Meeting Abstract
Cnidarian nerve nets are believed to represent the ancestral nervous system that gave rise to centralized nervous systems (CNS), a trait of bilaterians. Determining how neural patterning occurs in the net-like ancestral nervous system will allow us to understand the origin and evolution of patterning mechanisms that gave rise to the CNS. Previous work identified neurogenic programs that act broadly to specify N. vectensis early neurogenesis, yet the mechanisms that specify neural subtypes are poorly understood. Our work aims to improve our understanding of the developmental mechanisms that control neuronal fate. Previous work suggests that the Wnt gradient established oral-aboral (OA) axis of N. vectensis is homologous to the AP axis of bilaterians, and that molecularly defined spatial domains along the OA axis are like those found to pattern the CNS along the AP axis. We hypothesized that spatial domains established by axial patterning cues contribute to neuronal patterning in N. vectensis. To test this, we disrupted the cnidarian aboral domain marker Nvsix3/6. Loss of Nvsix3/6 resulted in loss of aboral neural genes while misexpression of Nvsix3/6 expanded aboral neural gene expression orally. As Nvsix3/6 is known to regulate known Wnt inhibitors we wanted to confirm that Nvsix3/6 promotes aboral neuronal fates directly, independent of suppressing Wnt activity. To test this, we overexpressed Nvsix3/6 in animals treated with the Wnt agonist azenkenpallone. In a high Wnt background, Nvsix3/6 promoted aboral neural gene expression suggesting that the Wnt gradient patterns the OA axis and neural subtypes in parallel. Our data demonstrate a link between Wnt patterning and neuronal specification in cnidarians and bilaterians but suggest that in bilaterians Wnt signaling specifies axial domains, which in turn promote neuronal fate specification.
