- Article -

Volume 3

Special Issue
BGRS 2002

Full article

Making the body plan: Precision in the genetic hierarchy of Drosophila embryo segmentation

Alexander V. Spirov^{1, 2} and David M. Holloway ^{3, *}

¹Department of Applied Mathematics and Statistics and The Center for Developmental Genetics, The State University of New York at Stony Brook, New York, 11794-3600, USA. Email: spirov@kruppel.ams.sunysb.edu
² The Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez Ave., St. Petersburg, 194223, Russia.
³ Mathematics Department, British Columbia Institute of Technology, 3700 Willingdon Ave., Burnaby, B.C., Canada, V5G 3H2; and Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada, V6T 1Z1. Email: David_Holloway@bcit.ca

^* corresponding author


Edited by E. Wingender; received September 30, 2002; accepted December 12, 2002; published December 16, 2002

Abstract

We quantify fluctuations in protein expression for three of the segmentation genes in the fruit fly, Drosophila melanogaster. These proteins are representative members of the first three levels of a signalling hierarchy which determines the segmented body plan: maternal (Bicoid protein); gap (Hunchback protein); and pair-rule (Even-skipped protein). We quantify both inter-embryo and inter-nucleus (within a single embryo) variability in expression, especially with respect to positional specification by concentration gradient reading. Errors are quantified both early and late in cleavage cycle 14, during which the protein patterns develop, to study the dynamics of error transmission. We find that Bicoid displays very large positional errors, while expression of the downstream genes, Hunchback and Even-skipped, displays far more precise positioning. This is evidence that the pattern formation of the downstream proteins is at least partially independent of maternal signal, i. e. evidence against simple concentration gradient reading. We also find that fractional errors in concentration increase during cleavage cycle 14.

Key words: morphogens, pattern formation, gradient reading, genetic cascades, positional information, gene networks, signalling hierarchy, concentration noise, embryo segmentation, maternal genes, gap genes, pair-rule genes, embryo-to-embryo variability, nucleus-to-nucleus variability, genetic algorithms, stochastic, error transmission, axis specification, image processing, Drosophila melanogaster