Institut für Neuro- und Bioinformatik
Seelandstraße 1a,
23569 Lübeck, Germany
Phone: +49 451 3909-585
Fax: +49 451 3909-545
Email: kim@inb.mu-luebeck.de
Regulatory gene networks, consisting of transcription factors and the genes encoding them, are an important mechanism for organizing developmental processes according to genetic information. As a generic formalism for specifying dynamic models of regulatory gene networks,transsys has been developed and integrated within an Lindenmayer system framework, called L-transsys (see http://www.inb.mu-luebeck.de/transsys/, [1]). Genes belonging to the DEF subfamily and the GLO subfamily of MADS box genes [2] encode transcription factors which act as heterodimers. Initially, this was described for Antirrhinum genes [3]. The DEF/GLO heterodimers function as master switches activating the morphogenesis of petals and stamens. The genes def and glo are among the targets of the DEF/GLO heterodimer which upregulates expression of both genes. Thus, a positive autoregulatory feedback loop is formed which is required to maintain expression of def and glo. Loss of function in either of these genes results in homeotic transformations of petals to sepals and of stamens into carpels.
Regulatory control by heterodimers (or higher order protein complexes) is an important component in regulatory gene networks. In this contribution, a refined L-transsys model of flower morphogenesis, which includes is presented.
transsys programs describe regulatory networks by specifying the essential properties of their constituent genes and proteins in corresponding blocks. Gene blocks comprise promoter blocks which determine the cis-regulatory properties of a gene:
gene defgene
{
promoter { def: activate(0.3, 1.0); }
product { default: def; }
}
This example shows the transsys specification of defgenewhich is activated by its own product def (please refer to the transsys website for full details). Modelling of regulation by heterodimers is enabled by a simple extension of the transsyssyntax: In an activate statement, factor combinations are permitted in addition to single factors:
gene defgene
{
promoter { def + glo: activate(0.3, 1.0); }
product { default: def; }
}
An L-transsys model of flower morphogenesis including the autoregulatory loop described above has been developed. The model captures some essential aspects of the spatiotemporal process of flower development. Most importantly, all simulations of mutations on the genetic level result in realistic effects on the phenotypic level.
The refined model presented here is an intermediate step towards building a full model of the regulatory network organizing flower morphogenesis.