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fitz 9th > 20 - Pigmentation and Melanocyte Biology > Flashcards

20 - Pigmentation and Melanocyte Biology Flashcards

1
Q

Specialized cells of the epidermis and hair follicle whose primary function is to synthesize and transfer melanjn to adjacent keratinocytes

A

Melanocytes

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2
Q

Melanin synthesis occurs in a specialized organelle

A

Melanosome

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3
Q

Y/N: Melanocyte numbers are different in individuals of different racial backgrounds

A

No - similar

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4
Q

Location of melanocytes

A

Basal layer of the epidermis
Hair bulb
Outer root sheath

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5
Q

Melanocytes contain (round/oval) nuclei slightly (larger/smaller) than that of surrounding keratinocytes

A

Oval

Smaller

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6
Q

Melanocytes are present at about ______ the number of keratinocytes

A

1/10

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7
Q

Silver stains that rely on the ability of melanin to become impregnated with silver

A

Fontana-Mason stain

Warthin-Starry stain

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8
Q

Y/N: Silver stains react with melanocytes from eumelanotic, but not pheomelanotic skin tissue

A

Yes

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9
Q

Immunohistologic identification of melanocytes using antibodies directed against

A

Tyrosinase
MITF
Melan-A/Mart1

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10
Q

Although less specific for melanocyte lineage, antibodies directed against _____ protein have long been used with great sensitivity to detect melanocytes and melanoma

A

S100

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11
Q

Immunostaining with antibody _____ is negative in normal adult melanocytes but offers additional specificity for examination of melanocytic neoplasms

A

HMB-45

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12
Q 
Reduced pigmentation of iris and retina
Photosensitivity
Decreased visual acuity
Nystagmus
Strabismus
Misrouting of optic nerve
A

Ocular albinism

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13
Q 
Cutaneous albinism (pigmentary dilution of skin and hair)
Ocular albinsim
A

Oculocutaneous albinism

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14
Q

OCA: tyrosinase-negative (severe) albinism (complete loss of tyrosinase function)

A

OCA1A

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15
Q

OCA: tyrosinase-positive (mild to moderate) albinism

A

OCA1B

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16
Q

OCA: “Brown” albinism

A

OCA2

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17
Q

OCA: “Rufous albinism”

A

OCA3

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18
Q

OCA: variable degrees of albinism

A

OCA4

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19
Q 
Piebaldism
Congenital deafness
Heterochromia irides
Synophrys
Broad nasal root
Dystopia canthorum
A

Waardenburg syndrome

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20
Q

WS: classic type

A

WS1

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21
Q

WS: lacks dystopica canthorum

A

WS2

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22
Q

WS: limb abnormalities (hypoplasia, syndactyly)

A

WS3

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23
Q

WS: Hirschsprung disease

A

WS4

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24
Q

Tyrosinase-positive cutaneous albinism
Deafness
Eyebrow hypoplasia

A

Tietz syndrome

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25
Q

Depigmented forelock and abdominal skin

A

Piebaldism

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26
Q 
Tyrosinase-positive oculocutaneous albinism (melanosome dysfunction)
Bleeding diathesis (platelet granule dysfunction)
A

Hermansky-Pudlak syndrome

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27
Q

HPS: interstitial pulmonary fibrosis

A

HPS 1, 2, 4

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28
Q

HPS: granulomatous colitis

A

HPS 1, 4

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29
Q

HPS: neutropenia and cytotoxic T-cell dysfunction

A

HPS2

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30
Q 
Tyrosinase-positive oculocutaneous albinism (melanosome dysfunction)
Bleeding diathesis (platelet granule dysfunction)
Progressive neurologic dysfunction (mechanism unknown)
Severe immunodeficiency (NK cell, cytotoxic T cell, neutrophil dysfunction)
Lymphomalike syndrome (overwhelming infiltration of organs by defective white blood cells)
Giant lysosome-related organelles (these large granules are visible within leukocytes in PBS)
A

Chediak-Higashi syndrome

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31
Q

Pigmentary dilution of skin and hair (clumping of melanin within melanocytes)

A

Griscelli syndrome

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32
Q

GS: neurologic abnormalities

A

GS1

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33
Q

GS: immunodeficiency

A

GS2

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34
Q

Generalized patches of hyperpigmentation of skin and mucous membranes without systemic symptoms

A

Familial progressive hyperpigmentation

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35
Q

Diffuse hyperpigmented and hypopigmented patches without systemic symptoms
Variable penetrance

A

Familial progressive hyper- and hypopigmentation

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36
Q

Eumalonosome stage: melanosomes are round, approximately 0.3 um in diameter, and contain small intraluminal vesicles reminiscent of multivesicular bodies of the early endosomal compartment

A

Stage I

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37
Q

Eumalonosome stage: melanosomes are oval in shape and approximately 0.5 um in diameter and exhibit deposition of a parallel fibrillar matrix

A

Stage II

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38
Q

Eumalonosome stage: melanosomes demonstrate deposition of pigment along the filaments

A

Stage III

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39
Q

Eumalonosome stage: melanosomes are fully melanized, with the electron-dense melanin completely obscuring the underlying structures

A

Stage IV

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40
Q

Pheomelanosomes exhibit similar ultrastructural stages of maturation with _____ pheomelansomes exhibiting melanization obscuring underlying structures

A

Late stage III and IV

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41
Q

(Pheo-/eumelanosomes) are smaller, retain a rounded morphology at all stages, and contain a disorganized and less dense filament network

A

Pheomelanosomes

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42
Q

Cutaneous interfollicular melanocytes are present at highest density in the _____, and at lower density in the skin of the _____

A

Facial and genital skin

Trunk and extremities

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43
Q

Characterized by a melanocyte and each of the keratinocytes that it physically contacts

A

Epidermal melanin unit

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44
Q

Each melanocyte contacts and delivers melanin to approximately _____ keratinocytes

A

40

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45
Q

Under the pathologic circumstance of nerve injury, _____ may undergo dedifferentiation to generate ectopic melanocytes

A

Schwann cells

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46
Q

Y/N: Within the hair follicle, the melanocyte population varies by the stage of the hair cycle

A

Yes

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47
Q

Melanocyte stem cells reside within the

A

Permanent bulge/secondary hair germ

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48
Q

During the anagen phase of the hair cycle, the McSCs become activated via

A

Wnt signaling

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49
Q

Differentiated melanocytes of the hair bulb undergo apoptosis during

A

Late catagen

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50
Q

Y/N: Gradual loss of McSC population occurs through each hair cycle

A

No - McSC population persists through each hair cycle

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51
Q

Y/N: Gradual loss of McSCs occurs with age

A

Yes

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52
Q

Has been demonstrated as a niche for McSCs of the acral epidermis

A

Lower permanent portion of the eccrine gland

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53
Q

Acral melanomas are diagnosed with high sensitivity and specificity as a result of their preferential pigmentation of the eccrine-rich _____ of the dermatoglyphs

A

Ridges

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54
Q

Synthesize melanin and form melanosomes but these cells are derived from the neuroectoderm and are developmentally unrelated to the neural crest/melanocyte lineage

A

Retinal pigment epithelium

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55
Q

(Lighter/Darker) eye pigmentation is associated with decreased incidence of age-related macular degeneration

A

Darker

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56
Q

Autoimmunity directed agains melanocytes can lead to severe CNS inflammation in

A

Vogt-Koyanagi-Harada syndrome

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57
Q

In the cochlea of the ear, melanocytes are located in and required for the normal development and function of the _____ layer

A

Stria vascularis

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58
Q

Sensorineural deafness

Pigmentation defects

A

Waardenburg and Tietz syndromes

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59
Q

Dysfunction of cardiac melanocytes predispose to

A

Arrhythmias

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60
Q

Melanocytes are exclusively derived from the highly migratiry and multipotent _____ population

A

Neural crest

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61
Q

Transient cell population that forms at the margin of the early forming neural tube

A

Neural crest

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62
Q

Neural crest cell migration between the somites and the ectoderm

A

Dorsolateral migration pathway

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63
Q

Second wave of melanocytes derived from Schwann cell precursors that migrate along developing nerves

A

Ventromedial migratory pathway

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64
Q

Melanocyte precursors

A

Melanoblasts

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65
Q

Master melanocyte transcription factor that is first expressed in melanoblasts shortly after exit from neural tube at embryonic day 10.5-11

A

MITF

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66
Q

Structure between the neural tube and somites where melanoblasts paude before traveling upon the dorsolateral migration pathwayl

A

Migration staging area

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67
Q

Other markers of melanoblast specification such as the melanogenic enzymes _____ are expressed during the dorsolateral migration

A

Dct

TYRP1

68
Q

Melanocytes express the key melanigenic enzyme _____ by embryonic day 14.5

A

Tyrosinase

69
Q

Melanocytes display pigmentation by embryonic day

A

16.5

70
Q

Y/N: Most premigratory and migratory neural crest cells give rise to multiple cell types and likely retain developmental plasticity

A

Yes

71
Q

Factors that regulate melanocyte development, survival and migration: transcription factors

A 
MITF
PAX3
SOX10
SOX2
FoxD3
72
Q

Germline mutations in _____ were identified in Waardenburg syndrome type 2, characterized by pigmentation defects and hearing loss

A

MITF (microphthalmia-associated transcription factor)

73
Q

Defects in retinal pigment epithelium, osteoclasts, and mast cells
Loss of melanocytes of the skin and inner ear

A

Microphthalmia

74
Q

Most lineage selective in specifying melanocyte differentiation

A

MITF, in particular the melanocyte-specific isoform m-MITF)

75
Q

Also regulate expression of other lineages, including certain muscle groups and enteric ganglia/neurons

A

SOX10

PAX3

76
Q

Mutation of _____ results in prominent pigment cell-related phenotypes wherease mutations of _____ produce pigment cell defects as well as certain nonpigmentary phenotypes (such as megacolon for _____)

A

MITF
SOX10 and PAX3
SOX10

77
Q

Required for the survival, proliferation and differentiation of melanocytes
Acts as an oncogene and is amplifies in a subset of melanoma

A

MITF

78
Q

The E318K MITF polymorphism found at low frequency in European, North American, and Australian populations is associated with significantly increased melanoma risk, an effect likely mediated by disruption of a concensus MITF _____ site

A

Sumoylation

79
Q

One of the earliest markers of the neural crest
Mutations result in pigmentation defects, abnormalities of neural crest derivatives of the sensory and sympathetic ganglia, Schwann cells, and cardiac neural crest
Positive regulator of the MITF promoter in melanocytes and melanoma

A

PAX3 (Paired Box 3)

80
Q

Mutated in human Waardenburg syndromes types 1 and 3 (hearing loss, pigmentation defect, arm and hand developmental defects)

A

PAX3

81
Q

Required for the development of neural, glial, and melanocyte neural crest lineages
First expressed in premigratory neural crest cells
Loss leads to complete absence of melanoblasts
Required for survival of postnatal melanocytes, melanocyte stem cells, nevi, and melanoma

A

SOX10 (SRY-Box 10)

82
Q

One of 4 transcription factors required for reprogramming of somatic cells to induced pluripotent stem cells
Play a role in specifying the melanocyte lineage during development
Binds and represses the MITF promoter

A

SOX2

83
Q

Factors that regulate melanocyte development, survival and migration: growth factor signaling

A

Ednrb
c-Kit
Wnt/Beta-Catenin
Neuregulin/ErbB2/ErbB3

84
Q

G-protein-coupled receptor that activates several signaling pathways, including PKC, MAPK and CAMP/PKA
Does not seem to be required for the initial specification of melanoblasts; required mainly for proper melanoblast migration
Induce melanocyte proliferation and skin pigmentation

A

Ednrb (endothelin receptor type B)

85
Q

Ednrb agnosists, the endothelins, are encodes by 3 genes:

A

Edn1
Edn2
Edn3

86
Q

Ednrb mutation results in

A

Hirschsprung disease

87
Q

Edn3 mutation results in

A

Waardenburg plus megacolon

88
Q

Upregulated during neural crest development and is important for establishing the neural crest lineage
Loss leads to loss of most neural crest-derived stuctures
Represses MITF to favor the Schwann cell fate

A

FoxD3 (Forkhead Box D3)

89
Q

Mutated in Waardenburg type IV (Waardenburg plus megacolon)

A

SOX10

90
Q

Also known as Steel factor or stem cell factor

A

cognate Kit ligand (KITLG)

91
Q

KITLG exists in transmembrane and soluble forms and is produced by

A

Endothelial cells and keratinocytes

92
Q

Mutation of c-Kit results in _____, which is characterized by a depigmentation of the forelock and abdominal skin

A

Piebaldism

93
Q

Does not appear to be necessary for the specification of melanoblasts
Deficiency results in melanoblasts soon disappearing after migration from the neural tube
Regulating survival and differentiation/pigmentation of mature melanocytes

A

c-Kit

94
Q

Polymorphisms in KITLG has been shown to cause

A

Familial progressive pigmentation

Familial progressive hyper- and hypopigmentation

95
Q

Enlarging hyperpigmented patches corresponding to increased melanization without change in melanocyte number

A

Familial progressive pigmentation

Familial progressive hyper- and hypopigmentation

96
Q

Activating mutations and amplification of c-Kit drive the progression of a subset of

A

Acral lentiginous, mucosal, and lentigo maligna melanomas

97
Q

Consisting of APC, Axin1/2, and GSK3beta

Target beta-catenin for phosphorylation and ubiquitin-dependent degradation

A

Multiprotein membrane destruction complex

98
Q

Binding of a Wnt family ligand to a _____ family receptor signals _____ to inhibit the membrane destruction complex, allowing for beta-catenin to enter the nucleus and to activate gene transcription

A

Frizzled

Dishevelled

99
Q

Beta-catenin pathway activation also (potentiates/inhibits) melanoma formation and metastasis in mouse models

A

Potentiates

100
Q

Controls Schwann cell proliferation, migration, and myelination

A

ErbB2/ErbB3 heterodimer tyrosine kinase receptor

101
Q

ErbB2/ErbB3 heterodimer tyrosine kinase receptor ligand

Promotes Schwann cell fate and represses the melanocyte fate

A

Neuregulin

102
Q

Factors that regulate melanocyte development, survival and migration: regulation of melanocyte motility and migration

A

Rac1

103
Q

Belongs to the Rho superfamily of GTPases

When deleted, melanoblasts migrate less efficiently

A

Rac1

104
Q

Mutation of _____, a guanine nucleotide exchange factor, occurs frequently in human melanomas, and these mutations may promote melanoma through activation of Rac1

A

PREX2

105
Q

The 2 forms of melanin, eumelanin

and pheomelanin, are both derived from the precursor

A

Tyrosine

106
Q

Tyrosinase converts tyrosine to

A

Dopaquinone

107
Q

Brown/black melanin

A

Eumelanin

108
Q

Yellow/orange melanin

A

Pheomelanin

109
Q

Composed of polymers of 5,6-dihydroxyindole and the carboxylate form 5,6-dihydroxyindole-2-carboxylic acid

A

Eumelanin

110
Q

Formed by oxidation and polymerization of sulfur-containing cysteinyldopa

A

Pheomelanin

111
Q

Eu- vs pheomelanin: may act as a pro-oxidant

A

Pheomelanin

112
Q

UVA interacts with pheomelanin, and to a lesser extent, eumelanin, leading to melanin degradation products that induce CPD formation long after UV exposure has ended

A

Dark CPD

113
Q

Tyrosinase requires binding of ______ for proper function

A

Copper

114
Q

Two tyrosine-related proteins, _____, show significant homology to tyrosinase and play key roles in melanogenesis (proper trafficking and stabilization of tyrosinase)

A

TYRP1

TYRP2/Dopachrome tautomerase (DCT)

115
Q

Defects of tyrosinase, TYRP1, and DCT cause

A

Oculocutaneous albinism

116
Q

Eumelanogenesis: Dopaquinone spontaneously undergoes intramolecular cyclization to form

A

Cyclodopa

117
Q

Eumelanogenesis: Cyclodopa then undergoes redox exchange with a second molecule of dopaquinone to form

A

Dopachrome

Dopa

118
Q

Eumelanogenesis: Dopachrome spontaneously decarboxylates to form _____ (less soluble, black) and _____ (more soluble, lighter black/brown)

A

DHI

DHICA

119
Q

Eumelanogenesis: Although the uncatalyzed reaction favors DHI formation, the presence of the _____ favors production of DHICA

A

(DCT) protein

120
Q

Eumelanogenesis: DHI and DHICA are then oxidized and polymerized to form

A

Eumelanin

121
Q

Eumelanogenesis: _____ exhibits DHICA-oxidase activity, promoting incorporation of DHICA into eumelanin

A

TYRP1

122
Q

Pheomelanogenesis: Nonenzymatic addition of sulfhydryl groups to dopaquinone results in the formation of

A

5-S-cysteinaldopa

2-S-cysteinaldopa

123
Q

Pheomelanogenesis: _____ serves as a major source of sulfhydryl groups, with the other source being ______

A

Cysteine

Glutathione

124
Q

Cysteinaldopa synthesis predominates in the presence of ______, whereas high tyrosine and/or low cysteine favor ______

A

Cysteine

Eumelanogesis

125
Q

Pheomelanogenesis: Cysteinaldopa then undergoes redox exchange with dopaquinone to produce

A

Cysteinaldopaquinones

126
Q

Pheomelanogenesis: Oxidation and cyclization of cysteinaldopaquinones is followed by dehydation, rearrangement, and decarboxylation to form

A

Benzothiazole intermediates

127
Q

Pheomelanogenesis: The benzothiazole intermediates then polymerize to form

A

Pheomelanin

128
Q

Melanosomes are lysosome-related organelles that exist only in

A

Melanocytes

Retinal pigment epithelium

129
Q

As melanosomes mature, the key ultrastructural feature is the appearance of the

A

Parallel fibrillar network

130
Q

Pigment cell-specific protein that has been shown to be the main component of the parallel fibrillar network

A

PMEL (gp100 or silver)

131
Q

First site of PMEL deposition

A

Intraluminal vesicles of stage I melanosomes

132
Q

Increased organization of PMEL amyloid into visible proteinaceous fibrils, which push the intraluminal vesicles outward to fuse with the melanosome membrane

A

Stage II melanosomes

133
Q

Become increasingly pigmented as melanogenic enzymes are delivered and melanin synthesis has ceases

A

Stage III melanosomes

134
Q

Fully pigmented, and tyrosinase activity and melanin synthesis has ceased

A

Stage IV melanosome

135
Q

Mutations of any of the 10 genes encoding components of the BLOC-1, BLOC-2, BLOC-3, and AP-3 protein complexes have been long known to be responsible for

A

Hermansky-Pudlak syndrome

136
Q

Hypopigmentation due to melanosome dysfunction in addition to platelet dysfunction, immunodeficiency, and lung fibrosis due to abnormalities of other lysosome-related organelles

A

Hermansky-Pudlak syndrome

137
Q

Coordinated the action of microtubule- and actin-dependent machineries to allow proper formation and stabilization of recycling endosomal tubules required for transfer of cargoes to melanosomes

A

BLOC1

138
Q

Acts to properly direct recycling endosomal tubular transport intermediates to maturing melanosomes to promote melanogenic cargo delivery

A

BLOC-2

139
Q

Also important for sorting cargo proteins bound for melanosomes, and in different scenarios can act in concert with or independently of BLOC complexes

A

AP-3

140
Q

The final step in the delivery of cargo to melanosomes is the fusion of cargo-containing vesicle and tubules with the developing melanosome. This involve _____ that are required for membrane fusion

A

SNARE protein

141
Q

SNARE responsible for BLOC-1-dependent delivery of TYRP1 to the melanosome

A

VAMP7

142
Q

Is required for the subsequent recycling of VAMP7 after delivery of cargo to the melanosome

A

BLOC-3

143
Q

Stage IV melanosomes are first transferred to the dendrite tips by _____-mediated microtubule-dependent anterograde transport. _____-mediated retrograde transport melanosomes away from the melanocyte dendrites have been reported

A

Kinesin

Dynein

144
Q

GTPase _____ is incorporated into the melanosome membrane by a hydrophobic geranylgeranyl tail

A

Rab27a

145
Q

The adapter protein _____ binds Rab27a and serves a linker to the actin-binding motor protein _____, following transport and retention of melanosomes on the actin cytoskeleton

A

Melanophilin (Mlph)

MyosinVa (MyoVa)

146
Q

Mutations in Rab27a, Mlph, and MyoVa have been identified in

A

Griscelli syndrome (partial albinism and immunodeficiency)

147
Q

Melanosomes are transferred by dynein-mediated retrograde transport to a perinuclear location (“_____”) to protect basal keratinocytes from UV-induced DNA damage

A

Nuclear capping

148
Q

In (dark-/light-) skinned individuals, melanosomes are smaller, and are grouped in membrane-enclosed clusters of 4-8 melanosomes

A

Light

149
Q

In (darker-/lighter-) skinned individuals, melanosomes are larger, more numerous, and are distributed individually

A

Darker

150
Q

Y/N: Melanosomes are thought to be degraded during the keratinocyte terminal differentiation process

A

Yes

151
Q

Keratinocytes derived from (darker-/lighter-) skinned individuals degrade melanosomes more slowly

A

Darker

152
Q

G-protein-coupled receptor expressed primarily by melanocytes
Critical role in determining if a melanocyte produces predominantly eumelanin or pheomelanin

A

MC1R (melanocortin 1 receptor)

153
Q

(Gain-/Loss-) of-function variants of MC1R are associated with the “red hair phenotype”

A

Loss

154
Q

Canonical agonist for MC1R

A

Alpha-melanocyte stimulating hormone

155
Q

Alpha-MSH is derived from proteolytic processing of its precursor

A

Proopiomelanocortin (POMC)

156
Q

_____ gene mutation, in addition to endocrine dysfunction, display the red hair phenotype

A

POMC

157
Q

Antagonist of MC1R signaling

A

Agouti protein

158
Q

Transcriptionally activated by MITF in melanocytes and serves as a negative feedback regulator that degrades cAMP

A

Phosphodiesterase D4

159
Q

Human pigmentation is categorized into

A

Constitutive and inducible responses

160
Q

Inducible pigmentation after UV exposure (sun tanning) has 2 components that are wavelength dependent

A

Immediate tanning

Delayed tanning

161
Q

Immediate tanning occurs within minutes to hours after sun exposure, and is mainly a response to _____ radiation. It is most noticeable in _____-skinned individuals and is mediated by oxidation and redistribution of existing melanin

A

UVA

Darker

162
Q

Delayed tanning is mainly a response to _____ and peaks at about 3 days to 1 week after sun exposure

A

UVB and shorter-wavelength UVA

163
Q

Immediate vs delayed tanning: much more protective against subsequent sun exposure

A

Delayed

164
Q

Y/N: Pigmentary pathways downstream of a defective MC1R remain intact

A

Yes

165
Q

UV radiation of keratinocytes (increases/decreases) TGFbeta1 production

A

Decreases

fitz 9th (108 decks)

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