You foolish biologists, stop whatever you’re doing right now and learn from the wisdom of our physicist :
Now, about the dorso-ventral “gradient”. In general terms, the body exhibits a dorsal side and a ventral side, inherited from the existence of slightly diﬀerent cellular types on the endoderm and the ectoderm. This dorso-ventral polarity is also present in the hands, with an obvious palmar and a dorsal side. Bio-chemically, this difference seems to be related to the genetic pathway of en1 and wnt-7a , and analogous genes may be at play in the dorso-ventral polarity of insect wings . But the expression of speciﬁc genetic pathways is related actually to the geometry of the limb bud at the moment of formation: if the limb bud forms from endoderm and ectoderm21 , it has dorso-ventral polarity (like a normal hand), if a limb bud forms more proximally by a fold of ectoderm only, the limb paddle has double dorsal polarity . Therefore, the dorso-ventral polarity is a matter of gradient of molecules, but the boundary conditions for these molecules are geometrically carried by the respective layers of cells. From a geometrical point of view, the formation of the limb bud appears as a physical process, which does not require speciﬁc cell sheets, but it happens that ectoderm and endoderm have originally a molecular diﬀerence, and this suﬃces to induce a dorso-ventral “gradient” across the dorso-ventral direction. [p13, column 1, §2; emphasis mine]
Do you feel the power of clarification operating? Do you feel it? If so, please wake-up.
So, normal limbs buds [hands that’s it, normal hands] form from ectoderm and endoderm, according to Vincent Fleury at least. Now, you fucking stupid experimental biologists1, who know nothing, start correcting every single embryology notebook out there and put at the index those papers demonstrating the meso-ecto-dermal origin of limb buds’ tissues. The physicist have a point of view which doesn’t fit reality, so let’s change reality. You don’t expect him to RTFM and conform with it, do you? He has his point of view, right?
I wonder how one could induce a limb bud more proximally (not dorsally, proximally), but our physicist knows better and will explain, maybe, if he is in the mood to do so. Or not.
Thus, if you induce a limb bud more proximally, by a fold of endoderm only, you lost ventral polarity 😀
OK, let’s be serious.
On p12, column 2, §2, dealing with the proximo-distal axis, in reference to the “edge itself”, Vincent Fleury interpret the edge to be “the line of suture of the endoderm and the ectoderm” whis is pattetly a misunderstanding which can’t be originated by the figure and legend3.
- Vincent Fleury haven’t read an embryology textbook2.
- Vincent Fleury don’t understand dorso-ventral and proximo-distal axes.
- The referees of the paper are not best informed than the author about embryology. What an embarrassment for the editorial board of EPJ AS and the Editor-in-Chief, B. Drévillon, a physicist originating from Ecole Polytechnique, the same as Vincent Fleury (what a coincidence!) .
With his poor understanding of embryo’s geometry and embryology he have built a point of view and expect to clarify tertrapods’ embryogenesis.
1. I’m kidding, I’m kidding … That’s a simple side effect of intense loling
2. or if he did read one and he didn’t understood it, one could bet that don’t know what AER stand for, that’s being Apical Ectodermal Ridge. But he do know, the name is found in extenso in his text, he probably just don’t understand it.
3. [click for a larger view, figure and legend from doi: 10.1242/10.1242/dev.01787]
Fig. 1. Normal expression of Tbx3 in the chick (A-F). (A) At stage13, Tbx3 is expressed in the presumptive forelimb (FL) and hindlimb (HL) levels (arrowheads). (B) At stage 16, Tbx3 expression is more robust in the posterior of the limb (arrowheads). (C) Stage16 section at the forelimb level. Tbx3 is expressed in the lateral plate mesoderm and somite. (D) Higher magnification of section in C. Tbx3 is present in the mesoderm but not ectoderm of the wing and in the ventrolateral lip of the dermomyotome. (E) Stage 19, Tbx3 is located in the posterior limb mesenchyme (arrowheads). (F) Stage 25, Tbx3 is present in the limbs in two stripes in the anterior and posterior limb mesenchyme (arrowheads). (G) Schematic diagrams of Tbx3 constructs. (H) Bar chart representing the relative luciferase activity obtained in luciferase assays with Tbx3 constructs. S, somite; LP, lateral plate mesoderm; V, ventral lip of dermomyotome; M, mesoderm; E, ectoderm.