galanterie

Il y a des galanteries franchement puantes et il y a des galanteries franchement rafraîchissantes. OldC m’a passé un coup de fil il y a un peu plus de 45 min, qui s’est conclu par :  » à toi l’honneur ».

Si M. Fleury a écrit à Tabin et que lui a transmis à Logan il se peut que les deux puissent rigoler allègrement de M. Fleury et de son ignorance (entre autres de la littérature scientifique du sujet sur le quel il semble travailler)

OldC quand il fait de la biblio la fait à fond. Il est parti pour quelques jours de vacances en embarquant de quoi lire : la biblio complète de Tabin et Logan en fait. Dans le tram il est tombé sur un « bijou tout mignon« , comme il dit, et il m’a appelé pour me le signaler et me demander si j’aurais l’obligeance de me charger à le poster ici. Ce n’est pas de l’obligeance, c’est un plaisir évident.

Il se trouve que Malcolm Logan a continué à travailler sur Pitx1 et son rôle dans la morphogenèse; il y a un an à peu près il signait ce papier :


Pitx1 determines the morphology of muscle, tendon, and bones of the hindlimb

April DeLaurier, Ronen Schweitzer and Malcolm Logan

The vertebrate forelimb and hindlimb are serially homologous structures; however, their distinctive morphologies suggest that different mechanisms are associated with each limb type to give rise to limb-type identity. Three genes have been implicated in this process; T-box transcription factors Tbx5 and Tbx4, which are expressed in the forelimb and hindlimb, respectively, and a paired-type homeodomain transcription factor Pitx1, expressed in the hindlimb. To explore the roles of Pitx1 and Tbx4 in patterning the hindlimb, we have ectopically misexpressed these genes in the mouse forelimb using transgenic methods. We have developed a novel technique for visualising the structure and organisation of tissues in limbs in 3D using optical projection tomography (OPT). This approach provides unparalleled access to understanding the relationships between connective tissues during development of the limb. Misexpression of Pitx1 in the forelimb results in the transformation and translocation of specific muscles, tendons, and bones of the forelimb so that they acquire a hindlimb-like morphology. Pitx1 also upregulates hindlimb-specific factors in the forelimb, including Hoxc10 and Tbx4. In contrast, misexpression of Tbx4 in the forelimb does not result in a transformation of limb-type morphology. These results demonstrate that Pitx1, but not Tbx4, determines the morphological identity of hindlimb tissues.

Keywords: Pitx1; Limb-type identity; Hoxc10; 3-D imaging; OPT

doi:10.1016/j.ydbio.2006.06.055

L’accès est libre, le papier vient juste de sortir de derrière le paywall. Ainsi, si vous voulez aborder le sujet doucement, ne cliquez pas pour voir la suite du post. Cliquez pour ouvrir le papier lui-même.


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Ca en fait des effets un gène, ne trouvez vous pas ? Et c’est une souris transgénique, pas besoin de « mettre par force brute » quoi que ce soit. Intéressant mon cher Watson, intéressant !

4 Réponses

  1. MESSAGE DE VF A CLIFF TABIN:

    Dear Prof Tabin

    please find in attachment a figure of a paper from you and Logan, in Science, about
    transfected wings expressing pitx1, which « look like » legs, in this article you state
    that « the normal flexure of the wing has changed (with respect to the wild type)  »
    You mean, the flexure of the wrist, don’t you?

    the flexure of the elbow is unchanged, is that right?

    I ask you this, because I have a biomechanical model of development that shows that legs
    and « arms » have to flex in opposite direction, whatever the genes they express, by laws
    of biomechanics, and some biologists tell me « oh it is well known that you can change the
    flexion of limbs by expressing different genes », this is based on your article in
    Science, and I think this statement is wrong.

    Best regards

    Vincent Fleury

    REPONSE DE CLIFF TABIN

    Dear Vincent,

    On the one hand, your observations on our paper are correct, the reversed flexure upon Pitx misexpression is limited to the wrist.

    (similar results have been obtained in teh mouse–see Dev Biol. 2006 Nov 1;299(1):22-34.
    Pitx1 determines the morphology of muscle, tendon, and bones of the hindlimb.
    DeLaurier A, Schweitzer R, Logan M.)

    However, I do not understand how a biomechanical model can possibly force the flexure of the limbs in particular directions. There are many classical experiments in chick that would seem to argue against this. For example, if one simply rotates the early limb bud 180 degrees, the limb bud that grows out has all flexures reversed, as its dorsal/ventral and anterior/poosterior axes are both reversed. The DV axis is controlled by the ectoderm, and thus dissociating the ectoderm hull, and rotating it 180 degrees and then putting it back on the mesenchyme reverses the dorsal/ventral axis while the anterior/posterior axis is unaffected. This actually only affects the distal limb , but the wrist and digits reverse their flexture along with their dorsal/ventral polarity. Finally, fgf activity in the flank is sufficient to induce an ectopic limb. If one places a an Fgf bead into the flank closer to the wing than the leg field, an ectopic wing results. It has reversed anterior/posterior polarity (because the source of Sonic hedgehog is at teh anterior side of the ectopic limb, while at the posterior side of teh endogenous wing). The flexture of every joint from teh shoulder on down is reversed (see attached image). One can also do the bead implantation in conjunction with surgical removal of the endogenous limb field. If one does this, there are only two limbs on the experimental side, a wind and a leg, with identical flexture at each limb segment.

    I hope this helps.

    Cliff

    REPONSE DE VF a CLIFF TABIN

    Dear Cliff,

    this is the sweetest reply of all. All your replies feet perfectly into the biomechanical model.

    thank you so much, it truly confirms that there exists a hyperbolic flow of cells towards the presumptive navel.

    Let me explain :

    at early stages, the blastula of the chick is a flat disk

    during convergent extension, the flow of cells has the shape of two jets of cells colliding head on in the area of the presumptive navel

    due to conservation laws of physics, these two jets split into four vortices which wind away fom a neutral point of stretch (stagnation point) which is evetually the navel

    each of these windings has a flow pattern which is a rotational engulfment, akin to « a tornado ». These are the LATERAL PLATES

    As you know rotating streams have a singularity of pressure in the center (think of tornadoes, which have a low pressure in the center)

    as a consequence, each winding bumps out and « feels » like getting more outwards

    these are the LIMB BUDS

    but, as a consequence of the flow map, the areas of the flows have mirror symmetry around the navel

    whatever the genes expressed in these areas, the boundary condition created by the rotation has mirror symmetry, and the true limbs will form with approximately a mirror symmetry, the arm flexing towards the head after the elbow, and the leg flexing towards the tail after the knee

    during development, there exists a twist of the cell lines in the upper limb buds and in the hindlimb buds which has mirror symmetry such that, during further development they limbs extend out like « a garden chair » which you open.

    With my best regards

    vincent

    A tous je dis : CHAMPAGNE

  2. Hello!

    Que de billets (pas toujours doux… j’ai vu indûment traîner « ducon » et « fasciste » au cours de mon survol) produits durant mes courtes vacances. Je vais m’atteler à une lecture plus approfondie et… c’est oui, pour l’invite😉

  3. […] suite #1 Posted by oldcola under biblio  Le papier de DeLaurier et al. qu’Agathi a présenté, “Pitx1 determines the morphology of muscle, tendon, and bones of the hindlimb”, est […]

  4. Bienvenue Pangolina

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