Early Development Flashcards
Exam 1
Cleavage pattern: Complete
Division in animal and vegetal pole
Cleavage pattern: Incomplete
No division in either pole (animal or vegetal)
Cleavage pattern: Superficial
Division only in animal pole
Know the role of the yolk in cleavage patterns. Explain how rapid cell division is achieved.
Yolk factors –> energy supplied by egg for embryo development
- Synchronous (early)
- No G1/G2
- Maternal factors
- Asynchronous (later)
- There is some G1/G2
Animal vs vegetal poles
Animal pole: Pole of the egg where [yolk] is relatively low
Vegetal pole:Pole containing the yolk
Cytoplasmic determinants can be …. (2) Where can they be found (3 each)
- Maternal mRNA (egg & zygote)
(Differential degradation, cytoskeleton localization, local entrapment) - Protein level
(Differential degradation, translation, and cytoskeleton localization)
Define amniote egg.
Egg with extra-embryotic membranes that provide nourishment and environmental needs to developing embryo
Ex: birds
Define yolk sac.
Grows over the yolk and provides nutrition.
Define chorion.
Extra-embryonic membrane essential for gas exchange
Define allantois.
Stores urinary wastes and mediates gas exchange
Define amnion.
“water sac” AKA membrane protecting embryo with surrounding amniotic fluid.
Define placenta.
Organ that serves the interface between fetal and material circulations
Gastrulation: Ingression + example
Movement of cells from surface layer into interior of embryo
EX: sea urchin mesoderm
Gastrulation: Invagination + example
infolding of epithelium of cells
EX: sea urchin endoderm
Gastrulation: Involution + example
tissue moving inside along the outer layer
ex: frog mesoderm
Gastrulation: Epiboly + example
movement of epithelial sheets that spread as a unit to enclose embryo FROM THE OUTSIDE
EX: sea urchin ectoderm
Gastrulation: Convergent Extension + example
Movement of lateral cells towards midline to drive anterior-posterior axis elongation
Ex: ectoderm and mesoderm of mammals
Which statement is true about genetic control of cell division during cleavage in most species?
A. Expression of embryonic genes begins as soon as fertilization occurs and material gene products have little effect beyond this point.
B. The zygotic genome is highly active beginning with the first cleavage division, making it the primary determinant of division patterns.
C. Early patterns of cell division are directed by products of maternal genes and later directed products of by embryonic genes.
D. Maternal proteins are important in regulating cell activities only until fertilization occurs.
C. Early patterns of cell division are directed by products of maternal genes and later directed products of by embryonic genes.
Which term best describes ingression?
A. An individual cell undergoes a change that allows them to migrate (the epithelial-mesenchymal transition).
B. A region of epithelial tissue folds inward to form a dent in the surface of the embryo.
C. Two layers of cells separate, forming a space in the region between them.
D. Cells from the outer epithelial layer move along the surface to an opening and then spread below the epithelial layer.
A. An individual cell undergoes a change that allows them to migrate (the epithelial-mesenchymal transition).
What, if any, regulatory transcription factors are necessary for cells of a mammalian inner cell mass to demonstrate pluripotency?
A. No regulatory transcription factors are necessary as regulation is provided by the cell niche.
B. Oct4 and Sox2 only
C. Sox2 and Nanog only
D. Oct 4, Sox2, and Nanog
D. Oct 4, Sox2, and Nanog
What is the trophectoderm (Trophoblast)?
External cells of the early mammalian embryo (i.e., the morula and the blastocyst) that will bind to the uterus
Describe the formation of the trophectoderm and inner cell mass.
- Morula (older blastula) develops outer and inner cells
- Outer cells = apical side, stuck tightly w/ E-cadherin –> later become trophectoderm
- Inner cells = lumen express Oct4, activates pluripotency genes –> form inner cell mass
Trophectoderm vs inner cell mass
outer cells for ectoderm vs inner cells that form embryo
Role of Oct4, Nanog, Sox2, Klf4 in development process.
stem cell gene regulatory network
4 genes in the stem cell gene regulatory network
- Oct4
- Sox2
- Nanog
- Klf4
Explain the difference between diploblast and triploblast.
-
Diploblast: “Two-layer” animals; they possess endoderm and ectoderm
Triploblast: Animals with three germ layers
Describe the mechanism behind the decision between the epiblast and primitive endoderm/hypoblast at the blastocyst stage
(key terms: Nanog, Fgf signaling and cell sorting)
Epiblast: Cells expressing Nanog
PreE: Cells recievinf fgf signaling AKA inhibits Nanog
Both seperate through cell sorting to form proper layer formation
Which extraembryonic tissue do monozygotic twinning share depending on the timing of separation?
Before trophoblast formation
Each own chorion and amnion
Which extraembryonic tissue do monozygotic twinning share depending on the timing of separation?
After trophoblast formation but before amnion formation
Each own amniotic sacs but one chorion
Which extraembryonic tissue do monozygotic twinning share depending on the timing of separation?
After amnion formation
One amniotic sac and one chorion
Give examples of a diploblast and triphoblast
Diploblast: Jellyfish
Triphoblast: Frog
Describe the cell/tissue movement happening during gastrulation in Xenopus (6)
- Epiboly of the animal cap over entire embryo
2.Vegetal Rotation - Bottle cells initiate invagination
- Forms dorsal blastopore lip
- Involution of vegetal cells
- Closure of the blastopore by onvergent extension
What is vegetal rotation?
internal rearrangement, pushing prospective mesodermal cells toward the future dorsal side
What is the blastopore?
Invagination point where gastrulation begins
What is the Involuting marginal zone?
Cells near equator that involute during Xenopus gastrulation.
FIRST: head mesoderm and pharyngeal endoderm
NEXT: future notochord cells
Epiblast vs Hypoblast
Epiblast: The outer layer of the epibolizing blastoderm
Hypoblast: The inner layer of the epibolizing blastoderm
What is the archenteron?
Primitive gut
What is the yolk plug?
Cells that remain exposed on the vegetal surface surrounded by the blastopore following gastrulation
Mesenchyme is the ….
Head mesoderm
Notochord
gives rigidity and is a signaling center
What is the term for the slit-like structure formed by the invagination of Xenopus epithelium as mesoderm and endoderm move deeper into the embryo?
A. The archenteron
B. The gray crescent
C. The blastopore
D. The chordamesoderm
C. The blastopore
Which structure is generated by invaginating cells from the node in humans?
A. Gut
B. Neural crest
C. Notochord
D. Neural plate
C. Notochord
Which structure is essential for the movement of cells during gastrulation in birds and mammals but not in amphibians?
A. The primitive streak
B. The area pellucida
C. The dorsal blastopore lip
A. The primitive streak
Germ Layer Specification: Endoderm
Via maternal cytoplasmic determinants
Nodal
↑
VegT –> Sox17
↑
VegT mRNA
Germ Layer Specification: Mesoderm
Nodal + Smad 2–> activates zygotic genes with VegT –> form mesoderm
Germ Layer Specification: Ectoderm
Cells without any signaling
Dorsal blastopore lip mechanism
Wnt signaling:
Wnt
↓ (binds)
Frizzled
↓(Recruits)
Dishevelled (Dsh)
┴ (Recruits)
GSK3
┴ (Phosphorylates, target for degration)
B-catenin
↓ (To nucleus)
Activates transcription w/ TCF/Lef
Dsh on one side bc on vegetal pole, where B-catenin is activated. Cortical rotation changes position
What can the dorsal blastopore induce?
A second axis
Describe the cell/tissue movement happening during gastrulation in human (5)
- Primitive streak forms midline of epiblast
- Primitive groove AKA depression
- Cells ingress through groove (forms mesoderm and endoderm)
- Groove becomes Node (contains notochord)
- Convergent extension
What does the primitive endoderm form?
Hypoblast AKA mesoderm and endoderm
Give the function of the protein coded by the gene and their role in developmental processes: Chordin, noggin
Organizer genes/proteins involved in the dorsal blastopore lip formation
What is the primitive streak? Homologous to the…
The first sign of gastrulation in amniotes
Homologous to the amphibian blastopore.
How are segment identities established along the anterio-posterior axis in Drosophila? Draw a diagram with the different gene families.
Maternal Effect Genes (A vs. P)
↓
Gap Genes
↓ ↓ (Homeotic genes)
Pair Rule
↓
Segment Polarity –> Homeotic genes
Gap genes definition + Phenotype
Lack of large regions
Phenotype: Absence of broad body regions
Pair-rule genes definition + Phenotype
Lack portions of every other segment. 7 segments
Phenotype: lack portions of every other segment.
Segment polarity genes definition + Phenotype
Parts of every segment lost
Phenotype: Defects in eery segment
Homoeotic genes definition + Phenotype
Mutations of homeotic selector genes. Can be loss of function (Ubx genes manipulation) or gain of function (overexpression)
Phenotype: one structure is replaced by another (as where an antenna is replaced by a leg).
Maternal effect genes + example
Mother genes (mRNA or proteins) found in the egg that determine anterior/posterior positioning
Ex; Bicoid and caudal mRNA/ protein
Describe how Bicoid and Caudal morphogen gradient is established in Drosophila.
Bicoid mRNA stabilized, creates Bicoid protien and inhibit Caudal mRNA and therefore Caudal protein
[Bicoid] bigger anterior (mRNA/protein)
[Caudal] mRNA THE SAME
[Caudal] protein bigger posteriorly
Describe the co-linearity of the homeotic genes/hox genes, how it influences their expression and its conservation between species
relationship between the order of Hox genes and the order expressed in an embryo
