Tbx1 haploinsufficiency induces bone-to-cerebellar deformity in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11DS) substantially increases the risk of cognitive decline and psychiatric disease. However, neuroanatomic changes in 22q11DS are of a subtle-to-moderate degree and their connection to brain function is not clear. Here we report a severe (~70%) and specific reduction (dysplasia) of two cerebellar lobules, paraflocculus and flocculus (PF/F) and associated deficits in vestibulo-ocular reflex (VOR) in mouse models of 22q11DS (22q11DS mice). A specific but less severe PF/F dysplasia was confirmed in humans with 22q11DS. Tbx1 haploinsufficiency recapitulated the PF/F and VOR deficits in 22q11DS mice. The 22q11DS-associated PF/F dysplasia was not due to altered neural composition or neurogenesis. Rather, a part of temporal bone called subarcuate fossa (SF), which encapsulates the PF/F, and semicircular canals of the inner ear, which connects to the SF were malformed in 22q11DS and Tbx1-deficientmice. Our single-nuclei RNA Sequencing and immunohistochemistry data revealed that Tbx1 haploinsufficiency caused precocious differentiation of chondrocyte to osteoblasts in the petrous bone, but no changes in cell type compositions in the PF/F. These data suggest a novel structure-function pathogenic interrelationship in 22q11DS, where Tbx1 haploinsufficiency causes a skeletal deformity occluding cerebellar development and resulting in motor learning deficiency. Transcriptome profiling by snRNA-seq in the developing petrous bone and paraflocculus/flocculus from the wild type and Tbx1+/- mouse at P5.5. The study included five mice in each group, with two replicates per group22q11.2缺失综合征（22q11.2 deletion syndrome, 22q11DS）会显著升高认知衰退与精神疾病的发病风险。然而，22q11DS相关的神经解剖学改变多为轻至中度，且其与脑功能的关联尚未阐明。本研究报道了22q11DS小鼠模型（22q11DS小鼠）中两个小脑小叶——绒球旁小叶与绒球（paraflocculus and flocculus, PF/F）出现约70%的严重特异性减少（发育异常），并伴随前庭眼反射（vestibulo-ocular reflex, VOR）功能缺陷。研究在22q11DS人类患者中亦验证了PF/F存在特异性但程度较轻的发育异常。Tbx1单倍剂量不足可重现22q11DS小鼠的PF/F发育异常与VOR缺陷。22q11DS相关的PF/F发育异常并非由神经组成改变或神经发生异常所致。与之相反，包裹PF/F的颞骨结构弓下窝（subarcuate fossa, SF），以及与SF相连的内耳半规管，在22q11DS小鼠与Tbx1缺陷小鼠中均出现畸形。本研究的单细胞核RNA测序（single-nuclei RNA Sequencing, snRNA-seq）与免疫组织化学数据显示，Tbx1单倍剂量不足会导致岩骨内软骨细胞向成骨细胞的过早分化，但PF/F内的细胞类型组成未发生明显改变。上述研究结果提示22q11DS中存在一种全新的结构-功能致病关联：Tbx1单倍剂量不足引发骨骼畸形，进而阻碍小脑发育，最终导致运动学习功能缺陷。本研究对野生型与Tbx1+/-小鼠出生后第5.5天（P5.5）的发育中岩骨及绒球旁小叶/绒球开展了snRNA-seq转录组分析，每组包含5只小鼠，每组分设2个生物学重复。