Mechanism for the establishment of D-V positional information

-gradient of DL protein activity in cells along D-V axis is established

-DL protein is a transcription factor encoded by the dorsal (dl) gene

-DL protein:
    1) active transcription factor in nucleus

    2) inactive protein in cytoplasm (here it is segregated in a complex that is bound to CACT protein of the cactus (cact) gene

- active form determines cell fate along D-V axis
-DL protein and dl mRNA are now not uniformly distributed in oocyte, instead there is a gradient of active DL protein with the highest point located at the ventral midline of the embryo

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How is the DL active protein gradient established by the D-V positional information?

-SPZ ligand (encoded by spaetzle (spz) gene) is synthesized and secreted from oocyte-follicle

complex

-Active SPZ ligand binds to TOLL transmembrane receptor.

-SPZ-TOLL complex triggers a signal transduction pathway

-pathway causes the phosphorylation of inactive DL and CACT cytoplasmic proteins of

DL-CACT complex.

-conformational changes break apart cytoplasmic complex

-free phosphorylated DL protein migrates to nucleus where is serves as a transcription factor