Vincent Fleury: Dynamic topology of the cephalochordate to amniote morphological transition: A self-organized system of Russian dolls

It takes a physicist, and not your random physicist but a very special one, Vincent Fleury, to teach you that the Cephalochordata have no head! How ignorant one must be to say that a subphylum named after the particularity that the notochord is reaching into the head, yes head|tête|κεφαλή, has no head?

This comes straight out of his new paper: V. Fleury, Dynamic topology of the cephalochordate to amniote morphological transition: A self-organized system of Russian dolls, C. R. Biologies (2011), doi:10.1016/j.crvi.2010.11.009 [Abstract & Résumé]

Fleury is observing the world through the keyhole of his theory, nicely summarized here, and that may explain how he came to see the anatomy of the chorion as a dorsal fold (which de considered only for the amniotic folds as if the rest of the membrane didn’t existed)

954F800D-AF97-458D-842C-BF443ACCDD59.jpg

[source]

The visibility field being low, he missed also a few of the hagfish’s hearts.
He does reference Jensen’s 1965 paper, The Aneural Heart of the Hagfish (doi: 10.1111/j.1749-6632.1965.tb4), but I really wonder if he read it. Probably not. Not that I expect Fleury to understand what he is supposed to have read neither… He seems to have missed the portal heart and you can’t miss it if you read the paper. Clearly visible in figure 4

hcs-jensen.jpg

And part of the principal subject of the paper concerned by the aneural hearts, as stated in the end of the introduction:

The remainder of this report, therefore, is a presentation of certain fundamental data on transmembrane potentials of the systemic and portal hearts of hagfish.

Along with the portal heart are gone the cardinal hearts (not mentioned by Jensen) described in 1926 by Cole (mentioned by Johansen, 1965, doi: 0.1111/j.1749-6632.1965.tb49417.x.
And Fleury seems to think that the caudal heart is the aneural one:

The model would predict that there should exist animals with a heart located symmetrically to the heart in the chest, therefore near the tail. By searching in the litterature, I was surprised to see that it is indeed the case, there exist primitive fish, hagfish, with an aneural heart[8]

Well, the caudal heart is the only one known to be innervated in the hagfish. (check « Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfish Eptatretus burgeri Girard« , I. Inoue et al, The Journal of Experimental Biology 205, 3535-3541 (2002), not a recent discovery neither, dating back to 1890, made by Retzius [and no, I haven’t read Retzius paper, it’s in German])


While reading Fleury’s report, several questions pop-up:

• What the fuck happened during the review process? Both the editor and the referees where unable to spot the error about these cephalochordates lacking a head? Or the chorion being a dorsal fold? I mean, these are huge errors! So much for Comptes Rendus [de l’Académie des Sciences] Biologies, Organe officiel de l’Academie des sciences.

• What kind of recruitment system can pick up this kind of scientists and warranty them a carrier-long salary and what kind of lab directors give them access to working benches?

I’ll let you find answers to these questions😉


Abstract

This note presents a mechanistic explanation of the transition between the morphology of cephalochordates to that of amniotes. By a careful study of the morphogenetic movements which occur during the early stages of development of a typical amniote (a chicken embryo), we are able to show that the formation of a vertebrate body follows a sequence: first, formation of dorsal folds, then head and heart as dorsal and ventral folds, and finally another dorsal fold, which eventually builds up the chorion. This order has a physical origin linked to the velocity field of the tissue flow. These folds form at right angles to the flow direction, and the topology of the chordates flow is hyperbolic. This mechanism explains the differences between the successive bauplans, by the cumulate forward and backward movement of the flow. Eventually, the entire phenomenon can be described as a self-organized system of Russian dolls, by which the heart finds itself inside the embryo, and the embryo itself inside the chorion. In addition, the phenomenon has a mirror symmetry in the anterior and in the posterior part, thereby explaining naturally the existence of animals having a caudal heart.

Résumé

Cette note présente une explication mécaniste de la transition de morphologie entre les céphalochordés et les amniotes. En étudiant en détail les mouvements morphogénétiques ayant lieu au cours de premiers jours de développement d’un amniote typique (le poulet), on constate que la formation du dos, de la tête et du cœur, puis du sac amniotique, obéissent à une logique physique, liée au sens dans lequel avance l’écoulement des tissus, en formant une succession de plis perpendiculaires au sens de l’écoulement. Les premiers plis créés par cet écoulement forment la région dorsale de l’embryon, et correspondent à un embryon sans tête. Les seconds plis sont dorsaux–ventraux et créent le cœur et la tête. Le troisième pli est dorsal et façonne en se contractant le sac amniotique (chorion). Les différences entre les plans d’organisation des chordés résulteraient en partie, des avancées relatives cumulées vers l’avant, ou vers l’arrière, de ces écoulements tissulaires. L’ensemble du phénomène aboutit à un emboîtement auto-organisé analogue à une succession de poupées russes: le cœur dans l’embryon, et l’embryon dans le sac amniotique formant trois « poupées » emboitées. Il existe également une symétrie miroir entre la partie antérieure et la partie postérieure, en sorte que les plis se forment aux deux extrémités, ce qui explique naturellement l’existence d’animaux ayant un cœur caudal.

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