Lab 3 - early development and model systems - xenopus and zebrafish

Question 1

What makes zebrafish a good model organism?

Answer 1

• transparent
• eggs are not bound in jelly
• large number of eggs
• mutagenesis
• molecule biology techniques
• vertebrate

Question 2

What makes xenopus a good model organism?

Answer 2

• differentiation of animal and vegetal pole
• egg is large, allows for egg fractionation (isolation of proteins)
• vertebrate

Question 3

What are some disadvantages of xenopus and zebrafish

Answer 3

• costly
• generate slowly

Question 4

What is the egg type and cleavage type of xenopus?

Answer 4

egg type = mesolecithal
cleavage type = unequal holoblastic, radial

Question 5

What is the egg type and cleavage type of zebrafish?

Answer 5

egg type = extreme teloecithal
cleavage type = discoidal meroblastic

Question 6

Describe some characteristics of frog cleavage

Answer 6

1. sperm entry determines the D-V axis
   - point of sperm entry = V
   - grey crescent = D
2. animal pole –> micromeres
3. vegetal pole –> macromeres
4. grey crescent –> blastopore –> dorsal lip of blastopore = dorsal organizer
5. blastocoel –> gives space for future development, signaling barrier

Question 7

Describe some characterisitics of zebrafish cleavage

Answer 7

1. no blastocoel
2. cytoplasm –> blastodisc
3. yolk syncytial layer –> nuclei are above but open to the yolk
4. cleavage occurs on top of yolk
5. blastula will slowly lose connections with the yolk
6. first cell movement = epiboly

Question 8

Describe the steps of frog gastrulation

Answer 8

1. cells at the AP divide and rapidly migrate down to the dorsal lip of the blastopore (epiboly)
2. at the dorsal lip the cells enter the interior (involution)
3. endodermal cells are pulled towards the AP (involution)
4. C&E –> new cavity (archenteron)
5. neural plate is induced in ectoderm and extends anteriorly from the blastopore (delamination)
6. mesoderm will form notochord which induces formation of the neural tube (delamination)

Question 9

Describe zebrafish gastrulation

Answer 9

1. involution –> epiblast + hypoblast = future mesoderm
2. epiboly of ectoderm
   - C&E occurs at the shield
3. shield forms at 50% epiboly (shield = dorsal organizer, presumptive tail)
4. yolk plug forms at 90% epiboly

Question 10

Describe neuralation of the frog

Answer 10

1. notochord (meso) induces ectoderm to thicken and form neural plate
2. neural plate begins to hinge and enclose
3. early nerula –> neural plate hasn’t enclosed yet
4. mid neurula –> neural ridge + groove
   - delamination of mesoderm –> somatic meso + splanchnic meso
5. late neurula –> neural tube

Question 11

Describe eye formation

Answer 11

1. neural ectoderm evaginates outwards –> optic vesicle
2. optic vesicle induces epidermis to become the lens placode (neural - non-neural induction)
3. lens placode induces formation of neural retina (non-neural neural induction)
   - steps 2 and 3 = recipricol induction

Question 12

Describe some characterisitcs of zebrafish neuralation and somatogenesis

Answer 12

• co-occur
• somites formed by paraxial meso
• neural plate –> neural kneel –> neural rod –> neural tube

Question 13

What is the function of BMP

Answer 13

• expressed in the ventral axis

Question 14

Name two BMP inhibitors and their sources

Answer 14

DMH1 = external
chordin = produced by the shield