BIO 448
MOLECULAR BIOLOGY OF
DIFFERENTIATION
Role of Differential Gene Expression in Establishing Body Segmentation
fruit fly; Drosophila
Maternal Effect Genes
• Determine Polarity
• Polarity depends on the distribution of the morphogen.
Maternal Effect Genes
• Morphogens are products of the specific
“maternal effect genes” in the mother and are often distributed unevenly to the eggs.
• determines the dorsoventral (back-abdomen) and anteroposterior (head-tail) axes.
• bicoid
• nanos
Segmentarion genes and Homeotic Genes
Segmentarion genes
• show their effects after maternal effect genes
• the number, limits, and polarity of the larval segments are determined by the proteins encoded by the segmentation genes.
• maternal effect genes activate the segmentation genes.
• Three classes of segmentation genes
• gap genes
• double rule genes
• segment polarity genes
• gap genes: organize large areas
along the anteroposterior axis.
• double rule genes: divide the
embryo into two segmented units
each.
• segment polarity genes: determine
the boundaries of the segments and
the anteroposterior organization.
• provides differences between segments
• Exp. Drosophila