Biology subjects

Tam, J. M.

Publications and source records attributed to Tam, J. M..

3 recordsLinked to original sources

bioRxiv2025

Altered Protein Phosphorylation in a Novel Midbrain Organoid Model for Bipolar Disorder

Bipolar disorder (BD) is a severe psychiatric condition marked by episodes of mania and depression, with neurotransmitter imbalance in the midbrain believed to play a critical role in its pathophysiology. Despite this, there is currently no validated midbrain model for examining BD-associated molecular changes available. Leveraging recent advances in stem cell technology, we developed a midbrain organoid model using human induced pluripotent stem cells (hiPSCs) from BD patients and healthy controls (CTR). To address issues of variability and enhance the throughput in organoid production, we implemented liquid handling and high-content imaging techniques. Quality control metrics were established to identify organoids unsuitable for further study. Electrophysiological analysis via high-density microelectrode arrays (MEAs) revealed significantly elevated neuronal properties in individual BD organoids, including increased mean amplitude, conduction velocity, and extended axonal and dendritic growth. Transcriptome and proteome analyses indicated significant dysregulation of BD-relevant signaling pathways--such as those involving phosphatidylinositol, glycogen synthase kinase-3 beta, and AKT. Notably, we identified dysregulated casein kinase 2 (CSNK2A1) and calmodulin 3 (CALM3) in BD organoids, which were reversed by lithium treatment, highlighting potential novel targets for therapeutic intervention. This study validates the midbrain organoid model as a valuable tool for exploring the molecular underpinnings of BD and identifying new treatment avenues.

cell biology↗

bioRxiv2024

Preventing escape and malfunction of recoded cells due to tRNA base changes

Engineering the genetic code restricts DNA transfer (cellular bioisolation) and enables new chemistries via non-standard amino acid incorporation. These distinct properties make recoded cells state-of-the-art safe technologies. However, evolutionary pressures may endanger the longevity of the recoding. Here, we reveal that recoded Escherichia coli lacking 18,214 serine codons and two tRNASer can express wild-type antibiotic resistance genes and escape up to seven orders of magnitude faster than expected. We show a two-step escape process whereby recoded cells mistranslate antibiotic resistance genes to survive until modified or mutated tRNAs reintroduce serine into unassigned codons. We developed genetic-code-sensitive kill switches that sense serine incorporation and prevent cellular escape while preserving encoding of three distinct non-standard amino acids. This work lays the foundation for the long-term controlled function of cells that incorporate new chemistries, with implications for the design, use, and biosafety of synthetic genomes in clinical and environmental applications where physical containment is insufficient.

synthetic biology↗

bioRxiv2020

Humans surviving cholera develop antibodies against Vibrio cholerae O-specific polysaccharide that inhibit pathogen motility

The mechanism of protection against cholera afforded by previous illness or vaccination is currently unknown. We have recently shown that antibodies targeting O-specific polysaccharide (OSP) of Vibrio cholerae correlate highly with protection against cholera. V. cholerae is highly motile and possesses a flagellum sheathed in O-specific polysaccharide (OSP), and motility of V. cholerae correlates with virulence. Using high speed video microscopy, and building upon previous animal-related work, we demonstrate that sera, polyclonal antibody fractions, and OSP-specific monoclonal antibodies recovered from humans surviving cholera block V. cholerae motility at both subagglutinating and agglutinating concentrations. This anti-motility effect is reversed by pre-adsorbing sera and polyclonal antibody fractions with purified OSP; and is associated with OSP-specific but not flagellin-specific monoclonal antibodies. F[ab] fragments of OSP-specific polyclonal antibodies do not inhibit motility, suggesting a requirement for antibody-mediated crosslinking in motility inhibition. We show that OSP-specific antibodies do not directly affect V. cholerae viability, but that OSP-specific monoclonal antibody highly protects against death in the murine cholera model. We used in vivo competitive index studies to demonstrate that OSP-specific antibodies impede colonization and survival of V. cholerae in intestinal tissues, and that this impact is motility-dependent. Our findings suggest that the impedance of motility by antibodies targeting V. cholerae OSP contributes to protection against cholera. IMPORTANCECholera is a severe dehydrating illness of humans caused by Vibrio cholerae. V. cholerae is a highly motile bacterium that has a single flagellum covered in lipopolysaccharide (LPS) displaying O-specific polysaccharide (OSP), and V. cholerae motility correlates with its ability to cause disease. The mechanisms of protection against cholera are not well understood; however, since V. cholerae is a non-invasive intestinal pathogen, it is likely that antibodies that bind the pathogen or its products in the intestinal lumen contribute to protection from infection. Here, we demonstrate that OSP-specific antibodies isolated from humans surviving cholera in Bangladesh inhibit V. cholerae motility and are associated with protection against challenge in a motility-dependent manner.

microbiology↗