Positively regulates the activity of the minus-end directed microtubule motor protein dynein. May enhance dynein- mediated microtubule sliding by targeting dynein to the microtubule plus end. Required for several dynein- and microtubule-dependent processes such as nuclear migration during cell division; mitotic spindle formation and the removal of mitotic checkpoint proteins from kinetochores at the metaphase to anaphase transition. Required for several aspects of neurogenesis including neuroblast proliferation; neuronal cell differentiation; dendritic growth; branching and maturation and axonal transport. Required for synchronized cell divisions in the germline; fusome integrity and oocyte differentiation. Acts together with BicD; Egl; dynein and microtubules to determine oocyte identity during oogenesis. Also required for nurse cell to oocyte transport during oocyte growth and for the positioning of the nucleus in the oocyte. {ECO:0000255|HAMAP-Rule:MF_03141; ECO:0000269|PubMed:10498683; ECO:0000269|PubMed:10559989; ECO:0000269|PubMed:10993674; ECO:0000269|PubMed:11056531; ECO:0000269|PubMed:16105886; ECO:0000269|PubMed:16107559}.