The Role of N-WASP in ORC4 Mediated Polar Body Extrusion

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2020

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Oocyte meiosis is completed though two asymmetric cellular divisions, where the oocyte extrudes half of its DNA two times, into two smaller daughter cells called polar bodies. N-WASP is an important factor in the actin polarization pathway. We investigated whether N-WASP is required for the extrusion of both polar bodies during mouse female meiosis. Previous work in our laboratory demonstrated that the DNA replication protein origin recognition complex 4 (ORC4) forms a cage around the chromosomes that will be extruded during polar body extrusion (PBE), but not the chromosomes that remain in the oocyte. My hypothesis is that N-WASP’s involvement in action polarization may be important for PBE, and related to ORC4 cage formation. We first localized N-WASP during oocyte progression through meiosis and found that it co-localizes with ORC4, except that N-WASP was not present in the initial stage, GV oocytes, while ORC4 was. This finding suggested the possibility that N-WASP was synthesized during meiosis. We tested this by injecting siRNA into GV oocytes upon collection, then allowing them to mature. We found that only 23.2% + 2.5% (MEAN+SD) of oocytes injected with siRNA directed towards N-WASP progressed to MII (the normal end point for in vitro GV maturation), while 92.9% + 10.1% of oocytes injected with control siRNA progressed to MII. These data suggest that (1) N-WASP may function in the same process that regulates PBE that ORC4 does, (2) that N-WASP is synthesized during meiosis, and (3) that N-WASP is required for progression to MII.

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Developmental biology, chromosomes, embryo development, N-WASP, polar body extrusion

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46 pages

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