L7 - Gastrulation & Segmentation in vertebrate embryos Flashcards
Which end does the primitive streak start at?
Posterior end
Where does the primitive streak form?
On the surface of the blastula, the stage prior to the blastocyst
The blastocyst undergoes gastrulation which forms three germ layers. What are those three layers?
- Endoderm
- Mesoderm
- Ectoderm
Endoderm:
The innermost layer of cells, which will give rise to the lining of the gut, lungs, liver, and other internal organs
Mesoderm:
The mesoderm is the middle layer of cells, which will give rise to the bones, muscles, heart, kidneys, and other internal structures
Ectoderm:
The outermost layer of cells, which will give rise to the skin, hair, nervous system, and other external structures
The neural tube forms during gastrulation. Where does it derive from?
Ectoderm
What is its function?
It is a hollow tube that runs the length of the embryo, and it gives rise to the entire central nervous system, including the brain and spinal cord
Where are somites derived from?
Mesoderm
What is their function and how do they form?
The paraxial mesoderm that lies alongside the neural tube undergoes segmentation, forming pairs of somites on either side of the neural tube. Involved in the development of the musculoskeletal system, giving rise to the muscles, vertebrae, and ribs
Primitive streak forms upwards. Mesoderm then forms. Mesoderm then forms the somites
Which end do somites start to form pairs at?
Anterior end
What happens when Fibroblast Growth Factors (FGF) are highly expressed in the posterior end?
Leads to a reduction in somite production
How does this work? (FGF reducing somite production at posterior end)
FGF inhibits the segmentation clock. The segmentation clock is a molecular oscillator that regulates the periodic production of somites, downregulating the expression of key clock genes such as Lfng (Lunatic fringe).
What about at the anterior end?
Low FGF allows for increased clock gene expression for genes such as Long and Hes7
