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Fig. 8. Model of hb regulation in NB lineage development.
Expression of svp mRNA starts in the NB in a lineage-specific time
window, which is dependent on an unknown timing mechanism. In the case of two
Hb-dependent GMCs with different fates, svp expression starts after
the birth of the first GMC (GMCa). Before the next mitosis, most of the
svp mRNA is kept in the nucleus, allowing only a limited translation
of Svp protein. The resulting Svp activity leads to a reduction of hb
expression, which is necessary to specify the fate of GMCb. Subsequently, as a
result of the next mitotic division, the translation of svp mRNA is
enhanced and hb expression is switched off in the NB. Within GMCb,
Svp is inhibited by Pros, which has segregated into the GMC during mitosis,
thereby maintaining hb expression in this cell.
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