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B3.0 > Hox, ParaHox, NK: Germ Layers And Tail In Animal Evolution > Flashcards

Hox, ParaHox, NK: Germ Layers And Tail In Animal Evolution Flashcards

1
Q

Big “transitions” in the history of animal life

A
  1. Origin of life (replicators)
  2. Origin of cells
  3. Eukaryagenesis
  4. Origin of multicellularity
  5. Origin of bilaterians
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2
Q

Bilaterians

A
  • Lophotrochozoa
  • Ecdysozoa
  • Deuterostomia
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3
Q

Bilaterian characteristics

A
  • bilateral symmetry
  • A-> P axis (brain and sense organs)
  • centralised nerve cord and co-ordination
  • muscle blocks each side
  • “through-gut”; mouth and anus
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4
Q

3D exploration

A
  • burrowing
  • nutrient mixing
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5
Q

Evo-Devo @ bilaterian origin challenges;

A

1) large suite of changes
2) stem lineage
3) deep time (540-555Mya)

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6
Q

Predictions ?

A
  • single genetic change : NOH
  • new genes (maybe)
  • rewiring existing GRNs (probably…)
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7
Q

How to study deep time

A
  1. Hypothesis-free; looking for new genes, compare gen- / proteo-omes of non-bilaterians and bilaterians
  2. Hypothesis-guided
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8
Q

New genes? Analysis

A

Compare:
- 36 bilaterans
- 8 non-bilaterians
- 18 non-animals

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9
Q

New genes? Finding

A
  • 1580 new genes
  • zero retained by all
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10
Q

New genes? Update.

A
  • 102 genomes
  • 1699 new genes
  • 0 retained by all
  • more work needed to resolve what they do
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11
Q

Hypothesis guided

A

Genes involved in
1) AP pattern
2) through-gut (mouth and anus)
3) mesoderm (muscle)
4) nerve cord

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12
Q

Genes involved in AP patterning

A
  • Hox
  • what tissue type?
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13
Q

Drosophila

A
  • ectoderm (cuticle, nerve cord)
  • mesoderm
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14
Q

C. elegans

A
  • ectoderm
  • mesoderm
  • endoderm (transient)
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15
Q

Mus

A
  • Ectoderm (nerve cord, neural crest)
  • mesoderm (somites, visceral organs)
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16
Q

Amphioxus

A

Ectoderm (epidermis, nerve cord)

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17
Q

Tunicates

A

Ectoderm

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18
Q

Were Hox genes recruited or rewired to pattern ectoderm?

A

Good q

19
Q

Mesoderm and through gut

A
  • patterned by other, Hox-like Homeobox clusters
20
Q

Homeobox

A

> 200 (shown by idiogram)

21
Q

Gene classes

A
  • ANTP
  • PRD
22
Q

Clustered ANTP: NK

A
  • in Drosophila: 6 genes (180kb)
  • 4 sets due to WGD + loss
  • re-arranged across chromosomes
  • a bit broken up in chordates
  • understudied
23
Q

tinman

A
  • in Drosophila
  • has duplicated vertebrate orthologs
  • LOF mutant: no heart
  • expressed in vertebrate developing heart (mesoderm)
24
Q

Drosophila heart

A
  • Pulsatile muscular vesicle that pumps haemolymph around the body
  • mesodermal structure
25
Q

NKX2.5 KO

A
  • Heart defect in mus
  • human mutations: congenital heart disease
26
Q

All NK cluster homeobox genes are involved in

A
  • mesoderm
  • but not A-> P
  • cross-sectionally
27
Q

Some NK cluster homeobox genes are

A

Expressed in nerve tissue; extra function

28
Q

What about endoderm (gut) + lining?

A
  • another gene classes? ANTPs?
29
Q

ParaHox

A
  • ANTP homeobox cluster (in some animals)
  • discovered in Amphioxus (Pdx)
  • Gsx, Pdx, Cdx
  • humans: Chr13
  • 3 other cluster remnants; gene loss!!
30
Q

Pdx

A
  • expressed in middle of gut in Amphioxus
  • lost in insects
  • present in some Ecdysozoa
  • expressed in pancreas/duodenum (Mus, humans)
  • Mus mutation = pancreas absent, gut defect
  • human mutations = diabetes predisposition
31
Q

Cdx

A
  • aka Chordal
  • a lil bit into nerve cord
  • Amphioxus, Drosophila, frog: end of gut/anus
32
Q

Cdx KO expts

A
  • difficult in Amphioxus
  • anus does not break through
  • larval explosion
33
Q

3 homeobox gene clusters

A
  • Co-opted to pattern 3 germ layers
  • allows bilatera to evolve
  • due to duplication
34
Q

Gsx

A
  • not expressed in mouth in Amphioxus, vertebrates or Drosophila
  • Amphioxus, Drosophila: expressed in brain (data from more species needed)
35
Q

Gibula

A
  • trochophore mollusc (marine snail)
  • expressed in embryo stomadium (mouth)
  • and brain
  • ancestral situation has been modified in different lineages?
36
Q

Where did these genes come from,

A

And when? They are not bilaterial

37
Q

Hox + ParaHox

A
  • Bilateria
  • Cnidaria
38
Q

Hox + ParaHox + NK

A
  • bilateria
  • Cnidaria
  • sponges
39
Q

Homeobox evolution

A

1) ANTP class expanded thru much duplication
2) in bilateria, 3x clusters held as “islands”; others dispersed
3) recruitment (other genes and GRN: also key)

40
Q

Fox Class TFs

A
  • recruited for Bilaterian mesodermal patterning
  • lots! Early duplication
  • Drosophila, honeybee, sea urchins, H. sapiens
41
Q

Can evolution bring unrelated genes into a cluster to create a functional unit under common control, to start patterning new structures?

A

1) compare genome sequences
2) look for micro-synteny

42
Q

Microsynteny

A

Genes consistently found together, despite all the shuffling

43
Q

Pharyngeal gene cluster in Deuterostomes

A
  • Nkx2.1, Nkx2.2, Pax1/9, Foxa1 all expressed in same region

B3.0 (23 decks)

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