Protochordates

Tetsukawa, A., Nakamura, J., and Fujiwara, S. (2010). Identification of chondroitin/derma-tan sulfotransferases in the protochordate, Ciona intestincdis. Comp. Biochem. Physiol. 157, 205-212. 

Cannon, J.P., Haire, R.N. and Litman G.W. (2002) Identification of diversified genes that contain immunoglobulin-like variable regions in a protochordate. Nat. Immunol. 3, 1200-1207. 

Lacalli TC. 2001. New perspectives on the evolution of protochordate sensory and locomotory systems, and the origin of brains and heads. Philos Trans R Soc Lond B Biol Sci 356 1565-1572. 

Fig. 1. The C-terminal structure of members of the gastrin family. The members are characterized by the same active site, i.e., the C-terminal tetrapeptide amide (shown in the internal box). Another characteristic is an O-sulfated tyrosyl residue close to the active site. In gastrin peptides the sulfated tyrosyl residue is located in position six (as counted from the C-terminus) in cholecystokinins it is position seven. The frog skin peptide caerulein therefore acts as cholecystokinin in mammals. Cionin is a neuropeptide from the protochordate, Ciona intestinalis. Cionin is unique in having O-sulfated tyrosyl residues in both positions six and seven. The cionin structure is therefore likely to correspond to that of the common ancestor of gastrin and cholecystokinin.

J3. Johnsen, A. H., and Rehfeld, J. F., Cionin, a di-sulfotyrosyl hybrid of cholecystokinin and gastrin from the neural ganglion of the protochordate Ciona intestinalis. J. Biol. Chem. 265, 3054-3058 (1990). 

Fig. 4. A simplified phylogenetic tree of the Metazoa indicating the major phyla and species where Otx-related genes have been isolated. The asterisks point to the two possible positions of the first Otx duplication from a single ancestral gene. The presence of only one Otx-like gene in protochordates suggests that the Otx duplication observed in the flour beetle Tribolium castaneum and in the planaria Dugesia japonica are likely independent events occurred in these organisms. Members of the recently established Crx gene family are underlined.

Indeed, the brain vescicle of protochordates has been deeply and suddenly modified in a much more complex brain that has been maintained in its basic topography until mammals. This morphogenetic event might have coincided with duplication, recruitment, and stabilization of conserved genetic functions into new cell-types that in turn, have refined/modified or created new versions of pre-existing developmental pathways possibly by increased combinations of new molecular interactions (Holland, 1999 Acampora et al., 2001). Indeed, it might be that... 

The protochordates (amphioxus and tunicates) occupy a pivotal position in chordate phylogeny, being the closest living invertebrates to the vertebrates. In spite of their evolutionary significance, these animals do not feature commonly in modern developmental biology research. This has not always been the case indeed, amphioxus ranked as one of the principal animals for embryological description in the early part of this century. The ascidia (one group of tunicates) have received intensive study as a model for determinative development, and considerable experimental and molecular data have been accumulated over the past few decades (1). 

There is no unequivocal evidence for single cells migrating from the neural plate or neural tube of protochordates. Some authors have suggested that lateral movement of dorsal epidermal cells towards the midline during amphioxus neurulation may be compared to the migratory behaviour of vertebrate neural crest cells (Holland et al. 1996). However, amphioxus cells move as an epithelial cell sheet and represent a fundamentally different cell behaviour from that shown by mesenchymal neural crest... 

Kemp, A. and Nicoll, R.S. (1995) Protochordate affinities of conodonts . Courier Forschungsinstitut Senckenberg, 182, 235—45. 

Lambert, G., Lambert, C.C. and Lowenstam, H.A. (1990) Protochordate biomineralisation , in Carter, J.G. (ed.) Skeletal biomineralisation patterns, processes and evolutionary trends. New York Van Nostrand Reinhold, pp. 461-9. 

Rinkevich, B. and Rabinowitz, C. (1993) In vitro culture of blood cells from the colonial protochordate Botryllus schlosseri. In Vitro Cell. Dev. Biol, 29A, 79-85. 

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