Lecture 7: Gastrulation Flashcards
What are the 5 different cell and tissue movements during development?
Intercalation: two layers interlace
Epiboly: cells spreading and flattening out to allow more coverage of more surface area
Invagination: tissue folding inward or outward
Involution: cells move over a lip of tissue into the interior
Convergent extension: cell layers thin out and extend out to cover mor e surface area
What happens before Gastrulation?
As embryo sinks into endometrium —. Delaminating and implantation occurs
Explain the process of Forming Epiblast and Hypoblast.
Forms Epiblast & Hypoblast
Epiblast —> columnar cells that form embryo proper
Hypoblast —> cuboidal cells below Epiblast that contribute to development of yolk sac
Explain the process of the sperm-egg becoming Bilaminar.
ICM cells of two types:
Nanog —> induce inner cells to become Epiblasts
Gate-6 —> induces inner cells to become Hypoblasts
- after 2 weeks, embryo consists of 2 layers of Epiblast cells and a Hypoblast visceral and parietal endoderm
What is the Time Inside - Time Outside Hypothesis?
Early cells entering inner cell mass (secrete FGF4 to induce later cells to express Gata-6; which increases adhesive properties and mobility —> creating Hypoblasts) —> Nanog —> perpetuation of pluripotency (make up different structures)—> epiblast
State the Cell lineages in the human embryo
What is the process of Gastrulation?
- forms the ectoderm, mesoderm, and endoderm from epiblast cells —> referred to as Gastrula
Why is Gastrulation so important?
- generates the basic body plan of embryo
- involved in movements, shape changes, and defined cell divisions
- acts as the first phase for dramatic changes in developments where cells, axes, and embryo is organized and connected
What are the structures formed at the Initiation of Gastrulation?
- Primitive Streak starts forming from caudal to cranial of the bilaminar disks
- Primitive Node forms at the anterior end of primitive streak
- Primitive Pit forms within the primitive node; extends to embryo as the Primitive Groove
- Primitive Pit (Hensen’s node) forms anterior to primitive groove; becoming thicker.
What is the purpose of Inducer tissue and Responder Tissue?
Inducer tissue influences responder tissue by telling responder on how to specifically change gene
What is the process of Induction of the Primitive Streak?
Wnt —> AVE produces nodal inhibitors —> induces primitive streak —> node expresses Noggin and Chordin when done development to stop development
Describe tissue formation following Gastrulation.
Timing of tissue formation is important:
What is Epithelial-mesenchymal transformation (EMT)?
- first in columnar shape (within epiblast) starts forming as “bottle-like” cells as they move through primitive streak
- EMT is complete b when “bottle-like” cells separate from epiblast layer to become mesenchymal cells
How does EMT expression occur?
Cells within primitive streak synthesize FGF, which controls movement by down regulation of E-cadherin expression, promoting EMT.
- Transition from E-Cadherin to N-cadherin facilitaltes loss of adhesions between cells to slip away
What are the 3 regions of the Mesoderm?
- Paraxial mesoderm (closer to endoderm) —> YELLOW
- Intermediate mesoderm —> GREEN
- Lateral Plate mesoderm (closer to ectodoerm) —> RED
