Nature , | doi:10.1038/nature07005
The branching programme of mouse lung development
Ross J. Metzger, Ophir D. Klein, Gail R. Martin & Mark A. Krasnow
Il n’y a pas longtemps je discutais de la bonne modélisation, enfin, bonne dans le sens ou je l’aime. Et je l’aime basée sur des données, réaliste.
Un nouvel exemple ici avec un modèle qui doit une grande part de son élégance à sa simplicité, accompagné d’une description détaillée du sujet, qui pourra probablement profiter même à des spécialistes et certainement aux spécialistes. Il arrive même avec un peu de génétique, ce qui n’est plus assez fréquent à mon goût.
De la bonne, à consommer sans modération, malgré les effets enivrants (le café aide 
)
Abstract: Mammalian lungs are branched networks containing thousands to millions of airways arrayed in intricate patterns that are crucial for respiration. How such trees are generated during development, and how the developmental patterning information is encoded, have long fascinated biologists and mathematicians. However, models have been limited by a lack of information on the normal sequence and pattern of branching events. Here we present the complete three-dimensional branching pattern and lineage of the mouse bronchial tree, reconstructed from an analysis of hundreds of developmental intermediates. The branching process is remarkably stereotyped and elegant: the tree is generated by three geometrically simple local modes of branching used in three different orders throughout the lung. We propose that each mode of branching is controlled by a genetically encoded subroutine, a series of local patterning and morphogenesis operations, which are themselves controlled by a more global master routine. We show that this hierarchical and modular programme is genetically tractable, and it is ideally suited to encoding and evolving the complex networks of the lung and other branched organs.
[... un papier entier ici]
Evolution of branching networks
Branching networks come in many sizes, cellular architectures and branching complexities that differ between organs and species. For example, the human bronchial tree contains millions of branches, several orders of magnitude more than in mouse, whereas the lobes of frog lungs are unbranched sacs. Human and mouse lungs also differ in lobation and branch pattern.
The modular logic of the mouse lung branching programme suggests how such structural diversity is created during evolution. New branching patterns can arise by reiterative use of subroutines or new patterns of their deployment. Indeed, although limited, the developmental data available for human and pig provide evidence that at least domain branching and orthogonal bifurcation are used in other animals. New branching patterns can also arise by local modifications of subroutines, like the increased number and altered positions of domain branches in Spry2 and shifty mutants, and the reduction of the standard four-domain structure to three domains for the accessory lobe branch R.Ac. More extreme modifications could create entirely new subroutines: orthogonal bifurcation may have evolved from planar bifurcation by acquisition of the rotator function. Branching subroutines controlled by a master routine may represent a general biological strategy for encoding and evolving complex branch patterns.
