Embryonic development of the nervous system in the planarian Schmidtea polychroa

• Published in: Developmental biology Vol. 397; no. 2; pp. 305 - 319
• Main Authors: Monjo, Francisco, Romero, Rafael
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.01.2015
• Subjects: Amino Acid Sequence; Animals; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; bHLH; Bilateria; Central nervous system; Embryonic development; Image Processing, Computer-Assisted; Immunohistochemistry; Metazoa; Microscopy, Fluorescence; Molecular Sequence Data; Nervous System - embryology; Neurogenesis; Neurogenesis - physiology; Phalloidine; Phylogeny; Planarian; Planarians - embryology; Platyhelminthes; Schmidtea polychroa; Sequence Alignment; soxB; SOXB1 Transcription Factors - genetics; SOXB1 Transcription Factors - metabolism; Spiralia; Embryonic development; Planarian; soxB; Neurogenesis; Central nervous system; bHLH
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2014.10.021

The development of a nervous system is a key innovation in the evolution of metazoans, which is illustrated by the presence of a common developmental toolkit for the formation of this organ system. Neurogenesis in the Spiralia, in particular the Platyhelminthes, is, however, poorly understood when compared with other animal groups. Here, we characterize embryonic neurogenesis in the freshwater flatworm Schmidtea polychroa and analyze the expression of soxB and a set of proneural bHLH genes, which are gene families with a well-established role in metazoan early neural development. We show that the nervous system is fully de novo assembled after the early embryo ingests the maternal nutrients. At early stages of neurogenesis, soxB1 genes are expressed in putative neural progenitor cells, whereas soxB2 and neural bHLH genes (achaete-scute, neuroD and beta3) are associated with late neurogenesis and the specification of neural subpopulations of the central and peripheral nervous system. Our findings are consistent with the role of proneural genes in other bilaterians, suggesting that the ancestral neural-specific gene regulatory network is conserved in triclads, despite exhibiting a divergent mode of development. •We provide a thorough molecular description of embryonic neurogenesis in Schmidtea polychroa.•Planarians form the definitive nervous system de novo from stage 4 onwards.•Many soxB and proneural bHLH genes are expressed during CNS and PNS formation.•The ancestral neural-specific developmental toolkit remains conserved in triclads.