The Case of Fur Color Evolution in Beach Mice or

The Case of Fur Color Evolution in Beach Mice

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Wouldn’t it be nice if I had white fur???

Anatomy of a Hair Follicle• The hair shaft is

made of cornified cells – that is, dead cells filled with keratin.

• Within the region of matrix stem cells are specialized pigment-producing melanocyte cells.

Image adapted from: http://www.nature.com/ng/journal/v38/n3/fig_tab/ng0306-273_F1.html

Melanocyte cells

Image: http://www.dermnetnz.org/doctors/principles/images/hair-bulb.gif

Hair Color• Two pigments– Eumelanin– Pheomelanin

Image adapted from: http://www.nature.com/ng/journal/v38/n3/fig_tab/ng0306-273_F1.html

EumelaninRoland Mattern

PheomelaninRoland Mattern

Melanocyte cells

Hair Color

• Dark Hair: Lots of eumelanin• Fair Hair: More pheomelanin, less eumelanin• Red Hair: Lots of pheomelanin

How is melanin produced?

• Transmembrane proteins that are stimulated by a hormone.

• When these melanocortin receptor proteins are stimulated…. LOTS of eumelanin is produced.

• Stimulation of MC1R leads to lots of cAMP

production.

• cAMP leads to the expression of at least

four genes: c(tyr), Tyrp1, Tyrp2, p

Image from: http://www.sciencedirect.com/science/article/pii/S0021967307010199

c(tyr)

Tyrp1Tyrp2

p


production.



• MC1R stimulation leads to lots of cAMP

production which means Tyrp1, Tyrp2

and p are expressed lots of eumelanin.


c(tyr)

Tyrp1Tyrp2

p


production.



• Inadequate MC1R stimulation leads to

less cAMP production which means Tyrp1, Tyrp2 and p are not

expressed less eumelanin; more

pheomelanin.


c(tyr)

Tyrp1Tyrp2

p


production.



• MC1R is a pretty big deal.


c(tyr)

Tyrp1Tyrp2

p

Eumelanin and Pheomelanin

Images from: www.chem.sc.edu/analytical/chem107/lab4_032205.pdf

The Natural History ofFur Color in Beach Mice

1.0

Fact Sheet: Peromyscus polionotus

• Common names: Beach Mouse or Old Field Mouse.

• Location: Southeastern U.S.A.• Habitat: Sand burrows in dunes or

old fields.• Home-range: ~1000 m2

• Breeding: Monogamous pair-bonding. Litters of 2-8 pups, every 30 days.

• Lifespan: 9-12 months.

1.1

Fur ColorSubspecies:

leucocephalus

trissyllepsis

allophrys/peninsularis

ammobates

subgriseus

1.2

How are populations of these sub species distributed within the range

of the Beach Mouse?

1.3

? ?

?

??

The Spatial Distribution of Fur Color

Lighter colored sub-species live on light sand beaches; darker colored sub-species live in darker habitat.

1.5

QuestionAssuming that ancestral populations of beach mice had dark brown fur, what could have happened to explain the occurrence of light-colored coastal sub-species?

1.6

The Melanocortin-1-Receptor (MC1R)

• What can you tell me about the MC1R protein?– Write three things down.



• Do you think there are any differences between the MC1R protein of dark haired mice and the MC1R protein of light haired mice? If so, what?– Write something down.



• Do you think there are any differences between the MC1R protein of dark haired mice and the MC1R protein of light haired mice? If so, what?– Write something down.

• Do you think there are any differences between the mc1r allele of dark haired mice and the mc1r allele of light haired mice?– Write something down.

Consequence of MutationThere is a change in the the amino acid identity at position #67: an Arginine vs. a Cysteine

4.6

Amino Acid Sequence Dark Fur:MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVSIPDGLFLSLGLVSLVENVLVVIAITKNRNLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQLDNVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIXGIWVASIFFSTLFITYYNHTAVLICLVTFFLAMLALMAXLYVHMLTRAYQHAQGIAQLQKRQGSTXQGFCLKGAXTLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW

Amino Acid Sequence Light Fur:MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVSVPDGLFLSLGLVSLVENVLVVIAITKNCNLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQLDNVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIVGIWVASIFFSTLFITYYNHTAVLICLVTFFLAMLALMAILYVHMLTRAYQHAQGIAQLQKRQGSTRQGFCLKGAATLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW

Freeman 4e Fig. 15.4

Substitution Mutation• A single nucleotide substitution mutation in the mc1r

gene causes a change in amino acid #67 in the MC1R protein chain.

• When amino acid #67 is cysteine, the MC1R protein is unable to effectively bind the α-MSH. This changes the pigment pathway and eumelanin is not produced.

mc1r Gene SequenceLet’s look at what happens when ONE SPECIFIC nucleotide is changed….

5’-ATGCCCACCCAGGGGCCTCAGAAGAGGCTTCTGGGTTCTCTCAACTCCACCTCCACAGCC ACCCCTCACCTTGGACTGGCCACAAACCAGACAGGGCCTTGGTGCCTGCAGGTGTCTGTC CCGGATGGCCTCTTCCTCAGCCTGGGGCTGGTGAGTCTGGTGGAGAATGTGCTGGTCGTG ATAGCCATCACCAAAAACCGCAACCTGCACTCGCCCATGTATTCCTTCATCTGCTGTCTG GCCCTGTCTGACCTGATGGTGAGTATAAGCTTGGTGCTGGAGACGGCTATCATCCTGCTG CTGGAGGCAGGGGCCCTGGTGACCCGGGCCGCTTTGGTGCAACAGCTGGACAATGTCATT GACGTGCTCATCTGTGGCTCCATGGTGTCCAGTCTTTGCTTCCTTGGTGTCATTGCCATA GACCGCTACATCTCCATCTTCTATGCATTACGTTATCACAGCATTGTGACGCTGCCCCGG GCACGACGGGCCATCGTGGGCATCTGGGTGGCCAGCATCTTCTTCAGCACCCTCTTTATC ACCTACTACAACCACACAGCCGTCCTAATCTGCCTTGTCACTTTCTTTCTAGCCATGCTG GCCCTCATGGCAATTCTGTATGTCCACATGCTCACCCGAGCATACCAGCATGCTCAGGGG ATTGCCCAGCTCCAGAAGAGGCAGGGCTCCACCCGCCAAGGCTTCTGCCTTAAGGGTGCT GCCACCCTTACTATCATTCTGGGAATTTTCTTCCTGTGCTGGGGCCCCTTCTTCCTGCAT CTCACACTCATCGTCCTCTGCCCTCAGCACCCCACCTGCAGCTGCATCTTTAAGAACTTC AACCTCTACCTCGTTCTCATCATCTTCAGCTCCATCGTCGACCCCCTCATCTATGCTTTT CGGAGCCAGG AGCTCCGCATGACACTCAGGGAGGTGCTGCTGTGCTCCTGGTGA- 3’

mc1r Gene SequenceLet’s look at what happens when ONE SPECIFIC nucleotide is changed….

5’-ATGCCCACCCAGGGGCCTCAGAAGAGGCTTCTGGGTTCTCTCAACTCCACCTCCACAGCC ACCCCTCACCTTGGACTGGCCACAAACCAGACAGGGCCTTGGTGCCTGCAGGTGTCTGTC CCGGATGGCCTCTTCCTCAGCCTGGGGCTGGTGAGTCTGGTGGAGAATGTGCTGGTCGTG ATAGCCATCACCAAAAACTGCAACCTGCACTCGCCCATGTATTCCTTCATCTGCTGTCTG GCCCTGTCTGACCTGATGGTGAGTATAAGCTTGGTGCTGGAGACGGCTATCATCCTGCTG CTGGAGGCAGGGGCCCTGGTGACCCGGGCCGCTTTGGTGCAACAGCTGGACAATGTCATT GACGTGCTCATCTGTGGCTCCATGGTGTCCAGTCTTTGCTTCCTTGGTGTCATTGCCATA GACCGCTACATCTCCATCTTCTATGCATTACGTTATCACAGCATTGTGACGCTGCCCCGG GCACGACGGGCCATCGTGGGCATCTGGGTGGCCAGCATCTTCTTCAGCACCCTCTTTATC ACCTACTACAACCACACAGCCGTCCTAATCTGCCTTGTCACTTTCTTTCTAGCCATGCTG GCCCTCATGGCAATTCTGTATGTCCACATGCTCACCCGAGCATACCAGCATGCTCAGGGG ATTGCCCAGCTCCAGAAGAGGCAGGGCTCCACCCGCCAAGGCTTCTGCCTTAAGGGTGCT GCCACCCTTACTATCATTCTGGGAATTTTCTTCCTGTGCTGGGGCCCCTTCTTCCTGCAT CTCACACTCATCGTCCTCTGCCCTCAGCACCCCACCTGCAGCTGCATCTTTAAGAACTTC AACCTCTACCTCGTTCTCATCATCTTCAGCTCCATCGTCGACCCCCTCATCTATGCTTTT CGGAGCCAGG AGCTCCGCATGACACTCAGGGAGGTGCTGCTGTGCTCCTGGTGA- 3’

The Cytosine at position 199 has now changed to a Thymine.

Consequence of MutationThe specific amino acid sequence is very important. One mutation within the sequence can have affect how the protein interacts with the melanocyte-stimulating hormone (α-MSH).

Amino Acid #67 = Arginine Amino Acid #67 = Cysteine

4.7

The Role of the MC1R Protein

When amino acid #67 is cysteine, the MC1R protein is unable to effectively bind the α-MSH. This changes the pigment pathway and eumelanin is not produced.

4.9

Plausible Mechanism; Observable Pattern

• In biological research, to say that something at the molecular or genetic level is responsible for a phenotypic trait, a plausible mechanism and an observable relationship should be identified.

5.1

Mechanism: Alleles of mc1r Gene• The mc1r gene has two alleles:

Allele R [Arginine at pos #67] Codes for a functional

MC1R protein.

The genetic code for these two alleles differs by a single nucleotide substitution.

Allele C [Cysteine at pos #67]

Codes for a non-functional MC1R protein.

5.2

Observable Relationship:Genes vs. Fur Color

• There are three possible genotypes associated with the mc1r gene:

5.4


• There are three possible genotypes associated with the mc1r gene:1. RR Arginine-Arginine: Indicates that both copies of

chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin

5.4




2. CC Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin

5.4




2. CC Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin

3. RC Arginine-Cysteine: Indicates that one copy of chromosome 16 has an arginine amino acid on position #67 of the mc1r gene; the other copy has a cysteine in position #67 of the mc1r gene. ? Eumelanin

5.4


• Is there a relationship between the fur color of beach mouse individuals and the allele combinations (genotypes) they possess?

CC homozygous = ?

RR homozygous = ?

RC heterozygous = ?

5.5

House Mouse Karyotype (Mus musculus)

Chromosome 8 is approx. 130,000,000 bp

Observable Pattern: Color Scoring

Ear

Cheek

Eyebrow

Whiskers

Rostrum

AnkleVentrum

5.6

Observable Relationship: Scoring System

2

2

2

1

2

1

1

0

0

0

0

0

2

0

1

1

5.7

Observable Pattern:Rostrum Color

Mice with the genotype RR have the darkest rostrum color.

RR RC CC0

0.2

0.4

0.6

0.8

1

Light (0)

Medium (1)Dark (2)

Mouse Genotype

Prop

ortio

n o

f Ind

ivid

uals

5.8

Observable Pattern: All Body Parts

RR Individuals2.001.421.281.831.130.911.06

Body PartRostrumWhiskerCheekEyebrowEarVentrumAnkle

RC Individuals1.811.001.251.540.800.550.82

CC Individuals0.810.450.690.790.280.000.29

Average Color Scores for:

Average 1.38 1.11 0.47

Hoekstra et al 2006

5.9a

RR Individuals2.001.421.281.831.130.911.06

Body PartRostrumWhiskerCheekEyebrowEarVentrumAnkle

RC Individuals1.811.001.251.540.800.550.82

CC Individuals0.810.450.690.790.280.000.29

Average Color Scores for:

Average 1.38 1.11 0.47

5.9b

Question: What does the above table tell you? Does it confirm or refute a genetic basis for differences in fur

color among mice?

Questions:There is a clear pattern: beach mice with the RR genotype tend to be darker than those with the RC or CC genotype. 1. Why is the average score for RR mice score less

than 2 for most body parts? 2. Why is the average score for CC mice greater

than 0 for most body parts?3. RC mice are closer in fur color to RR mice than

CC mice. Does this mean that R is dominant over C? Be prepared to explain your answer.

5.10

Question:Differences in fur color among beach mouse populations can be fully explained by the relative frequency of C and R alleles present within each population.

1. Strongly Agree2. Agree3. Unsure/Confused4. Disagree5. Strongly Disagree

5.11

Predict Allele Frequencies

___% R___% C

___% R___% C ___% R

___% C

___% R___% C

___% R___% C

___% R___% C

5.12a

Actual Allele Frequencies

100% R

0% C

70% R30% C 95% R

5% C

30% R70% C

5% R95% C

100% R0% C

5.12b

Fur color differences among beach mouse sub-species (i.e. populations) cannot be fully explained by differences in R:C allele frequencies. Why not?

5.13

In Class Exercise on Mouse EvolutionScenario: Start with an ancestral, inland population

in which all individuals have dark fur. The ancestral population evolves, resulting in one

population that is still inland, and another that now lives on the beach.

Ancestral Inland Population

Present-day BeachPopulation

Present-day Inland Population

Time

In Class Exercise on Mouse Evolution:Questions for Student Teams to Consider When did the ancestral population live? How big was it (number of

individuals)?

• What were the mc1r genotype frequencies? The mc1r allele frequencies?

How big is the present day inland population (number of individuals)?

• What are the mc1r genotype frequencies? The mc1r allele frequencies?

How big is the present day beach population (number of individuals)?

• What are the mc1r genotype frequencies? The mc1r allele frequencies?

Where along the timeline did an R C substitution in MC1R occur?

The Ecology ofFur Color in Beach Mice

2.0

Beach Mouse Food Facts:2.1

Hunting Style of Predators

Sight and SoundHunters Taste/Smell

Hunter

2.2

Predator-Prey Experiment(The Advantage of Fur Color)

2.3

Predator-Prey Experiment(The Advantage of Fur Color)

• Owls catch dark mouse first 64% of the time

• Owls catch light mouse first 36% of the time.

• Owls catch dark mouse first 37% of the time

• Owls catch light mouse first 63% of the time.

2.4

Regional Pattern:Fur Color and Habitat Color

- Researchers examined fur color in nine beach mouse populations.

- Fur color brightness was significantly correlated to soil brightness where each population lived.

2.5

Predation Study – Clay Mice

(A) Two locations with different color soil where predation on clay mice was tested. (B) Most attacks in light soil environments were on dark mice; most attacks in dark soil environments were on light mice.

2.6

Attack on a Clay Mouse2.6b

Summary• Evidence suggests

that fur color may have evolved as a result of selective predation.

• Fur coloration matching the habitat coloration leads to less detection by predators and increases the odds of successful reproduction.

2.7

Clicker Q1The C T substitution at position 199 of the mc1r gene:A. arose by a mutation in the beach mouse populations in

response to a need for protection from predation.B. leads to the failure of melanocytes to make an MC1R protein.C. arose by a mutation then increased in frequency because it was

selectively advantageous in the beach mouse populations.D. had no effect on the beach mouse populations.E. produced an alternate allele that was detrimental to mice on

the white sand beaches

6.6

Clicker Q2What was the reason for the lighter coat colors of the mice on the white sand beaches?

A. Owls and other carnivores prey on beach mice that do not carry the mutant allele.

B. A substitution of cysteine for arginine at position 67 of the MC1R protein.

C. A substitution of thymine for cytosine at position 199 of the mc1r gene nucleotide sequence.

D. The failure of melanocytes to lay down melanin pigment in the cortex of hairs of the lighter colored beach mice.

E. The poorer binding affinity for α-MSH and the lower amount of cAMP produced by individuals with the mutated MC1R protein.

6.7

Documents

The Case of Fur Color Evolution in Beach Mice or