3 The genetics of vertebrate development

In the third section of the paper Fleury starts to display his incredulity of genetic explanations of developmental morphogenesis, concluding by p16, col2, §2:

The review presented here highlights that inductive cascades of unidirectional gradients of scalar quantities cannot explain morphogenesis.

The review is incomplete and often bogus,which explain why Fleury is reaching this conclusion.

Certainly a lot is to be discovered in the field of developmental biology, but also a lot is known and one can’t just ignore it just because it doesn’t fit his point of view.

For those unfamiliar with biology I will try to point gross errors (factual or conceptual) and propose more appropriate readings.

The rhetoric of Fleury’s argumentation will be discussed as well, as they are one of the most interesting elements of the paper and may help understanding his point of view more clearly than his knowledge of the subject.

An overview of what will be discussed.

3.1 The homeobox genes in vertebrates

Fleury doesn’t deliver what is announced in the title. He rather focus on mammalian Hox genes, letting aside the evolutionary history of Hox, which starts with urbilateria, long before the appearance of vertebrates. The lack of evolutionary perspective is a huge handicap, both for the reader and the author.

And focusing just to Hox genes while trying understand development is not really clever, the error becomes rapidly evident as other gene families are discussed.

Particular emphasis will be on the way the author considers the relations between the genome’s content and patterns of expression and morphogenesis.

3.2 Limb patterning in tetrapods

Limb positioning and patterning of the limbs are discussed. Positioning isn’t announced despite the fact that it is central to Fleury’s point of view and occupies a large part of this subsection and th e central place of his incredulity.
It is quite difficult, I suppose, for one voluntarily ignoring the importance of genetic information to specify everything biological, even it is involves cells’ mechanosensitivity, to get a clear view of the studied phenomena. Fleury fails to get one.

In this subsection he makes a series of quite important remarks concerning experimental methodology and empirical approaches and the value he attribute to results. He is between the urge to acknowledge the obvious and the fact that it doesn’t fit in his point of view and try to find some way to make everything at least physical if not mechanical.
A little extension beyond the present paper will be made to examine Fleury’s approaches, experimental or simply descriptive, as they are of importance to understand the fallacy of some of his statements.

3.3 The limb field

There are at least two definitions of the word “field” to cosider. The one embryologists use and which is well defined, and the one Fleury use, which isn’t clearly defined, neither in the text of in the glossary.

This is the place where he try desperately to convince people that we don’t know where the lateral plate come from! And this make this subsection quite funny if you don’t just get angry with the peer-review process that let this paper be accepted.

Some things in life are bad
They can really make you mad
Other things just make you swear and curse.
When you’re chewing on life’s gristle
Don’t grumble, give a whistle
And this’ll help things turn out for the best…

And…always look on the bright side of life…
Always look on the light side of life…

words and music by Eric Idle

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