A Dynamic Splicing Program Ensures Proper Synaptic Connections in the Developing Cerebellum

Abstract

Highlights d A dynamic splicing program shapes the cerebellar transcriptome during development d Autism-spectrum-disorder-related genes exhibit developmental splicing regulation d Sam68 establishes a splicing signature that ensures proper synaptic maturation d Sam68 regulates genes associated with autism spectrum disorder and social behavior

Sam68 splicing regulation contributes to motor unit establishment in the postnatal skeletal muscle

“…Sam68 is well known for its role in the regulation of alternative splicing ( Frisone et al, 2015 ). Several studies have identified Sam68 target genes that are involved in synaptic transmission, metabolism, and apoptosis ( Paronetto et al, 2007 , 2011 ; Iijima et al, 2011 ; La Rosa et al, 2016 ; Farini et al, 2020 ), which may underlie the motor neuron defects observed in our study. Changes in the splicing outcome of the tomosyn-2 gene ( Stxbp5l ) are particularly relevant for the phenotype.…”

“…Previous work indicated that Sam68 is highly expressed in the motor neurons of the spinal cord ( Pagliarini et al, 2015 ), suggesting an important function of this protein in these cells. Sam68 is known to modulate splicing of several genes encoding for synaptic proteins ( Iijima et al, 2011 ; Danilenko et al, 2017 ; Witte et al, 2019 ; Farini et al, 2020 ). To test whether Sam68 regulates splicing of such synaptic genes in the spinal cord, we selected splicing events from several RNA-sequencing and microarray experiments carried out in Sam68-depleted mouse tissues or cells ( Ehrmann et al, 2008 ; Chawla et al, 2009 ; Iijima et al, 2011 ; Paronetto et al, 2011 ; La Rosa et al, 2016 ; Danilenko et al, 2017 ; Witte et al, 2019 ; Farini et al, 2020 ).…”

“…Sam68 ablation also affected the alternative inclusion of exon 22 of the syntaxin-binding protein 5-like ( Stxbp5l , alternatively known as tomosyn-2 ) gene ( Fig 1B ), encoding a protein required for normal motor performance and involved in neurotransmission at motor endplates ( Geerts et al, 2015 ). Furthermore, we investigated the regulation of postsynaptic scaffolding molecules that are potential targets of Sam68 and play a central role in synaptic functions or glutamatergic synapses ( Witte et al, 2019 ; Farini et al, 2020 ). Among them, we selected either of the GABAergic post-synaptic proteins collybistin ( Arhgef9 ), gephyrin ( Gphn ), and densin-180 ( Lrrc7 ), the subunits of the glutaminergic AMPA receptor (AMPAR) Gria2 and Gria3 , which mediates the vast majority of fast synaptic transmission in the central nervous system ( Li et al, 2016 ), and of the ATP-sensitive potassium channel SUR2, encoded by the Abcc9 gene (Nichols, 2016) .…”

“…In particular, inclusion of exon 10a in Arhgef9 ( Fig 1C ), of exon 10 in Gphn ( Fig 1D ), and of exon 24 in Lrrc7 ( Fig 1E ) was significantly increased in Sam68 −/− mice. Furthermore, RT-qPCR analysis revealed an increase in the retention of intron 11 of Gria2 , intron 12 of Gria3 , intron 16 of Ncam2 , and of intron 5 of Abcc9 transcripts in Sam68 −/− mice compared with wild-type littermates ( Fig 1F–I ), events that are likely associated with premature termination of the transcripts and reduction of the functional proteins ( Farini et al, 2020 ).…”

“…Moreover, Sam68 −/− male mice are infertile ( Paronetto et al, 2009 ), whereas females display delayed mammary gland development and reduced fertility ( Richard et al, 2008 ; Bianchi et al, 2010 ). Sam68 deficiency was also reported to impair motor coordination ( Lukong & Richard, 2008 ) and social behavior ( Farini et al, 2020 ). On the other hand, Sam68 has been involved in the pathogenesis of fragile X-associated tremor/ataxia syndrome ( Sellier et al, 2010 ) and spinal muscular atrophy ( Pedrotti et al, 2010 ; Pagliarini et al, 2015 ), as well as in brain development and function ( Iijima et al, 2011 ; Danilenko et al, 2017 ; Witte et al, 2019 ; Farini et al, 2020 ) through modulation of neuron-specific splicing events.…”