OOCYTE MATURATION AND POSTFERTILIZATION DEVELOPMENT OF ARENICOLA-MARINA (L.) (ANNELIDA, POLYCHAETA)

Oocyte maturation in the lugworm Arenicola marina takes place in the c oelomic fluid and is induced by a coelomic maturation factor (CMF) (Wa tson and Bentley, 1997). CMF production itself results from the action of a prostomial maturation hormone. A recently described in vitro ass ay for oocyte maturation in A, marina has been adopted, distinguishing immature (full sized, prophase I) from mature (full sized, metaphase I) oocytes and enabling the action and nature of CMF to be investigate d (Watson and Bentley, 1997). In this study, immunocytochemical techni ques were used to characterize microtubule structures during oocyte ma turation and postfertilization development. Prior to the discovery of CMF, mature oocytes could be obtained only by collecting eggs from fem ales that had spawned spontaneously in the laboratory or following the injection of homogenized prostomia thereby inducing maturation and sp awning of the oocytes. Mature oocytes can now be obtained by the in vi tro incubation of oocytes in coelomic fluid containing CMF. These thre e methods of maturation were employed and compared with respect to mei otic spindle morphology and post-fertilization development. Oocytes ma tured in vitro have a meiotic spindle identical to those matured in vi vo. Post-fertilization development in in vitro matured oocytes is, how ever, retarded by approximately one mitotic cycle after 5 h incubation at 10 degrees C. These results suggest that oocytes matured in vivo d iffer in some way from those matured in vitro. The modification of dev elopment time in spawned vs. in vitro matured oocytes is discussed.