ON THE ORIGIN AND MORPHOLOGY OF MYOEPITHELIAL CELLS OF APOCRINE SWEAT GLANDS* D J. GOLDSTEIN, MB., B.Cn., B. Sc.Horcs. In view of the importance of myoepithelial MATERJAL AND METHODS cells in the functioning of sweat glands (Shelley The glands studied were apoerine sweat glands and Hurley (1); IHiurley and Shelley (2)), it is("ceruminous glands"—Shelley and Perry (17)), surprising that more attention has not been paidof the external auditory meatus of man aud of the to their origin and development (Hdggqvist (3)).Vervet monkey (Cercopithecus acthiops). First described by Koelliker in 1547, myo- Paraffin sections of material freshly fixed in epithelial cells were claimed to be ectodermal inHelly's or Bouin's fluids were stained with hema- origin by Ranvier in 1875 (both cited bytoxylin and eosin, the periodic acid-Schiff (P.A.S.) Haggqvist, (3)). Supporting this view is the situa-method, a modified Wilder's method for reticulin, tion of the myoepithelial cells superficial to theReidenhain's iron-hematoxylin or Altmann's aniline-acid fuchsine. Free-floating frozen sections basement membrane (Schaffer, (4); Leeson, (5)).of monkey material fixed in chilled formalin were Further, it has been claimed that in the embryostained with Scharlach H for fat, or were incubated the basal layer of the originally two-layered sweatfor varying times in the Gomori glycero -phosphate gland tube differentiates into myoepithelial cellssubstrate for the demonstration of alkaline phos- in the secretory portion of the gland, while thephatase (Pearse, (18)). epithelium retains its stratification in the duct In addition, mitotic figures were sought in (Schaffer, (4)). Myoepithelial cells of embryonicserial sections of the external auditory meatuses salivary glands are similarly related to the basalof a female Vervet monkey treated witb eolchicine. cells of the duct (Heidenhain, (6)). This animal, weighing approximately 2.7 Kg, was given 6mg colchicine in 3 ml saline subcutaneously In the adult, cells intermediate in structureat 10.30 p.m., and was killed five hours later, at between myoepithelial cells and the secretory3.30 a.m. An ampoule of hyaluronidase cells of the sweat gland have been described by("Hyalase") was added to the injection to facili- Hibbs (7) in electron micrographs, but were nottate absorption. found in salivary or lacrimal glands by Scott and Pease (8), using the same technique. In oBsEnvATroNs general, workers with the light microscope have Occurrence of Transitional Forms failed to find such transitional forms in sweat, In large apocrine sweat glands of the human salivary or laerimal glands. external auditory meatus, stained with P.A.S. It has often been noted (Brunn, (9); Stohr,and hematoxylin, or with hematnxylin and (10); Hoepke, (ii)) that the myoepithelial celleosin, typical myoepithelial cells are visible layer of adult sweat glands is a continuation ofbetween the basement membrane and the secre- the basal cell layer of the duct. Cells interme- tory cells of the gland. They are pale-staining diate in structure between the two types do notelongated cells with their long axes approxi- however seem to have been described in themately parallel to the long axis of the tubule. adult, and a number of authors have stated orNuclei of myoepithelial cells are elongated or implied that such transitional forms do not flattened, are usually darkly stained, and contain occur (Alverdes, (12); Way and Memmesheimer,rather coarsely granular ehromatin. (13); Bunting et at., (14); Hurley and Shelley, Basal cells of the two- or three-layered duet (2); Horstmann, (15); Hibbs, (7); Lee, (16)). epithelium characteristically have round or The present paper discusses the relationshipslightly oval, pale-staining nuclei, containing of myoepithelial cells to the basal cells of thefine granules of ehromatin. duets of adult, functioning apocrine sweat At the junction between the secretory portion glands, and presents evidence relating to this. of the gland and the duct, nuclei are frequently *Fromthe Department of Anatomy, Univer-found which are intermediate in appearance sity of the Witwatersrand Medical School, Hos-between the nuclei of the myoepithelial cells pital St., Johannesburg, South Africa. Received for publication January 26, 1961. and those of the duct cells (figs. 1, 2, 3 and 4). 301 302 THEJOURNAL OF JNVESTIGATIVE DERMATOLOGY On following a series of basal nuclei from the The basal cells of the duct arc devoid of hire- duct towards the secretory portion of the gland,fringcncc, whether examined in transverse or in typical duct nuclei as described above arclongitudinal section (figs. 17—20). The more gradually replaced by nuclei which progressivelysuperficial cells of the duct frequently contain become flatter and more darkly stained, untildiscrete bircfringcnt fibrils. These do not re- finally the typical appearance of a myocpithelialsemble the more diffusely bircfringent myofibrils ccli nucleus, as described above, is found. Similarof myocpithclial cells, and arc probably tono- transitional forms arc sometimes found in thefibrils (figs. 17—20). apocrine glands of the external auditory meatus of the Vervct monkey. Basement Membrane A small number of cccrinc sweat glands from The basement membrane underlying the various parts of the human body has beensecretory portion of the apocrinc sweat gland examined, and well marked transitional formsbears a characteristic relation to the myoepithclial are not present in most glands. Careful study ofcells. Not only does it underlie the cells, but pro- serial sections has however revealed them in ajections from the basement membrane penetrate few glands, and transitional cells possibly occurfor some distance into the cpithclium, thus in most or all types of sweat gland, but happencnsheathing the myocpithclial cells in a sort of to be particularly easily demonstrated in thetrough. Since the long axes of the elongated apocrine glands of the ear. myocpithclial cells lie roughly parallel to the In the present material no cells have beenlong axis of the gland tubule, these projections found intermediate in appearance betweenof the basement membrane arc well seen in trans- myoepithclial cells and the secretory cells of theverse or tangential sections (figs. 7, 15), but not gland. in sections parallel to the long axis of the gland The occurrence of cells intermediate in char-(fig. 11). The intra-epithelial projections of acter between myoepithelial cells and the basalbasement membrane stain with P.A.S., but not cells of the duct, suggests that the two cell typeswith Wilder's reticulin method. arc related in some way. To investigate this Similar invaginations of the basement mem- relationship, several properties of the cells havebrane were not found related to the duct. been investigated and compared. Several differ- ences which have been found are reported here. Alkaline Phosphatase Myocpithclial cells are strongly positive for Myofibrils Stainable with Iron-Hematoxylin alkaline phosphatasc. After short (30 minutes) Myofibrils of myocpithclial cells, althoughincubation, myocpithclial cells are blackened usually not individually resolvable with thealmost selectively, with little or no staining of light micrpscope, are readily stainable with iron-the overlying secretory cells (figs. 6, 21). Studies hematoxylin. Under similar conditions of stain-with polarized light (figs. 21, 22) indicate that ing, the cytoplasm of the basal duct cells remainsthe initial deposition of precipitate is along the unstained (fig. 5). cell borders of the myocpithelial cell, rather than in the substance of the cytoplasm. This is shown Birefringence by the fact that bircfringencc (due to myofibrils The highly oriented molecules of the myo-in the cytoplasm) and deposition of precipitate fibrils impart positive bircfringcncc to the cyto-are not found in the same region of the cell. plasm of myoepithclial cells. This bircfringcncc, After longer (two hours) incubation, the entire which appears to fill the entire cytoplasm, is seensecretory portion of the sweat gland is intensely in longitudinally or tangentially, but not inblackened, but the duct is still completely free transversely sectioned cells (figs. 11—16). from precipitate (fig. 23). Birefringent material is occasionally seen in the cytoplasm of cells morphologically inter- Incidence of Mitosis mediate between myocpithelial cells and duct After preliminary studies on material fixed at cells (figs. 15, 16). The material studied is9 a.m. had indicated that mitoscs were rare in insufficient to generalize about the stage of theVervet apocrine sweat glands, tissues were taken transition sequence in which cytoplasmic hire-in the early hours of the morning from an animal fringence can first be detected. treated with colchicine (see above for details). ORIGIN AND MORPHOLOGY OF MYOEPITHELTAL CELLS 303 This was done in ease a diurnal cycle of mitosisFirstly, myocpithclial cells and duct cells may occurs in this animal (Bullough. (19, 20)). have certain common functions, and secondly, Due to the spindle destruction caused by theone cell type may become transformed into the coichicine, typical mctaphasc plates were notother even in adult life. seen, and it was sometimes difficult to distinguish Since the only known function of myocpi- mitotic figures from pyknotic nuclei. Excludingthelial cells is contraction, particular attention doubtful mitoses, approximately 30 cell divisionswas paid to morphological or cytochcmical were found in 36 glands completely traced infeatures of the duct cells