Visuosocial memory is defined as stored visual information containing social context. Primates have a powerful ability to associate visuosocial memory with episodic memory. However, the existence of visuosocial memory in mice remains unclear. Here, we design a novel vision-specific social memory test using a portrait picture or mirrored self-image and demonstrate that mice can distinguish conspecific from other species by forming a visuosocial memory. Because CA2 hippocampus has been reported as a critical brain region for social memory, we develop CA2-specific blockade of memory formation through deletion of phospholipase C gamma 1 (PLCγ1), which is a key molecule in the brain-derived neurotrophic factor (BDNF) signaling pathway. Interestingly, these mice have intact sociability but impaired social memory in three chamber test and five-trial social memory test, which is highly dependent on visual information. Finally, PLCγ1 deletion in CA2 impairs visuosocial preference memory, but not avoidance memory, whereas non-social object recognition is intact. Our study proposes that mice have visuosocial memory, just as primates and humans.

Adeno-associated virus (AAV)-mediated gene delivery has been proposed to be an essential tool of gene therapy for various brain diseases. Among several cell types in the brain, astrocyte has become a promising therapeutic target for brain diseases, as more and more contribution of astrocytes in pathophysiology has been revealed. Until now, genetically targeting astrocytes has been possible by utilizing the glial fibrillary acidic protein (GFAP) promoter. In some brain areas including thalamus, however, the GFAP expression in astrocytes is reported to be low, making it difficult to genetically target astrocytes using GFAP promoter. To study the function of astrocytes in thalamus, which serves as a relay station, there is a great need for identifying an alternative astrocyte-specific promoter in thalamus. Recently, a new astrocyte-specific promoter of ALDH1L1 has been identified. However, it has not been examined in thalamus. Here we developed and characterized an AAV vector expressing Cre recombinase under the human ALDH1L1 promoter, AAV-hALDH1L1-Cre. To test the cell-type specific expression of AAV-hALDH1L1-Cre, AAV virus was injected into several brain regions of Ai14 (RCL-tdTomato) mouse, which reports Cre activity by tdTomato expression. In thalamus, we observed that tdTomato was found mostly in astrocytes (91.71%), with minimal occurrence in neurons (2.67%). In contrast, tdTomato signal was observed in both neurons and astrocytes of the amygdala (neuron: 68.13%, astrocyte: 28.35%) and hippocampus (neuron: 76.25%, astrocyte: 18.00%), which is consistent with the previous report showing neuronal gene expression under rat ALDH1L1 promoter. Unexpectedly, tdTomato was found mostly in neurons (91.98%) with minimal occurrence in astrocytes (6.66%) of the medial prefrontal cortex. In conclusion, hALDH1L1 promoter shows astrocyte-specificity in thalamus and may prove to be useful for targeting thalamic astrocytes in mouse.
Amygdala ; Animals ; Astrocytes ; Brain ; Brain Diseases ; Dependovirus ; Gene Expression* ; Genetic Therapy ; Glial Fibrillary Acidic Protein ; Hippocampus ; Humans* ; Mice* ; Neurons ; Prefrontal Cortex ; Rats ; Recombinases ; Thalamus* ; Ventral Thalamic Nuclei

Astrocyte is the most abundant cell type in the central nervous system and its importance has been increasingly recognized in the brain pathophysiology. To study in vivo function of astrocyte, astrocyte-specific gene-targeting is regarded as a powerful approach. Especially, hGFAP-CreERT2, which expresses tamoxifen-inducible Cre recombinase under the human GFAP promoter, has been developed and characterized from several research groups. However, one of these mouse lines, [Tg(GFAP-Cre/ERT2)13Kdmc] from Ken McCarthy group has not been quantitatively analyzed, despite its frequent use. Here, we performed comprehensive characterization of this mouse line with quantitative analysis. By crossing this mouse line with Ai14 (RCL-tdTomato), a very sensitive Cre reporter mouse line, we visualized the Cre-expressing cells in various brain regions. For quantitative analysis, we immunostained S100β as an astrocytic marker and NeuN, tyrosine hydroxylase or calbindin as a neuronal marker in different brain regions. We calculated ‘astrocyte specificity’ as the proportion of co-labelled S100β and tdTomato positive cells in the total number of tdTomato positive cells and the ‘astrocyte coverage’ as the proportion of co-labelled S100β and tdTomato positive cells in the total number of S100β positive cells. Interestingly, we found varying degree of astrocyte specificity and coverage in each brain region. In cortex, hypothalamus, substantia nigra pars compacta and cerebellar Purkinje layer, we observed high astrocyte specificity (over 89%) and relatively high astrocyte coverage (over 70%). In striatum, hippocampal CA1 layer, dentate gyrus and cerebellar granule layer, we observed high astrocyte specificity (over 80%), but relative low astrocyte coverage (50–60%). However, thalamus and amygdala showed low astrocyte specificity (about 65%) and significant neuron specificity (over 30%). This hGFAP-CreERT2 mouse line can be useful for genetic modulations of target gene either in gain-of-function or loss-of-function studies in the brain regions with high astrocyte specificity and coverage. However, the use of this mouse line should be restricted to gain-of-function studies in the brain regions with high astrocyte specificity but low coverage. In conclusion, hGFAP-CreERT2 mouse line could be a powerful tool for gene-targeting of astrocytes in cortex, striatum, hippocampus, hypothalamus, substantia nigra pars compacta and cerebellum, but not in thalamus and amygdala.
Amygdala ; Animals ; Astrocytes* ; Brain* ; Calbindins ; Central Nervous System ; Cerebellum ; Dentate Gyrus ; Hippocampus ; Humans ; Hypothalamus ; Mice* ; Neurons ; Pars Compacta ; Recombinases ; Sensitivity and Specificity* ; Thalamus ; Tyrosine 3-Monooxygenase