JAK/STAT signaling regulates defective proventriculus (dve) to determine dorso-ventral patterning in Drosophila eye

Long range signaling plays an important role in patterning and growth. During organogenesis, axial patterning is involved in delineation of Antero-Posterior (AP), Dorso-Ventral (DV) and Proximo-Distal (PD) axes. We employ Drosophila eye model to study the mechanisms behind DV patterning, which marks the first lineage restriction event. We have identified a new dorsal eye selector gene, defective proventriculus (dve, a Homeobox gene), an ortholog of SATB homeobox 1 (special AT-rich sequence binding protein 1), which controls expression of wingless (wg), a negative regulator of the eye development, to determine the head fate. Loss-of-function of dve results in dorsal eye enlargement by downregulating Wg, which is similar to the gain-of-function of JAK STAT signaling in the eye. Here we present that Unpaired (Upd), a long-range secreted ligand for JAK STAT pathway, plays an important role in DV patterning by regulating Dve expression in the dorsal eye. Gain-of-function of JAK STAT pathway in the eye disc exhibits dorsal eye enlargement by downregulating dve and its downstream wg. Conversely, inactivation of JAK STAT pathway causes dorsalization of the entire developing eye field due to ectopic induction of Dve and Wg in the ventral eye domain resulting in no-eye phenotype. Our data strongly imply that JAK STAT signaling plays a central role in DV axis determination by limiting the functional domain of the dorsal fate selector and thereby determine the boundary of eye versus the head field in the developing eye.