Lecture 20: Intermediate Filaments Part II

Are intermediate filaments (IFs) stable?

yes, they are

What are the 6 types of intermediate filaments?

1. acidic keratin

2. basic keratin

3. desmin, vimentin, GFAP

4. neurofilaments

5. lamins

6. nestin

Where is acidic keratin distributed?

epithelial cells

Where is basic keratin distributed?

epithelial cells

Where is desmin, vimentin, and GFAP distributed?

muscle, mesenchymal cells, and glia

Where are neurofilaments distributed?

neurons

Where are lamins distributed?

plant and animal nuclei

Where is nestin distributed?

embryonic neurons

How many vertebrae genes encode the previously 6 classes of IF proteins?

70 genes

True or False: IFs generally constitute 1% of cellular proteins, but in some cell types such as neurons and epidermal keratinocytes, IFs can be 85% of the total protein.

true

Do IFs bind nucleotides?

no, they do not

What were the progenitors of the IF superfamily?

lamins

When did cytoplasmic IFs arise in animals?

after plants branched off from animals

What happened when lamins lost their NLSs and prenylation regions?

the lamins were localized in the cytoplasm

What families to cytoplasmic lamins form?

• skin

• nerves

• muscles

How can one determine the orientation of monomers in dimers and tetramers?

through immunogold electron microscopy

What is a protofilament?

many tetramers stacked end-to-end

How many proto-fibrils are in 1 intermediate filament?

4 proto-fibrils

How many protofilaments are in 1 intermediate filament?

16 protofilaments

Do IFs recover after photobleaching?

yes, they are dynamic molecules

True or False: Cells that produce IFs will independently assemble in vitro.

true

What did the study involving microinjecting antibodies to block assembly of TFs in tissue culture cells reveal?

IFs are disrupted but the rest of the cell is unharmed

True or False: Some animals such as insects don’t have cytoplasmic IFs.

true

How can researchers make a transgenic organism (with a dominant allele) that results in a loss of function phenotype?

What does dominant negative mutations cause?

the prevention of multimer assembly

What type of model is associated with dominant negative mutations?

the “poisoned polymer”

What happens in dominant negative keratin mutation in a transgenic animal?

filament assembly is blocked in the basal layer—causing skin blisters due to weakening of basal cells

What does keratin provide to skin cells?

mechanical integrity and continuity to serve as a barrier

Who is associated with dominant negative K14?

Elaine Fuchs

What are some diseases caused by keratin mutations?

• epidermolysis bullosa simplex

• epidermolytic hyperkeratosis

• epidermolytic palmoplantar keratoderma

• pachyonychia congenita

• white sponge nevus

• meesmann’s corneal dystrophy

• monilethrix

What does Desmin do in skeletal muscle?

provides mechanical strength and connects Z-disks

What does a desmin mutation in humans cause?

disorganization of myofibrils and generalized muscle failure

True or False: There is a neuron in the human body that rungs from the spine to the big toe.

true

What do neurofilaments do?

increases the diameter of the axon and the rate of electrical signal

True or False: The longer the axon diameter, the faster the electrical signal.

true

When did the keratin family begin?

when animals with soft exteriors appeared

What are the 2 basic roles of IFs?

• distribute tensile forces across cells in tissues

• integrate cells into tissues

Where did humans first emigrate from?

Africa

How long ago was the neanderthal-human divergence?

600,000 years ago

Did humans or neanderthals leave Africa first?

neanderthals did

How long ago did modern humans migrate our of Africa?

100,000 years ago

How long ago and where did humans interbreed with neanderthals?

50,000-60,000 years ago in the Middle East

How many years ago did modern humans migrate to Europe and Northern Asia?

40,000-45,000 years ago

How long ago did neanderthals die out?

30,000 years ago

What did Svante Paabo do?

• sequenced the entire Neanderthal genome from the Altai mountains

• resurrected surviving Neanderthal lineages from modern human genomes

What alleles in non-African human DNA are derived from Neanderthals?

• BNC2

• POUF2F3

• cluster of keratin genes

What is BNC2?

a zinc finger protein associated with light skin pigmentation

What is POUF23?

a TF expressed in the epidermis that mediates keratinoxyte proliferation and development