Radial Astroglia Form Novel Structures to Engulf Neuronal Cell Bodies during Zebrafish Optic Tectum Development

Abstract
During development, networks between neurons must be established and maintained, with unnecessary
neurons requiring timely removal. The contributions of astroglia to these developmental processes are only just
being explored. The zebrafish optic tectum (OT), the major visual processing center, is a common model for
investigating neural circuitry. Using in vivo, time-lapse imaging of Tg(slc1a3b:myrGFP-P2A-H2AmCherry)
transgenic larvae, I observed OT radial astroglia extending projections from their pial processes basally
towards the ventricular zone. These small processes often formed large spherical structures, measuring
approximately 5 micrometers in diameter and lasting up to 10 hours before dissipating. Currently, the identity
and function of these projections are unclear. Using molecular characterization, we have begun assaying the
nature of this developmental phenomenon. From my preliminary data, at least some of the spherical structures
contain dying neurons. I also observe these structures interacting with microglial processes, with microglial
processes invading the structures to remove their contents (i.e. dying neurons). Due to their shape, size,
movement, and engulfment of other cell nuclei, I tentatively dub these structures “scyllate heads”, in reference
to the multi-headed Odyssean figure Scylla. Due to an observed association with microglia, I hypothesize that
scyllate heads sequester developmental debris, including exuberant neurons, for later phagocytosis by
professional phagocytes. Here I propose a project to describe scyllate heads, discern their function in OT
development, and explore their interactions with other cell types.

Grant Number: 5F31EY035961-02
NIH Institute/Center: NIH
Principal Investigator: Heather Barber