Melanocytes

Obtained from www1.imperial.ac.uk/

Location

Melanocytes are specialized skin cells located in the basal (bottom) layer of the epidermis.

skin pigmentation is determined by the melanocytes of the epidermis

 

 

Function

Melanocytes produce and secrete melanin, the pigment that gives skin color and protects the DNA in skins cells from UV radiation. 

 

How cell structure relates to function

Melanocytes are rounded cells with long, branch-like extensions called dendrites.  The dendrites extend into the lower layers of the epidermis. 

 

The production of melanin takes place in modified organelles within the melanocyte called melanosomes.  Melanosomes are derived from the SER, RER and golgi apparatus and are unique to melanocytes.  Melanocytes express a gene that codes for the tyrosinase enzyme.  Within the melanosome, tyrosinase catalyzes the reaction that produces melanin.  A defect in the enzyme prevents production of melanin and results in albinsm. 

http://z.about.com/d/sanfrancisco/1/0/n/Z/-/-/P9184096.jpg

 

 

After the melanin is produced, the dendrites of the melanocytes transfer the melanosome (with the melanin) to keratinocytes (the pigment storing cells of the skin).  The melanosomes are deposited over the nucleus of the keratinocytes to protect the DNA from UV radiation.  Differences in skin pigmentation are not due to the activity of the melanocytes, but the keratinocytes.  In Caucasians, lysosomes in the keratinocytes actually degrade some of the melanin.  Less pigment means lighter skin.  The melanosomes in individuals with darker skin are not degraded.

 

distribution of melanin in the epidermis

 

How Melanocytes Form 

Melanocytes form during embryonic development from a layer of tissue called the neural crest.  They are fully differentiated before you are even born.  They are NOT replenished during your lifetime by an adult stem cell.

 

How often melanocytes divide

Like other cells derived from neural crest tissue, melanocytes do not divide.  This means the melanocytes you are born with will remain with you for life (or most of life).  After the cells differentiate during embryonic development, they enter a resting or dormant stage called G0.  They remain here for the rest of their (your) life.  They continue to produce and secrete melanin, but they do not go through the growth and division portions of the cell cycle.  As you age, your melanocytes begin to die.  However, since they don't divide and are not replaced by adult stem cells, they slowly decline in number.  This is why elderly individuals have such light skin.     

 

Click here to learn about another specialized cell in the human body.