Altered neurotransmission and anxiogenic response in CircTulp4 KO mice

GIUSTI, SEBASTIÁN A.; NATALIA S. PINO; PANNUNZIO, CAMILA; OGANDO, M; ARMANDO, NG; MERINO, FLORENCIA L.; MARIN-BURGIN, A; HÖLTER, SABINE; GIESERT, FLORIAN; WOLFGANG WURST; REFOJO, D

Cold Spring Harbor

Congreso; 2022 Cold Spring Harbor meeting: Regulatory & Non-coding RNAs; 2022

Cold Spring Harbor Laboratory

Circular RNAs are highly expressed in the brain. However, with the exception of CDR1as, which lacks a co-transcribed linear isoform, no genetic model deficient in a circRNA in the brain has yet been described in mammals, plausibly due to the technical difficulties that mouse genetics impose to generate circRNA KO mice.We previously showed that circTulp4 is one of the most highly expressed circRNAs in the brain and is particularly abundant in synapses. To investigate its role in vivo we applied CRISPR/Cas9 editing to generate a circTulp4-specific KO mouse line. CircTulp4 KO mice evidenced unaffected mendelian ratios and anatomically normal brains.Orchestrating behavior is the ultimate goal of neuronal processing in the CNS. However due to the multiplicity of behavioral repertoires in mammals, a thorough exploration of behavioral traits is difficult to assess. To circumvent this problem we took advantage of the German Mouse Clinic (GMC) phenotyping facility and studied a multiplicity of physiological parameters and behavioral features (motor skills, learning and memory, exploratory behavior, stress reactivity, emotional states, sensorimotor gating, cognitive flexibility, reward and social behavior, etc). CircTulp4 KO mice consistently displayed an increased sensitivity to stressful and anxiogenic stimuli. Synaptic defects might stem at the bases of this altered behavior. In fact, CircTulp4-deficient neurons displayed a mild, though significant alteration in synapse number, and a mass spectrometry analysis of synaptosomal fractions showed significant changes in key post-synaptic proteins involved in excitatory neurotransmission. Yet the intimate mechanisms behind remained unclear. To answer this question, we performed electrophysiological experiments in neuronal cultures and hippocampal slices from circTulp4 KO mice and in utero-electroporated WT mice. These studies consistently showed a strong decrease in the frequency of miniature excitatory postsynaptic currents (EPSCs) which specifically reports the activity of glutamatergic AMPA receptors in the synapse. These effects are independent of the translation of the ORF encoded in the circRNA and the potential mechanistic role of specific interactors are currently under validation.Thus, these data indicate that circTulp4 exerts very precise actions on excitatory neurotransmission, controlling the recruitment of AMPA-receptors in the post-synapse and orchestrating emotional behavior.