Final Exam - Mouse Development

Question 1

Fertilization

Answer 1

• the fusion of sperm and egg to form the zygote

- occurs in the oviduct

Question 2

Cleavage

Answer 2

• a series of slow (in mouse every 12 hours) cell divisions without cell growth that occurs after fertilization and divides the embryo up into a number of small cells called blastomeres
• two-cell, four-cell, eight-cell, compacted morula, blastocyst

Question 3

Blastomere compaction

Answer 3

• difference from frogs
• happens at the 8-cell stage
• asymmetry within embryo is established
• cells become polarized
• cells have smooth membranes inside the embryo
• outer membranes become covered with microvilli to increase surface area of cell-cell contact

Question 4

Morula

Answer 4

• the very early stage in a mammalian embryo when cleavage has resulted in a solid ball of cells
• forms at the 8-cell stage (characterized by blastomere compaction)
• has 32 cells with two distinct groups: trophectoderm and inner cell mass (ICM)

Question 5

Trophectoderm

Answer 5

• a group of outer cells of the morula
• the outer layer of cells (20 cells) of the early mammalian embryo
• it gives rise to extra-embryonic structures and tissues such as the placenta

Question 6

Inner cell mass (ICM)

Answer 6

• a group of inner cells of the morula
• a discrete mass of cells in the blastocyst of the early mammalian embryo which is derived from the inner cells of the morula, and which will give rise to the embryo proper and some extra-embryonic membranes

Question 7

Blastocyst

Answer 7

• the stage of a mammalian embryo that corresponds in form to the blastula stage of other animal embryos , and is the stage at which the embryo implants in the uterine wall
• is formed as trophectoderm pumps in fluid to create a blastocoel (inner cell mass becomes created on one end)

Question 8

Primitive endoderm

Answer 8

-in mammalian embryos, that part of the inner cell mass that contributes to extra-embryonic membranes

Question 9

Primitive endoderm

Answer 9

• in mammalian embryos, that part of the inner cell mass that contributes to extra-embryonic membranes
• later becomes parietal endoderm, a sticky layer of protective cells

Question 10

Epiblast/primitive ectoderm

Answer 10

• in mouse and chick embryos, a group of cells within the blastocyst or blastoderm, respectively, that gives rise to the embryo proper
• in the mouse, it develops from cells of the inner cell mass

Question 11

Placenta

Answer 11

• a structure that forms in the uterine wall at which the blood systems of mother and embryo form an interface with each other
• mammalian embryos (with the exception of the monotremes like egg-laying platypus and echidnas) are nourished by the mother by the passage of nutrients through the placenta
• formed by trophectoderm (its normal fate), which consists in part of trophoblast giant cells

Question 12

Parietal endoderm

Answer 12

• starts out as primitive endoderm which then becomes the parietal endoderm
• is a sticky layer of protective cells

Question 13

Visceral endoderm

Answer 13

• tissue derived from the primitive endoderm that develops on the surface of the egg cylinder in the mammalian blastocyst
• Lies next to epiblast (embryo)
• Has an early developmental function

Question 14

Trophoblast giant cells

Answer 14

• found in placenta
• Are specialized cells that endoreduplicate (many copies of its genome in a single nucleus, make more copies of DNA to make more genes) = production machines
• Invade the uterine wall and mediate the interface between vascular systems of the mother and embryo

Question 15

Primitive streak

Answer 15

• gastrulation initiates with the formation of the primitive streak
• the site of gastrulation in avian and mammalian embryos and the forerunner of the antero-posterior axis
• it is a strip of ingressing cells that extends into the epiblast from the posterior margin
• epiblast cells move through the streak into the interior of the embryo to form mesoderm and endoderm

Question 16

Mouse (Mus musculus) embryos

Answer 16

• Embryos are very small (approx. 1/10 of a mm)

- Implantation, placenta development

Question 17

Embryonic stem cells (ES cells)

Answer 17

• pluripotent cells derived from the inner cell mass of a mammalian embryo, most commonly mouse embryo, that can be indefinitely maintained in culture
• when injected into another blastocyst, they combine with the inner cell mass and can potentially contribute to all the tissues of the embryo
• can stay in the stem cell fate, grow and replicate
• can be used to genetically manipulate transgenic (chimeric) animals
• The modified ES cells can be injected back into the blastocyst and can contribute to the inner cell mass
• This creates chimeric embryos (a mix of donor and host tissue)
• If these cells contribute to the germ line they will be inherited by the next generation
• These can be called clones

Question 18

Transgenic/chimeric animals

Answer 18

• an organism whose genetic make-up is the result of the deliberate introduction of new DNA
• ex) new genes, genes with specific mutations, DNAs that cause the inactivation of specific genes
• term is also used to describe the various genetic engineering techniques that can be used to accomplish this
• becomes a clone
• Can be manipulated (such that their genomes can be modified) so new genes are introduced=transgenes
• Genes could be manipulated such that genes could be knocked out
• chimeric embryo=a mix of donor and host tissue, a clone

Question 19

Transgenes

Answer 19

• trans=coming from an external source
• a gene, sometimes from another organism, that has been introduced into a cell or organism by genetic engineering techniques

Question 20

Genetic “knock-outs”

Answer 20

• the complete and permanent inactivation or deletion of a particular gene in an organism by means of genetic manipulation
• genes can be deleted and/or removed

Question 21

What are the stages undergone by the early embryo?

Answer 21

1) cleavage
2) blastomere compaction
3) morula (8-cell stage)
4) morula (32-cell stage with trophectoderm and inner cell mass)
5) blastocyst

Question 22

Drug-resistance selection

Answer 22

-Drug-resistance selection is used for selection of ES (embryonic stem) cells that have been modified

Question 23

Cre recombinase/loxP

Answer 23

• Cre recombination through loxP sites
• Genes that are to be deleted are flanked by loxP sites
• These are acted upon by cre-recombinase which expressed under specific enhancers/promoters
• This was used to knockout genes
• Promoters can be tissue and time specific such that gene knockout can be targeted to specific time in development

Question 24

Crisper/Cas9

Answer 24

• Cas 9 is a nuclease (endonuclease) derived from bacteria
• These nucleases can cleave DNA
• Guide RNA encoded by a Crisper array
• These target the nuclease to specific sites
• Cleavage is then repaired by the cell’s normal DNA repair mechanisms
• This is used by researchers to incorporate custom DNA sequences into the genome

Question 25

Implantation

Answer 25

• Implantation occurs half a day later (day 5)

- The blastocyst attaches to the uterine wall

Question 26

What are the stages undergone by the early embryo?

Answer 26

1) cleavage
2) blastomere compaction
3) morula (8-cell stage)
4) morula (32-cell stage with trophectoderm and inner cell mass)
5) blastocyst: Pre-implantation, Implantation and Post-implantation
6) primitive endoderm
7) visceral endoderm
8) epiblast (embryo that is cup-shaped and has 1000 cells)
9) primitive streak formation
10) gastrulation

Question 27

Post-implantation

Answer 27

• The trophectoderm gives rise to placenta (its normal fate) which consist in part of trophoblast giant cells
• Are specialized cells that endoreduplicate (many copies of its genome in a single nucleus, mak more copies of DNA to make more genes) = production machines
• Invade the uterine wall and mediate the interface between vascular systems of the mother and embryo

Question 28

Epiblast

Answer 28

• cup shaped embryo

- 1000 cells

Question 29

Senescence

Answer 29

• cells that divide and will eventually die
• ex) normal skin cells
• the impairment of function associated with aging

Question 30

Insertional mutagenesis

Answer 30

• Homologous recombination is used to disrupt the function of a gene
• Drug-resistance selection is used for selection of ES (embryonic stem) cells that have been modified

Question 31

Maternal determinants

Answer 31

maternal determinants are not as important in the mouse embryo