6.2 Chicken Development Flashcards
Equivalents! primitive streak primitive groove hensons node
- primitive streak - blastopore lip
- primitive groove - frog blastopore
- hensons node - frog dorsal blastopore lip (organizer)
Cell futures: epiblast cells that move though
- primitive streak
- henson’s node
- primitive groove
- primitive streak & groove
- primitive streak –> blastocoel
- henson’s node –>head mesenchyme and notochord
- primitive groove –> endoderm and lateral mesoderm
- primitive streak & groove –>get filled up so that primivie streak regresses and shortens
Labelling cells with green fluorescent protein (GFP)
allows the movements of cells through the primitive
streak to be tracked:
- first
-back
-middle
- The first cells migrate forward and become the prechordal plate and notochord
- Cells migrating through the streak further back converge to make somites and notochord
- The cells that migrate through the middle of the streak make intermediate and lateral plate mesoderm
Cell Migration through the primitive streak
Separate in two layers:
• Deep layers join the hypoblasts along the midline displacing hypoblasts and forms endoderm and extra-embryonic membranes.
• Second migrating layer forms a loose layer of cells (Mesoderm).
Primitive streak expresses Fgf8 that repels the cells away from it leading to their movement into the blastocoel.
Neural folds
ectodermal thickenings derived from the flattening of neural plate
Neural plate: formation and future
broad ectodermal thickening on top of the Henson’s node. Neural plate eventually grows and folds over to form a tube called the neural tube
Somites
- develop into mesoderm structures, muscles and connective tissue
- Cells migrating through the streak further back converge to make somites and notochord
Cells migrating in the anterior region of the primitive streak (Henson’s node) form:
- Pharyngeal endoderm (foregut)
- Prechordal plate mesoderm (forms the forebrain and midbrain)
- Chordamesoderm (forms hind brain and notochord).
Induction of Organizer &
-what Inhibits the Primitive Streak
- Posterior Marginal Zone contains cells which are equivalent to Nieukoop Centre.
- Koller’s sickle is equivalent to Nieukoop Center.
- Nodal activity is high in the region where primitive streak is formed.
- In the rest of PMZ cerberus inhibits the formation of primitive streak
Molecular mechanisms of primitive streak formation how does it go straight in the center
- Epiblast cells next to Koller’s sickle activate the Wnt-planar cell polarity pathway.
- If blocked then the mesoderm and endoderm form peripherally rather than centrally.
- Wnt pathway inturn is activated by the fibroblast growth factors (FGFs) synthesized by the hypoblasts.
- If the position of hypoblast is altered so is the orientation of primitive streak.
- hyboblasts make fgf which activates Wnt pathway
Wnt Signalling Pathway: Canonical Pathway (A)
- wnt binds to frizzled which activates Dsh
- Dsh inhibits GSK
- therefore B-cat is acivated
- B-Cat enter nuc binds to gene and trasciption
Wnt-Planar Cell polarity pathway: Non-Canonical (B and C)
Planar Cell polarity (PCP) Wnt Signaling pathway
- Belongs to the category of non-canonical pathway.
- Wnt binds to Frizzled and ROR activate DSH
- DSH activates RhoA-GTPase and Rac.
- Rho-GTPase activates the kinases that phosphorylate the cytoskeletal proteins that alter cell shape and movements.
Specification of chick anterior-posterior axis by
gravity
Rotations of the ovum in the oviduct at 15rph. Centerfugal forces applied to egg. Separate molecules based i density. Yolk rotes and lighter part of yolk in on top and denser darker is on bottom. Therefore blastoderm laughter sure is on the posterior side. Leads to the movement of light yolky region towards the posterior side.
Experiment: Formation of Henson’s node from Koller’s
sickle
Just before gastrulation, cells in the anterior end of Koller’s Sicle (epiblast and middle layer) were labelled with green dye. Cells in the posterior portion of Koller’s Sickle were labelled with red dye. As the cells migrated, the anterior cells formed the Henson’s Node and its notochord derivates. The posterior cells formed the primitive streak.
Experiment: Transplantation of Henson’s node
Transplantation of Henson’s node to epiblast induces primitive streak in new cll gasultaton in new site. Introduces a snd embryo axis. Therefore hensons = organizer in chicks. Hensons node has BMO inhibitors.
