Differential expression of paralog RNA binding proteins establishes a dynamic splicing program required for normal cerebral cortex development

The paralog RNA binding proteins (RBPs) Sam68 and SLM2 are co-expressed in the cerebral cortex and display very similar splicing activity. However, their relative function(s) in this context is unknown. By performing a time-course analysis, we found that these RBPs exhibit an opposite expression pattern during development. Sam68 expression declines postnatally while SLM2 increases after birth, and this developmental pattern is reinforced by hierarchical control of Sam68 expression by SLM2. Analysis of Sam68:Slm2 double knockout (Sam68:Slm2dko) mice revealed hundreds of exons that are sensitive to concomitant ablation of these proteins. Moreover, parallel analysis of single and double knockout cortices indicated that exons regulated mainly by SLM2 are characterized by a dynamic splicing pattern during development, whereas Sam68-dependent exons are spliced at relatively constant rates. Dynamic splicing of SLM2-sensitive exons is completely suppressed in the Sam68:Slm2dko developing cortex. Sam68:Slm2dko mice die perinatally with defects in neurogenesis and in neuronal differentiation, and the development of a hydrocephalus, consistent with splicing alterations in genes related to these biological processes. Thus, our study reveals that maintenance of the Sam68 and Slm2 paralog genes encoding homologous RBPs enables the orchestration of a dynamic splicing program while ensuring a robust redundant mechanism that supports proper cortical development. 3 cortex of Wild type mice at the embrional day of 18.5 and 3 cortex of Sam68:Slm2ko mice at the embrional day of 18.5旁系同源RNA结合蛋白（RNA Binding Proteins, RBPs）Sam68与SLM2在大脑皮层中共表达，且展现出高度相似的剪接活性。然而，二者在该组织中的相对功能仍未明确。本研究通过时间进程分析发现，这类RNA结合蛋白在大脑发育过程中呈现相反的表达模式：Sam68的表达在出生后逐渐下调，而SLM2的表达则于出生后上调；且SLM2对Sam68表达的层级调控进一步巩固了这一发育特征。对Sam68:Slm2双基因敲除（double knockout, dko）小鼠的分析显示，数百个外显子的剪接会因这两种蛋白的同时敲除而受到显著影响。此外，对单敲除与双敲除皮层组织的平行分析表明，主要受SLM2调控的外显子在发育过程中具有动态剪接模式，而依赖Sam68的外显子则以相对恒定的速率进行剪接。在Sam68:Slm2dko小鼠的发育皮层中，SLM2敏感外显子的动态剪接被完全抑制。Sam68:Slm2dko小鼠会在围产期死亡，并伴随神经发生、神经元分化缺陷以及脑积水表型，这与上述生物学过程相关基因的剪接异常相一致。综上，本研究揭示，编码同源RNA结合蛋白的Sam68与Slm2旁系同源基因的维持，能够协调动态剪接程序，同时保障稳健的冗余机制，以支持正常的大脑皮层发育。本研究所用样本为：3份野生型小鼠胚胎第18.5天的大脑皮层，以及3份Sam68:Slm2双敲除小鼠胚胎第18.5天的大脑皮层。