Biology subjects

Newman-Smith, E.

Publications and source records attributed to Newman-Smith, E..

3 recordsLinked to original sources

bioRxiv2025

The dorsal/ventral subdivision of the hindbrain predates the tunicate/vertebrate split

While the CNSs of the chordate sister clades Tunicata and Vertebrata have unmistakable homology, the extent of their conservation is still being uncovered. We report that the hindbrain of the tunicate Ciona, like those of vertebrates, has functionally-distinct dorsal and ventral domains. The Ciona dorsal hindbrain functions as a relay and processing center for peripheral sensory neurons, while in vertebrates the dorsal hindbrain forms the cerebellum. Despite the different fates of dorsal hindbrains in Ciona versus vertebrates, we present evidence from analysis of gene expression, developmental mechanisms, and neural circuit architecture that they share a common origin. While it is generally agreed that the cerebellum evolved in vertebrates, our findings indicate that a dorsally-positioned precursor to the cerebellum has much deeper roots.

evolutionary biology↗

bioRxiv2023

An single oscillating proto-hypothalamic neuron gates taxis behavior in the primitive chordate Ciona

Ciona larvae display a number of behaviors, including negative phototaxis. In negative phototaxis, the larvae first perform short spontaneous rhythmic casting swims. As larvae cast in a light field, their photoreceptors are directionally shaded by an associated pigment cell, providing a phototactic cue. This then evokes an extended negative taxis swim. We report here that the larval forebrain of Ciona has a previously uncharacterized single slow-oscillating inhibitory neuron (neuron cor-assBVIN78) that projects to the midbrain, where it targets key interneurons of the phototaxis circuit known as the photoreceptor relay neurons. The anatomical location, gene expression and oscillation of cor-assBVIN78 suggest homology to oscillating neurons of the vertebrate hypothalamus. Ablation of cor-assBVIN78 results in larvae showing extended phototaxis-like swims, but which occur in the absence of phototactic cues. These results indicate that cor-assBVIN78 has a gating activity on phototaxis by projecting temporally-oscillating inhibition to the photoreceptor relay neurons. However, in intact larvae the frequency of cor-assBVIN78 oscillation does not match that of the rhythmic spontaneous swims, indicating that the troughs in oscillations do not themselves initiate swims, but rather that cor-assBVIN78 may modulate the phototaxis circuit by filtering out low level inputs while restricting them temporally to the troughs in inhibition.

neuroscience↗

bioRxiv2019

Parallel Visual Circuitry in a Basal Chordate

A common CNS architecture is observed in all chordates, from vertebrates to basal chordates like the ascidian Ciona. Currently Ciona stands apart among chordates in having a complete larval CNS connectome. Starting with visuomotor circuits predicted by the Ciona connectome, we used expression maps of neurotransmitter use with behavioral assays and pharmacology to identify two parallel visuomotor circuits that are responsive to different components of visual stimuli. The first circuit is characterized by glutamatergic photoreceptors and responds to the direction of light. These photoreceptors project to cholinergic motor neurons, via two tiers of cholinergic interneurons. The second circuit is responsive to changes in ambient light and mediates an escape response. This circuit starts with novel GABAergic photoreceptors which project to GABAergic interneurons, and then to cholinergic interneurons shared with the first circuit. Our observations on neurotransmitter use and the behavior of larvae lacking photoreceptors indicate the second circuit is disinhibitory.

neuroscience↗