Independence of fushi tarazu expression with respect to cellular density in Drosophila embryos.

Regularly spaced repeated morphological structures are a common developmental theme among higher eukaryotes. In Drosophila, this is evident in the repeated segments of the larval and the adult cuticle. It has been demonstrated through cell transplantation and more recently through molecular techniques that these repeated segmental units are established as early as nuclear cycle 14 in the blastoderm embryo. A number of genes have been shown to express their transcripts, and in two instances their protein products, in a spatially restricted manner at this early stage. Immunofluorescence probes against the protein product of one such gene, fushi tarazu (ftz), reveal that it is distributed in seven evenly spaced stripes across the cellularized cycle-14 blastoderm embryo. The mechanisms that determine such spatial patterns of gene expression are of fundamental importance for the development of multicellular organisms, but in no case are they well understood. Here we examine the ftz pattern on blastoderm embryos derived from maternal-haploid 1182 (mh 1182) and daughterless-abo-like (dal) females which possess cell densities and sizes both above and below the wild-type levels. The number, spacing and width of the ftz protein positive bands are not altered in these abnormal embryos relative to the wild-type pattern, suggesting that the mechanism by which distance is measured with respect to the ftz protein is independent of cell size and density.