MCDB 240: Embryogenesis

Question 1

define genetic imprinting

Answer 1

certain genes are expressed in a parent-of-origin specific manner. This is independent of classical Mendellian inhereitance.

Question 2

describe an example of an experiment that examined genetic imprinting

Answer 2

if mother and father nuclei were identical, then any two combos -> same embryo

results: two maternal nuclei and two paternal nuclei lead to embryos that don’t develop normally
- need for one maternal and one paternal nuclei for embryos
- only found in mammals

Question 3

describe why is it so important to have paternal and maternal nuclei

Answer 3

b/c both show different methylation patterns

Question 4

define therian and protherian

Answer 4

therian mammals can’t undergo parthenogenesis

protherian (egg-laying) mammals shows no genomic imprinting

Question 5

what is the role of males and females, reproductively

Answer 5

male provides as much resources as possible to embryo; female wants to conserve physiological resources but also wants to preserve offspring

Question 6

describe the fertilization process in humans

Answer 6

1) egg fertilized in ampula of Fallopian tube
2) moves down tube, released in uterus
3) embryo becomes blastocyst (cleavage)
4) blastocyst hatches from ZP, can implant in endometrium in placenta
* *note** humans have transcription in cleavage

Question 7

define anuploid

Answer 7

abnormal number of chromosomes

Question 8

is fertilization successful usually?

Answer 8

no; 50% spontaneous abortion, large # of embryos have abnormal # of chromosomes, problems w/ maternal mitosis

Question 9

describe the development of the embryo in its various stages

Answer 9

embryo divides by mitosis, but NOT in size
1 one-cell stage
2) 2-cell stage: transcription begins
3) 4-cell stage: each cell is still totipotent (each can form whole organism)
4) >10 cells, embryo -> blastocyst, and cells are no longer equivalent/totipotent
5) 16-cell stage (morula), ovum still is in ZP

Question 10

describe the role of the inner cell mass and the outer cell mass; what do they become?

Answer 10

inner cell mass -> fetus
outer cell mass -> placenta

trophoblast: outer layer (cells of placental wall)
inner cell mass: pluripotent, rise to epiblast and hypoblast (no extraembryonic tissues!)

epiblast gives rise to vast majority of the real embryo

Question 11

divisions in a mammalian cell: synchronous or asynchronous?

Answer 11

aynchronous; no well-defined division, no 2-4-8, etc

Question 12

describe the hatching of the blastocyst and the importance of ZP

Answer 12

blastocyst is still w/i ZP until uterus, prevents premature implantation (due to signals secreted on surface)

Question 13

describe how identical twins are produced

Answer 13

atypical hatcting leads to identical twins, when the embryo splits, each receives enough ICM and trophoblast to subsist (most common stage for twins to be produced)

Question 14

describe the process of implantation

Answer 14

embryo interfaces w/ synctiotrophoblast, an epithelial covering of highly vascular embryonic placental villi, which allows for the embryo to implant into the uterine wall for nutrient connection

Question 15

is the mother’s body aware of the difference b/t an unfertilized egg or a developing embryo?

Answer 15

no; only at attachment to blood supply is when pregnancy officially starts

Question 16

describe gastrulation

Answer 16

1) single layer of cells -> 3D structure; surface of desk of cells move inside
2) endoderm first to move in
3) mesoderm moves in
4) outer cells form ectoderm

Question 17

define gastrulation

Answer 17

process of cells of epiblast moving to the primitive streak (what’s this?)

Question 18

describe and define the fate map

Answer 18

fate map: map of future differentiation of certain parts of early embryo into different tissue types

from top to bottom, ventral to dorsal (left to right):

epidermis, nervous system, blood & kidney, somites & heart, notochord, and endoderm

Question 19

describe the differentiation of the inner cells mass

Answer 19

inner cell mass to epiblast and hypoblast

epiblast to amnion or embryonic epiblast

embryonic epiblast to ectoderm, mesoderm, and endoderm

hypoblast to yolk sac

Question 20

define what do the ectoderm, mesoderm, and endoderm give rise to

Answer 20

ectoderm: nervous system and skin
mesoderm: muscle
endoderm: gut, related structures

Question 21

define spina bifida

Answer 21

incomplete closure of the neural folds, prevented w folic acid, quite devastating

Question 22

what’s unique about transcription during cleavage?

Answer 22

only observed in mammals

Question 23

does everything develop at once?

Answer 23

no; different regions on disc will give rise to different structures in later developmental stages

Question 24

is there a consistent pattern in gastrulation?

Answer 24

in fact, yes; there is a consistent lineage that allows us to make a statement tat certain cells will differentiate into something

Question 25

if we damage a part of the fate map, what happens?

Answer 25

damage certain regions of embryo - altering ability of embryo to give rise to certain structures; some embryos good at recovering, others not

Question 26

describe the Dolly experiment

Answer 26

1) donor cell nucleus was removed from udder, fused w/ enucleated egg cell
2) cell stimulated to divide via electric shock -> blastocyst

conclusion: we can take somatic cell nucleus and put it into an egg, forcing it to reprogram

Question 27

how did the Dolly experiment work; what was the role of epigenetics?

Answer 27

the nucleus environment alters the DNA via methylation, as the genetic info is relatively preserved b/t differentiated and undifferentiated; thus, the somatic cell nucleus was returned to totipotency

Question 28

define cloning in sea urchins

Answer 28

fragmenting sea urchins blastocysts at a 4-cell stage leads to 4 blastomeres with identical larval stages

Question 29

define chimera

Answer 29

inner cell mass of one primate blastocyst into another blastocyst -> chimera

Question 30

question: can somatic cell nucleus transfers occur in primates?

Answer 30

theoretically, yes; but haven’t happened yet exactly as the Dolly experiment

Question 31

rhesus monkey experiment w/ totipotent nuclei: describe it and its significance

Answer 31

same methods of manipulation, but in the monkey cells, we got donor cells from 8th cell embryo (totipotent), which we already know gives rise to full individual.

key difference: same manipulation, but no reprogramming.

results: we got identical monkeys, so no extensive reprogramming, but we know that the procedure works

Question 32

second experiment w/ somatic cell nucleus:

Answer 32

w/ a fully differentiated somatic cell nucleus, we tried to do the same thing.

results: failure, BUT able to generate embryos w/ ICM that can behave like an embryo, that when challenged, gives rise to differentiated cell lines from all germ layers.

Question 33

third experiment w/ ICM injection:

Answer 33

cells from ICM injected to embryos of normal monkeys, but was unsuccessful DESPITE success in mice.

Question 34

fourth experiment w/ two entire cell embryos combined?

Answer 34

failed in primates; in other animals, we would only get chimeras (mix of two geneotypes at fusion)