Module 1 Lecture 1: Gastrulation and Neural Induction

Question 1

examples of protostomes

Answer 1

nematodes (round worms), platyhelminthes (flatworms), molluscs (snails, slugs, octopus), annelids (earthworms), arthropods (crabs, spiders, insects)

Question 2

examples of deuterostomes

Answer 2

echinoderms (starfish, sea cucumbers), chordates (tunicates [sea squirts], vertebrates)

Question 3

neuronal characteristics of sponges

Answer 3

no neurons, some synaptic genes

Question 4

neural characteristics of radiata

Answer 4

neurons, diffuse nerve nets

Question 5

neural characteristics of bilateria

Answer 5

organized nerve nets, centralized nervous systems, brains

Question 6

major discovery by hodgkin & huxley

Answer 6

discovered ionic mechanisms of action potential propogation in squid giant axon

Question 7

major discovery by Carlsson, Greengard, and Kandel

Answer 7

molecular basis of learning and memory in sea slug

Question 8

what makes a good model organism?

Answer 8

accessibility, convenience, experimental advantages, momentum

Question 9

characteristics of Caenorhabditis elegans as a model organism

Answer 9

• accessible
• convenient (live on petri dishes, females are hermaphrodites, 3 day reproductive cycle)
• experimental advantages (transparent, invariant development, connectome has been created)
• momentum

Question 10

characteristics of Drosophila melanogester as a model organism

Answer 10

• accessible
• convenient (cheap to maintain by 1000s, 10-day reproductive cycle)
• experimental advantages
• momentum (genome 60% homologous to humans; 75% known human diseases have homologs, connectome known)

Question 11

characteristics of Strongylocentrotus purpuratus

Answer 11

• accessible
• convenient (easy to maintain and yields large numbers of synchronized embryos)
• experimental advantages (echinoderms have bilaterally symmetric larvae, transparent embryos and larval stage)
• momentum (model for cell fate decisions of early embryogenesis)

Question 12

characteristics of Danio reria as a model organism

Answer 12

• accessible
• convenient (spawns 100s eggs every 2-3 days, reproductive cycle 90 days)
• experimental advantages (transparent embryo, external development)
• momentum (advanced tools and techniques for forward genetic screens)

Question 13

characteristics of Xenopus laevis and Gallus gallus domesticus as model organisms

Answer 13

• accessible
• convenient (embryos readily available)
• experimental advantages (robust, externally developing embryos, can cut, graft, and inject material, large eggs provide material for protein biochemistry)
• momentum (modern molecular techniques being incorporated)

Question 14

characteristics of Mus musculus as a model organism

Answer 14

• accessible
• convenient (produce 8 litters of 8 pups per year, 60-day reproductive cycle)
• experimental advantages (designer mice)
• momentum (reverse genetic powerhouse)

Question 15

what does ectoderm become

Answer 15

all outer layer (skin, hair, tooth enamel), CNS, PNS

Question 16

what does endoderm become

Answer 16

digestive system, liver, pancreas, bladder, lungs, etc

Question 17

what does mesoderm become

Answer 17

muscle, bone, cartilage, connective tissue, fat, circulatory and lymphatic systems, etc

Question 18

what does a blastula develop from

Answer 18

early cell divisions after fertilization

Question 19

where does the blastula invaginate to create what?

Answer 19

blastula invaginates at the blastopore to create the archenteron (small pocket)

Question 20

blastocoel

Answer 20

cavity inside blastula/gastrula

Question 21

mesenchyme

Answer 21

loosely organized mesodermal cells

Question 22

animal/vegetal poles significance

Answer 22

non-yolky/yolky; shows that before gastrulation, blastula already polarized

Question 23

protostome main feature

Answer 23

mouth forms from the blastopore
- mouth first

Question 24

deuterostome main feature

Answer 24

anus forms from the blastopore
- mouth second

Question 25

coelom

Answer 25

body cavity between digestive tract and body wall

Question 26

amniote animals

Answer 26

primates, rodents, crocodiles, dinosaurs & birds

Question 27

amniote meaning

Answer 27

eggs have amnion membrane surrounding embryo; exchanges gases and waste

Question 28

advantages of amniote evolution

Answer 28

allowed animals to develop on land - no larval stage

Question 29

anamniote animals

Answer 29

amphibians, ray-finned fish, sharks

Question 30

anamniote meaning

Answer 30

eggs laid in water - facilitates gas and water exchange

Question 31

where does cell division occur in a blastopore

Answer 31

animal pole

Question 32

epiboly meaning

Answer 32

layer of cells spreads out from the animal pole and covers the rest of the vegetal pole

Question 33

when does gastrulation occur

Answer 33

when epiboly reaches the bottom of the vegetal pole; forms germ layer

Question 34

which pole is the blastopore closer to

Answer 34

animal pole

Question 35

where is cell division more frequent

Answer 35

animal pole

Question 36

where does the archenteron form

Answer 36

in the cavity beyond the dorsal lip

Question 37

first step of avian gastrulation

Answer 37

posterior epiblast cells change shape and thicken, forming the primitive streak

Question 38

second step of avian gastrulation

Answer 38

cells migrate, converging at the primitive streak and causing it to elongate

Question 39

third/fourth step of avian gastrulation

Answer 39

the primitive streak narrows and lengthens, forming the primitive groove (the chick blastopore) - cells migrate inward through the primitive groove and Hensen's node

Question 40

fifth step of avian gastrulation

Answer 40

cells generated in Hensen's node and passing into the gastrula migrate anteriorly and form head structures and notochord - conveyor belt moving in

Question 41

what does gastrulation involve

Answer 41

cells moving in through the primitive streak/groove to form the three germ layers

Question 42

at what point does the fertilized egg have two axes

Answer 42

before first cleavage

Question 43

what are the two first axes of the fertilized egg

Answer 43

animal - vegetal axis, and dorsal-ventral axis (gray crescent)

Question 44

how does the ectoderm choose between different fates?

Answer 44

neural induction

Question 45

what is the dorsal blastopore lip derived from

Answer 45

the gray crescent

Question 46

what determines the location of the gray crescent

Answer 46

where the sperm enters

Question 47

what happens if the gray crescent is not equally distributed between the two halves of the fertilized egg

Answer 47

one tadpole develops a nervous system and the other stays as a "belly piece"

Question 48

what was the outcome of the Spemann-Mangold experiment

Answer 48

when the dorsal lip of one embryo was transplanted into a host embryo, the host organism became conjoined to the donor embryo

Question 49

what is the Spemann-Mangold organizer

Answer 49

the dorsal lip of the blastopore

Question 50

what happens when a normal fertilized egg is treated with lithium

Answer 50

it becomes a hyper dorsalized embryo

Question 51

what happens when a normal fertilized egg is treated with UV

Answer 51

it becomes a ventralized embryo - nervous system missing, similar to belly piecew

Question 52

what happens when polyA mRNA from Li-treated fertilized egg is implanted in a UV-treated fertilized egg?

Answer 52

a normal embryo develops - rescues nervous system development

Question 53

how did scientists determine which gene induces nervous system development

Answer 53

- created a cDNA library - broke into 3 pieces, pooled it, and injected into UV-treated animals => 1 subpool rescues nervous system development - repeat process until you get the one thing that causes nervous system development

Question 54

which gene induces nervous system development

Answer 54

Noggin - dose dependent manner (no Noggin = no nervous system development, lots of Noggin = full development or hyperdorsalization)

Question 55

what is Noggin?

Answer 55

a soluble protein that induces overlying ectoderm to adopt a neural fate

Question 56

what does knocking down follistatin, chordin, and noggin cause

Answer 56

severe loss of neural structures (loss-of-function experiment)

Question 57

what do dissociated pre-gastrula animal cells grow into

Answer 57

neurons

Question 58

what do dissociated pre-gastrula animal cells cultured with BMP grow into

Answer 58

skin

Question 59

what do intact pre-gastrula animal caps cultured with BMP inhibitors grow into

Answer 59

neurons

Question 60

what does BMP made by the animal cap do

Answer 60

inhibits neural fate

Question 61

what does BMP stand for

Answer 61

bone morphogenic proteins

Question 62

what group is BMP a part of

Answer 62

TGF-beta super family, a large group of secreted proteins

Question 63

first step of BMP cell signaling cascade

Answer 63

BMP binds to its receptor from the outside of the cell

Question 64

second step of BMP cell signaling cascade

Answer 64

the binding leads to activation of the intracellular part of the receptor

Question 65

third step of BMP cell signaling cascade

Answer 65

activated receptor phosphorylates an intracellular protein called SMAD

Question 66

fourth step of BMP cell signaling cascade

Answer 66

Pi-SMAD binds co-SMAD and they move to the nucleus

Question 67

fifth step of BMP cell signaling cascade

Answer 67

in the nucleus, Pi-SMAD and co-SMAD regulate gene expression

Question 68

noggin, chordin, and follistatin function

Answer 68

prevent BMP from binding its receptor - signaling cascade that selects epidermal fate is not switched on

Question 69

default model

Answer 69

the default fate of ectoderm is neural; this fate is repressed by neighboring cells through BMP signaling - the organizer de-represses neural fate by inhibiting BMP signaling