Hunchback prevents notch-induced apoptosis in the serotonergic lineage of Drosophila Melanogaster.

The serotonergic lineage (NB7-3) in the Drosophila ventral nerve cord produces six cells during neurogenesis. Four of the cells differentiate into neurons: EW1, EW2, EW3 and GW. The other two cells undergo apoptosis. This simple lineage provides an opportunity to examine genes that are required to induce or repress apoptosis during cell specification. Previous studies have shown that Notch signaling induces apoptosis within the NB7-3 lineage. The three EW neurons are protected from Notch-induced apoptosis by asymmetric distribution of Numb protein, an inhibitor of Notch signaling. In a numb 1 mutant EW2 and EW3 undergo apoptosis. The EW1 and GW neurons survive even in a numb 1 mutant background suggesting that these cells are protected from Notch-induced apoptosis by some factor other than Numb. The EW1 and GW neurons are mitotic sister cells, and uniquely express the transcription factor Hunchback. We present evidence that Hunchback prevents apoptosis in the NB7-3 lineage during normal CNS development and can rescue the two apoptotic cells in the lineage when it is ectopically expressed. We show that hunchback overexpression produces ectopic cells that express markers similar to the EW2 neuron and changes the expression pattern of the EW3 neuron to a EW2 neuron. In addition we show that hunchback overexpression can override apoptosis that is genetically induced by the pro-apoptotic genes grim and hid. [Display omitted] • Hunchback is necessary to prevent apoptosis of the GW neuron during specification of the Drosophila NB 7-3 lineage. • Ectopic Hunchback expression rescues apoptotic cells in the Drosophila NB 7-3 lineage. • Ectopic Hunchback produces ectopic serotonin neurons that resemble the EW2 neuron in the Drosophila NB 7-3 lineage. • Ectopic Hunchback can prevent apoptosis induced by the misexpression of pro-apoptotic genes in the Drosophila NB 7-3 lineage. [ABSTRACT FROM AUTHOR]