Polymodal sensory perception drives settlement and metamorphosis of Ciona larvae

Sensory cells in tunicates: insights into mechanoreceptor evolution

“…The aATENs occur as two left/right pairs on either side of the dorsal midline (4 total neurons), while the four pATENs appear to lie directly on the midline ( Ryan et al, 2018 ). Although all trunk epidermal neurons contribute to the larval ASNET, like CENs their mechanosensory abilities have never been tested ( Abitua et al, 2015 ; Poncelet et al, 2022 ; Hoyer et al, 2024 ). The three subtypes all have well-developed axons but show different connectivity within the PNS network, hinting at distinct functions.…”

“…Larval metamorphosis in Ciona depends on mechanosensation, as larvae attach to a solid substrate to initiate tail regression and the transition to the post-metamorphic, sessile stage. Mechanical stimulation of the papillae were shown to be sufficient and necessary for triggering metamorphosis, while impairing PN development or function can block metamorphosis ( Wakai et al, 2021 ; Sakamoto et al, 2022 ; Hoyer et al, 2024 ).…”

“…Knocking out Pou4 blocks PN differentiation and metamorphosis ( Sakamoto et al, 2022 ; Johnson et al, 2023b ). Similarly, using chemogenetics to inhibit PN function also inhibits metamorphosis ( Hoyer et al, 2024 ). Candidate effectors of PN functions have also been knocked down/out, resulting in similar loss of metamorphosis.…”

“…However, the exact mechanotransduction channel in the PNs has yet to be identified. Based on Ca 2+ imaging, PNs also respond to chemical cues, suggesting they may be polymodal sensory cells ( Hoyer et al, 2024 ). Certain chemicals can promote or inhibit tunicate settlement and metamorphosis, suggesting that the larvae rely on both biotic and abiotic cues for optimal settlement site selection ( Durante, 1991 ; Rae Flores and Faulkes, 2008 ; Hoyer et al, 2024 ).…”

“…Based on Ca 2+ imaging, PNs also respond to chemical cues, suggesting they may be polymodal sensory cells ( Hoyer et al, 2024 ). Certain chemicals can promote or inhibit tunicate settlement and metamorphosis, suggesting that the larvae rely on both biotic and abiotic cues for optimal settlement site selection ( Durante, 1991 ; Rae Flores and Faulkes, 2008 ; Hoyer et al, 2024 ). Interestingly, the ACCs at the very center of the papillae also respond to mechanical stimuli ( Hoyer et al, 2024 ), which may reflect independent mechanosensory ability, or local communication between PNs and ACCs.…”