In this week's Science, a multi-institute research team reports on the discovery that certain classes of the bacterial protein Cas, which is used in the gene-editing system CRISPR, are fused to a reverse transcriptase gene. As a result, these Cas proteins can capture and incorporate RNA, suggesting that certain CRISPR systems can not only obtain information from the genomes of DNA-based viruses but also from the gene expression program they contain. The researchers hypothesize that such Cas proteins could be used to target CRISPR to parasitic RNA species or to alter host bacterial gene expression.
And in Science Translational Medicine, European investigators report the results of a broad analysis of the mutations, genomic instability, lymphatic and blood vascularization, and the immune contexture of more than 1,500 colorectal cancer tumors, showing that it is the cancer's microenvironment that largely drives metastasis and not the tumor itself. The team found similar patterns of mutations in key cancer-related genes and genomic instability between metastatic and non-metastatic cancer patients, but different patterns of immune-related gene expression in these groups. An analysis of the tumor microenvironment revealed that, although the density of blood vessels feeding tumors was similar across all patients, the presence of lymphatic vessels was significantly reduced in patients with metastatic cancer. They speculate that fewer lymphatic vessels might prevent immune cells from reaching the tumor, thereby promoting metastasis. GenomeWeb has more on this study here.