7. Early Embryonic Development Flashcards
(25 cards)
When does human embryo development begin?
Fertilization in the fallopian tube (ampulla region)
What occurs during the cleavage stage of embryo development?
Rapid cell divisions converting large zygote into cluster of smaller cells (blastomeres)
What is the purpose of cleavage in embryo development?
Increase nucleus-to-cytoplasm ratio for proper development
What is unique about cleavage in mammals?
Asynchronous divisions resulting in odd cell numbers (2→3→5→etc.)
What characterizes isolecithal eggs?
Even yolk distribution, complete division (holoblastic)
What happens during compaction at the 8-16 cell stage?
Blastomeres adhere tightly to each other, losing distinct boundaries
What adhesion molecule mediates compaction?
E-cadherin
What are the three distinct cell lineages formed during blastocyst development?
- Epiblast (inner cell mass proper)
- Hypoblast (primitive endoderm)
- Trophectoderm
What is the role of the Hippo signaling pathway in early development?
Controls first cell fate decision
Which transcription factors form the core pluripotency network?
- Oct4
- Sox2
- Nanog
What is the significance of the blastocoel formation?
Establishes cavity within the embryo, driven by ionic gradients
When does implantation occur in humans?
Days 8-10
Fill in the blank: Hatching from the zona pellucida occurs at day ______ in humans.
5.5
What prevents polyspermy after fertilization?
Zona pellucida
What is the function of trophoblast cells during hatching?
Produce enzymes (especially plasmin) to facilitate hatching
What is the first step in cell polarization during compaction?
Formation of tight junctions
True or False: The maternal genome undergoes rapid demethylation after fertilization.
False
What are the features of the hypoblast?
Forms from cells on surface of inner cell mass, contributes to extraembryonic membranes
Which transcription factor is specific to the trophectoderm?
Cdx2
What triggers the activation of Yap transcription factor in outer cells?
Lower cell-cell contact, Hippo pathway inactive
What is the result of Oct4 expression suppression in outer cells?
Activation of Cdx2 expression
What are the molecular changes during compaction?
- Reorganization of actin cytoskeleton
- Formation of junctional complexes
- Cell polarization
What happens to the inner cell mass during blastocoel expansion?
Pushed to one side
What is the timing of hatching in mice?
Day 4
