1.1 Intro to Developmental Biology

Question 1

What is developmental biology?

Answer 1

Study of transient stages between egg and birth

How egg produces adult and how adult produces egg

Question 2

What areas of science do developmental studies inform?

Answer 2

Birth defects research 
Role of genes in disease
Cancer 
Stem cells 
Regeneration 
Evolution

Question 3

How does developmental biology inform medicine?

Answer 3

Permits development of preventative regimes and treatments for pathological conditions
- experimental model = mouse
^Identify gene sonic hedgehog (shh)
^Shh requires cholesterol
^Cholesterol inhibitors: Alkaloids - plants
^Alkaloids in animal fodder = cyclopic lamb

Question 4

What are the mechanisms driving embryonic development?

Answer 4

1. Generation of cells - mitosis and growth
2. Cell differentiation - totipotent = any cell type
   Pluripotent = several cell types
   Differentiated have a final character
3. Generation of tissues/organs/whole body - morphogenesis

Question 5

Definition of morphogenesis

Answer 5

Creation of structure or form; two major forms during embryogenesis

Question 6

What is the difference between mesenchymal and epithelial cells?

Answer 6

Mesenchyme = single or loosely linked cells of irregular shape

Epithelial = cells tightly attached to each other or a common membrane, regular shape

Question 7

What is anatomical embryology?

Answer 7

How anatomy changes with and between embryos

- easier in larger animals

Question 8

What is experimental embryology?

Answer 8

Mechanics of development

- easier in larger animals

Question 9

What is genetic embryology?

Answer 9

How genes control development

- smaller animals, shorter gestation

Question 10

What are the pros and cons of using fruit flies?

Answer 10

• short life span - both
• easy to handle large numbers - pro
• easily mutated and easy to make transgenics - pro
• ideal genetic model - pro
• not a vertebrate - con

Question 11

What are the pros and cons of using zebrafish embryos? - Danio rerio

Answer 11

Small, cheap and easy to keep - pro
Develop external to mother - pro
Transparent, good for anatomical development - pro
Easy to mutate - transgenics - pro
small eggs but can perform experimental embryology - pro
Can generate large numbers easily and rapidly - pro

Question 12

What are the pros and cons of using chick embryos? - Gallus gallus

Answer 12

Develop external to mother - pro
large embryo - pro 
Easily experimentally manipulated - pro 
not good for genetics - con 
Closer to humans then Xenopus and zebrafish - pro

Question 13

What are the pros and cons of using mouse embryos ?- Mus muscuelus

Answer 13

Mammalian - closest to human - pro
Same no. of genes in the same order - pro
Good for genetics: transgenics - knockouts - pro
Small, short, breeding cycle - pro
Poor for experimental embryology studies - cons
Develops inside mother - cons

Question 14

What are the pros and cons of using frog embryos? - Xenopus laevis

Answer 14

Large eggs - pro
Develop external to mother - pro
Easily manipulated for experimental embryology - pro
Genetics difficult as they have 4 copies of each gene - con
Can generate large numbers easily and cheaply - pro

Question 15

What is drosophila segmentation?

Answer 15

Relationship between adult anatomy and embryonic segmentation - obvious 
- head mandibular maxillary labial = 1 
-thorax = 3 
- abdominal segments = 10 
14 segments in total

Question 16

What is the Drosophila maternal effect gene?

Answer 16

Genes expressed in mothers ovaries

- mRNA’s diffuse into egg and are transplanted upon fertilisation

Question 17

How do the anterior - posterior regions develop?

Answer 17

Anterior = bicoid + hunchback genes
Posterior = caudal + nanos genes
Both are maternal effect genes

Question 18

What happens in the absence of bicoid?

Answer 18

All tail no head

Question 19

What are the drosophila zygotic segmentation genes?

Answer 19

Divide early embryo into segments (primordia) along A-P axis 
- expressed sequentially 
syncytial blastoderm 
1st = gap genes 
2nd = pair-rule genes 
Cellularisation 
3rd = segment polarity genes 
4th = homeotic selector genes

Question 20

What are the gap genes?

Answer 20

Divide embryo into 4 broad domains
1st genes that drosophila embryo expresses (zygotic genes)
Encode transcription factors (hunchback, giant, krüppel, knirps, tailless)
Controlled by maternal effect genes
Cross replication ensure discrete expression domains

Question 21

What are pair-rule genes?

Answer 21

Group of transcription factors including; hairy, even-skipped, runt , fushi, tarazu, odd-skipped, paired
Expressed in stripes, dividing embryo into 4 subunits (parasegments)
Expression controlled by gap proteins

Question 22

What are segment polarity genes?

Answer 22

Mainly signalling molecules e.g hedgehog (hh) and wingless (wnt)
divide each parasegment into anterior and posterior compartments
Expression controlled by pair-rule proteins - mutual repression
parasegments (early embryo) - segments (late embryo)
hh expressed in anterior of parasegment but in posterior of segment

Question 23

How to make segments unique?

Answer 23

• homeosis - transformation of whole segment or structure into a related one
  Drosophila homeotic mutants
  identification of homeotic complex (hom-c)

Question 24

What is the homeotic complex?

Answer 24

HOX genes
Homeobox - containing transcription factors
8 genes, 1 chromosome - expressed in specific segments
Controlled by gap and pair rule gene
Later repressed by adjacent homeotic genes

Question 25

What is a ultrabithorax mutant?

Answer 25

T3 converted to T2 I.e two sets of wings
UBX no longer expressed in T3
ANTP expression expands from T2 into T3

Question 26

What is a proboscipedia mutant?

Answer 26

Labial pulps transformed into T1 (legs)
pb no longer expressed in labial pulps
Scr now expressed

Question 27

What are zygotic genes?

Answer 27

Expressed in zygote
zygotic mutation would normally cause a phenotype in the zygote (embryo)
- hedgehog (hh)

Question 28

What are morphogens?

Answer 28

Proteins expressed at different concentrations in the embryo
Come from a discrete source, tell the cells what do to
Cells seeing an increased conc. respond differently to cells seeing a decreased conc.
- drosophila, hedgehog (hh)
- vertebrate, shh in lim development