Patterns of ionic currents around the developing oocyte of the German cockroach, Blattella germanica

The development of patterns of current around vitellogenic oocytes of the cockroach, Blattella germanica, was examined by means of a two-dimensional vibrating probe. Previtellogenic oocytes exhibited small unstable currents. Shortly after vitellogenic uptake began (oocytes 0.6-0.8 mm anterior to posterior) currents were either all inward or all outward at the plane of measurement. A dorsoventral pattern of currents was first observed around oocytes a little larger than 0.8 mm. Current exited dorsally (source) and entered ventrally (sink). In these oocytes source and sink were small, less than half the anterior-posterior length. As oocytes grew, relative sizes of source and sink increased until they extended across the major part of dorsal and ventral surfaces. Many late vitellogenic oocytes had a pattern of dorsal outward current with a bimodal distribution. At the onset of chorionation measured currents were again small, unstable, and exhibited no well-defined pattern. Current density was greatest during midvitellogenesis.     

The mutagenic effect of deoxynucleotide substrate imbalances during DNA synthesis with mammalian DNA polymerases

The frequency of reversion of phi X174 amber mutants to wild-type, resulting from in vitro DNA synthesis catalyzed by eucaryotic DNA polymerase-alpha or -beta, varies over a 10- to 1000-fold range. This variation is dependent on the relative ratio of deoxyribonucleotide substrates present during in vitro DNA synthesis. The effect is observed at two different loci in the genome and with several different DNA polymerases. In addition, the effect is observed using an unfractionated cellular extract. These results provide support for the hypothesis that altered nucleotide pools cause mutations in mammalian cells by decreasing the fidelity of DNA synthesis.