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The Formation of the Primate Nail Plate. an Autoradiographic Study in Squirrel Monkey* Nardo Zajas, M.D

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The Formation of the Primate Nail Plate. an Autoradiographic Study in Squirrel Monkey* Nardo Zajas, M.D TilE JOURNAL OF INVESTIGATIVE DELZMATOLOGY Vol. 51, No. 2 Copyright 1968 by The Williams & Wilkins Co. Primed in U.S.A. THE FORMATION OF THE PRIMATE NAIL PLATE. AN AUTORADIOGRAPHIC STUDY IN SQUIRREL MONKEY* NARDO ZAJAS, M.D. AND JTIANA ALVAREZ The classical concept that the human nailoped and stained with hematoxylin-eosin stains plate is solely produced by the nail matrixfollowing routine autoradiographic technics. (1—3) has been challenged by several investi- Normal anatomical considerations gators (4—6) who feel that the nail plate has The gross and microscopic anatomical similari- a tripartite origin: 1) the largest component,ties of the squirrel monkey's finger and toe nails the intermediate portion of the nail plate,with human nails have been previously described arising from the matrix, 2) a dorsal portion,(8). The normal primate nail organ consists of four arising from the proximal nail fold and 3) aepidermal structures: the proximal nail fold ventral portion, from the nail bed and(PNF) (Fig. 2), matrix (M) (Fig. 2), nail bed hyponychiurn. The present study clearly dem-(NB) (Fig. 3), and hyponychium (HYP) (Fig. onstrates a single origin of the nail plate,4). These structures are seen in Fig. 1. The nail plate is produced by the matrix. The matrix basal totally and solely produced by the matrix. cells exhibit a keratinization process, typical of hard keratinous structures, which is devoid of a METHODS AND MATERIALS granular layer. The basal cells in their movement Tritiated glycine, incorporated into the epider-to the surface flatten, undergo nuclear lysis and mal proteins of the nail, was followed by autoradio- condensation of their cytoplasms becoming horny graphic technics, allowing the study of the forma-cells, which, unlike those of the stratum corneum, tion of the nail plate, as well as other aspectsare not shed but become adherent to each other of nail plate movement. to form a sheet-like structure, the nail plate. The Fingers and toes of 4 squirrel monkeys werezone of cytoplasmic condensation just prior to used in this study. Tritiated glycine (sp act = 1.3becoming nail plate cells is termed the kerato- C/mM) was injected intraperitoneally into twogenous zone (KZ white arrow) (Fig. 2). The nail monkeys and intradermally into the nail area inplate grows outward and distally. The proximal the other two. The amount of intraperitoneal gly-nail fold is a fold of skin that covers most of the cine was calculated to deliver a tissue concentra-matrix. The dorsal surface of the PNF is the tion of at least 2 microcuries of tritiated glycineepidermis of the dorsum of the finger while the per gram body weight. In the intradermally in-ventral portion of the PNF is made up of slightly jected monkeys 0.05—0.1 cc of fluid (50—100 micro- modified epidermis. The boundary between the curies) was injected into the skin around all thePNF and the matrix is easily recognized by follow- nails. ing the granular layer of the PNF as it fades into The digits were amputated at varying times after the non-granular-layer containing epidermis of the the injection of the isotope: i.e. 1 hour, 1, 2, 3, 4, 6, matrix (arrow Fig. 2). The same is true of the 8, 10, 14, 21 and 28 days. The digits were fixed inboundary between the nail bed and the hypo- 10% buffered formalin for 24 hours and then trans-nychium (Fig. 4) where the heavy granular layer ferred to a solution containing 10% formalin andof the hyponychium epidermis fades proximally 5% trichloroacetic acid to decalcify for about 72to become agranular epidermis of the nail bed. hours. The digits were processed by routine alco-The PNF and hyponychium produce a stratum hol-paraffin histologic technics as well as by thecorneum which hi the case of the former becomes polyethylene glycol-pyroxylin embedding technicadherent to the surface of the nail as the cuticle (7). Sections, cut 3—6 micra thick, were placed on (Fig. 1) and in the latter accumulates slightly previously subbedded microscope slides with 1%under the distal portion of the nail plate (Fiv &\ gelatin and dipped in Kodak NTB3 liquid eniul-and is normally shed. ion. Sections were exposed for 4—5 weeks, devel- RESULTS This study was supported in part by a grant from the National Institutes of Health, Public One Day Health Service ROl AM 09692-01 GM and in part by Dermatology Training Grant AM 05262 from In the one day specimens only the viable the National Institute of Arthritis and Metabolic Diseases, NIH. epidermal structures incorporate the radio- Accepted for publication March 28, 1968. active glycine into their proteins. No labelinz * From the Department of Dermatology. Urn- versity of Miami School of Medicine, Miami,occurs in the superficial dead horny layer Florida 33136. (Figs. 5, 12—15, 19 and 22). Differences in tha 120 FORMATION OF THE PRIMATE NAIL PLATE 121 !LW 4 ., 'L ..,t_- FIG. 1. Longitudinal section through distal digit of squirrel monkey showing relation of nail structures to phalanx. Proximal nail fold (PNF); nail bed (NB); nail plate (NP); hy- ponychium (HYP). ll&E X 18. concentration of the incorporated glycine canthe tagged nail plate has moved distally and be seen on comparison of the density andhas reached the boundary between the proxi- quality of the precipitated silver dots in themal nail fold and the matrix, which is clearly emulsion film overlying the various epidermallandmarked by the granular layer (KH) of the components. The greatest concentration offormer. It can now be appreciated that the glycine is incorporated in the proximal foldnail plate is formed from the entire length of and volar epidermis, a lesser amount is in-the matrix. corporated in the matrix, and the lowest The proximol nail fold—The labeled pro- concentration is in the nail bed (Figs. 12—15). teins in the Malpighian layers of the proximal nail fold epidermis have moved into the Three Days stratum eorneum (arrows up Fig. 6). No con- The contribution of the various epidermaltribution to the nail plate is seen at this structures to the nail plate can be readilytime from this structure. seen. The nail bed—The nail bed epidermis has The matrix—The labeled proteins in theincorporated smaller concentrations of glyeine cells of the viable strata of the matrix (Fig. 5)than the other epidermal nail structures. have moved superficially and are now locatedThese tagged proteins remain in the Mal- in the nail plate (Fig. 6). The proximal por-pighian layers and do not contribute to the tions of the matrix form the superficial layernail plate at this time (Figs. 16, 20, 21). of the nail plate while the distal portion of The hyponychium and valor epidermis.— the matrix, the lunula, forms the lower-mostThe hyponyehium and the volar epidermis layers of the nail plate. The direction oftagged proteins (Fig. 23) move in a manner growth of the matrix cells and the nail platesimilar to the proteins of Ihe proximal nail is distalward and pointed dorsally on emergingfold epidermis. At this time, there is no con- from under the proximal nail fold. At thetribution from the hyponyehium to the ventral most proximal area of the matrix (Fig. 6),aspect of the nail plate. •w '' — -—:.'-.t.'-:•-— •--,t..p.. , • 'ta.e'-.Ci 4.,:..r-. ..•'-'t)•. - I t_ gt e' a Fm. 2. Higher magnification of the proximal nail fold (PNF) and matrix (M) area in Fig. 1. Keratogenous zone (white arrow); nail plate (NP); the boundary of NPF and matrix (arrow) can be seen hy the disappearance of keratohyaline granule layer of the PNF. H&E>< 176. Fro. 3. Higher magnification of boundary between matrix (lunula) and nail bed (NB) epidermis in Fig. 1, showing how keratogenous zone (white arrow) projects distally and dorsally into nail bed area. Nail plate (NP). H&E ><134. Fm. 4. Higher magnification of hyponyohial area in Fig. 1 showing boundary (arrow), demarcated by disappearance of keratohyaline layer (white arrow) of the hyponyohiom into nail bed. Stratum corneuin (SC) of hyponyohiom accumulates under the nail plate (NP) and is shed off. H&E ><176. 122 FORMATION OF THE PRIMATE NAIL PLATE 123 Six Days The plate has received no contributions from Matrix-nail plate—The labeled nail platethe PNF and the hyponychium. New horny continues its distal movement and the sheet-layers from the PNF and the hyponychium like formation can be readily appreciatedhave replaced the labeled horny layers and (Figs. 8, 18). At its proximal end the nailare now entire'y isotope free. plate has passed the boundary of the PNF DISCUSSION and the matrix (Fig. 7). The plate has re- ceived no contributions from the PNF. The This study clearly shows that in primates distal portion of the tagged nail plate isthe nail matrix is solely responsible for the moving distally over the nail bed and hasformation of the nail plate in normal circum- not received any contribution from it (Fig. 8). stances. The theory of a three-component Proximal nailfold-cuticle .—The labelednail plate formation formulated by Lewis (4) proteins continue toreplace the existingis based primarily on tinctorial differences when stratum corneum and by the fourth day havehuman embryo fingers are stained by the completely replaced the thin horny layers ofsilver proteinate method and is completely the proximal areas of the ventral componentinvalidated by the evidence presented in of the PNF (Fig. 7) and have not contributedthis study. to the nail plate. In contrast to this, the There is no qualitative difference in the in- dorsal PNF component has replaced only onecorporation of tritiated glycine into the nail fourth of its thicker horny layer (Fig. 9). structures from isotope given either intra- The nail bed.—The nail bed continues toperitoneally or intradermally at the nail site.
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