Gastrulation and Asymmetry

Question 1

sperm capacitated

Answer 1

made competent for fertilization by an unknown process (change in acrosome, sperm’s digestiv ezyme)

Question 2

cumulus cells

Answer 2

also called follicle cells, surround egg.

Question 3

sperm cross cumulus by

Answer 3

releasing acrosome

Question 4

why one sperm only?

Answer 4

acrosome causes wave of Ca in oocyte, causes cortical granules in oocyte to fuse with zona pellucida

Question 5

the first cleavage

Answer 5

combines the two pronuclei of egg and sperm

Question 6

reductive cleavage

Answer 6

after first, cells get smaller after every split into many cells called blastomeres

Question 7

blastomeres are totipotent up to

Answer 7

+/- 4 cell stage

Question 8

compaction

Answer 8

occurs at 8 cell stage, determines inside and outside

Question 9

only a few of the compancted cells become epiblastic, meaning

Answer 9

progenitors of the embryo

Question 10

Trophectoderm

Answer 10

16 cell stage, outside cells, determined by Cdx

Question 11

Cdx 2

Answer 11

turned on in edge cells via hippo pathway

Question 12

Hippo pathway

Answer 12

inside cells have high cell-to-cell contact, so Yap is phosphorylated and does NOT enter the nucleus to turn on cdx

Question 13

what TF determines inner cell mass?

Answer 13

Oct-4 (makes ES cells)

Question 14

inner cell mass is the same as

Answer 14

ES cells

Question 15

primitive endoderm (hypoblast) Tfs

Answer 15

gata6, gata4

Question 16

primitive ectoderm Tf

Answer 16

nagog

Question 17

apoptosis in first week

Answer 17

20% of cells. Why? Nobody knows!

Question 18

by end of first week, trophectoderm becomes

Answer 18

placenta

Question 19

by end of first week, inner cell mass becomes

Answer 19

epiblast making ectoderm, mesoderm, definitive endoderm AND parietal and visceral endoderm

Question 20

implantation: blastocele facing ____, epiblast facing ____

Answer 20

blastocele outward, epiblast inward toward uterine wall

Question 21

TGFbeta factor Nodal

Answer 21

binds TGFbeta s/t receptors and coreceptor Cripto, turns on SMAD2/3 and SMAD 4

Question 22

SMAD 2/3 and SMAD 4

Answer 22

bind foxh1 promotor, turns on Nodal and Lefty, a Nodal inhibitor

Question 23

How does Lefty inhibit Nodal?

Answer 23

binds to its TGFbeta receptor

Question 24

Nodal morphogen function

Answer 24

diffuses, elicits dose dependent response (ratio of nodal and lefty)

Question 25

Nodal /Cripto is expressed throughout

Answer 25

the epiblast

Question 26

distal visceral endoderm sets up oppositional field using

Answer 26

Lefty and Cerberus, both Nodal inhibitors

Question 27

Anterior cells express highest level of what where?

Answer 27

Lefty and Cerberus, anterior (head)

Question 28

Posterior cells express highest level of what where?

Answer 28

Nodal and Crypto, at the primitive streak in the posterior wall of the embryo

Question 29

Because lefty diffuses farther than nodal:

Answer 29

reduces range of Nodal to a discreet zone on the posterior (future caudal) side of embryo

Question 30

Wnt3 inhibitor

Answer 30

DKK1

Question 31

Wnt inhibitors are

Answer 31

posterior, like with Nodal

Question 32

gastrulation happens when?

Answer 32

third week

Question 33

gastrulatio nmeans what?

Answer 33

Epiblast cells migrate into streak and under epiblast.

Question 34

what do gastrulating epiblasts creat first?

Answer 34

definitive endoderm, then cells generating mesoderm

Question 35

epiblasts are what initially?

Answer 35

epithelial cells, but convert to mesenchyme during migration

Question 36

how do epithelial cells convert to mesenchyme?

Answer 36

downregulation of epithelial adhesion proteins, expression of SNAIL (inhibits e-cadherin expression) and CXCR4 (a receptor of SDF1, a “promigratory” pathway)

Question 37

cells moving to the anterior end of the cell in gastrulation

Answer 37

become axial-prechordal mesoderm & cardiac mesoderm

Question 38

what organizes the axis?

Answer 38

blastopore lip, through Wnt8 and Nodal

Question 39

head and neural tissue formation

Answer 39

anterior visceral endoderm signals to the epiblast, uses Lefty and Wnt to protect the head

Question 40

Dorsal-ventral patterning

Answer 40

signals between notochord and neural plate, via SHH.

Question 41

Left-right development disorders

Answer 41

situs inversus, isomerism (symmetrical), heterotaxia (random)

Question 42

symmetry broken by flow of fluid how?

Answer 42

cilia! (ciliary defects cause situ inversus, “Kartagener's disease” in humans)

Question 43

assymetry propagates via what signal?

Answer 43

Nodal

Question 44

Nodal induced on which side?

Answer 44

Left, with lefty, who inhibits Nodal particularly on the right!

Question 45

Left side Nodal signal turns on

Answer 45

Pitx2 expression, Islet1, who maintain assymetry via magic.

Question 46

When Nodal coreceptor Criptic is inhibited

Answer 46

randomized postion of organs, e.g., right pulmonary isomerism, wrong-sided aorta