BG9

Question 1

hox genes origin

Answer 1

all metazoans but sponges have hox genes

- discovered by DNA radioactive probes

Question 2

GRNs

Answer 2

animal development has a heirachy of GRNs
postgastrula axiel patterning GRN
Body part specificaiton GRN
Body pattern formation GRN
cell fate specification GRN

Question 3

AP axis

Answer 3

all bilateria have ap axis - head and tail

potential homology?

Question 4

specification of regions in drosophila

Answer 4

syncitum = TFs specifiy
- other organisms use small molecule morphogens like RA that bind to CSRs
drosoph
maternal effect, hb protein gradient, gapt genes, pair rule genes, segmeented polarity genes nad homeotic genes in that order

Question 5

drosophila - what specifies the posterior axis

Answer 5

caudal = maternal effect TF
posterior expression of caudal is ancient
found in vertebrata and nematoda
homologs in c. elegans = Pal-1
homologs in xenopus = xcad2

Question 6

specification of anteriror axis in bilateria

Answer 6

expression domains of tf six3/6 and optx mark the head region in many biilateria
ecdysozoa, lophotrochozoa, vertebrates etc.

Question 7

anterior effect gene in drosophila

Answer 7

bicoid

Question 8

ap axis homology in bilateria?

Answer 8

seems to be homolloogous in animas

but many genes are not ancient, e.g. bicoid

Question 9

cnidarian ap axis

Answer 9

cniderians ahve oral/aboral axis
Nematostella anenome has six3/6 expressed at aboral pole of larvae and foxq2 which is also expressed anteriorlly in bilateria

• suggests aboral is homologous to anterior.

Question 10

scenario for aboral to anterior

Answer 10

gastrea like creature flopped on side so aboral became anteiror

Question 11

radially symmetrical creatures dorsal ventral axis?

Answer 11

dont have, would imply were radial is had both axis.

Question 12

nematostella radial symmetry

Answer 12

has a ciliate groove off to one side - the siphonoglyph - creates currents of water in the pharynx
- must be positional info for this, so cannot be radial.
** homologs of a variety of genes import in axis formation in vertebrates are expressed assymmetrically in nematostella larvae
noggin, chordin and two hox genes

Question 13

what is dorsal and ventral?

Answer 13

hard to decide
geoggrey st hillaire first noted organs are dorsal in some animals and ventral in others.
lobster upside down = CNS - nerve chord is found ventrally, where ours is dorsal

Question 14

dv axis specifcation in drosophila

Answer 14

works by a series of signals along dv axis
cell terrioties are marked by two interacting gradients of signalling molecules
* dorsal gradient of Dpp
ventral one of sog. which antagonise

Question 15

dv axis specfication in xenopus

Answer 15

vertebrates dorsal side forms the blastopore lip = organiser

dorsal chordin is one of the key signalling molecules of the organised, antagonised by ventral bmp4

Question 16

homology of dv axis

Answer 16

ventral sog is homologous to dorsal chordin
dorsal dpp is homologous to ventral bmp4

• inverted
  dorsal and ventral definitons are redundant?

Question 17

hemichordates acorn worm

Answer 17

potential LCA of deuterostomes.
closely related too echinoderms, dont have laters dervied radial geometry.
however both have similar larvae - trochophore.

Question 18

Saccoglossus ventral axis

Answer 18

no cns no nerve net
mouth is ventral
chordin is expressed ventrally
bmp is expressed dorsally
like insects rather than vertebrates
suggests inversion happens after split from hemichordates
potentially in response to specification of a new CNS?

Question 19

CNS of animals

Answer 19

DEL have very diff CNS.
verebrates form CNS via neurulation (dorsal neuroectoderm folds into a tube) - E and L dont do this.

• thought therefore CNS = convergent in superphyla. vertebrates and invertebrates.
  as LCA of vertebrates didnt have a CNS free to form dorsally or ventrally.
• however CNS appears homolgous

Question 20

Homology of CNS drosophila and xenopus

Answer 20

1. both drosophila and xenopus CNS arises from 3 coloumns of neuroblasts
2. both these neuroblasts are specified by particular TFs
   - from out to in msh/Msx -> ind/Gsh-1
3. insects and vertebrate both have a tripartite brain - regions of brain specfied in the same way.
   drosophila and xenopus and platyneris annelis the tfs incolved in ap patterning are similar.
   **otd/otx, optic/six etc.

Question 21

homology in brain structure

Answer 21

in mammals basal ganglia and in drosophila central complex are both rich in dopaminergic neurons and both responsible for motor control
thought to be homologous.

Question 22

proposed homologies in brain structure

Answer 22

mammalian cudate nucleus (found in basal ganglia) and plutamen correspond to insect fan shaped boy and protocerebral bridge (found in central complex).
mammalian external and internal globus pallidus (found in basal ganglia) correspond to ellipsoid body (found in central complex)

Question 23

gut and mouth homology?

Answer 23

protostomes - actually gives rise to mouth and anus simultaneosuly.
deuterstomes - blastopore gives rise o anus and mouth forms later.
mouth and anus thought not to be homologous
however brachyury TF is expressed in fore and hind gut in similar way - suggesting homology

Question 24

what must a model for evo of metazoan geometry account for

Answer 24

1. bilaterian AP axis homology
2. bilaterian DV axis specification homology
   - and inversion
3. bilaterian fore and hind gut homology
4. bilaterian cns homology
5. bilaterian tripartite brain homology

Question 25

what does a model taking all major things into account for metazoan geometry sugesst

Answer 25

1. acoels and xenoturbella separated before rest of bilateria.
2. LCA of ec/lop/duet was a swimming creature like a modern trochophore larvae and had a brain - CNS and through gut
3. creature setlled either on one side or other giving rise to ec and lop and or else higher deuterstomes and hemichordates setttled seperately and lost their cns.