On the trail of the `new head' in Les Treilles

Abstract

The vertebrate brain develops in association with neighboring tissues: neural crest, placodes, mesoderm and endoderm. The molecular and evolutionary relationships between the forming nervous system and the other craniofacial structures were at the focus of a recent meeting at the Fondation des Treilles in France. Entitled 'Relationships between Craniofacial and Neural Development', the meeting brought together researchers working on diverse species, the findings of whom provide clues as to the origin and diversity of the brain and facial regions that are involved in forming the 'new head' of vertebrates. IntroductionThe vertebrate brain develops in close association with neighboring tissues, including cells from the neural crest, mesoderm and endoderm, such that their development is interlinked and interdependent. Together, these tissues form the central and peripheral nervous systems and the craniofacial skeleton of the vertebrate head. A recent meeting at the Fondation des Treilles in Provence, organized by Sophie Creuzet

Ion Channel Clustering at the Axon Initial Segment and Node of Ranvier Evolved Sequentially in Early Chordates

“…This conclusion represents an addendum to the influential “new head” hypothesis linking neural crest and ectodermal placode evolution to vertebrate origins and success [92],[97],[98], complementing ongoing studies of systems level morphological reorganization and its genetic control [99],[100] with a new focus on subcellular, intrinsic, neuronal electrical signaling. The new head required more elaborate mechanisms for sensation (e.g.…”

An Advanced Filter-Feeder Hypothesis for Urochordate Evolution

“…Although there are currently two alternative homology hypotheses regarding the origin of the neural crest, the detailed data on cell lineages in tunicates support the latter hypothesis of Abitua et al (2012). The a9.49 cells are derived from a6.7 progenitors, which are located adjacent to the developing neural tube and have fates that give rise to both the ectodermal nervous system, sensory pigment cells, and epidermis, thus showing similarities to what is known about the vertebrate neural crest (e.g., Bronner-Fraser, 2008;Betancur et al, 2010). However, it is worth pointing out that the cell lineages of vertebrates and the cell lineages and fate maps of cephalochordates are not known in as much detail as those of tunicates, although newly developed techniques show some promise in filling these gaps in our knowledge (e.g., Mikut et al, 2013;Rizzi and Peyrieras, 2014;Loulier et al, 2014).…”

Multiple developmental mechanisms regulate species-specific jaw size

“…NC cells that migrate out of the midbrain and first and second rhombomeres of the hindbrain populate the mandibular primordia (Couly et al, 1993;Köntges and Lumsden, 1996;Le Lièvre and Douarin, 1975;Noden, 1978). Although the gene networks orchestrating these processes appear to be highly conserved across vertebrates, reflecting a fundamental adaptation of the new head (Bronner-Fraser, 2008;Depew and Olsson, 2008;Nikitina et al, 2008;Glenn Northcutt, 2005), much remains to be understood about how diversity in the size and shape of NC derivatives is achieved. Given the emphasis in the literature on the ability of NC to regenerate, NC progenitor number is assumed to be crucial to proper regulation of size.…”