Neuromesodermal Lineage Contribution to CNS Development in Invertebrate and Vertebrate Chordates

Abstract

Ascidians are invertebrate chordates and the closest living relative to vertebrates. In ascidian embryos a large part of the central nervous system arises from cells associated with mesoderm rather than ectoderm lineages. This seems at odds with the traditional view of vertebrate nervous system development which was thought to be induced from ectoderm cells, initially with anterior character and later transformed by posteriorizing signals, to generate the entire anterior-posterior axis of the central nervous system. Recent advances in vertebrate developmental biology, however, show that much of the posterior central nervous system, or spinal cord, in fact arises from cells that share a common origin with mesoderm. This indicates a conserved role for bi-potential neuromesoderm precursors in chordate CNS formation. However, the boundary between neural tissue arising from these distinct neural lineages does not appear to be fixed, which leads to the notion that anterior-posterior patterning and neural fate formation can evolve independently.

Ascidian embryonic cells with properties of neural-crest cells and neuromesodermal progenitors of vertebrates

“…Previous studies 19,28 have shown that b8.17 (posterior LNPCs, pLNPCs) give rise to cells near the tip of the tail of tailbud embryos. These cells are two pairs of muscle cells and four cells of posterior parts of the nerve cord and endodermal strand.…”

Building consensus in neuromesodermal research: Current advances and future biomedical perspectives

“…A recent re-appraisal of urochordate embryology is a promising start for this research, as it highlighted that during gastrulation some progenitors give rise to neural and mesodermal cells in the tail. This occurs after segregation of anterior neural and mesodermal lineages [52]. As in many developmental processes, there is broader conservation, beyond chordates, of GRNs involved in axis patterning.…”

Early transcriptional similarities between two distinct neural lineages during ascidian embryogenesis

“…This consists of a sensory vesicle, or brain, followed by a trunk ganglion and tail nerve cord (Fig 1A). The structure and underlying specification mechanisms of the ascidian larval CNS are well documented (reviewed in (Hudson, 2016; Hudson and Yasuo, 2021; Liu and Satou, 2020; Ryan and Meinertzhagen, 2019)). Uniquely among chordates, ascidian embryos develop with an invariant cleavage pattern and their cell lineages are well described.…”