The Drosophila Jak kinase hopscotch is required for multiple developmental processes in the eye.

Jak kinases are critical signaling components in hematopoiesis. While a large number of studies have been conducted on the roles of Jak kinases in the hematopoietic cells, much less is known about the requirements for these tyrosine kinases in other tissues. We have used loss of function mutations in the Drosophila Jak kinase Hopscotch (Hop) to determine the role of Hop in eye development. We find that Hop is required for cell proliferation/survival in the eye imaginal disc, for the differentiation of photoreceptor cells, and for the establishment of the equator and of ommatidial polarity. These results indicate that hop activity is required for multiple developmental processes in the eye, both cell-autonomously and nonautonomously.