Ciliopathies - Tran

Question 1

What are the two types of cilia? Where are they found (and # found) and what is their primary function?

Answer 1

Motile cilia: function = beat; found in: brain ventricles, embryonic node, respiratory tract, sperm and female reproductive tract; varies but mostly more than one per cell

Non-motile primary cilia: function = signal; found in almost all vertebrate cells; one per cell

Question 2

What was first found in algae? What is so important about this process?

Answer 2

Intraflagellar transport (IFT); builds and maintains cilia…allows for protein movement up and down the cilia

Question 3

How are primary and motile cilia differentiated structurally?

Answer 3

primary: “9+0”…have the doublet microtubules only
motile: “9+2”…have outer dynein arms (ODA), inner dynein arms (IDA), radial spokes, and central microtubule pair

Question 4

What is associated with anterograde and retrograde transport?

Answer 4

anterograde: Kinesin and IFT complex B
retrograde: Dynein and IFT complex A

Question 5

What is the structure of primary cilia?

Answer 5

basal body: mother + daughter centriole
transition zone: gatekeeper
axoneme: main part of cilia that extends out from cell

Question 6

What are the proteins associated the transition zone?

Answer 6

ciliary gate: MKS, NPHP

BBSome: required to shuttle ciliary proteins from Golgi to base of transition zone

Question 7

Disruption of AAA causes ciliary structural defects due to BBB. Describe each type of AAA and how this would look under EM.

Answer 7

AAA: IFT components
BBB: defective protein trafficking

no IFT-B: no cilia
no IFT-A: as you go toward the tip of the cilia, the axoneme becomes more congested with proteins - appears oval
no dynein: more severe that IFT-A; cilia are short and a round bud (filled with proteins) will form

Question 8

What are signals the Primary Cilium receive and receptors on the Primary Cilium?

Answer 8

signals: flow/movement, morphogens, light, chemical signals, growth factors
receptors: PC2, PC1, Ca+2, Patched, Frizzled, GPCR, PDGF-alpha

Question 9

What provides motility?

Answer 9

dynein arms and central microtubule pair

Question 10

What do primary cilia extend from and what does this affect?

Answer 10

extend from a modified centriole - influences the cell cycle

Question 11

What is the only motile ciliopathy? What are some fo the most common clinical features?

Answer 11

primary ciliary dyskinesia (PCD) - can have a range of severity

clinical features: hydrocephalus, respiratory abnormalities, laterality defects (situs inversus), congenital heart defects, infertility

Question 12

What causes PCD?

Answer 12

any gene mutation that affects: nexin-dynein regulatory complex, outer dynein arm, inner dynein arm, central pair of microtubules or radial spoke

Question 13

What are the most common non-motile ciliopathies?

Answer 13

Bardet-Biedl Syndrome (BBS) - obesity, retinal degenration
Meckel Syndrome (MKS) - clinical triad: anencephaly, polydactyly, renal cystic dysplasia
Nephronophthisis (NPHP) - fibrorenal cystic disease with corticomedullary cysts
Joubert Syndrome (JBTS) - molar tooth sign (cerebellar defect)
Jeune Syndrome (JS) - skeletal defect: narrowed rib cage, shortened fingers and toes
Ellis-van Creveld Syndrome (EVC) - skeletal defect: dwarfism
PKD
Von Hippel Lindau Syndrome (VHL)

Question 14

What are the most common features of non-motile ciliopathies? How do you know if it is not a non-motile cilipathy?

Answer 14

clinical signs that are NOT non-motile ciliopathies: infertility, respiratory anomalies

clinical signs that ARE non-motile cilipathies: cerebellum, obesity, skeletal deformations, renal cysts, and thoracic skeleton

Question 15

Describe the genetics of non-motile ciliopathies.

Answer 15

typically autosomal recessive, however there was a case of triallelic inheriatance in BBS (Bardet-biedl syndrome); many genes are involved

Question 16

What are two ciliary diseases that present with obesity? How?

Answer 16

Bardet-Biedl syndrome (BBS) and Alstrom Syndrome

cilia in the brain are affected - signaling pathways that correlate with eating are messed up and these individuals are always hungry

Question 17

What causes PKD?

Answer 17

ARPKD: mutation in PKHD1 (1/20,000 children)…FPC protein cannot get to membrane

ADPKD: mutation in PKD1 (85%), PKD2 (15%) (1/500 adults)…PC1 and PC2 (from PKD1/2) cannot get to the membrane in the axonome of the cilia

Note: all tubular epithelial cells contain one mutated and one unaffected PKD1 or PKD2 allele; the other allele can mutate or over time the kidneys will mature and the cysts will increase in size…think of the two-hit hypothesis or the 3-hit hypothesis

Question 18

What are the major cellular abnormalities of PKD?

Answer 18

increased cell proliferation and increased fluid secretion

Question 19

What are the major factors affecting ADPKD progression?

Answer 19

age (younger diagnosis = worse outcomes)
genotype (truncating PKD1)
sex (male)
race (African-Americans, Asians)
hypertension
gross hematuria
environmental (water intake, caffeine consumption)
other genes

Question 20

What does PC deficiency lead to?

Answer 20

decreased intracellular calcium levels, which causes an area of abnormal cell proliferation which then causes continued cell proliferation and fluid secretion into the cysts

decreased Ca leads to an abnormal response to cAMP

Question 21

explain the role of cAMP, Ca and normal/PKD kidney cells

Answer 21

ADPKD cells: intracellular cAMP levels are elevated and causes increased proliferation of ADPKD cells

cAMP -> PKA -> Ras -> Braf (inhibited by Ca) -> MEK -> ERK -> cell proliferation

in normal cells, PKA will not affect Ras…will actually inhibit Raf-1 which then is not able to stimulate MEK and thus prevents cell proliferation

Question 22

describe fluid secretion in relation to PKD

Answer 22

vasopressin (anti-diuretic) stimulates cAMP which then acts on CFTR to increase amount of water in the cysts (Cl- goes from blood to cyst cells via NKCC1 and then from cyst cells to inside of cyst via CFTR…causes water to follow)

Question 23

what is the only therapeutic drug for PKD? how does it function?

Answer 23

tolvaptan; competitive inhibitor of vasopressin receptor….leads to the decreased production of cAMP

patients are VERY thirsty because the anti-diuretic is being inhibited - do not retain water very well

not as effective in humans as mice - PKD is a multifactorial disease

Question 24

what are the ciliopathies that are predisposing to cancer? How do they arise?

Answer 24

Von Hippel Lindau (VHL) and Birt Hogg Dube

these gene products do not localize to primary cilium

Question 25

When are the two main times that cilia defects occur? what are the mechanisms that are being disrupted and what is the severity of the resulting disease?

Answer 25

1. during morphogenesis: cilia defect occurs early in life which leads to problems with signaling and causes severe disease
2. during tissue maintenance: cilia defect occurs later in life which leads to problems with cell proliferation and differentiation - tend to be less severe diseases