Lateral habenula dysfunctions in Tm4sf2-/y mice model for neurodevelopmental disorder

Implications of Genetic Factors Underlying Mouse Hydronephrosis: Cautionary Considerations on Phenotypic Interpretation in Genetically Engineered Mice

Hydronephrosis, the dilation of kidneys due to abnormal urine retention, occurs spontaneously in certain inbred mouse strains. In humans, its occurrence is often attributed to acquired urinary tract obstructions in adults, whereas in children, it can be congenital. However, the genetic factors underlying hydronephrosis pathogenesis remain unclear. We investigated the cause of hydronephrosis by analyzing tetraspanin 7 (Tspan7) gene-modified mice, which had shown a high incidence of hydronephrosis-like symptoms. We found that these mice were characterized by low liver weights relative to kidney weights and elevated blood ammonia levels, suggesting liver involvement in hydronephrosis. Gene expression analysis of the liver suggested that dysfunction of ornithine transcarbamylase (OTC), encoded by the X chromosome gene Otc and involved in the urea cycle, may contribute as a congenital factor in hydronephrosis. This OTC dysfunction may be caused by genomic mutations in X chromosome genes contiguous to Otc, such as Tspan7, or via the genomic manipulations used to generate transgenic mice, including the introduction of Cre recombinase DNA cassettes and cleavage of loxP by Cre recombinase. Therefore, caution should be exercised in interpreting the hydronephrosis phenotype observed in transgenic mice as solely a physiological function of the target gene.

Neuronal network activity and connectivity are impaired in a conditional knockout mouse model with PCDH19 mosaic expression

Mutations in PCDH19 gene, which encodes protocadherin-19 (PCDH19), cause Developmental and Epileptic Encephalopathy 9 (DEE9). Heterogeneous loss of PCDH19 expression in neurons is considered a key determinant of the disorder; however, how PCDH19 mosaic expression affects neuronal network activity and circuits is largely unclear. Here, we show that the hippocampus of Pcdh19 mosaic mice is characterized by structural and functional synaptic defects and by the presence of PCDH19-negative hyperexcitable neurons. Furthermore, global reduction of network firing rate and increased neuronal synchronization have been observed in different limbic system areas. Finally, network activity analysis in freely behaving mice revealed a decrease in excitatory/inhibitory ratio and functional hyperconnectivity within the limbic system of Pcdh19 mosaic mice. Altogether, these results indicate that altered PCDH19 expression profoundly affects circuit wiring and functioning, and provide new key to interpret DEE9 pathogenesis.

Diencephalic organoids - A key to unraveling development, connectivity, and pathology of the human diencephalon

The diencephalon, an integral component of the forebrain, governs a spectrum of crucial functions, ranging from sensory processing to emotional regulation. Yet, unraveling its unique development, intricate connectivity, and its role in neurodevelopmental disorders has long been hampered by the scarcity of human brain tissue and ethical constraints. Recent advancements in stem cell technology, particularly the emergence of brain organoids, have heralded a new era in neuroscience research. Although most brain organoid methodologies have hitherto concentrated on directing stem cells toward telencephalic fates, novel techniques now permit the generation of region-specific brain organoids that faithfully replicate precise diencephalic identities. These models mirror the complexity of the human diencephalon, providing unprecedented opportunities for investigating diencephalic development, functionality, connectivity, and pathophysiology in vitro. This review summarizes the development, function, and connectivity of diencephalic structures and touches upon developmental brain disorders linked to diencephalic abnormalities. Furthermore, it presents current diencephalic organoid models and their applications in unraveling the intricacies of diencephalic development, function, and pathology in humans. Lastly, it highlights thalamocortical assembloid models, adept at capturing human-specific aspects of thalamocortical connections, along with their relevance in neurodevelopmental disorders.

Integrin β1/FAK/SRC signal pathway is involved in autism spectrum disorder in Tspan7 knockout rats

TSPAN7 is related to various neurological disorders including autism spectrum disorder (ASD). However, the underlying synaptic mechanism of TSPAN7 in ASD is still unclear. Here, we showed that Tspan7 knockout rats exhibited ASD-like and ID-like behavioral phenotypes, brain structure alterations including decreased hippocampal and cortical volume, and related pathological changes including reduced hippocampal neurons number, neuronal complexity, dendritic spines, and synapse-associated proteins. Then, we found that TSPAN7 deletion interrupted the integrin β1/FAK/SRC signal pathway that was followed by the down-regulation of PSD95, SYN, and GluR1/2, which are key synaptic integrity-related proteins. Furthermore, reactivation of SRC restored the expression of synaptic integrity-related proteins in primary neurons of TSPAN7 knockout brains. Taken together, our results suggested that TSPAN7 knockout caused ASD-like and ID-like behaviors in rats and impaired neuronal synapses possibly through the down-regulation of the integrin β1/FAK/SRC signal pathway, which might be a new mechanism on regulation of synaptic proteins expression and on ASD pathogenesis by mutated TSPAN7. These findings provide novel insights into the role of TSPAN7 in psychiatric diseases and highlight integrin β1/FAK/SRC as a potential target for ASD therapy.

Loss of tetraspanin-7 expression reduces pancreatic β-cell exocytosis Ca2+ sensitivity but has limited effect on systemic metabolism

BACKGROUND

Tetraspanin-7 (Tspan7) is an islet autoantigen involved in autoimmune type 1 diabetes and known to regulate β-cell L-type Ca²⁺ channel activity. However, the role of Tspan7 in pancreatic β-cell function is not yet fully understood.

METHODS

Histological analyses were conducted using immunostaining. Whole-body metabolism was tested using glucose tolerance test. Islet hormone secretion was quantified using static batch incubation or dynamic perifusion. β-cell transmembrane currents, electrical activity and exocytosis were measured using whole-cell patch-clamping and capacitance measurements. Gene expression was studied using mRNA-sequencing and quantitative PCR.

RESULTS

Tspan7 is expressed in insulin-containing granules of pancreatic β-cells and glucagon-producing α-cells. Tspan7 knockout mice (Tspan7^y/- mouse) exhibit reduced body weight and ad libitum plasma glucose but normal glucose tolerance. Tspan7^y/- islets have normal insulin content and glucose- or tolbutamide-stimulated insulin secretion. Depolarisation-triggered Ca²⁺ current was enhanced in Tspan7^y/- β-cells, but β-cell electrical activity and depolarisation-evoked exocytosis were unchanged suggesting that exocytosis was less sensitive to Ca²⁺ . TSPAN7 knockdown (KD) in human pseudo-islets led to a significant reduction in insulin secretion stimulated by 20 mM K⁺ . Transcriptomic analyses show that TSPAN7 KD in human pseudo-islets correlated with changes in genes involved in hormone secretion, apoptosis and ER stress. Consistent with rodent β-cells, exocytotic Ca²⁺ sensitivity was reduced in a human β-cell line (EndoC-βH1) following Tspan7 KD.

CONCLUSION

Tspan7 is involved in the regulation of Ca²⁺ -dependent exocytosis in β-cells. Its function is more significant in human β-cells than their rodent counterparts.

Involvement of the habenula in the pathophysiology of autism spectrum disorder

The habenula is a small epithalamic structure with widespread connections to multiple cortical, subcortical and brainstem regions. It has been identified as the central structure modulating the reward value of social interactions, behavioral adaptation, sensory integration and circadian rhythm. Autism spectrum disorder (ASD) is characterized by social communication deficits, restricted interests, repetitive behaviors, and is frequently associated with altered sensory perception and mood and sleep disorders. The habenula is implicated in all these behaviors and results of preclinical studies suggest a possible involvement of the habenula in the pathophysiology of this disorder. Using anatomical magnetic resonance imaging and automated segmentation we show that the habenula is significantly enlarged in ASD subjects compared to controls across the entire age range studied (6-30 years). No differences were observed between sexes. Furthermore, support-vector machine modeling classified ASD with 85% accuracy (model using habenula volume, age and sex) and 64% accuracy in cross validation. The Social Responsiveness Scale (SRS) significantly differed between groups, however, it was not related to individual habenula volume. The present study is the first to provide evidence in human subjects of an involvement of the habenula in the pathophysiology of ASD.

Tetraspanin 7 regulates osteoclast function through association with the RANK/αvβ3 integrin complex

Actin rings are unique structures that facilitate the attachment of osteoclasts to the bone matrix during bone resorption. Previous studies have shown that tetraspanin7 (TSPAN7) plays an important role in the reorganization of the cytoskeleton necessary for the bone-resorbing activity of osteoclasts. However, questions remain as to the mechanisms by which TSPAN7 regulates this cytoskeletal rearrangement. In this study, we investigated the roles of TSPAN7 in osteoclasts by deleting the Tm4sf2 gene in mice, which encodes TSPAN7. The Tm4sf2 global knockout model showed protective effects on pathological bone loss, but no discernible changes in bone phenotypes under physiological conditions. In vitro study revealed that ablation of Tm4sf2 caused significant defects in integrin-mediated actin ring formation, thereby leading to significantly decreased bone resorption. Additionally, we demonstrated an association between TSPAN7 and the receptor activator of nuclear factor-кB/αvβ3 integrin. Overall, our findings suggest that TSPAN7 acts as a novel modulator regulating the bone-resorbing function of osteoclasts.