The basement membrane (BM) acts as a barrier that usually prevents cells from moving between tissues. However, cells cross the BM during certain developmental processes, such as neural crest cell migration, or in disease contexts, such as cancer metastasis. Here, David Sherwood and colleagues investigate this process using the Caenorhabditis elegans anchor cell (AC), which invades the BM during the larval stage in a stereotyped manner. They isolate ACs from C. elegans and use RNA sequencing to identify around 1500 genes that are upregulated in the AC during invasion. An RNAi screen on a subset of these genes, selected because they encode protein classes implicated in invasive behaviour, uncovers 13 novel invasion regulators. The authors also find that the AC transcriptome is enriched for genes encoding ribosomal proteins. Depletion of these, or of ribosome biogenesis genes, produces severe invasion defects. Using a modified split-GFP approach to monitor ribosome assembly, they show that the upregulation of pro-invasive proteins in the AC is preceded by a burst of ribosome biogenesis. These ribosomes localise to the endomembrane system, which also undergoes expansion prior to invasion. Overall, this work suggests that BM invasion requires ribosome biogenesis and endomembrane expansion to support the production of pro-invasive proteins.
