Evolution of Multicellularity

Question 1

Structure of choanoflagellates

Answer 1

Single celled organism: has a collar (full of actin) and flagella (full of tubulin)

Question 2

What was conserved between choanoflagelletes and choanocytes (part of porifea)

Answer 2

RTK and CTK present in organisms past choanoflagelletes, but CTK present in their previous ancestor. CTK in porifea phosphorylate Src which inhibits it. But in choanoflagelletes it doesnt lead to inhibition of Src. B-catenin is not found in choanoflagelletes therefore no Wnt signalling

Question 3

Whats the difference between cadherens in animals and choanoflagelletes?

Answer 3

Choanoflagelletes have genes associated with them that are not present in animals. Choanoflagelletes have 23 cadheren genes. Observed in the collar. Suggests that cadherens first evolved as a way to eat bacteria

Question 4

Describe Wnt signalling pathway

Answer 4

• Wnt is secreted then binds to frizzled receptor
• which recruits GSK3B pulling it away from phosphorylating B-catenin
• free B-catenin goes to nucleus and binds to TCF (a TF) and turns on genes

Question 5

What family has anterior-posterior axis?

Answer 5

radiata have one axis (A-P) and bilateralia have two (dorsal-ventral and left-right)

Question 6

What axis does Wnt signalling influence

Answer 6

Radiata: oral-aboral (high on oral)
bilateralia: anterior -posterior axis , (higher on posterior)

In Wnt3 knockout mouse lower half is compeltely deformed

Question 7

After which organism did nerves evolve?

Answer 7

Cnteophores were the first to have nerves (nerve nets). Porifera do not have nerves or mucsles

Question 8

Describe sensory-motor transformation

Answer 8

Cililary locomotion (using tubulin)/phototaxis -> muscle locomotion

Phototaxis= detecting light and moving away (choanocytes do this)
Cillary locomotiion is essentially response to sensory input (DOES NOT NEED NERVES OR MUSCLE)

Question 9

What are the sensor cells in porifera?

Answer 9

Flask cells, form vesicles between adjacent cells that are v similar to synapses. Can activate range of cells (next to them)
Flask cells thought to be nerve precursor bc flask cells also make loads of proteins found in synapses in animals.

Proteins (like GRIP or HOMER) that are known to be in synpases in animals are expressed in flask cells, and they have a lot of them. Thought that flask cells evolved into neurons in ctenophora, and diversified what the flask cells could react to, and extend their mechanisms to go to other cells