Developmental Biology of Marine Organisms

In contrast to the situation found in the bivalves Barnea Candida and Spisula solidissima prophase arrested oocytes of Ruditapes philippinarum cannot be fertilized when extracted from the ovary. They must first undergo germinal vesicle breakdown (GVBD) under the influence of the neurohormone serotonin (5-HT) which drives them to a second block occurring in metaphase of the first maturation division. We used Fluo-3 to investigate the possibility that calcium was involved as a second messenger in controlling this first step in meiosis reinitiation. Our data showed that, in addition to 5-HT, ionophore, thapsigargin and the weak bases ammonia and procaine could induce prophase-arrested oocytes of Ruditapes to resume meiosis.

Action of phorbol myristate acetate (PMA) at fertilization of mouse oocytes in vitro

Phorbol ester (PMA) in concentration 5 and 10ng ml−1 blocks cytokinesis of the second maturation division in mouse oocytes. Karyokinesis is not impaired and digynic triploid oocytes are obtained which undergo first cleavage division. Effectiveness of blocking cytokinesis is dependent on the timing of exposure of oocytes to PMA action. When oocytes are subjected to PMA at the onset of the second maturation division only 14·5% of eggs are triploid. PMA present during fertilization in vitro (about 1 h exposure to PMA) induces triploidy in 40% eggs. Extending the time of exposure of oocytes to 2 h produces 76% tripronucleate eggs. Applicability of PMA is compared with the use of cytochalasin B to induce triploidy in the mouse.

Haplodiploidy in Aspiculuris tetraptera (Nitzch) (Heteroxynematidae) and Syphacia obvelata (Rudolphi) (Oxyuridae), nematode (Oxyurida) parasites of Mus musculus

Cytological aspects of gametogenesis are studied in the common oxyuroid (Nematoda) parasites of Mus musculus, Syphacia obvelata (Oxyuridae) and Aspiculuris tetraptera (Heteroxynematidae). Both species are shown to be haplodiploid: males develop from unfertilized eggs and are haploid and females develop from fertilized eggs and are diploid. In female A. tetraptera there are 12 chromosomes in oogonial divisions; meiosis is normal and six bivalents were observed in ova. There are two maturation divisions and embryos in eggs in utero contain 6 or 12 chromosomes. In males, there are six chromosomes in spermatogonial divisions; there is a single maturation division and all spermatozoa have six chromosomes. Gametogenesis was similar in Syphacia obvelata but the chromosome numbers are four in males and eight in females.