Diurnal rhythms in neurexins transcripts and inhibitory/excitatory synapse scaffold proteins in the biological clock.
The neurexin genes (NRXN1/2/3) encode two families (α and β) of highly polymorphic presynaptic proteins that are involved in excitatory/inhibitory synaptic balance. Recent studies indicate that neuronal activation and memory formation affect NRXN1/2/3α expression and alternative splicing at splice sites 3 and 4 (SS#3/SS#4). Neurons in the biological clock residing in the suprachiasmatic nuclei of the hypothalamus (SCN) act as self-sustained oscillators, generating rhythms in gene expression and electrical activity, to entrain circadian bodily rhythms to the 24 hours day/night cycles. Cell autonomous oscillations in NRXN1/2/3α expression and SS#3/SS#4 exons splicing and their links to rhythms in excitatory/inhibitory synaptic balance in the circadian clock were explored. NRXN1/2/3α expression and SS#3/SS#4 splicing, levels of neurexin-2α and the synaptic scaffolding proteins PSD-95 and gephyrin (representing excitatory and inhibitory synapses, respectively) were studied in mRNA and protein extracts obtained from SCN of C3H/J mice at different times of the 24 hours day/night cycle. Further studies explored the circadian oscillations in these components and causality relationships in immortalized rat SCN2.2 cells. Diurnal rhythms in mNRXN1α and mNRXN2α transcription, SS#3/SS#4 exon-inclusion and PSD-95 gephyrin and neurexin-2α levels were found in the SCN in vivo. No such rhythms were found with mNRXN3α. SCN2.2 cells also exhibited autonomous circadian rhythms in rNRXN1/2 expression SS#3/SS#4 exon inclusion and PSD-95, gephyrin and neurexin-2α levels. rNRXN3α and rNRXN1/2β were not expressed. Causal relationships were demonstrated, by use of specific siRNAs, between rNRXN2α SS#3 exon included transcripts and gephyrin levels in the SCN2.2 cells. These results show for the first time dynamic, cell autonomous, diurnal rhythms in expression and splicing of NRXN1/2 and subsequent effects on the expression of neurexin-2α and postsynaptic scaffolding proteins in SCN across the 24-h cycle. NRXNs gene transcripts may have a role in coupling the circadian clock to diurnal rhythms in excitatory/inhibitory synaptic balance.
Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
Mika
M
Shapiro-Reznik
Anje
A
Jilg
Hadas
H
Lerner
David J
DJ
Earnest
Nava
N
Zisapel
D017398:Alternative Splicing; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000235:genetics*; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002492:Central Nervous System Depressants / Q000494:pharmacology; D002940:Circadian Rhythm / Q000187:drug effects / Q000235:genetics*; D000076122:Disks Large Homolog 4 Protein; D051528:Guanylate Kinases / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D019006:Neural Cell Adhesion Molecules / Q000235:genetics* / Q000378:metabolism; D056950:Period Circadian Proteins / Q000235:genetics; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000378:metabolism; D013569:Synapses / Q000378:metabolism*; D014158:Transcription, Genetic
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D002492:Central Nervous System Depressants; D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D008565:Membrane Proteins; D019006:Neural Cell Adhesion Molecules; C527193:Nrxn1 protein, mouse; D056950:Period Circadian Proteins; D012333:RNA, Messenger; C073441:gephyrin; D051528:Guanylate Kinases; D008550:Melatonin