The target of rapamycin complex 2 controls dendritic tiling of Drosophila sensory neurons through the Tricornered kinase signalling pathway.

To cover the receptive field completely and non-redundantly, neurons of certain functional groups arrange tiling of their dendrites. In Drosophila class IV dendrite arborization (da) neurons, the NDR family kinase Tricornered (Trc) is required for homotypic repulsion of dendrites that facilitates dendritic tiling. We here report that Sin1, Rictor, and target of rapamycin (TOR), components of the TOR complex 2 (TORC2), are required for dendritic tiling of class IV da neurons. Similar to trc mutants, dendrites of sin1 and rictor mutants show inappropriate overlap of the dendritic fields. TORC2 components physically and genetically interact with Trc, consistent with a shared role in regulating dendritic tiling. Moreover, TORC2 is essential for Trc phosphorylation on a residue that is critical for Trc activity in vivo and in vitro. Remarkably, neuronal expression of a dominant active form of Trc rescues the tiling defects in sin1 and rictor mutants. These findings suggest that TORC2 likely acts together with the Trc signalling pathway to regulate the dendritic tiling of class IV da neurons, and thus uncover the first neuronal function of TORC2 in vivo.

Sirolimus relieves seizures and neuropsychiatric symptoms via changes of microglial polarity in tuberous sclerosis complex model mice.

Tuberous sclerosis complex (TSC) is a genetic disorder involving a variety of physical manifestations, and is associated with epilepsy and multiple serious neuropsychiatric symptoms. These symptoms are collectively known as TSC-associated neuropsychiatric disorders (TAND), which is a severe burden for patients and their families. Overactivation of the mechanistic target of rapamycin complex 1 (mTORC1) by mutations in TSC1 or TSC2 is thought to cause TSC, and mTORC1 inhibitors such as sirolimus and everolimus are reported to be effective against various tumor types of TSC. However, there are various reports on the effect of mTORC1 inhibitor therapy on TAND in patients with TSC, which may or may not be effective. In our previous investigations, we generated TSC2 conditional knockout mice (Mitf-Cre, Tsc2 KO; Tsc2 cKO). These mice developed spontaneous epileptic activity. In the current study, we further analyzed the detailed behaviors of Tsc2 cKO mice and confirmed that they exhibited phenotypes of TAND as well as epileptic seizures, indicating that Tsc2 cKO mice are a useful model for TAND. Furthermore, the olfactory bulb and piriform cortex caused epilepsy and TAND in Tsc2 cKO mice, and neurodegeneration was observed. Immunohistology and immunophenotypic analysis of cells, and quantitative RT-PCR suggested that changes in microglial polarity were involved in the onset of TSC epilepsy and neuropsychiatric symptoms. Although the effect of mTORC1 inhibitors on TAND has not been established, the results of this study might help elucidate the mechanism of TAND pathogenesis and suggest that sirolimus may be a valuable therapeutic tool for TAND.

Clustered Protocadherins Are Required for Building Functional Neural Circuits.

Neuronal identity is generated by the cell-surface expression of clustered protocadherin (Pcdh) isoforms. In mice, 58 isoforms from three gene clusters, Pcdhα, Pcdhß, and Pcdhγ, are differentially expressed in neurons. Since cis-heteromeric Pcdh oligomers on the cell surface interact homophilically with that in other neurons in trans, it has been thought that the Pcdh isoform repertoire determines the binding specificity of synapses. We previously described the cooperative functions of isoforms from all three Pcdh gene clusters in neuronal survival and synapse formation in the spinal cord. However, the neuronal loss and the following neonatal lethality prevented an analysis of the postnatal development and characteristics of the clustered-Pcdh-null (Δαßγ) neural circuits. Here, we used two methods, one to generate the chimeric mice that have transplanted Δαßγ neurons into mouse embryos, and the other to generate double mutant mice harboring null alleles of both the Pcdh gene and the proapoptotic gene Bax to prevent neuronal loss. First, our results showed that the surviving chimeric mice that had a high contribution of Δαßγ cells exhibited paralysis and died in the postnatal period. An analysis of neuronal survival in postnatally developing brain regions of chimeric mice clarified that many Δαßγ neurons in the forebrain were spared from apoptosis, unlike those in the reticular formation of the brainstem. Second, in Δαßγ/Bax null double mutants, the central pattern generator (CPG) for locomotion failed to create a left-right alternating pattern even in the absence of neurodegeneraton. Third, calcium imaging of cultured hippocampal neurons showed that the network activity of Δαßγ neurons tended to be more synchronized and lost the variability in the number of simultaneously active neurons observed in the control network. Lastly, a comparative analysis for trans-homophilic interactions of the exogenously introduced single Pcdh-γA3 isoforms between the control and the Δαßγ neurons suggested that the isoform-specific trans-homophilic interactions require a complete match of the expressed isoform repertoire at the contacting sites between interactive neurons. These results suggested that combinations of clustered Pcdh isoforms are required for building appropriate neural circuits.

Distinct and Cooperative Functions for the Protocadherin-α, -ß and -γ Clusters in Neuronal Survival and Axon Targeting.

The clustered protocadherin (Pcdh) genes are divided into the Pcdhα, Pcdhß, and Pcdhγ clusters. Gene-disruption analyses in mice have revealed the in vivo functions of the Pcdhα and Pcdhγ clusters. However, all Pcdh protein isoforms form combinatorial cis-hetero dimers and enter trans-homophilic interactions. Here we addressed distinct and cooperative functions in the Pcdh clusters by generating six cluster-deletion mutants (Δα, Δß, Δγ, Δαß, Δßγ, and Δαßγ) and comparing their phenotypes: Δα, Δß, and Δαß mutants were viable and fertile; Δγ mutants lived less than 12 h; and Δßγ and Δαßγ mutants died shortly after birth. The Pcdhα, Pcdhß, and Pcdhγ clusters were individually and cooperatively important in olfactory-axon targeting and spinal-cord neuron survival. Neurodegeneration was most severe in Δαßγ mutants, indicating that Pcdhα and Pcdhß function cooperatively for neuronal survival. The Pcdhα, Pcdhß, and Pcdhγ clusters share roles in olfactory-axon targeting and neuronal survival, although to different degrees.

Low-grade endometrial stromal sarcoma recurring after 9 years.

A 61-year-old Japanese woman had recurrent low-grade endometrial stromal sarcoma (ESS) after primary treatment 9 years earlier. Initial and recurrent tumors showed the same configuration that the polycystic part showed in the solid tumor ultrasonographically. The central part of both the initial and recurrent tumors showed typical histologic findings, but bizarre cells were detected in the peripheral layer of the recurrent tumor. They resembled glandular cells, Comet cells of high-grade ESS, fibroblasts, decidual cells, and predecidual endometrial stromal cells at the middle to late secretory phases. The change and differentiation of low-grade ESS by therapy and environment seem to be the same as the differentiation in mesenchymal stem cells. We speculate that recurrence and prognosis of low-grade ESS are related by extrauterine development but not by mitotic activity or DNA content.