Functional Analysis of Apoptosis-Related Genes, POSH, ALG-2 and AIP1 in Drosophila. M. Tsuda , K. Seong , T. Matsuo , T. Aigaki. Biological Sciences, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan.

   Misexpression of DPOSH ( Drosophila Plenty of SH3s), a protein containing a RING finger and four SH3 domains produces various morphological phenotypes such as loss of crossvein, notched wing, and disordered hair polarity. We showed that these phenotypes are caused through activation of JNK signaling pathway, based on the facts that 1) the misexpression of DPOSH induces ectopic expression of puckered, a target gene of the JNK pathway, and that 2) misexpression phenotypes were suppressed by a mutation of Drosophila JNK (bsk) or JNKK (hep). To gain insight into the mechanism by which POSH activates JNK pathway, we performed a yeast two-hybrid screen using Drosophila adult cDNA library. We identified a Drosophila homolog of apoptosis-linked gene-2 (DALG-2), an EF hand calcium-binding protein. In mice, ALG-2 has been shown to form a complex with ALG-2 interacting protein 1 (AIP1) in a calcium dependent manner and is necessary for cell death. Interestingly, AIP1 contains the proline-rich domain, which has high affinity to the SH3 domain. These findings suggest that DPOSH may interact with DALG-2 via Drosophila homolog of AIP1. Therefore, we isolated and characterized DALG-2 and Drosophila AIP1 (DAIP1) cDNA. We could show that both DPOSH and DALG-2 are capable of binding to the proline-rich domain of DAIP1. To examine the biological activity of these genes, we generated transgenic flies bearing UAS-DALG-2 and UAS-DAIP1. Overexpression of each of these genes was sufficient to induce cell death in the developing eye imaginal discs. We confirmed that ectopic expression of DALG-2 or DAIP1 induces puckered gene expression. Taken together, these results suggest that DPOSH cooperates with DALG-2 and DAIP1 in JNK signaling pathway.