SCS colloquium: "Variation and canalization of gene expression in the Drosophila blastoderm."

Program:

-Speaker: Maria Samsonova (Department of Computational Biology, Center 
for Advanced Studies, St.Petersburg State Polytechnical University)

-Title: "Variation and canalization of gene expression in the 
Drosophila blastoderm."

Abstract
Development is surprisingly robust to environmental, genetic and 
stochastic variation. The widespread variation affecting morphogenic 
pathways exists in nature, but is usually silent due to buffering 
mechanisms.  To  formalize the concept of developmental stability 
against genetic and environmental perturbation C.H. Waddington 
presented his now famous "epigenetic landscape" and 
"canalization"( Waddington, 1940). The further development of 
Waddington's concepts is of great importance because it provides a 
scientific connection between the reliability and invariance of the 
formation of cell types and tissues in the face of underlying 
molecular variability. The morphogenetic field controlling 
segmentation in fruit fly Drosophilais a suitable model to address 
these problems due to a thorough characterization of this field at 
both molecular and genetics levels (Ingham, 1988; Surkova et al., 2008).
A particularly important class of phenomena concerns variation in the 
location of  expression domain boundaries, as the segmentation gene 
cascade defines the boundaries of wg and en expression, that in turn 
define the parasegment boundaries. We showed that the positionsof 
these boundaries  are highly variable, when the expression domains 
form, and that this variation is dynamically reduced, or canalized, 
over time (Surkova et al., 2008).

Here we have used the gene circuit method to investigate the variance 
reduction phenomena in detail.  We showed  that the canalization of 
extensive variation in early gap gene expression patterns occurs by 
gap gene cross regulation.  To explore how the canalization arises we 
undertook the analysis of the gap gene border formation in the model  
in terms of the phase portrait of the dynamical system. We 
demonstrated   that the variation reduction of gap gene expression 
patterns is a consequence of the action of robust attracting states. 
We further showed that the complex patterning of the gap gene system 
reduces to the three qualitative dynamical mechanisms of (1) movement 
of attractors, (2) selection of attractors, and (3) selection of 
states on a one dimensional manifold. The last of the three mechanisms 
also causes the domain shifts of the gap genes, providing a simple 
geometric explanation of a transient phenomenon.

-Computational Science 5 minutes

- Drinks