# Developmental transformations of Purkinje cells tracked by DNA electrokinetic mobility

## TL;DR

The paper introduces a new method called stereo-tracking to study how Purkinje cells develop in the cerebellum, revealing unexpected structures and developmental patterns.

## Contribution

The novel contribution is the stereo-tracking technique, which uses DNA electrokinetic mobility to label and track cells in 3D progenitor zones during brain development.

## Key findings

- Purkinje cells follow embryonically committed developmental trajectories from progenitor zone subfields to the mature cerebellar cortex.
- A new subcellular structure called 'axon bubbles' was identified on Purkinje cell axon initial segments during late development.
- Stereo-tracking reveals how progenitor zone depth influences neural development and topography in the cerebellum.

## Abstract

Brain development begins with neurogenesis in progenitor zones and ends with expansive, intricately-patterned cellular diversity in the adult brain. We took advantage of bioelectric interactions between DNA and embryonic tissue to perform “stereo-tracking,” a developmental targeting strategy that differentially labels cells at different depths within progenitor zones. This 3D labeling was achieved by delivery of plasmids with distinct electrokinetic mobilities in utero. We applied stereo-tracking with light sheet imaging in the cerebellum and identified that Purkinje cells follow embryonically committed developmental trajectories, linking distinct progenitor zone subfields to the mature topography of the cerebellar cortex. We additionally identified an unexpected subcellular structure on the axon initial segment of Purkinje cells that we termed “axon bubbles.” These structures were revealed by glycosylphosphatidylinositol (GPI)-linked surface labeling and confirmed by electron microscopy. Our findings demonstrate organization of neural progenitor zones in three dimensions, exemplifying the potential of stereo-tracking to uncover new biology within developing systems.

•DNA size and electrokinetic mobility determine electroporation depth in neural tissue•Stereo-tracking uses DNA mobility to label progenitor zones at distinct depths•Axon bubbles appear on Purkinje cell axon initial segments during late development•Progenitor zone subfields map to Purkinje cell topography in the cerebellar cortex

DNA size and electrokinetic mobility determine electroporation depth in neural tissue

Stereo-tracking uses DNA mobility to label progenitor zones at distinct depths

Axon bubbles appear on Purkinje cell axon initial segments during late development

Progenitor zone subfields map to Purkinje cell topography in the cerebellar cortex

Understanding how progenitor zone organization determines the complex topography of mature neural circuits remains challenging, particularly in regions like the cerebellum, where developmental trajectories are intricate. Current methods for tracking neuronal migration typically rely on birthdate labeling or lineage tracing, but lack the ability to simultaneously distinguish cells from different spatial positions within 3D progenitor fields. This limitation hinders our ability to map how spatial organization in embryonic zones translates to the stereotyped patterns observed in adult brain circuitry. A method enabling differential labeling based on progenitor zone depth would provide critical insights into developmental patterning principles.

By harnessing the bioelectric properties of DNA, Brandenburg et al. develop “stereo-tracking,” a method to label neural progenitors based on depth within the ventricular zone. This enables 3D mapping of neuronal development in vivo, uncovering remarkable developmental trajectories and unexpected axonal features in Purkinje cells.