scaffold depleted in testicular seminomas impacts spindle 1 orientation in germline stem cells

18 Running Title: A mitotic kinase scaffold impacts spindle orientation 19 20 ABSTRACT 24 25 Correct orientation of the mitotic spindle in stem cells underlies organogenesis. 26 Spindle abnormalities correlate with cancer progression in germline-derived 27 tumors. We discover a macromolecular complex between the scaffolding protein 28 Gravin/AKAP12 and the mitotic kinases, Aurora A and Plk1 that is down 29 regulated in human seminoma. Depletion of Gravin correlates with an increased 30 mitotic index and disorganization of seminiferous tubules. Biochemical, super-31 resolution imaging and enzymology approaches establish that this Gravin 32 scaffold accumulates at the mother spindle pole during metaphase. Manipulating 33 elements of the Gravin-Aurora A-Plk1 axis prompts mitotic delay and prevents 34 appropriate assembly of astral microtubules to promote spindle misorientation. 35 These pathological responses are conserved in seminiferous tubules from Gravin 36 knockout mice where an overabundance of Oct3/4 positive germline stem cells 37 display randomized orientation of mitotic spindles. Thus we propose that Gravin-38 mediated recruitment of Aurora A and Plk1 to the mother (oldest) spindle pole 39 contributes to the fidelity of symmetric cell division.