Project description:Organisms possessing genetic codes with unassigned codons raise the question of how cellular machinery resolves such codons and how this could impact horizontal gene transfer. Here, we use a genomically recoded Escherichia coli to examine how organisms address translation at unassigned UAG codons, which obstruct propagation of UAG-containing viruses and plasmids. Using mass spectrometry, we show that recoded organisms resolve translation at unassigned UAG codons via near-cognate suppression, dramatic frameshifting from at least -3 to +19 nucleotides, and rescue by ssrA-encoded tmRNA, ArfA, and ArfB. We then demonstrate that deleting tmRNA restores expression of UAG-ending proteins and propagation of UAG-containing viruses and plasmids in the recoded strain, indicating that tmRNA rescue and nascent peptide degradation is the cause of impaired virus and plasmid propagation. The ubiquity of tmRNA homologs suggests that genomic recoding is a promising path to impair horizontal gene transfer and confer genetic isolation in diverse organisms.
Project description:Classifying leukemias of ambiguous lineage as either acute myeloid leukemia or acute lymphoid leukemia using microRNA expression profiling
Project description:The transcriptional programs that establish neuronal identity evolved to produce a rich diversity of neuronal cell types that arise sequentially during development. Remarkably, transient expression of certain transcription factors (TFs) can also endow non-neural cells with neuronal properties. To decipher the relationship between reprogramming factors and transcriptional networks that produce neuronal identity and diversity, we screened ~600 TF pairs and identified 76 that produce induced neurons (iNs) from fibroblasts. By intersecting the transcriptomes of iNs with those of endogenous neurons, we define a “core” cell-autonomous neuronal signature. The iNs also exhibit diversity; each TF pair produces iNs with unique transcriptional patterns that can predict their pharmacological responses. By linking distinct TF input “codes” to defined transcriptional outputs, this study uncovers cell autonomous features of neuronal identity and expands the reprogramming toolbox to enable more facile engineering of induced neurons with desired patterns of gene expression and related functional properties.
Project description:Motor neurons (MNs) are the cellular targets of multiple adult-onset diseases. Because distinct MN populations differ in disease susceptibility, it is important to define in animal models the degree of diversity within adult MNs. Here, we generated a comprehensive molecular resource of adult MNs in C. elegans. Single-cell RNA-sequencing of 12,603 cells revealed that all eight morphologically defined MN classes of the ventral nerve cord and its flanking ganglia subdivide into 29 distinct subclasses, almost quadrupling the degree of their previously described diversity. We find that four of the six C. elegans Hox genes delineate most, but not all MN subclasses. Strikingly, all 29 subclasses are delineated by unique expression codes of neuropeptide genes and receptors, critical for extra-synaptic (wireless) signaling. Leveraging the C. elegans connectome, we found a strong correlation between molecularly and connectivity defined MN subclasses. Beyond providing a valuable resource and searchable database (spinalcordatlas.com), our study identifies Hox and neuropeptide codes as key molecular descriptors of adult MN diversity, codes likely conserved in MNs across species.