biostudies-literatureUnknown104(8)Steinmetz PRDuring frog and fish development, convergent extension movements transform the spherical gastrula into an elongated neurula. Such transformation of a ball- into a worm-shaped embryo is an ancestral and fundamental feature of bilaterian development, yet this is modified or absent in the protostome model organisms Caenorhabditis or Drosophila. In the polychaete annelid Platynereis dumerilii, early embryonic and larval stages resemble a sphere that subsequently elongates into worm shape. Cellular and molecular mechanisms of polychaete body elongation are yet unknown. Our in vivo time-lapse analysis of Platynereis axis elongation reveals that the polychaete neuroectoderm converges and extends by mediolateral cell intercalation. This occurs on both sides of the neural midline, the line of fusioProceedings of the National Academy of Sciences of the United States of America2727-32https://www.ebi.ac.uk/biostudies/studies/S-EPMC1815249biostudies-literaturePolychaete trunk neuroectoderm converges and extends by mediolateral cell intercalation.PMC1815249Arendt DSteinmetz PRBurgtorf CWittbrodt JZelada-Gonzales FfalsePolychaete trunk neuroectoderm converges and extends by mediolateral cell intercalation.During frog and fish development, convergent extension movements transform the spherical gastrula into an elongated neurula. Such transformation of a ball- into a worm-shaped embryo is an ancestral and fundamental feature of bilaterian development, yet this is modified or absent in the protostome model organisms Caenorhabditis or Drosophila. In the polychaete annelid Platynereis dumerilii, early embryonic and larval stages resemble a sphere that subsequently elongates into worm shape. Cellular and molecular mechanisms of polychaete body elongation are yet unknown. Our in vivo time-lapse analysis of Platynereis axis elongation reveals that the polychaete neuroectoderm converges and extends by mediolateral cell intercalation. This occurs on both sides of the neural midline, the line of fusio2007-01-01T00:00:00Z2007 Feb2026-03-31T11:15:49.42Z2019-03-27T02:03:32ZS-EPMC18152491730124410.1073/pnas.0606589104