Hox, ParaHox, NK: Germ Layers And Tail In Animal Evolution Flashcards
1
Q
Big “transitions” in the history of animal life
A
- Origin of life (replicators)
- Origin of cells
- Eukaryagenesis
- Origin of multicellularity
- Origin of bilaterians
2
Q
Bilaterians
A
- Lophotrochozoa
- Ecdysozoa
- Deuterostomia
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
4
Q
3D exploration
A
- burrowing
- nutrient mixing
5
Q
Evo-Devo @ bilaterian origin challenges;
A
1) large suite of changes
2) stem lineage
3) deep time (540-555Mya)
6
Q
Predictions ?
A
- single genetic change : NOH
- new genes (maybe)
- rewiring existing GRNs (probably…)
7
Q
How to study deep time
A
- Hypothesis-free; looking for new genes, compare gen- / proteo-omes of non-bilaterians and bilaterians
- Hypothesis-guided
8
Q
New genes? Analysis
A
Compare:
- 36 bilaterans
- 8 non-bilaterians
- 18 non-animals
9
Q
New genes? Finding
A
- 1580 new genes
- zero retained by all
10
Q
New genes? Update.
A
- 102 genomes
- 1699 new genes
- 0 retained by all
- more work needed to resolve what they do
11
Q
Hypothesis guided
A
Genes involved in
1) AP pattern
2) through-gut (mouth and anus)
3) mesoderm (muscle)
4) nerve cord
12
Q
Genes involved in AP patterning
A
- Hox
- what tissue type?
13
Q
Drosophila
A
- ectoderm (cuticle, nerve cord)
- mesoderm
14
Q
C. elegans
A
- ectoderm
- mesoderm
- endoderm (transient)
15
Q
Mus
A
- Ectoderm (nerve cord, neural crest)
- mesoderm (somites, visceral organs)
16
Q
Amphioxus
A
Ectoderm (epidermis, nerve cord)
17
Q
Tunicates
A
Ectoderm
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
NKX2.5 KO
- Heart defect in mus
- human mutations: congenital heart disease
26
All NK cluster homeobox genes are involved in
- mesoderm
- but not A-> P
- cross-sectionally
27
Some NK cluster homeobox genes are
Expressed in nerve tissue; extra function
28
What about endoderm (gut) + lining?
- another gene classes? ANTPs?
29
ParaHox
- ANTP homeobox cluster (in some animals)
- discovered in Amphioxus (Pdx)
- Gsx, Pdx, Cdx
- humans: Chr13
- 3 other cluster remnants; gene loss!!
30
Pdx
- 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
Cdx
- aka Chordal
- a lil bit into nerve cord
- Amphioxus, Drosophila, frog: end of gut/anus
32
Cdx KO expts
- difficult in Amphioxus
- anus does not break through
- larval explosion
33
3 homeobox gene clusters
- Co-opted to pattern 3 germ layers
- allows bilatera to evolve
- due to duplication
34
Gsx
- not expressed in mouth in Amphioxus, vertebrates or Drosophila
- Amphioxus, Drosophila: expressed in brain (data from more species needed)
35
Gibula
- trochophore mollusc (marine snail)
- expressed in embryo stomadium (mouth)
- and brain
- ancestral situation has been modified in different lineages?
36
Where did these genes come from,
And when? They are not bilaterial
37
Hox + ParaHox
- Bilateria
- Cnidaria
38
Hox + ParaHox + NK
- bilateria
- Cnidaria
- sponges
39
Homeobox evolution
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
Fox Class TFs
- recruited for Bilaterian mesodermal patterning
- lots! Early duplication
- Drosophila, honeybee, sea urchins, H. sapiens
41
Can evolution bring unrelated genes into a cluster to create a functional unit under common control, to start patterning new structures?
1) compare genome sequences
2) look for micro-synteny
42
Microsynteny
Genes consistently found together, despite all the shuffling
43
Pharyngeal gene cluster in Deuterostomes
- Nkx2.1, Nkx2.2, Pax1/9, Foxa1 all expressed in same region
