Further studies on the maternal effect of the o gene in the Mexican axolotl

Publisher Website
Google Scholar
Abstract
Axolotl females homozygous for o produce eggs which are fertilizable and cleave normally, but are invariably arrested during gastrulation. This block can be corrected by injecting the eggs with nuclear sap from normal (o+/o+ or o+/o) ovarian oocytes. The factor responsible for the correction is designated o+ substance. In this paper we show the following: 1. The o+ substance is not species specific. Oocyte nuclear sap from a variety of amphibians is about as effective as that of the axolotl itself in correcting the maternal effect of o. The cytoplasm of ovarian oocytes is inactive or very weakly active. That of some species (e.g., Xenopus laevis) exerts no discernable effect. That of others (e.g., Rana pipiens) is highly toxic, killing axolotl eggs shortly after it is injected into them. 2. The o+ substance is synthesized during most of the growth of the oocytes. Oocytes assayed just at the beginning of yolk deposition or at intermediate stages contain o+ substance of about the same activity, volume for volume, as that of fully grown oocytes. 3. Uncorrected o+/o and o/o offspring of o/o females are indistinguishable — all stop at gastrulation. When corrected by injections of o+ substance they respond equally at first and develop to an advanced embryonic stage (St. 37). At this time 50% of the embryos (o/o) stop, the other 50% (o+/o) continue to develop. These results indicate that the o+ gene does not function in early development, but can begin to do so in advanced embryos.