a syneitinm. REFERENCES 1. WYCHOFF, R. S. C.: Electron Microscopy. New York, nterscience Publishing Co., PEASE, D. C. AND BAKER, R. F.: Sectioning techniques for electron microscopy using a conventional microtome. Proc. Soc. Exper. Biol. & Med. 67: 470, FTJLLAM, E. F. AND GE55LER, A. E. : A high speed microtome for the electron microscope. Rev. S. C. L. nst. 17: 23, NEwMAN, S. B., BoEvsKo, E. AND SwEEnnow, M.: New sectioning techniques for light and electron microscopes. Science 110: 66, O'BRiEN, H. C. ANT) MCKNaEY, G. M.: New Microtome and sectioning methods for electron microscopy. Science 98: 455, PEASE, D. C. AND BAKER, R. F.: mproved sectioning techniques for electron microscopy. J. Applied Physics 20: 480, HLLER, J. AND GETTNER, M.D.: Sectioning of tissue for electron microscopy. Science 112: , S. WATSON, M. L.: U. of Rochester, A. E. P. quarterly. Tech. Report, January 1, March UR-164, pp , section LE GROS CLARK, W. E.: The Tissues of the Body, Oxford Press, Second edition. 10. ADOLPH, W. E., BAKER, R. F. AND LEBY, G. M.: Electron microscopic study of epidermal fibers. Science 113: 685, CESSLEE, A. E., GREY, C. E., SCHUSTER, M. C., KELSCH, J. J. AND RCHTER. M. N.: Notes on the electron microscopy of tissue sections. Cancer Research 8: 513, 1948.