PHOSPHORYLATION OF MICROTUBULE-ASSOCIATED PROTEINS FROM THE OVARIES OF HEMIPTERAN INSECTS BY MPF AND MAP KINASE - POSSIBLE ROLES IN THE REGULATION OF MICROTUBULES DURING OOGENESIS

Nutritive tubes that link the developing oocytes to the nurse cells in ovarioles of hemipteran insects contain extensive arrays of microtubu les. These are established, then later depolymerised, by developmental ly regulated processes. Breakdown of the microtubules corresponds with the; activation of M-phase promoting factor (MPF) and mitogen-activat ed protein kinase (MAP kinase), late in oogenesis, as the oocytes proc eed to arrest at the first meiotic metaphase [Lane and Stebbings, Roux 's Arch Dev Biol 205:150-159 (1995)]. The mechanisms that lead to the breakdown of nutritive tube microtubules are unknown. Here, we have in vestigated the possibility that the insect ovarian microtubules are re gulated by MPF- or MAP kinase-dependent phosphorylation, focusing upon the prominent high molecular weight microtubule-associated protein (H MW MAP) enriched in this system, which is a potential target for prote in kinase activity in vivo. We have purified the prominent HMW MAPs fr om the ovaries of two species of hemipterans, and have shown them to b e substrates in vitro for the activities of MPF and MAP kinase. Howeve r, although the catalytic component of MPF (p34(cdc2)) is present with in microtubule-rich portions of hemipteran ovarioles, we have found th at neither this protein nor its regulatory partner (cyclin B) co-purif y with microtubules during taxol-mediated microtubule isolation. Arch. Insect Biochem. Physiol. 39:81-90, 1998. (C) 1998 Wiley-Liss, Inc.