Developmental Biology Catherine 1

Question 1

Techniques for analysing development

Answer 1

1. Description
   - Cellular description = direct observation of living embryos, needs transparency
2. Physical manipulation
   - Removal of cells/tissues like cell isolation
3. Genetics/molecular experiment
   - Forward genetics
   - Reverse genetics
   - Temp sensitive/epistasis

Question 2

Developmental principles

Answer 2

1. Development occurs by epigenesis
2. Development starts with a single cell
3. Progressive restriction in developmental potential
4. Proliferation vs cell death
5. Oriented + asymmetric cell divisions
6. Epithelial sheets importance
7. Developmental induction
8. Developmental fields
9. Boundaries (fields result in boundaries)
10. Signalling between cells
11. Choice of fate
12. Morphogenesis and cell affinities

Question 3

Benefits of using C elegans

Answer 3

• Simple but has all major cell types
• Easy to grow
• Transparent
• Different anatomy for XX vs XO
• Genetic analysis can be used to study development
• Vulva formation is a good example of tissue remodelling

Question 4

Steps in vulval development

Answer 4

1. Generating VPCs (3 fates 1o,2o,3o
2. Vulval precuror patterning (in L3, signal from the gonad specifies 3 VPCs to generate vulval cells, typically 3-3-2-1-2-3)
3. Generation of adult cells (can be VulA-F)
4. Anchor cell invasion (forms hole in epidermis)
5. Morphogenesis (forms 7 distinct toroids)

Question 5

Generating VPCs

Answer 5

• 11pnp cells are formed during L1 Laval stage

- How gene lin-39 = major determinant of VPC group + is expressed in p3p-p8p

Question 6

VPC 1o, 2o and 3o pattern formation

Answer 6

• 2 systems cooperate :
  1. graded signal of Lin-3 acting via Let-23
  2. sequential signal of DSL ligand acting via LIN-12

Question 7

Anchor cell

Answer 7

• Ablation prior to L3 stage completely blocks vulval development
• AC produce Lin-3, whose action is graded
• Vulvaless/multivulvaless mutations
• Lin3-let23-sem5-let60-lin45-lin-1
• Signalling terminates with modulation of TF like lin-1 that controls morphogenesis
• Lin-31/lin-1 ETS complex are phosph. by MAPK → no inhibition of vulva
• P6p receives most Lin-3, , p3p + p8p have negligible

Question 8

Lateral inhibition

Answer 8

• Stops adjacent cells also adopting primary fate
• ## Genes involved in lin-12 activation are unregulated by Ras in p6p, lead to activation of lin-12/notch in p5p/p7p, helping p5p/p7p adopt 2o fate

Question 9

Negative regulation of induction

Answer 9

• 3 classes of SynMuv gene
• Need mutation in 1 class A + 1 class B
• Prevents wrong LIN-3 expression

Question 10

Formation of axes

Answer 10

• asymmetric divisions establish 3 major axes

- 5 asymmetric divisions produce 6 founder cells: AB, MS, E, C, D, P4

Question 11

Establishing A/P axis

Answer 11

1. Breaking symmetry (sperm assembles PCM, CYK-4, 1st cleavage → Ab1 + P1)
2. PAR proteins (PAR 3+6 form complex w/ PKC-3, needs cdc-42 to maintain polarity, PAR1+2 localise in posterior cortex)
3. P granules (form germline, start in cytoplasm, move to posterior of cell)

Question 12

Spindle positioning

Answer 12

• Heterotrimeric G protein acts ds of PAR to transduce polarity
• GOA-1 + GPA-16
• GRP1/2
  Dynein

Question 13

Formation of D/V axis

Answer 13

• 1st division → big AB, smaller P
• AB = symmetrical division, controlled by PAR
• P1 = asymmetric division, spindle oriented on AP axis
• 2nd division → ABa, Abp, P2 + EMS
• D + V axis different (only AB daughter cell has GLP-1 receptor, P2 has APX-1)

Question 14

Formation of L/R axis

Answer 14

• Determined by division of ABa/ABp
• LH daughter are ↑ anterior to RH, causes cell to contract
• EMS divides 1st to make E + MS
• Then P2 divides to make C + P3 which divide again to make D + P4