Accumulation in the oöcyte nucleus of a gene product essential for embryonic development beyond gastrulation.

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Abstract
A recessive gene (o), recently discovered by Humphrey, exerts a maternal effect in the axolotl, modifying the egg cytoplasm during oogenesis in such a way as to lead invariably to a cessation of development much later on, during gastrulatton. The work reported in this paper shows that whole cytoplasm from mature normal (+/+ or +/o) eggs corrects the maternal effect of o. Fertilized eggs of o/o females, injected with normal cytoplasm at the 1 or 2 cell stage, are greatly improved in their development. It is also shown here that the corrective component is present in much higher concentration in the nuclear sap than in the cytoplasm of ovarian eggs prior to maturation. These results indicate that the normal allele of gene o elaborates a product during oogenesis which accumulates initially in the nuclear sap. Later this product isdispersedin the cytoplasm and subsequently plays an essential role in development beyond gastrulation.