Axes and pattern formation in Chick.pptx

Axes and pattern formation in Chick- Dr.M.Jothimuniyandi- Chick- Axes and pattern formation in Chick-Anterior-Posterior (AP) Axis Formation-Dorsal-Ventral (DV) Axis Formation-Left-Right (LR) Axis Formation-Patterning in the Chick Limb

1. Axes and pattern formation in Chick Dr.M.Jothimuniyandi Assistant Professor

2. The chick (Gallus gallus domesticus ) is a domesticated bird species widely used as a model organism in developmental biology due to its accessibility, ease of observation, and relevance to vertebrate development. Chick embryos develop in eggs, making them an ideal system for studying early embryogenesis, pattern formation, and tissue development without invasive procedures. Chick

3. Structure of Egg of Hen Source: https://www.notesonzoology.com/vertebrates/chick/development-of-chick-with-diagram-vertebrates-chordata-zoology/8645#

4. Axes and pattern formation in the chick embryo are essential processes during early development that define the body plan and establish the spatial organization of tissues and organs. The key axes involved are the anterior-posterior (AP), dorsal-ventral (DV), and left-right (LR) axes. Axes and pattern formation in Chick

5. Key signaling centers : The primitive streak and Hensen’s node are important in establishing the AP axis. Primitive streak: Formation of the primitive streak is one of the earliest events in chick development. It begins at the posterior end of the embryo and elongates towards the anterior, establishing the future body axis. Hensen's node: This is the chick equivalent of the Spemann organizer in amphibians and plays a key role in patterning along the AP axis. It secretes signalling molecules such as Nodal , Wnt , and BMP that help in specifying different regions along this axis. Anterior-Posterior (AP) Axis Formation

6. BMP signaling gradient: The DV axis is patterned by a gradient of Bone Morphogenetic Proteins (BMP). High BMP signaling specifies ventral fates, while low BMP signaling specifies dorsal fates. Noggin and Chordin : These molecules, secreted from Hensen's node and the notochord, inhibit BMP signaling on the dorsal side, ensuring proper DV axis specification. Dorsal-Ventral (DV) Axis Formation

7. Nodal signalling: Nodal, a member of the TGF-β family, plays a central role in establishing left-right asymmetry. It is initially expressed symmetrically but becomes restricted to the left side of the embryo through cilia-driven fluid flow in the Hensen's node. Asymmetric organ development: This signalling leads to the asymmetric placement of organs such as the heart and gut. Other molecules like Lefty and Pitx2 also contribute to the LR axis formation. Left-Right (LR) Axis Formation

8. Zone of Polarizing Activity (ZPA): The ZPA is a key signalling region that influences patterning along the AP axis of the limb. It secretes Sonic hedgehog ( Shh ) , which plays a critical role in specifying the digit identities. Apical Ectodermal Ridge (AER): The AER is essential for outgrowth and patterning along the proximal-distal axis of the limb. It secretes FGF (Fibroblast Growth Factors) that promote limb bud elongation. Dorsal-Ventral patterning of the limb: This is controlled by Wnt7a expression on the dorsal side of the limb bud and repression on the ventral side. Patterning in the Chick Limb

9. Fate maps of Chick blastoderm Source: https://www.notesonzoology.com/vertebrates/chick/development-of-chick-with-diagram-vertebrates-chordata-zoology/8645# Surface of epiblast Diagrammatic section of discoblastula

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