An Electron Microscopic Study of the Structure and Formation of Red Pigment Granules in Hair Follicles

An Electron Microscopic Study of the Structure and Formation of Red Pigment Granules in Hair Follicles


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Hair color is determined to a large extent by obtain information on the structure and mode of the quantity and type of pigment present in the formation of red pigment granules of the hair keratinized cells of the hair shaft. The pigment of follicle. In order to recognize differences in the the keratinized cells is derived from melanocytes, fine structure and mode of formation of red and the most important function of which is the syn- black pigment granules, an electron microscopic thesis and transfer of pigment granules into the investigation of pigment-forming cells of the hair differentiating hair cells. follicle of both black and red haired guinea pigs Several authors have studied with the electron was undertaken. In this paper new information is microscope the production of black pigment given on the structure and production of red piggranules (melanin) in the mclanocytes of hair ment granules. Furthermore, while certain findfollicles (1, 2, 3, 4). The formation of black pig- ings of previous workers arc confirmed, a few ment granules is a complex process: Small new observations are also presented on developvesicles, premclanosomes (3, 5, 6), containing mental forms of black pigment granules. parallel arrays of inner membranes, arc found MATERIALS AND METHODS first in the Golgi region of the melanocytes. The vcsicles grow in size and a melanin polymer Male guinea pigs, weighing 300—500 gm. with accumulates on the inner membranes. This struc- pure black or red fur were obtained from Rockland New Jersey. The hair follicles were disture is designated as the mclanosomc. As mclani- Farms, sected singly and intact from the skin and were zation proceeds, the membranes of the vesicles immersed in icc cold 1% or 2% osmium tetroxide arc masked and the final product, the melanin buffered to pH 7.4—7.6 with vcronal acetate buffer granule, appears as a structureless, uniformly (7). After fixation for two hours, the tissues were dehydrated in ethanol and embedded in epoxy dense body. resins according to the method of Luft (8). Sections Red hair pigment has received scant attention were cut with a Porter-Blum microtome, stained in the past and relatively little is known about its with lead hydroxide (9) and examined in RCA mode of formation, structure and chemical na- EMU 3F electron microscope. ture. Birbcck and Barnieot have made a few obRESULTS servations on pigment-forming cells of human One of the most characteristic properties of red hair follicles (1, 2). They noted vcsiclcs in the black pigment-producing cells of the hair follicle Golgi region possessing distinct, often concentric shells of dense material similar to those seen is the presence of a well-developed Golgi complex during initial stages of black pigment granule and numerous melanin granules in various stages formation. The mature granules seemed to be of formation. The Golgi complex of mclanoeytcs composed of loosely aggregated small particles; of the guinea pig hair follicle consists of many these appeared round, or slightly ovoid and in parallel arrays of agranular membranes and general smaller than the mature black pigment smooth surfaced vesicles. Premelanosomes, mclagranules.

The purpose of the present study has been to * From

the Department of Dermatology.

I' Boston University School of Medicine, Boston

nosomes and mature melanin granules arc seen in the Golgi region as well as in other parts of the cytoplasm (Fig. 1, 2). Prcmclanosomes appear round in cross sections and rod shaped in longitudinal

University Medical Center, Boston, Mass, and sections. These consisted of a smooth-walled the Department of Biology. vcsiclc containing many parallel oriented inner Brown University, Providence, R. I. membranes (Fig. 1, 2). The melanosomcs are This work was supported by Grants GM 10399-01 and AM 05779-02 from the National Institutes of somewhat larger than premelanosomes and have Health, U. S. Public Health Service. a roundish or oval appearance depending on the Presented at the Twenty-fourth Annual Meet- direction of sectioning. Their most characteristic ing of The Society for Investigative Dermatology, property is the presence of many dense and relaInc., Atlantic City, N. J., June 17, 1963. 275







Fio. I. Electron micrograph of a portion of a black melanocyte showing different stages in the formation of melanin granules. PM: Premelanosome showing oriented parallel array of membranes. M: Melanosome revealing tbick membranes with the accumulation of pigment. MG: A mature melanin granule appearing nniformly dense. X: A granule which represents an intermediate stage between the melanosome and a mature melanin granule. The body of the granule is divided into several compartments by electron dense partitions. X 45,080.



-• k M











FIG. 2. Electron micrograph of a part of a black melanocyte. Melanosomes and mature melanin granules are distributed in the cytoplasm. MG: Mature melanin granule. M: Melanosome. Y: Shows an anomalous melanin granule. While one part of the granule shows no internal structure and resembles a

mature melanin granule, the other part shows only partial melanization and appears similar to a melanosome. X 72,520.




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FIG. 3. The larger part of the electron mierograph shows part of a red melanocyte. In the upper right corner a portion of a keratinizing cell is seen. A portion of the nucleus of the red melanocyte (N), a well-developed Golgi complex (G) and many mitochondria (M) are shown. IG: A small granule represent-

ing the earliest recognizable stage ia the formation of red pigment. These granules are about 400 A in diameter. 1MG: Larger granules showing intermediary stages of red pigment formation. MG: Mature red pigment granules. CL: A clump of three red pigment granules are shown in a neighboring keratinizing cell. Inset: One granular and two homogeneous appearing red pigment granules. X 28,224.



tively thick inner membranes containing the Red pigment granules, as noted in this study, newly deposited melanin polymer (Fig. 1, 2). appear to be not only structurally different from The mature granules are rod-shaped and appear black pigment granules, but basic differences as dense structureless bodies enclosed by a thin

also seem to prevail with regard to their mode of

formation. Structurally, red pigment granules are either granular or homogeneous appearing melanin granules of different structural charac- roundish structures whereas mature black piglimiting membrane (Fig. 1, 2).

In addition to the forms described above,

teristics are also noted. One is a roundish melanin

ment granules are dense structureless rod-shaped bodies. Concerning the mode of formation, the

granule divided into several compartments by electron-dense partitions (Fig. 1). Another kind of granule resembles in one part the structure of a mature melanin granule while in the other part that of a melanosome (Fig. 2). Both the mode of formation and the structure of red pigment granules appear quite different

Whether there is a complete lack of a skeleton, or if it occurs in a disorganized form not recognizable by electron microscopy, cannot be re-

from that of black pigment granules. While there is a well-developed Golgi complex in the red pig-

solved at the present time. In regard to this problem, Moyer (10, 11) has noticed that the

ment-producing cells, premelanosomes are not seen, and the red pigment granules seem to be formed without an oriented precursor structure. Red pigment granules appear first as small, dis-

inner membranes of melanosomes of the mouse retinal pigment epithelium undergo a variety of structural changes in accordance with genetic factors. When the mutnnt allele is present in the homozygous condition at the P locus, the inner membranes of melanosomes become highly dis-

crete particles measuring approximately 400 A in

most striking difference appears to be that the production of red pigment granules proceeds

without formation of an oriented skeleton.

diameter. These uniformly dense, round bodies are occasionally encased by a thin limiting mem- organized. In view of this, it is probable that brane. Such granules occur not only in the Golgi some allelic change in the pigment controlling region but throughout the cytoplasm (Fig. 3). genetic loci might produce a disorganized supIn addition, larger granular and homogeneous porting framework in the red pigment-forming granules are numerous in the Golgi region and at cells of the hair follicle of the guinea pig. Perhaps scattered points of the cytoplasm (Fig. 3). The further experimentation will clarify this problem larger granules are considered to represent in- and will lead to a better understanding of the termediary and mature developmental forms of mode of formation of red pigment granules. red pigment. The mature red pigment granules occur singly or in clumps of two or three. Furthermore, aggregates of red pigment granules are seen


1. The fine structure and mode of formation of

in the cytoplasm of presumptive cortical and black and red pigment granules in the hair medullary cells. follicles of guinea pigs were studied with the DIscussIoN

The results of the present study confirm pre-

vious findings on the structure and mode of formation of black pigment granules in the mela-

nocytes of hair follicles (1, 2, 3). The roundish melanized granule, noted to be divided into several compartments, is a new form that has not been previously described. We think that this type represents an intermediary stage between the melanosome and the mature melanin granule.

The other type structurally resembled both a melanosome and a mature granule. This type of structure suggests that melanization in certain cases may proceed at different rates in different parts of the developing granule.

electron microscope.

2. Developmental forms of black pigment, the premelanosome, melanosome and melanin granule are described. In addition to these, two new forms are described for the first time. 3. Red pigment granules are produced without

the formation of a precursor structure, such as the premelanosome. The initial granule isa small,

round particle, measuring about 400 A in diameter. Intermediate and mature granules appear round and have a granular or homogeneous structure. REFERENCES 1. BARNICOT, N. A. AND BIRBECK, M. S. C.: The

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(Minneapolis, Minn.):

DR. PAUL F. PARAKKAL (in closing): Drs.

I wish to thank Dr. Parakkal for his interesting


presentation. We too have been studying red


and Barnicot have pointed out (1, 2)

the formation of red pigment is similar to that of the black pigment. However, we find that

granules, but in human hair rather than guinea pig hair follicles. Our findings differ in guinea pigs the red pigment formation follows from those presented this morning. We find a a different pattern from that of the black pigdefinite membrane structure during the formation ment. It is interesting to note that morphoof the granules, similar to that described in the logically human red pigment is different from that of the red pigment formed in the guinea pig. early stages of black pigment formation. pigment in



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