V2 interneuron development is regulated by multiple Delta-Notch signaling

○ Sayumi Okigawa 1, Miho Isoda 1, Maximiliano Suster 3, Hiroshi Kikuta 3, Koichi Kawakami3, &Motoyuki Itoh1,2

1)Nagoya Univ. Grad. Sch. Sci. ,Div. Biol. Soi. ,
2)Nagoya Univ. IAR, 3NIG.

In the spinal cord, V2-interneuron (V2-IN) progenitors develop into excitatory V2a-IN and inhibitory V2b-IN. Previous studies have shown that Notch signaling is involved in the maintenance of V2-IN progenitors (p2) and the V2a/V2b cell fate determination. Notch signaling pathway can be activated by different Notch ligands including Delta family proteins. Delta proteins require Mib -mediated ubiquitination for the effective signal sending to Notch. In zebrafish mib mutants, p2 was decreased and V2a-IN was increased at the expense of the V2b-IN, suggesting Mib-mediated ligand activation is involved in both p2 maintenance and V2 cell-fate choice. However, it remains unclear which Notch receptors and ligands play roles in two functions. To understand the roles of the Notch receptors and ligands in the V2 development, we knocked down the expression of Notch and ligands by morpholinos and used their mutants in zebrafish. We found that p2 was decreased in deltaA;deltaD double mutants and notch1a-knockdown embryos. In contrast, loss of DeltaA and DeltaD did not dramatically affect the V2a/V2b cell fate, whereas notch1a knockdown resulted in an increase in V2a-IN at the expense of V2b-IN. These results suggest that DeltaA and DeltaD play a role cooperatively in the maintenance of V2-IN progenitors thorough activation of Notch1a. On the other hand, Notch1a activation is involved in V2a/V2b cell fate determination, but its activation by DeltaA and DeltaD is not required or sufficient for the fate decision.