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Fig. 8. Model of Notch regulation of midline cell fate in
Drosophila. (A) Mesectodermal cells meet at the ventral
midline before the stage 8
1414 division. Little is known
regarding influences on midline cell development at this stage. (B)
After the stage 8 division, but before Notch signaling, the 16
midline cells can be considered as three equivalent groups of cells: MP1s,
MP3s and MP4s. (C) After Notch signaling, the 16 cells acquire
specific fates, and differ in their levels of Notch signaling as
indicated by the expression of Su(H)-lacZ reporter. For simplicity,
midline cells are shown as paired cells along the anterior-posterior axis. The
precise anterior-posterior and left-right positions of individual cells are
unknown, except that AMG, MP1 and MP3 tend to reside in the anterior half, and
PMG, MP5, MP6 and MNB in the posterior half. Different shades of blue indicate
relative levels of Notch signaling. (D) Asymmetric cell
division. Notch signaling is required for MP3-6 asymmetric cell
fates. Notch signaling is active (blue diagonals) in H-cell sib and
iVUMs, and inhibited in H-cell and mVUMs. Assayed genes expressed in the MP3
and VUM lineages are shown below each neuron: bold text indicates expression,
whereas the light, shaded text indicates repression. Genes are categorized as
either Notch-activated, Notch-repressed or
Notch-independent. Functional classes of genes are color-coded:
transcription factors (blue), neural function genes (red) and others
(black).