Maternal RNA content in oocytes of several mammalian and avian species

The amount of maternal RNA in the oocytes of several mammalian (mouse, rabbit, cow, pig, sheep) and avian (hen, Japanese quail, guinea hen, turkey) species was determined. For mammals these were in the range of 0.47 ng/oocyte (mouse) to 0.98 ng/oocyte (cow), with the exception of the rabbit, where it was up to 15 ng/oocyte. Birds' oocytes contain much higher levels of RNA, from 1.0 microgram (Japanese quail) up to 2.1 micrograms/oocyte (hen). The RNA levels were determined by direct measurement of EtBr-induced fluorescence of the oocyte homogenates without prior extraction and purification, and correlate well with standard spectrophotometric OD260 measurements. This method is useful when there are limited amounts of a sample, and it permits nucleic acid determination in the presence of proteins.