A Novel Automated Approach for Improving Standardization of the Marble Burying Test Enables Quantification of Burying Bouts and Activity Characteristics

Morphological and behavioral analysis of Slc35f1-deficient mice revealed no neurodevelopmental phenotype

SLC35F1 is a member of the sugar-like carrier (SLC) superfamily that is expressed in the mammalian brain. Malfunction of SLC35F1 in humans is associated with neurodevelopmental disorders. To get insight into the possible roles of Slc35f1 in the brain, we generated Slc35f1-deficient mice. The Slc35f1-deficient mice are viable and survive into adulthood, which allowed examining adult Slc35f1-deficient mice on the anatomical as well as behavioral level. In humans, mutation in the SLC35F1 gene can induce a Rett syndrome-like phenotype accompanied by intellectual disability (Fede et al. Am J Med Genet A 185:2238-2240, 2021). The Slc35f1-deficient mice, however, display only a very mild phenotype and no obvious deficits in learning and memory as, e.g., monitored with the novel object recognition test or the Morris water maze test. Moreover, neuroanatomical parameters of neuronal plasticity (as dendritic spines and adult hippocampal neurogenesis) are also unaltered. Thus, Slc35f1-deficient mice display no major alterations that resemble a neurodevelopmental phenotype.

Brain region and gene dosage-differential transcriptomic changes in Shank2-mutant mice

Shank2 is an abundant excitatory postsynaptic scaffolding protein that has been implicated in various neurodevelopmental and psychiatric disorders, including autism spectrum disorder (ASD), intellectual disability, attention-deficit/hyperactivity disorder, and schizophrenia. Shank2-mutant mice show ASD-like behavioral deficits and altered synaptic and neuronal functions, but little is known about how different brain regions and gene dosages affect the transcriptomic phenotypes of these mice. Here, we performed RNA-Seq-based transcriptomic analyses of the prefrontal cortex, hippocampus, and striatum in adult Shank2 heterozygous (HT)- and homozygous (HM)-mutant mice lacking exons 6–7. The prefrontal cortical, hippocampal, and striatal regions showed distinct transcriptomic patterns associated with synapse, ribosome, mitochondria, spliceosome, and extracellular matrix (ECM). The three brain regions were also distinct in the expression of ASD-related and ASD-risk genes. These differential patterns were stronger in the prefrontal cortex where the HT transcriptome displayed increased synaptic gene expression and reverse-ASD patterns whereas the HM transcriptome showed decreased synaptic gene expression and ASD-like patterns. These results suggest brain region- and gene dosage-differential transcriptomic changes in Shank2-mutant mice.

Biallelic PAX5 mutations cause hypogammaglobulinemia, sensorimotor deficits, and autism spectrum disorder

The genetic causes of primary antibody deficiencies and autism spectrum disorder (ASD) are largely unknown. Here, we report a patient with hypogammaglobulinemia and ASD who carries biallelic mutations in the transcription factor PAX5. A patient-specific Pax5 mutant mouse revealed an early B cell developmental block and impaired immune responses as the cause of hypogammaglobulinemia. Pax5 mutant mice displayed behavioral deficits in all ASD domains. The patient and the mouse model showed aberrant cerebellar foliation and severely impaired sensorimotor learning. PAX5 deficiency also caused profound hypoplasia of the substantia nigra and ventral tegmental area due to loss of GABAergic neurons, thus affecting two midbrain hubs, controlling motor function and reward processing, respectively. Heterozygous Pax5 mutant mice exhibited similar anatomic and behavioral abnormalities. Lineage tracing identified Pax5 as a crucial regulator of cerebellar morphogenesis and midbrain GABAergic neurogenesis. These findings reveal new roles of Pax5 in brain development and unravel the underlying mechanism of a novel immunological and neurodevelopmental syndrome.