Commentary

PIGMENT CELL INTEREST GROUP—A PORTRAIT

When an immigration officer at Dulles Airport recently asked a French graduate student what she was working on at NIH, she happily responded: "Studying the biology of pigment cells!  The officer shot back: "Do we really need French people for doing this?" 

One might as well ask, do we really need pigment cell research at NIH? The answer is a resounding "Yes!"  Pigment cells are not only for the fashion-conscious. We need them in the eye for vision. We need them—and this may come as a surprise—in the inner ear for hearing.

Their abnormalities can point to systemic disorders or lead to life-threatening melanomas. They are model cells for a host of basic studies—in developmental biology, cell biology, immunology, genetics, biochemistry, and more. They have yielded insights into G-coupled signaling pathways, intracellular transport, cell-lineage specification, and malignant transformation.

Pigment mutations in mice, which occur in more than 100 different genes, were among the first to be mapped in the genome.

In short, pigment cells are important.

Some Pigment Cell Basics

But what exactly are pigment cells? There are many types and many different colors in animals. The major type in mammals is the melanocyte, which is derived from the neural crest. Its pigment—melanin—is a biopolymer that is synthesized through a series of catalytic steps starting with the conversion of the amino acid tyrosine to dihydroxyphenylalanine by a copper-binding enzyme called tyrosinase.

Melanin comes in two versions: black eumelanin and yellow pheomelanin. Both versions are made in membrane-bound intracellular organelles called melanosomes.

Not every cell that contains melanosomes is a melanocyte, however, because melanocytes can transfer their melanosomes to other cell types that are not capable of producing melanin themselves. In human skin, for instance, melanosomes are transferred from melanocytes to keratinocytes and into hair shafts; in birds, they are found in feathers.

Melanocytes are present in the iris, which serves as an aperture to regulate the depth of focus and the amount of light that enters the eye. A reduction in iris pigmentation leads to blurred vision. Melanocytes are also found in the choroid behind the retina, where they serve to block the passage of light to deeper tissues.

Between retina and choroid, there is yet another layer of pigment cells, called the retinal pigment epithelium, that regulates the development of the eye in the embryo and the physiology of photoreceptor cells in the adult.

In the inner ear of mammals, melanocytes are found in a portion of the wall of the cochlear duct, where they regulate the ionic composition of the endolymph and ensure that auditory hair cells function normally.

Typically, there are three possible consequences of melanocyte misconduct: Their numbers can change, the amount and quality of pigment can change, or the cells can become malignant. Malignant potential is what makes melanocyte pathology a major health burden for humans. In the United States alone, more than 60,000 new melanoma cases are projected to arise this year—yet preventing melanoma is entirely feasible. For more information on melanoma, go to this website.

Pigment Cell Research at NIH

Over the years, the NIH Intramural Research Program has become one of the premier centers for pigment cell research worldwide. At least six institutes have active programs in this field, ranging from developmental biology to organelle and melanin biosynthesis to tumor biology, immunology, and epidemiology.

Last year, NIH hosted the International Pigment Cell Congress, chaired by Vincent Hearing, NCI. The meeting focused on human pigmentary diseases and attracted more than 400 attendees from all over the world.

In 2001 and again in 2004, two consecutive meetings of the Development Group of the International Federation of Pigment Cell Societies met on campus at the Cloisters. Co-chaired by NHGRI's William Pavan, they each drew more than 50 participants and generated a great deal of excitement.

The Pigment Cell Interest Group enables dynamic interactions among many labs both inside and outside NIH. This active group usually meets on the third Thursday of the month at 12:30 in the conference room of Building 49.

Each month, one of the many member labs presents its hottest results and discusses future approaches. In addition, students and postdocs have the opportunity to present practice talks for upcoming national or international meetings.

We welcome new members. Find out more about this group—and join up—right here.

Senior Investigator

Mammalian Development Section

Laboratory of Developmental Neurogenetics

NINDS

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