Understanding any brain circuit will require a categorization of its constituent neurons. In hippocampal area CA1, at least 23 classes of GABAergic neuron have been proposed to date. However, this list may be incomplete; additionally, it is unclear whether discrete classes are sufficient to describe the diversity of cortical inhibitory neurons, or whether continuous modes of variability are also required. We studied the transcriptomes of 3663 CA1 inhibitory cells, revealing 10 major GABAergic groups that divided into 49 fine-scale clusters. All previously described and several novel cell classes were identified, with three previously-described classes unexpectedly found to be identical. A common continuous mode of variation modulated the expression of many genes, reflecting a range from metabolically highly active faster-spiking cells that proximally target pyramidal cells, to slower-spiking cells that target distal dendrites or interneurons. Within classes, cells showed further variability along the continuum and this correlated with their spiking phenotype. Surprisingly, several cell types previously described as discrete classes represented ranges along this continuum. These results elucidate the complexity of inhibitory neurons in one of the simplest cortical structures, and show that characterizing these cells requires continuous modes of variation as well as discrete cell classes.

PTEN negatively regulates the Class I PI 3-kinases by metabolizing phosphatidylinositol(3,4,5)trisphosphate (PIP3) and acts as a tumor suppressor. Heterozygous germline PTEN mutations in humans manifest into a complex multiorgan disorder known as PTEN hamartoma tumor syndrome (PHTS). Patients present with hamartomatous skin lesions, benign GI polyps, have an increased risk of developing certain types of cancer (breast, colon, endometrium, thyroid, GI tract and kidney) and have macrocephaly and autism spectrum disorders (ASD). There is huge variability in disease symptoms in PHTS patients, the cause of which is unclear. It has been proposed that this correlates with the nature of the aberration in PTEN and its impact on PTEN expression and function, allowing to discriminate the following cancer-risk groups in PHTS patients: 1. High cancer risk: Patients expressing a catalytically inactive but stable PTEN protein (mis-sense PTEN mutations such as the C124S, G129R, R130Q etc.) have a severe phenotype, with benign tumors and aggressive malignant cancers at a young age of one of more tissues. 2. Medium risk: Patients with complete loss of PTEN expression due to insertions, deletions and truncations in the PTEN gene present with an intermediate severity with benign and malignant tumors. 3. Low risk: Patients with PTEN protein characteristics that do not fall into Group 1 or 2 but with some detectable suppression of AKT signaling. This covers a range of PTEN mutants, with often a mix of characteristics such as being unstable but active or even overactive, stable but partially inactive or no apparent activity defect. These patients have a mild phenotype, mainly related to a broad range of ASD symptoms such as macrocephaly, developmental delay and mental retardation. Some patients are severely autistic. Patients may have benign tumors and skin hamartomas, but malignant cancer is rare. Here we expand our analysis by characterizing a range of additional PHTS PTEN mutations using biochemical methods. Of the several mutations characterized, the R173C mutation leads to a PTEN enzyme that retains its activity but becomes partially unstable, putting it in Group 3. This mutation was of particular interest because the R173 site in PTEN is also the third most commonly somatically mutated PTEN site in cancer (COSMIC database; accessed September 2018). Mouse models such as the heterozygous PTEN heterozygous mice (PTEN +/- mice) and PTEN +/C124S represent Groups 1 and 2, and their characteristics coincide with the predicted phenotypes. However, no clinically relevant mouse models for the low-risk PHTS group have been reported. We have generated and characterized a PTEN +/R173C PHTS mouse model. We show that the PTEN +/R173C mice have macrocephaly, fewer tumors and a significantly longer tumor-free survival compared to the PTEN +/-, thus providing further evidence that the above-proposed PTEN genotype-phenotype correlation holds true in PHTS. Acknowledgment: This work has been supported by PTEN Research. Citation Format: Wayne Pearce, Nicoletta Kessaris, Nicholas R. Leslie, Bart Vanhaesebroeck, Priyanka Tibarewal, Gala Classen, Virginia A Garcia, Victoria Rathbone, Nisha Kriplani, Georgia Constantinou. Investigation of PTEN genotype-phenotype correlations in the PTEN hamartoma tumor syndrome (PHTS) using in vitro and in vivo approaches [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B22.

The WAS protein (WASp) coordinates actin polymerization at the leading edge of migrating cells and is defective in patients suffering from Wiskott Aldrich syndrome, resulting in severe immunodeficiency. To model this disease we are using translucent Zebrafish larvae and have begun to characterise a newly derived WASp mutant. The mutant codes for a heavily truncated protein, which we are assaying for functional activity.

No abstract

The enteric nervous system (ENS) is a complex network of neurons and glia within the gut wall which originate from neural

No abstract

No abstract

No abstract