formatting the body

Question 1

why did edward conkilin use sea squirts (Styella patita) to study developmental patterning

Answer 1

because the blastomeres of very early embryos shows a yellow pigment that is easy to follow

Question 2

what did the yellow pigmented cells of the Styella partita develop into

Answer 2

the posterior muscle elements of the tail

Question 3

how can we track specific cells in development to create fate maps

Answer 3

Inject fluorescent dye into a few cells, use a laser to activate v small number of cells (5) so only they are labelled with the dye, then have a fate map

Question 4

differences between development of human vs mouse embryos

Answer 4

Human epiblast turns into a disk whereas mouse develop as a cup

Question 5

what is the first thing to form in an embryo

Answer 5

the posterior to anterior axis with the formation of the primitive streak

Question 6

what is Hensons node and where does it form

Answer 6

aka primitive node - a thickening at the cranial/anterior end of the primitive streak - will be the organiser (in a chick embryo)

Question 7

what occurs when you transplant pieces of the primitive streak from and early and late embryo donor into another organism eg quail to chick

Answer 7

the graft from the early embryo will turn into a more complete structure with a wider combination of donor and recipient cells used (greater ability to induce)
the graft from the later stage embryo will only induce a more specific structure (eg just the trunk) and be mainly made up on donor cells

Question 8

how would you experimentally induce a human axis in a recipient embryo

Answer 8

Take pluripotent human embryo cells, induce with Wnt + activin (organiser fate) and graft into a donor chick embryo

Question 9

how does the head process form in a chick embryo

Answer 9

once hensons node has reached the most anterior part some cells will carry on under the epiblast and form the head process

Question 10

what determines the A-P streak in the chick

Answer 10

via gravity (embryo rotations cause the heaviest elements to go to the bottom to begin the posterior ingression of the primitive streak)

Question 11

describe the conversion of radial symmetry to bilateral symmetry in chick embryos

Answer 11

As the ovum passes through the hen’s reproductive tract, it rotates. This spinning, shifts the yolk such that its lighter components lie beneath one side of the blastoderm.
This imbalance tips up one end of the blastoderm, and that end becomes the posterior marginal zone (PMZ), adjacent to where primitive streak formation begins.

Question 12

what ultimately determines left right asymmetry in the chick

Answer 12

Nodal and PitX (only expressed on the left side

Question 13

describe the signalling cascade that determine left right symmetry in the chick

Answer 13

Shh is expressed from the node
on the left side: Shh activates cerebrus, which activates BMPs, which activates Nodal and PitX
on the right side

Question 14

describe the signalling cascade that determine left right symmetry in the chick

Answer 14

Shh is expressed from the node
on the left side: Shh activates cerebrus, which activates BMPs, which activates Nodal and PitX
on the right side: Shh expressed causing activin expression, inhibiting Fgf8 which inhibits cerebrus so there is no downstream signalling of nodal or pitx

Question 15

what determines A-P axis formation in the Xenopus

Answer 15

site of sperm entry

(cortical roation and definintion of the animal and vegetal pole then organiser formation at the site of entry)

Question 16

what structures form when you transplant a portion of the dorsal lip from young and advanced gastrulas

Answer 16

young dorsal lip = anterior structures

later stage dorsal lip = more trunk peices

Question 17

what is the next step after axis formation

Answer 17

segmentation

Question 18

what transcription factors confer identity to the segments

Answer 18

Hox genes

Question 19

what is Hox gene collinearity

Answer 19

relates the gene order of the Hox cluster in the chromosome (telomeric to centromeric end) with the serial activation of these genes in the ontogenetic units along the Anterior-Posterior embryonic axis

Question 20

the 3 and 5 prime ends of the hox cluster determine what

Answer 20

3' = head
5' = posterior structures

Question 21

invertebrates how many clusters of Hox genes are there

Answer 21

4 or more

mouse 4 chick 7

Question 22

hox genes have a sharp __________ boundary and a more diffuse ____________

Answer 22

sharp anterior boundary and more diffuse posterially

Question 23

what is homeotic transformation

Answer 23

Homeotic transformation is a transformation of tissues in which the developmental fate of an tissue is changed to that of another caused by misexpression of developmental/ Hox genes

Question 24

if a hox gene is knocked out what occurs

Answer 24

the more anterior hox gene continues its expression

Question 25

what are somites

Answer 25

precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae.

Question 26

where are osmite derived from

Answer 26

paraxial mesoderm (presomitic mesoderm)

Question 27

what is somitogenesis

Answer 27

a highly regulated process that determines “what, when, where, and how many” somites an organism makes. Anterior to posterior direction. – blocks of somites in the mesoderm on either side of (flank) the neural tube in the midline
- regulated periodic budding of somites

Question 28

where do somites form

Answer 28

on either side of the midline (neural tube)

Question 29

somitogenesis occurs simultaneously with________

Answer 29

the closing of the neural tube

Question 30

the mesoderm is partitioned into four distinct zones, what are they

Answer 30

lateral plate mesoderm, intermediate mesoderm, paraxial mesoderm and chordamesoderm

Question 31

the type of mesoderm is determined by …..

Answer 31

relation to the midline

Question 32

paraxial mesoderm differentiates into head and somite. somite differentiates into what 5 things and what do they develop into

Answer 32

sclerotome (cartilage)
syndetome (tendons)
myotome (skeletal muscles)
endotome (endothelial cells and dorsal aorta)
dermatome (dermis, skeletal muscles)

Question 33

what provides the signals that induce the somite lineage

Answer 33

the surrounding tissues: Signalling from lateral plate, notochord (Shh) and ectoderm (Wnt)

Question 34

what are the somite called when they are formed, forming and not yet formed

Answer 34

S1 formed
S0 is being formed
S-1 soon to be formed

Question 35

clock genes are components of what three signalling pathways

Answer 35

notch, fgf and wnt

Question 36

how are clock genes expressed

Answer 36

cyclic genes expression in an oscillatory pattern

Question 37

what direction does the wavefront move

Answer 37

anteriorly - moves from the posterior to anterior

Question 38

what direction are somites formed

Answer 38

anterior to posterior

Question 39

what system works in conjunction with the clock genes

Answer 39

a gradient system - the wavefront

Question 40

what opposing gradients control the wavefront/determination front

Answer 40

: retinoic acid in the anterior decreasing towards posterior, FGF and Wnt higher in the posterior moving anterior – where they intersect is where you get the wave front where the somites will form

Question 41

the intersection of what gradients is the location of somite formation

Answer 41

retinoic acid and fgf&Wnt

Question 42

what ways do the clock genes interact

Answer 42

The clock genes oscillate out of phase with the other clock signalling pathways – and also work in conjunction with each other

Question 43

what types of signalling is the notch pathway

Answer 43

juxtacrine signalling - physical contact between the cells is required

Question 44

briefly describe the notch singalling pathway

Answer 44

physical contact between notch receptor on one cell and ligand on another cell causes cleavage that allow the notch intracellular domain to induce expression of the target gene

Question 45

which end of the axis is retinoic acid highest

Answer 45

the anterior

Question 46

which end of the axis is fgf highest

Answer 46

in the posterior

Question 47

describe the process of somite boundary formation

Answer 47

Notch expressed in the presumptive somite activates Mesp2 in this area, downregulated in the caudal part just being expressed in the rostral (lower/posterior) part -> induces ephrin (ephrinA4) leading to epithelialisation (morphological boundary develops)

Question 48

what are the different timescale in somite formation in 4 vertebrates

Answer 48

In zebrafish = every 30 mins
In chick = every 90 mins
In mouse = every 2.5 hours
in human = every 5-6 hours

Question 49

when is the temporal order/identity of the somite determined

Answer 49

before somitogenesis early in development

Question 50

what confers identity of the segments

Answer 50

Hox genes

Question 51

what experimentation showed when somite identity is determined

Answer 51

transplanting presomitic mesoderm and flipping it, still showed the correct ordering of the development of somites

take some presomitic mesoderm transplant into a different position and you get the same structure it would originally be

Question 52

what causes segmental defects in humans

Answer 52

when somites arent formed in the synchronous fashion at the right times you get a mismatch of somites and vertebrae - caused by mutations in notch and other related signalling pathways

Question 53

whats structures other than the spine are segmented

Answer 53

skull and brain