PTBP1 and PTBP2 Serve Both Specific and Redundant Functions in Neuronal Pre-mRNA Splicing

Abstract

SUMMARY Families of alternative splicing regulators often contain multiple paralogs presumed to fulfill different functions. Polypyrimidine tract binding proteins PTBP1 and PTBP2 reprogram developmental pre-mRNA splicing in neurons, but how their regulatory networks differ is not understood. To compare their targeting, we generated a knock-in allele that conditionally expresses PTBP1. Bred to a Ptbp2 knockout, the transgene allowed us to compare the developmental and molecular phenotypes of mice expressing only PTBP1, only PTBP2, or neither protein in the brain. This knock-in Ptbp1 rescued a forebrain-specific but not a pan-neuronal Ptbp2 knockout, demonstrating both redundant and distinct roles for the proteins. Many developmentally-regulated exons exhibited different sensitivities to PTBP1 and PTBP2. Nevertheless, the two paralogs displayed similar RNA binding across the transcriptome indicating that their differential targeting does not derive from their RNA interactions but from possible different cofactor interactions.

ASCOT identifies key regulators of neuronal subtype-specific splicing

“…Although rods do not express many of the RNA-binding proteins (RBPs) thought to be involved in 127 regulating alternative splicing in neurons ( Fig. S3) 34 , they do show similar relative expression levels of repress many exons, and downregulation of Ptbp1 accompanied by an upregulation of Ptbp2 is an 130 important prerequisite for neuronal splicing [47][48][49][50][51][52][53][54] . We hypothesized that certain RBPs, acting as splicing 131 enhancers, could be selectively expressed in rods to mediate rod-specific splicing.…”

Polypyrimidine Tract Binding Proteins are essential for B cell development

“…PTBP1 and PTBP2 have specific and redundant functions (Ling et al, 2016;Spellman et al, 2007;Vuong et al, 2016). Therefore, expression of PTBP2 in PTBP1-deficient cells compensates for many functions of PTBP1 (Ling et al, 2016;Monzon-Casanova et al, 2018;Spellman et al, 2007;Vuong et al, 2016). To study the roles of PTBP1 in B cells, we and others deleted Ptbp1 in pro-B cells and found normal B cell development accompanied by PTBP2 expression (Monzon-Casanova et al, 2018;Sasanuma et al, 2019).…”

“…In germinal centre B cells, PTBP1 promotes proliferation, the c-MYC gene expression program induced upon positive selection and antibody affinity maturation (Monzon-Casanova et al, 2018). PTBP1 and PTBP2 have specific and redundant functions (Spellman et al, 2007;Vuong et al, 2016;Ling et al, 2016). Therefore, expression of PTBP2 in PTBP1-deficient cells compensates for many functions of PTBP1 (Spellman et al, 2007;Vuong et al, 2016;Ling et al, 2016;Monzon-Casanova et al, 2018).…”

“…In germinal centre B cells, PTBP1 promotes the selection of B cell clones with high affinity antibodies, in part, by promoting the c-MYC gene expression program induced upon positive selection following T cell help (Monzon-Casanova et al, 2018). PTBP1 and PTBP2 have specific and redundant functions (Ling et al, 2016;Spellman et al, 2007;Vuong et al, 2016). Therefore, expression of PTBP2 in PTBP1-deficient cells compensates for many functions of PTBP1 (Ling et al, 2016;Monzon-Casanova et al, 2018;Spellman et al, 2007;Vuong et al, 2016).…”

“…PTBP1 binds to Ptbp2 mRNA and, by inducing Ptbp2 exon 10 skipping, promotes NMD to suppress expression of PTBP2 (Boutz et al, 2007). PTBP1 and PTBP2 have specific and redundant roles and expression of PTBP2 in PTBP1deficient cells compensates for many functions of PTBP1 (Spellman et al, 2007;Vuong et al, 2016;Ling et al, 2016;Monzon-Casanova et al, 2018). To study the unique roles of PTBP1 in B cells, we and others have deleted Ptbp1 in pro-B cells and found normal B cell development accompanied by upregulated PTBP2 expression but important defects in germinal centre (GC) responses (Monzon-Casanova et al, 2018;Sasanuma et al, 2019).…”