Melanocytes/ Pigment Flashcards
Embryonic origin of melanocytes
Neural crest
Transcription factor expressed by transient neural crest cells
SOX10
Gene important for specifying melanoblasts
**MITF
+PAX3
(downregulation of FOXD3)
Cell signals for differentiation from melanoblast to melanocyte
Wnt
KIT/SCF
Endothelin 3/EDNRB
FGF
BMP
E-cadherin, P cadherin
Locations of melanocytes throughout body
Skin
Oral mucosa
Eyes
Leptomeninges
Ear
Location of non-melanocyte transient neural crest cells
Facial connective tissues
Heart
GI nervous system
Disorders of melanoblast migration (3)
- Piebaldism
-white spots on midline, normal ears/eyes - Waardenburg syndrome
-white coat, eyes/ears/muscle/etc affected
-Lethal white foal syndrome (EDNRB), megacolon - Tietz syndrome (MITF)
-white coat, eyes, deaf + microophalmia
Gene for piebaldism in brown swiss cattle, holstein, Simmental cattle
MITF
Gene for piebaldism in Birman cat (white glove), white spots in horses, cattle, pigs
KIT
Gene for white belting in cows
TWIST2
Gene for roan color in Belgian blue cattle, short horned cattle
SCF/KITLG
Genes (2) for increased digital SCC in poodles, Giant Schnauzers
MC1R
KITLG
Gene for coat color intensity
KITLG (# of copies of the gene)
Genes (2) for waardenburg syndrome in dogs
MITF, SILV
Genes for waardenburg syndrome in cats
KIT
Genes for waardenburg syndrome in cattle, pigs
MITF
Genes (3) for waardenburg syndrome in horses
EDNRB
PAX3
MITF
Gene for lethal white foal syndrome, lethal white lamb syndrome
EDNRB
Waardenburg type___ = lethal white foal syndrome
4
Clinical signs of lethal white foal syndrome
White coat, aganglionic megacolon
Piebaldism: clinical signs
White coat
Eyes/ears normal
Waardenburg syndrome: clinical signs:
White coat, senorineural deafness, depigmented iris, other NCC disorders
Tietz syndrome gene in cow
MITF
Clinical sign of Tietz syndrome in cow
White head, eyes, deaf
+ Microophthlamia
(overlap w/Waardenburg type 2)
Where are melanocyte stem cells in the skin?
Hair follicle (bulge), epidermis (basale), dermis, eccrine sweat glands
Cell signal to localize melanocyte stem cells to hair bulge (to live with keratinocyte stem cells!)
KIT/KIT-L interactions with keratinocytes!
(+cadherins, integrins, COL17)
Cell signal to localize melanocytes to anagen hair bulb (by keratinocytes)
KIT (melanocyte)/KIT-L (keratinocyte)
Cell signals for melanocyte stem cell interactions with the hair follicle
Wnt
B-RAF C-RAF
NOTCH
TGF-B
BDN
NFIB
What happens if melanocytes aren’t distributed evenly throughout the hair bulb
dilute coat color
(ie ancient horses)
How does TBX3 affect hair shaft color?
TBX3 suppresses KIT-L on keratinocytes
–> melanocytes are not recruited to the hair bulb
*Modern horses have mutation to inactivate TBX3, resulting in more robust hair color
2 incidents that can recruit melanocytes from follicle to epidermis
1) Wounding
2) UVB irradiation
Cell signal to recruit melanocytes from follicle to epidermis
MC1R
Damage to which type of cell can also cause injury to melanocytes –> causing greying
Ketatinocyte stem cells
Share a niche in the bulge
Which drug has been associated with reversible hair graying?
Tyrosine kinase KIT inhibitors –> Palladia
Autosomal dominant mutation of STX17 results in which phenotype?
Gray horse phenotype –> Premature graying
Gray horse phenotype mode of inheritance
Autosomal dominant
Gray horse phenotype gene
STX17
How old are grey horses when they lose nearly all their hair pigment?
Age 6-8 yrs old
What percent of grey horses develop cutaneous melanomas by age 15?
70-80%
What cancer are grey horses overrepresented for?
Cutaneous melanoma
What gene OTHER than STX17 is likely responsible for grey coat phenotypes in horses? (melanoma formation, vitiligo-like depigmentation, speckling)
ASIP
Etiology of grey horse phenotype?
Defect in hair follicle melanocyte stem cell survival
Which body parts receive melanosomes from keratinocytes?
Epidermis, hair follicle, mucosae
Melanosomes are lysosome-related organelles (LRO). Name 2 others
-Platelet dense granules
-Type II pneumocyte lamellar bodies
Eumelanin color
Black/brown
Pheomelanin color
Yellow/red
Stage I melanosome formation
Formation of organelle vesicle structure
(build the restaurant)
Stage II melanosome formation
-Put in supportive protein fibrils, which gives melanosome its shape
-Add enzymes to make the melanin; derived from golgi
Fibril function: support + shaping (premelanosome protein 17 [SILV]
+ MART-1, GPNMB)
(hire the servers)
Stage III melanosome formation
Melanin deposited along fibrils, but you can still see the fibrils
(make a few pizzas, soft open)
Stage IV melanosome formation
Melanosome is full of pigment, can no longer see fibrils
(Restaurant is a success. Full of pizzas)
Hermansky Pudlak Syndrome clinical signs
White coat, hypopigmented eyes, leukocyte problems!
“Pud Lacking blood”
Why do dogs with Hermansky Pudlak Syndrome also have blood cell issues?
Melanosomes and platelet dense granules have similar Lysosomal related organelle biomechanics
IHC targets for melanocytes, melanomas
Tyrosinase
MITG
Melan-A/Mart1
Also Vimentin, S-100
When are melanocytes activated during hair cycle
Anagen
Which cell signal is important for activating melanocytes during anagen
Wnt
What is the common precursor to both eumelanin and pheomelanin?
Dopaquinone
Main protein fibril in melanosomes
Premelanosome protein 17 (SILV)
Which cells other than melanocytes have LROs (lysosome related organelles)?
Platelets
Neutrophils
T cells
Type II pneumocytes
Other name for Gray Collie syndrome
Canine Cyclical Hematopoiesis
Clinical signs of Gray Collie syndrome/ Canine Cyclical Hematopoiesis
-Dilute skin/hair coat
-Cyclical neutropenia, thromocytopenia, anemia
-Recurrent infections
-Grey/dilute nasal planum
Cause of dilute coat in grey collie syndrome
Inadequate delivery of melanin synthesis enzymes from golgi to melanosome –> decreased melanization of melanosomes
Gene causing grey collie syndrome (HPS type 2)
AP3B1
(B1 subunit of the AP-3 complex that delivers biosynthesis enzymes from golgi to melanosome)
Coat color phenotye associated with HPS type 3 in French bulldogs (decreased platelet dense granules w/o bleeding)
Cocoa coat color
Gene mutation causing HPS type 3 of French bulldogs (decreased platelet dense granules w/o bleeding)
BLOC gene mutation (important for transportation of biosynthesis enzymes from golgi to melanosome)
Which breed with a cocoa coat phenotype develops HPS type 3 (decreased platelet dense granules w/o bleeding)
French bulldogs
Which breed of cat gets HPS type 5, BLOC-2 complex mutation
Donskoy cats
What color are Donskoy cats with HPS type 5, BLOC-2 complex mutation
Light brown skin, yellow irises, red-eye effect
Other than cats, which other animal also has HPS type 5
Horses with white markings
No deleterious effects
What does HPS stand for?
Hermansky-Pudlak syndrome
Gene mutation in AP3B1 causes _____
Gray Collie syndrome (canine cyclical hemtopoesis)
Mutation causing Merle coat color
SILV
Chediak-Higashi syndrome: clinical signs
-Hypopigmentation of hair, skin, eyes with silvery sheen
-Severe immunodeficiency
-Recurrent infections
-Neurologic signs
-Bleeding
-Pulmonary fibrosis
Chediak Higashi syndrome: gene mutations, function
CHS/LYST (lysosomal trafficking regulator) –> regulates vesicle fusion with plasma membrane
Histopathologic finding CLASSIC for Chediak Higashi syndrome
Neutrophils with large granules
Giant, intracytoplasmic accumulations of granular material, because can’t fuse with cell membrane
Also happens in other cells
Chediak Higashi syndrome: species
Hereford/Brangus/Japanese black cattle, Persian cats, beige mice, beige rats, minks, silver/blue foxes, killer wale
Clinical signs of dogs with Merle coat color 2’ SILV mutation
Congenital sensorineural deafness, blue irises
Equine multiple congenital ocular anomalies (silver, silver dapple horses) gene
SILV
Rat-tail syndrome (color dilution and hypotrichosis in calves) gene
SILV
Congenital Stationary Night Blindness + leopard spotting gene
TRPM1
(channel protein that affects melanocyte survival, retinal cell function)
True or false: melanin pigment can be cytotoxic if not contained in an organelle
TRUE!!!
Important cofactor for tyrosinase
Copper
Which enzyme is copper a cofactor for?
Tyrosinase
What is the rate limiting step of melanin synthesis
Tyrosinase
(L-tyrosine to L-Dopa)
(L-Dopa to Dopaquinone)
Which enzyme is required to convert Dopachrome to DHICA
TYRP2
Which enzyme is required to convert DHICA to eumelanin
TYRP1
Which amino acid needs to be available in high levels to make Pheomelanin
Cysteine
Cysteine is required for synthesis of which: eumelanin or pheomelanin
Pheomelanin
Is TYRP1 important for synthesis of eumelanin or pheomelanin?
Eumelanin
Pigment type switching (eumelanin to pheomelanin, etc) results in _____
Agouti coat
Agouti protein antagonizes ____ to promote pheomelanin
α-MSH
MC1R binds α-MSH to promote ______ (melanin type)
Eumelanin
T or F: animals with oculocutaneous albinism are deaf
FALSE
(have melanocytes, they just don’t make melanin. Disorder of melanin synthesis)
In addition to hypomelanosis of tissue, which other clinical sign is seen in many cases of oculocutaneous albinism?
Nystagmus
Which animal has nystagmus 2’ their oculocutaneous albinism?
Siamese cats
Mutation associated siamese coat (oculocutaneous albinism type 1), recessive
Tyrosinase (TYR)
Cat breeds with oculocutaneous albinism
Siamese
Burmese -> Mocha
Birman
Balinese
Himalayan
Oculocutaneous albinism type 2 in Doberman Pinscher gene. “White Doberman”
SLC45A2
Disease associated with a mutation in SLC45A2 (OCA type 2)
White doberman pinscher
Increased risk of melanoma
Potential risk factor with white dobermans
Increased risk of melanoma
SLC45A2
OCA type 1 gene
Tyrosinase (affect both eumelanin and pheomelanin)
OCA type 2 gene
TYRP1 (eumelanin only affected)
Which amino acids are crucial in the diet for appropriate pigmentation (2)
Phenylalanine
Tyrosine
Result of diet deficient in phenylalanine or tyrosine
Discoloration of hairs
Which element is crucial in the diet for appropriate pigmentation (1)
Copper
Copper deficient diet results in _____
“Ghost eyes” “Spectacle disease”
Graying of periocular hair
Coat greying in puppies
“Ghost eyes” etiology
diet deficient in copper
Epidermal melanin unit
1 melanocyte transfering melanosomes to 36 keratinocytes
Follicular melanin unit
1 melanocyte transfering melanosomes to 5 keratinocytes
Dendrites of melanocytes reach as high as ___ in the epidermis
Stratum spinosum
Proteins at dendrite tip of melanocyte, to transfer melanosome (3)
1) Rab27a
2) Melanophilin
3) Myosin-5a
Which level of epidermis has the most melanosomes
Stratum basale
Where does small melanosomes live within a keratinocyte?
Perinuclear cap
(microparasol)
Where do large melanosomes live within a keratinocyte?
Throughout cytoplasm
Mechanism that brings small melanosomes to perinuclear cap
Melanosome is endocytosed –> dynactin, dynein motor along microtubules to the correct spot
Genes implicated in Griscelli syndrome
MLPH, Myosin5a, Rab27a
Tips of melanocyte dendrites
Lavendar foal syndrome gene
Myo5a
Histopath from patient w/Lavendar foal syndrome
Clumped melanosome in cell bodies of melanocytes
Clinical signs Lavendar foal syndrome
Dilute coat, neurologic signs, lethal
Dog breed with Myo5a disease, GS type-1
Mini dachshunds
Dilute coat, neuro signs
Gene associated with color dilution alopecia
MLPH
D locus
Is MLPH mutation alone enough to induce CDA?
No. Other modifying factors required
Causes for hyperpigmentation (acquired) (3)
Solar
Inflammation
Pharmacologic (rubber?)
Causes of hypopigmentation by affecting both keratinocytes and melanocytes (acquired)
Trauma: burns, wounds, etc.
Disrupt epidermal and follicular melanin units
Causes of hypopigmentation by targeting melanocytes (3)
-Vitiligo
-Uveodermatologic syndrome (also targets keratinocytes)
-Alopecia areata (also targets keratinocytes)
Causes of hypopigmentation by epidermal cytotoxic disorders (4 +3 bonus)
-Keratinocyte viral infections
-CLE
-EM
-SJS/TEN
*also vascular/ischemic, CETL, AISBD
MITF increases transcription of ___ (4)
Tyrosinase
DOPA
TYRP1
TYRP2
Main adhesion molecule expressed by melanocytes to connect to the skin.
E-cadherin
Where are melanocytes in the ear?
Cochlea (Stria vascularis)
Special stains to visualize melanocytes
Fontana Masson, DOPA oxidase reaction, Schmorl’s method
Specialized cell for amphibian, fish, reptile, cephalodpod pigmentation
Chromatophores
-Reflect light in different ways to determine coloration
Cytokines released by melanocytes in inflammation
IL-8
IL-1α
TNFα
Do melanocytes increase or inhibit keratinocyte proliferation?
INHIBIT
Major difference between eumelanin and pheomelanin (chemically)
Pheomelanin has high sulfur
(yellow, like stinky eggs)
Cell signal primarily responsible for regulation of melanogenesis
MITF
How does UV radiation stimulate melanogenesis?
UV upregulates POMC, α-MSH, ACTH, and MC1R.
POMC is cleaved into α-MSH. α-MSH binds to MC1-R on melanocyte surface –> increases cAMP –> signal cascade –> upregulates MITF (tyr, tyrp1, more melanin!)
POMC is a precursor for α-MSH, which induces melanin synthesis. What else is POMC a precursor for?
ACTH
(ACTH can also increase cAMP, leading to more MITF expression/more melanin)
What is the agonist of MC1R
α-MSH
What is the antagonist of MC1R
agouti protein
(binds with higher affinity than α-MSH, producing pheomelanin instead)
Does α-MSH produce pheomelanin or eumelanin
eumelanin
(Agouti is antagonist for MC1R, which switches to pheomelanin)
Stimulators of melanogenesis (10)
1) α-MSH
2) ACTH
3) Endothelin 1
4) SCF
5) Leukotrienes (LTB4, LTC4)
6) Prostaglandins (PGE2, PGF2α)
7) UV radiation
8) Nitric oxide
9) Histamine
10) eutroprophins
Inhibitors of melanogenesis (3)
IL-1
IL-6
TNF-α
Inhibitor of differentiation from neural crest cells to melanocytes
BMP-4
Disease from breeding two Overo spotted paint horses (EdnrB)
Lethal white foal syndrome
Mode of inheritance Lethal white foal syndrome
Autosomal recessive
Who makes larger melanosomes: follicular or epidermal melanocytes?
Follicular
Disease of “Blaze” colored ferrets
Waardenburg syndrome
Flat skulls, wide set eyes, white stripe on top of head
Breed with LYST mutation, Chediak Higashi syndrome
Persian cats
Breed with lethal lavendar foal syndrome
Arabian horses
Breeds with hereditary vitiligo
Belgian Tervuren dogs
Rottweilers
Old English Sheepdogs
Dog breeds with vitiligo (+1 cat, + 1 horse)
Rottweiler, Doberman, Collie
Siamese
Arabian horse
Cells involved in vitiligo
CD8+ T cell attack at melanocytes (Melan-A)
Also NK cells, antibodies (against TYR, TRP1, TRP2)
Uveodermatologic target
Tyrosinase, TYRP1, TYRP2
Also gp100 in melanocytes
Histopath finding vitiligo
loss of melanocytes from the epidermis and/or hair follicle. Keratinocytes lack melanosomes
+pigmentary incontinence+ melanophages
+rare: lymphocytes around apoptotic melanocytes
3 phases of uveodermatologic syndrome in humans
1) Meningoencephalic phase: headaches, seizures, vomit
2) Acute ophthalmic phase: photophobia, eye pain, uveitis, retinal detachment
3) Dermatologic phase: vitiligo, poliosis, alopecia
Uveodermatologic syndrome breed
Akita
Equine leukoderma differentials (10)
1) Onchocerciasis
2) Dourine
3) Herpes coital exanthema
4) Lupus erythematosis
5) Pressure sores (saddle)
6) Ear papillomas
7) Ventral midline dermatitis
8) Regressing viral papillomatosis
9) Freezing/burning
10) Contact phenols/ rubber
Equine leukotrichia gene
Dominant W allele- albino, blano, cremello
Potential vitiligo variant in horses
Acquired idiopathic leukotrichia, aka “spotted leukotrichia”
Breeds: Thoroughbred, Shire, Arabians
Why are melanocytes important for hearing?
Melanocytes maintain the K+ potential in endolymph of the cochlea
MITF needed for cochlea development
What TF causes follicular melanocytes to proliferate and mature
SCF/c-kit
Released by follicular keratinocytes
Cause of Congenital Hereditary Sensorineural Deafness in Dalmations
Deafness = result of strial degeneration –> absence of strial melnocytes
-Dalmations
Piebald gene
(Also merle gene, but different breeds like Aussies!)