Fluorescent In Situ Hybridization Chain Reaction for RNA in the Drosophila Embryonic and Larval Central Nervous System.

In the Drosophila nerve cord, much is known about the generation of neurons from neuronal stem cells. Over the lifetime of a neuron, the cumulative expression of genes within that neuron determines its fate. Furthermore, gene expression in mature neurons determines their functional characteristics. It is therefore useful to visualize neural gene expression, which is often done via staining with antibodies to a protein of interest. In cases where there is no antibody to a desired gene product, or when it is useful to detect RNA rather than protein products, fluorescent in situ hybridization chain reaction for RNA (HCR RNA-FISH, or HCR for this protocol) can be used to detect and quantify RNA expression. RNA molecules reside predominantly in the cell soma, so HCR can facilitate determining neuron identity because somata position within the nerve cord is stereotyped across animals. HCR provides high-amplitude, high-fidelity signals. In principle, HCR can be broken down into a detection/hybridization stage and an amplification stage. During detection/hybridization, a probe set hybridizes to multiple sequences within a target gene. In the amplification step, concatemerized fluorescent hairpins bind to the hybridized probes. This two-step process increases the specificity of the fluorescent signal and helps reduce the likelihood of background fluorescence compared to traditional in situ hybridization techniques where the hybridizing probe itself contains the fluorescent signal. Here, we describe a protocol for using HCR to study gene expression in the Drosophila embryonic and larval nerve cord. We also describe how to combine HCR with immunofluorescence staining.

Mutations in RABL3 alter KRAS prenylation and are associated with hereditary pancreatic cancer.

Pancreatic ductal adenocarcinoma is an aggressive cancer with limited treatment options1. Approximately 10% of cases exhibit familial predisposition, but causative genes are not known in most families2. We perform whole-genome sequence analysis in a family with multiple cases of pancreatic ductal adenocarcinoma and identify a germline truncating mutation in the member of the RAS oncogene family-like 3 (RABL3) gene. Heterozygous rabl3 mutant zebrafish show increased susceptibility to cancer formation. Transcriptomic and mass spectrometry approaches implicate RABL3 in RAS pathway regulation and identify an interaction with RAP1GDS1 (SmgGDS), a chaperone regulating prenylation of RAS GTPases3. Indeed, the truncated mutant RABL3 protein accelerates KRAS prenylation and requires RAS proteins to promote cell proliferation. Finally, evidence in patient cohorts with developmental disorders implicates germline RABL3 mutations in RASopathy syndromes. Our studies identify RABL3 mutations as a target for genetic testing in cancer families and uncover a mechanism for dysregulated RAS activity in development and cancer.