Glial cell states bias the regeneration of neuron types across the newt life cycle

Salamanders have outstanding regenerative abilities, which tend to decline in post-metamorphic life stages. Among various tissues, these amphibians can regenerate the brain from ependymoglia cells, an adult neural stem cell population. Ependymoglia cells are heterogeneous; yet, whether ependymoglia cell diversity underlies variation of regenerative capacity across brain regions and life cycle stages remains poorly studied. Here we present a cell type comparison of regeneration in the pallium (dorsal telencephalon) of pre- and post-metamorphic newts. We found that ependymoglia cells exist in a continuum of cell states ranging from active proliferation to quiescence across life cycle stages, with a deep quiescence state featuring expression of mammalian astrocyte genes. Ependymoglia cell state changes are associated with a slower onset of proliferation and neurogenesis in post-metamorphic animals. Comparisons with developmental and adult neurogenesis reveal that pallial ependymoglia cells retain regional restrictions but can override temporal fate restrictions in response to an injury, producing neurons that are normally born only in early development. We thus find that brain regeneration in newts is not a simple amplification of adult neurogenesis, but a distinct process where the initial molecular state of ependymoglia cells biases the relative proportions of regenerated neuron types. Our findings establish post-metamorphic newts as a system to study how astrocyte-like glial cells can activate a neurogenic program in response to brain injury.