Detecting Boolean Asymmetric Relationships with a Loop Counting Technique and its Implications for Analyzing Heterogeneity within Gene Expression Datasets.

Many traditional methods for analyzing gene-gene relationships focus on positive and negative correlations, both of which are a kind of 'symmetric' relationship. Biclustering is one such technique that typically searches for subsets of genes exhibiting correlated expression among a subset of samples. However, genes can also exhibit 'asymmetric' relationships, such as 'if-then' relationships used in boolean circuits. In this paper we develop a very general method that can be used to detect biclusters within gene-expression data that involve subsets of genes which are enriched for these 'boolean-asymmetric' relationships (BARs). These BAR-biclusters can correspond to heterogeneity that is driven by asymmetric gene-gene interactions, e.g., reflecting regulatory effects of one gene on another, rather than more standard symmetric interactions. Unlike typical approaches that search for BARs across the entire population, BAR-biclusters can detect asymmetric interactions that only occur among a subset of samples. We apply our method to a single-cell RNA-sequencing data-set, demonstrating that the statistically-significant BARbiclusters indeed contain additional information not present within the more traditional 'boolean-symmetric'-biclusters. For example, the BAR-biclusters involve different subsets of cells, and highlight different gene-pathways within the data-set. Moreover, by combining the boolean-asymmetric- and boolean-symmetricsignals, one can build linear classifiers which outperform those built using only traditional boolean-symmetric signals.

Impact of TREM2 risk variants on brain region-specific immune activation and plaque microenvironment in Alzheimer's disease patient brain samples.

Identification of multiple immune-related genetic risk factors for sporadic AD (sAD) have put the immune system center stage in mechanisms underlying this disorder. Comprehensive analysis of microglia in different stages of AD in human brains revealed microglia activation to follow the progression of AD neuropathological changes and requiring the co-occurrence of beta-Amyloid (Aß) and tau pathology. Carriers of AD-associated risk variants in TREM2 (Triggering receptor expressed on myeloid cells 2) showed a reduction of plaque-associated microglia and a substantial increase in dystrophic neurites and overall pathological tau compared with age and disease stage matched AD patients without TREM2 risk variants. These findings were substantiated by digital spatial profiling of the plaque microenvironment and targeted gene expression profiling on the NanoString nCounter system, which revealed striking brain region dependent differences in immune response patterns within individual cases. The demonstration of profound brain region and risk-variant specific differences in immune activation in human AD brains impacts the applicability of immune-therapeutic approaches for sAD and related neurodegenerative diseases.

Single-molecule fluorescence studies of intrinsically disordered proteins and liquid phase separation.

Intrinsically disordered proteins (IDPs) are ubiquitous in proteomes and serve in a range of cellular functions including signaling, regulation, transport and enzyme function. IDP misfunction and aggregation are also associated with several diseases including neurodegenerative diseases and cancer. During the past decade, single-molecule methods have become popular for detailed biophysical and structural studies of these complex proteins. This work has included recent applications to cellular liquid-liquid phase separation (LLPS), relevant for functional dynamics of membraneless organelles such as the nucleolus and stress granules. In this concise review, we cover the conceptual motivations for development and application of single-molecule fluorescence methods for such IDP studies. We follow with a few key examples of systems and biophysical problems that have been addressed, and conclude with thoughts for emerging and future directions.