Figure 10

Figure 10

Lousy legend. Let’s go to the source.

Fig. 4 from Rallis et al. paper (direct link), corresponding to the top panel of cteappv’s figure 10:

Scanning electron micrographs of (A) control and (B) dominant-negative Tbx5 (Tbx5delta) injected limb buds at stage 20 show a dramatic reduction in limb size after Tbx5delta misexpression.

Certainly not “a mutant which lacks a given gene“.

This is a competition assay, between endogenous Tbx5 and injected Tbx5delta in wild type animals, gene’s transfer being via recombinant retroviruses.

Is the mutant presented at the bottom panel “a mutant which lacks a given gene“? Not. [see fig 1 of the source]

The transgenic mice have an inducible Cre recombinase expression under the Prx1 promoter. That means that the recombinase will be expressed in cells where Prx1 is naturally expressed. The Tbx5 gene is lox-ed: it can be excised from the genome by the action of Cre recombinase.

That means that Tbx5 expression will be impaired in cells expressing Cre recombinase under the control of the Prx1 promoter.

An elegant system allowing local knock-out of a gene otherwise essential for development, for which general knock-outs would be lethal. Allowing to validate a causal relation between an expression controlling element and a downstream situated gene. Once more, certainly not “a mutant which lacks a given gene“.

When one wants to present “Typical genetic assays on limb development“, especially to a public not accustomed with the presented techniques, it’s convenient for everybody that one understands what he is talking about.


3 Responses

  1. what’s the roblem here Mr Clever Guy?

  2. no roblem 😉 I see you have my kind of mistyping problems anon. You must be reading the paper, not easy stuff to go through, isn’t it ?

    First of all I expected that VF would do an effort for this manuscript. He didn’t, except for the rhetoric.
    I wonder if one or another of the regular readers of the journal will go through this opus and if so if he will feel afterwards that he learned some biology.

    Both experimental setting here do not concern animal lacking a given gene.
    The first one, quick and dirty (if one considers quick the preparation of the recombinant retrovirus) is the kind of experiments used to have a first idea of how a system works.
    The second one is more time consuming but it’s quite elegant: it establish a causal relation between the expression of anything with the transcription level controlled by the Prx1 promoter and the biological activity of Tbx5.
    Vincent Fleury often refers to such relations as correlations in his text. Apparently he don’t understand how genetic experiments work, and if so he should just avoid criticizing them as he do. Or, more important, draw ill informed conclusions.

    There is another point, I already mentioned: I hope no biologist reviewed the paper and left such messy stuff being published. That’s an important point and I’ll discuss it more extensively much later, once the different sections of the paper will be discussed.

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