First we knew, then we didn't. A factor, once known as oscillin, carried by sperm into the egg is crucial for promoting the oscillations in free calcium necessary to bring about a cascade of egg activation processes. Phospholipase C zeta (PLCZ1) is a strong candidate for oscillin. Eventually PLCZ1 undergoes nuclear translocation to the zygote's pronuclei where its ability to promote calcium oscillations ceases. One would reasonably think that a factor with such a crucial developmental role would behave commonly in many, if not all vertebrate species. In this case, one would be wrong, as now demonstrated by Ito et al. in a paper on p. 1081 of this issue. This study shows, for example, that PLCZ1 nuclear translocation does not occur in the rat, yet oscillations cease appropriately. Thus mechanisms controlling PLCZ1 translocation and its ability to promote calcium oscillations differ among species. Resolving the molecular bases of these species differences will provide fundamental information on mechanisms governing the initiation of vertebrate embryogenesis.
Masahiko Ito, Tomohide Shikano, Shoji Oda, Takashi Horiguchi, Satomi Tanimoto, Takeo Awaji, Hiroshi Mitani, and Shunichi Miyazaki. Difference in Ca2+ Oscillation-Inducing Activity and Nuclear Translocation Ability of PLCZ1, an Egg-Activating Sperm Factor Candidate, Between Mouse, Rat, Human, and Medaka Fish. Biol Reprod 2008; 78:1081-1090. Published online in BOR-Papers In Press 5 March 2008; DOI 10.1095/biolreprod.108.067801
PCB cocktails for two. Since the 1962 publication of Silent Spring by Rachel Carson, awareness of how environmental toxicants can impact fertility has increased. In an article on p. 1091 of this issue, Steinberg and colleagues provide evidence that adverse reproductive effects of toxicants may extend not only to the children of exposed individuals, but also to the next generation. They treated pregnant rats with a mixture of polychlorinated biphenyls (PCBs) and found that reproductive markers were disrupted not only in the female offspring of these rats, but also in the "grand offspring," which are derived from oocytes present in fetuses of the treated females. Changes in the second generation included blunting of preovulatory LH release, reduced progesterone concentrations and reduced uterine weights. The use of low doses of PCBs in this study increases the potential relevance of these findings to reproductive health.
Rebecca M. Steinberg, Deena M. Walker, Thomas E. Juenger, Michael J. Woller, and Andrea C. Gore. Effects of Perinatal Polychlorinated Biphenyls on Adult Female Rat Reproduction: Development, Reproductive Physiology, and Second Generational Effects. Biol Reprod 2008; 78:1091-1101. Published online in BOR-Papers In Press 27 February 2008; DOI 10.1095/biolreprod.107.067249