Patterns and functions of STAT activation during Drosophila embryogenesis.

The JAK/STAT pathway mediates cytokine signaling in mammals and is involved in the function and development of the hematopoietic and immune systems. To investigate the biological functions of the JAK/STAT pathway during Drosophila development, we examined the tissue-specific localization of the tyrosine-phosphorylated, or activated form of Drosophila STAT, STAT92E. Here we show that during Drosophila embryonic development STAT92E activation is prominently detected in multiple tissues and in different developmental stages. These tissues include the tracheal pits, elongating intestinal tracks, and growing axons. We demonstrate that stat92E mutants are defective in tracheal formation, hindgut elongation, and nervous system development. Conversely, STAT92E overactivation caused premature development of the tracheal and nervous systems, and over-elongation of the hindgut. These results suggest that STAT activation is involved in proper differentiation and morphogenesis of multiple tissues during Drosophila embryogenesis.