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Vet Derm Review > Melanogenesis > Flashcards

Melanogenesis Flashcards

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1
Q

What cells can have giant granules with Chediak-Higashi syndrome?

A

melanocytes, eosinophils, mast cells, lymphocytes, neutrophils, etc.

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2
Q

Which are red-yellow in color: eumelanin or phenomelanin?

A

pheomelanin

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3
Q

T/F: Homozygous mutation in PSMB7 (Harlequin locus) is embryonic lethal.

A

TRUE

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4
Q

What breeds of dogs are over-represented with color dilution alopecia?

A

Dobermans (esp. blue and fawn), Dachshunds, Great Danes, Whippets, Italian Greyhounds

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5
Q

What role do melanocytes play in the cochlea?

A

they are intermediate cells of the stria vascularis; maintain the endocochlear potential in endolymph –> allows hearing to take place

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6
Q

What is the rate limiting step in melanin synthesis?

A

conversion of L-tyrosine to L-DOPA (by tyrosinase OR tyrosine hydroxylase-1)

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7
Q

What is facultative pigment?

A

pigmentation that occurs in response to stimuli (such as UV light)

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8
Q

What changes in coat color can be seen with copper deficiency? Why?

A

Copper is a cofactor for Tyrosinase –> absence of copper –> graying of the hair coat

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9
Q

T/F: Leukoderma without leukotrichia is common.

A

False - usually accompanied by leukotrichia

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10
Q

T/F: With good supportive care, collies affected by Gray Collie Syndrome can have a normal life expectancy.

A

False - even with supportive care, are prone to anemia, arthritis, amyloidosis, glomerulonephritis, and lymphoid exhaustion

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11
Q

What is the function of Myosin 5A? What disease results from a mutation in the gene that encodes for it?

A

Myosin 5A is a motor protein involved in shuttling intracellular proteins; mutations in this protein lead to faulty melanosome transfer (among others) –> lavendar foal syndrome

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12
Q

Where are epidermal melanocytes located?

A

basal layer

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13
Q

T/F: Oculocutaneous albinism type 1 and type 3 primarily affect eumelanin synthesis.

A

TRUE

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14
Q

T/F: Leukotrichia without leukoderma is common.

A

TRUE

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15
Q

T/F: In piebaldism, the mutation is in the gene for KIT and results in absence of melanocytes in the affected area.

A

TRUE

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16
Q

Does steel (stem cell) factor stimulate or inhibit melanogenesis?

A

stimulate

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17
Q

What defect in neutrophils occurs with Gray Collie Syndrome?

A

lack neutrophil elastase (difficulty in making the neutrophil granules)

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18
Q

What cell type is targed in uveodermatologic syndrome?

A

melanocytes

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19
Q

Which is produced with ASP (agonist stimulating protein = agouti) binds to MC1R: eumelanin or pheomelanin?

A

pheomelanin

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20
Q

Does UV radiation stimulate or inhibit melanogenesis

A

stimulate

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21
Q

What breeds of dogs are over-represented with vitiligo?

A

Belgian Tervuren dogs, Rottweilers, Old English Sheepdogs

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22
Q

What cell type is targeted in cutaneous lupus erythematosus?

A

basal keratinocytes

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23
Q

T/F: Animals with oculocutaneous albinism have congenital deafness.

A

False - even though they have hypopigmentation, the melanocytes are still present - they just don’t produce pigment due to lack of tyrosinase

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24
Q

Lethal White Foal Syndrome is associated with a mutation in what gene? What are the clinical features?

A

Endothelin receptor type-B (EDNR-B); white hair coat, hypopigmented blue eyes, congenital sensorineural deafness, colonic aganglionosis

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25
Q

Which are larger: follicular or epidermal melanocytes?

A

follicular - they also are more dendritic and produce larger melanosomes

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26
Q

Does endothelin-1 stimulate or inhibit melanogenesis?

A

stimulate

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27
Q

What does ultraviolet radiation upregulate that can stimulate melanogenesis and produce increased pigmentation?

A

POMC gene expression –> POMC –> alpha-MSH & ACTH –> bind to MC1R –> increases activity of MITF

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28
Q

Does BMP-4 (bone morphogenetic protein-4) stimulate or inhibit melanogenesis?

A

inhibit

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29
Q

What is the function of the silver protein (premelanosome protein 17)? Mutations in this gene result in what clinical phenotype?

A

adds internal protein fibrils that hold melanin and give the ellipsoid melanosome shape; Mutations result in the Merle phenotype

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30
Q

What is the mode of inheritance in the Harlequin locus in Great Danes? In what gene is the mutation?

A

Autosomal dominant mutation in PSMB7 = beta-2 catalytic subunit of the proteasome

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31
Q

Does IL-1 stimulate or inhibit melanogenesis?

A

inhibit

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32
Q

Age-related graying is thought to be a disorder of what cell type?

A

stem cells (either melanocyte stem cells or hair follicle stem cells) – thought to be related to oxidative injury to these cells

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33
Q

What gene induces transcription of tyrosinase, TyRP-1, DOPA, and TyRP-2?

A

microphthalmia-associated transcription factor (MITF)

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34
Q

Neural crest cells that utilize the ventral track can differentiate into what cell types?

A

neural cells, glial cells, melanocytes

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35
Q

T/F: Animals with piebaldism may also be deaf due to aberrant melanocyte migration.

A

False - no other phenotypic abnormalities are present

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36
Q

T/F: Collies affected by Gray Collie Syndrome lack melanocytes.

A

False - they have melanocytes, the defect is in melanosome formation – can only may a stage 3 melanosome (reason color is dilute instead of albino)

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37
Q

Does ACTH stimulate or inhibit melanogenesis?

A

stimulate

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38
Q

If an animal has a defect in melanosome formation, what other organelles may be affected?

A

platelet dense granules, lymphocyte lytic granules

39
Q

Mode of inheritance of gray horse phenotype? In what gene in the mutation?

A

Autosomal dominant mutation in STX17

40
Q

Does TNF-alpha stimulate or inhibit melanogenesis?

A

inhibit

41
Q

Mode of inheritance of Oculocutaneous albinism-Type 1TS seen in Siamese and Burmese cats?

A

Autosomal recessive

42
Q

What is constitutive pigment?

A

pigmentation that is genetically determined in the absence of external influences

43
Q

Which has more structure to the melanosome: eumelanin or pheomelanin?

A

eumelanin

44
Q

Mode of inheritance of Chediak-Higashi Syndrome?

A

Autosomal recessive

45
Q

T/F: Horses with a gray phenotype lose pigment in the skin and hair follicles.

A

False - just the hair follicles –> predisposes them to cutaneous melanomas

46
Q

What is the mode of inheritance of Gray Collie Syndrome? What are the clinical signs associated with the disease?

A

Autosomal recessive; Cyclical hematopoiesis (congenital neutropenia); infections, gingivitis; fever, diarrhea, arthralgia; Gonadal hypoplasia

47
Q

What is the clinical presentation of animals affected with Chediak-Higashi syndrome?

A

hypopigmentatoin of the skin, hair coat, and eyes – silver-colored hair

48
Q

Mode of inheritance of lavendar foal syndrome? In what gene/protein is the mutation?

A

Autosomal recessive, homozygous lethal mutation in MYO5A – Myosin 5A

49
Q

Does nitric oxide stimulate or inhibit melanogenesis?

A

stimulate

50
Q

Which are black-brown in color: eumelanin or pheomelanin?

A

eumelanin

51
Q

T/F: Homozygous mutation in SILV (PMEL17) = Merle locus is embryonic lethal.

A

False - has a higher incidence of deafness

52
Q

What abnormalities results from a mutation in KIT? Mode of inheritance?

A

Piebaldism; autosomal dominant

53
Q

T/F: The hair of animals with color dilution alopecia contains more melanin than non-dilute counterparts.

A

True - they appear lighter in color due to the clumping and abnormal melanosomes

54
Q

Which is high in cysteine or glutathione: eumelanin or pheomelanin?

A

pheomelanin

55
Q

Do leukotrienes (LTB4, LTC4) and prostaglandins (PGE2, PGF2alpha) stimulate or inhibit melanogenesis

A

stimulate

56
Q

What is the role of KIT and its ligand SCF in melanogenesis?

A

involved in melanocyte migration to epidermis

57
Q

What enzyme controls the shade of eumelanin (black, brown)?

A

tyrosinase-related protein 1

58
Q

Where is the defect in melanogenesis with Chediak-Higashi syndrome?

A

melanosome biogenesis

59
Q

Besides the epidermis and hair follicle, where else are melanocytes located?

A

ducts of sebaceous and sweat glands, superficial dermis, uvea of eye, cardiovascular system, cochlea (stria vascularis), CNS, adipose tissue

60
Q

What processes can up-regulate MITF (microphthalmia-associated transcription factor)?

A

1) Binding of c-kit with steel factor (stem cell factor) –> leads to activation of cAMP pathway; 2) Binding of MC1R (melanocortin 1 receptor) by alpha-MSH and ACTH (eumelanin) and ASP (agonist stimulating protein = agouti) - pheomelanin

61
Q

Clinical features of oculocutaneous albinism

A

white hair coat, blue irides, nystagmus, photophobia

62
Q

What are the two microtubule proteins that transport melanosomes along the melanocyte dendrite?

A

dynein (retrograde motion) and kinesins (anterograde)

63
Q

Which is produced when alpha-MSH or ACTH binds to MC1R: eumelanin or pheomelanin?

A

eumelanin

64
Q

Where are melanocyte stem cells located?

A

epidermis, dermis (mouse), glands, “bulge” of hair follicle, Schwann cell precursors along nerves

65
Q

Does alpha-MSH stimulate or inhibit melanogenesis?

A

stimulate

66
Q

What are the three most important enzymes involved in melanin synthesis?

A

phenylalanine hydroxylase, tyrosine hydroxylase-1, tyrosinase

67
Q

What is the mode of inheritance of the Merle Phenotype? In what gene is the mutation?

A

Autosomal dominant mutation in SILV (PMEL17) = silver protein/premelanosome protein 17

68
Q

Which comes first with uveodermatologic syndrome: ocular or dermatologic signs?

A

ocular

69
Q

T/F: Phenylalanine is an essential amino acid.

A

TRUE

70
Q

Which contains higher sulfur content: eumelanin or pheomelanin?

A

pheomelanin

71
Q

Where are follicular melanocytes located?

A

outer root sheath and hair matrix of hair follicles

72
Q

In vitiligo, what cell type is targeted?

A

melanocytes – keratinocytes are normal!

73
Q

In what breed of horse has lavendar foal syndrome been reported?

A

Egyptian Arabians

74
Q

What shape are the melanosomes of pheomelanin?

A

spherical

75
Q

A mutation in AP3B1, which encodes the beta-subunit of the AP-3 complex that delivers the enzymes to developing melanosomes, results in what clinical disease in dogs?

A

Gray Collie Syndrome

76
Q

Does histamine stimulate or inhibit melanogenesis?

A

stimulate

77
Q

Describe the changes present in melanogenesis of cats with seal-points

A

Have a temperature-sensitive tyrosinase – only active on cooler areas of the body (ear tips, face, feet, tail) –> those are the only areas with pigment

78
Q

A mutation in the coat color gene at D locus results in what disease?

A

color dilution

79
Q

What is the role of endothelin-3 in melanogenesis?

A

involved in melanoblast migration from dermis to basal layer of epidermis; produced by ectodermal cells –> binds to endothelin receptor B on melanoblasts; essential for survival, proliferation, and migration of melanoblasts as well as normal formation of enteric nerves

80
Q

Does IL-6 stimulate or inhibit melanogenesis?

A

inhibit

81
Q

What is the role of endothelin-1 in melanogenesis?

A

activates tyrosinase, increases MC1R, increases TRP-1; stimulates melanocyte proliferation, increases dendrite formation; increased thymin dimer repair

82
Q

Why is it not recommended to breed two Overo spotted paint horses?

A

can result in lethal white foal syndrome – Waardenburg syndrome type IV

83
Q

What element is an important cofactor of tyrosinase?

A

copper

84
Q

Functions of melanocytes

A

1) Cosmetic appearance, 2) Protection against ionizing radiation - can absrob a wide spectrum ov UV and visible light wavelengths; 3) Scavenger of Cytotoxic free radicals and intermediates; 4) Secretion of pro-inflammatory cytokines: IL-8, IL-1alpha, TNF-alpha; 5) Inhibition of keratinocyte proliferation; 6) Calcium homeostasis

85
Q

What shape are the melanosomes of eumelanin?

A

elliptical

86
Q

What special stains are needed to visualize melanocytes on histopathology?

A

DOPA oxidase reaction, Fontana-Masson stain, Schmorl’s method; immunohistochemistry: vimentin, S-100 protein

87
Q

T/F: Animals with Waardenburg Syndrome lack melanocytes in hypopigmented areas.

A

True - defect is due to a failure in migration and development of melanoblasts

88
Q

Which is produced with high levels of tyrosinase: eumelanin or pheomelanin?

A

eumelanin

89
Q

Mutations in what genes have been reported with digital squamous cell carcinoma in Black Standard Poodles?

A

Kit Ligand (SCF), MC1R

90
Q

What changes in coat color can be seen with phenylalanine deficiency? Why?

A

Decreased melanin synthesis, most common color change is red-brown hair coat instead of black

91
Q

What abnormality would be present in a trichogram of an animal with Chediak-Higashi syndrome? Why?

A

large, irregular clumps of melanin in the hair shaft; due to defect in formation of melanosome => results in irregular dispersion and irregular size to the melanosome

92
Q

Conditions with white coat color in animals occurring with congenital sensorineural deafness and/or hypopigmented iridies are similar to what disease in humans?

A

Waardenberg syndrome type-2

93
Q

T/F: Tyrosine is an essential amino acid.

A

False - can be synthesized from Phenylalanine

Vet Derm Review (44 decks)

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