University of Cambridge > Talks.cam > Evolution and Development Seminar Series > From apical organs to the bilaterian forebrain: Duplication and divergence of neural circuits in central nervous system evolution

From apical organs to the bilaterian forebrain: Duplication and divergence of neural circuits in central nervous system evolution

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From apical organs to the bilaterian forebrain: Duplication and divergence of neural circuits in central nervous system evolution

Neural circuits, composed of interconnected neurons, represent the basic unit of the nervous system. The highly complex arrangement of cross-talking, serial and parallel circuits in bilaterian brains can only be understood if we gain insight into its evolutionary emergence. In my seminar I will focus on the neural circuits controlling the release of serotonin and melatonin in bilaterian brains. Melatonin, the “hormone of darkness”, is synthesized from serotonin that likewise modulates locomotor activity. To elucidate the evolutionary origin of the serotonin – melatonin-releasing photosensory-secretory circuits, we investigated locomotor control in the swimming ciliated larvae of the marine annelid Platynereis, a new molecular model species for marine zooplankton. We identify a small set of serotonin and melatonin-releasing light-sensitive neurons and show that serotonin and melatonin have opposite effects on ciliary beating frequency, mimicking day and night conditions, respectively. As in vertebrates, the Platynereis larval serotonin – melatonin locomotor control system acts downstream of the circadian clock, which is present in the same cells, and its development critically depends on functional rx (retina homeobox) transcription factor that specifies retina, pineal and hypothalamus, known sites of serotonin and melatonin production in the vertebrates. We propose that the vertebrate circadian control system evolved from a simple serotonin – melatonin system for the circadian control of ciliary locomotion in marine larvae.

This talk is part of the Evolution and Development Seminar Series series.

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