RT Journal Article
SR Electronic
T1 From spiral cleavage to bilateral symmetry: The developmental cell lineage of the annelid brain
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 268177
DO 10.1101/268177
A1 Pavel Vopalensky
A1 Maria Antonietta Tosches
A1 Kaia Achim
A1 Mette Handberg-Thorsager
A1 Detlev Arendt
YR 2018
UL http://biorxiv.org/content/early/2018/02/19/268177.abstract
AB The spiral cleavage pattern is characteristic for Spiralia (Lophotrochozoa), a large assembly of marine invertebrates. In most cases, spiral cleavage produces freely swimming, trochophora-type larvae with a simple nervous system that controls ciliary locomotion. These larvae acquire bilateral symmetry, as manifested for example in the larval brain. The transition from the rotational symmetry of spiral cleavage into the bilateral adult body has not yet been understood. Here, we present the developmental cell lineage of the brain of the annelid Platynereis dumerilii from the zygote until the mid-trochophore stage (~30 hpf), in combination with a gene expression atlas for several embryonic and larval stages. Comparison of multiple embryos reveals a highly stereotypical development and an invariant cell lineage of the differentiated cell types. In addition, we observe a fundamental subdivision of the larval brain into a highly proliferative dorsolateral region and an early differentiating ventromedial region that gives rise to the apical nervous system. The transition from rotational to bilateral symmetry progresses gradually from the lateral to the central regions. Strikingly, the spiral-to-bilateral transition does not involve extensive cell migration. Rather, corresponding cells in different spiral quadrants acquire highly divergent identities in line with their bilateral position.