Question

What would you expect to see if you placed a bead soaked in FGF8 on the segmental plate of a chick embryo?

	A.	formation of somites that lack sclerotome
	B.	inhibition of notch oscillations and an acceleration of somite formation
	C.	sustained notch oscillations and an acceleration of somite formation
	D.	sustained notch oscillations and an inhibition of somite formation

Answer 1

Answer .A

..Grafting FGF8 Beads Leads to Smaller Somite Formation

FGF8-mediated changes in gene expression in the vicinity of the bead, including a repressive effect on Otx2 and an inductive effect on En1, Fgf8 and Wnt1 expression.

bead soaked in FGF8b between the PSM (presomitic meaoderm.) and the lateral mesoderm of 10- to 20-somite stage embryos , the gradient of endogenous FGF8 becomes progressively displaced caudally during tail-bud extension, the bead will remain at a constant axial level, and thus the operation will locally alter the putative FGF8 concentration gradient in the adjacent PSM. the region adjacent to the bead had formed somites. In embryos grafted with beads soaked in FGF8, somites appeared smaller on the operated side, becoming offset from those on the control side over a region which could extend up to 6–7 somites rostral to the bead . Thus, the bead acts on cells located close to the level of the determination front at the time of bead implantation, where the peak of FGFR1 expression is seen , Caudally to the grafted bead, a larger somite is formed and thereafter a normal segmental pattern is observed.