Glutamine serves as a major energy source for all stages of preimplantation mouse embryo development, whether the embryos are raised in vivo or in vitro from the one-cell stage. Glutamate dehydrogenase (GDH) and glutamine synthetase (GS) are enzymes that are involved in the metabolism of glutamine. GDH catalyzes the conversion of glutamate into a-ketoglutarate, a primary component of the tricarboxylic acid cycle. GS catalyzes the conversion of glutamate to glutamine. The expression of GDH RNA and GS RNA were analyzed in preimplantation mouse embryos using reverse transcription (RT) with an oligo dT primer followed by Polymerase Chain Reaction (PCR) amplification of GDH and GS cDNAs using gene specific primers. Data show that GDH RNA is expressed in mouse embryos grown in vivo at the one-cell, two-cell, eight-cell, and blastocyst stages of development. GS RNA is not expressed at the one-cell stage, but first appears at the two-cell stage and is expressed at the eight-cell and blastocyst stages. Semiquantitative PCR analysis using a globin internal standard demonstrated that GS RNA is present at high levels at the two-cell stage and declines by 51 % by the blastocyst stage. These results suggest that, within the preimplantation mouse embryo, GDH RNA is expressed by both the maternal genome as well as the embryonic genome, while GS RNA is only expressed by the embryonic genome. This study provides an explanation for why glutamine is utilized as an energy source during preimplantation development, which allows for a better understanding of glutamine metabolism and its role during early mouse development. / Department of Biology

The cell cycle is a highly regulated process driven by endogenous factors that have regulatory functions. Certain proteins such as cyclins and cyclin-dependent kinases (cdks) are needed to progress through the four phases of the cell cycle. Cell cycle regulatory proteins have been characterized in somatic cells and exhibit phase specific expression patterns. However, the changes in expression of these proteins have not been characterized in early cleavage stage mouse embryos. This study utilized indirect immunofluorescence microscopy to determine the expression pattern of cell cycle regulators cyclin B 1, cyclin E, and CDK2 during the first three cell cycles of preimplantation mouse embryo development. Results suggest unique and specific patterns of expression for all three cell cycle regulators at different stages of the cell cycle. In G1 of the first cell cycle, cyclin E is expressed at high levels, whereas cyclin B 1 and CDK2 are expressed at moderate levels. During DNA synthesis (S phase), CDK2 levels slightly increase. However, cyclin B 1 and cyclin E levels begin to decline in S and continue to decrease to minimal levels in G2. CDK2 expression follows a similar trend during G2, decreasing considerably. During the second cell cycle, cyclin B 1 and CDK2 show staining patterns similar to the first cell cycle. The expression of cyclin E is maintained at a moderate level throughout the entire second cell cycle. Cyclin B 1, cyclin E, and CDK2 are all expressed at moderate levels during GI of the third cell cycle. During S phase, cyclin B 1 and CDK2 are maintained at moderate levels, but cyclin E is decreased to minimal levels. The expression of all three proteins was minimal during G2. This study provides baseline information on the unique expression patterns of cell cycle regulators in early mouse embryos. The determination of cell cycle protein expression will allow for a better understanding of the complex mechanisms in the division process during preimplantation mouse embryo development. / Department of Biology

The preimplantation mouse embryo undergoes many metabolic changes as development proceeds. One major change is the switch from a pyruvate based metabolism, to a glucose based metabolism. The phosphofructokinase enzyme is the regulatory enzyme of glycolysis and is thought to be a major contributor in controlling the block to glycolysis in early preimplantation mouse embryos. This study was undertaken to construct a system that would allow detection of RNA for the highly glycolytically active subunit (muscletype) of the phosphofructokinase (PFK) enzyme. A muscle specific mutant PFK plasmid was generated to provide mutant internal control RNA. Using this internal control, initial reverse transcriptionpolymerase chain reaction data collected from early embryo stages suggest that the muscle type PFK subunit RNA is not expressed in the preimplantation mouse at the 1-cell or blastocyst stages. This result suggests that PFK activity detected at the later morula and blastocyst stages must be from either a different PFK subunit or a novel embryonic form of PFK. / Department of Biology

The anticonvulsant drug, Dilantin, in many cases must be taken by epileptic mothers to control seizures during pregnancy, but unfortunately, it has been characterized as a human teratogen. It has also been demonstrated that many of the teratogenic effects of Dilantin occur during postimplantation, but some studies implicate a detrimental role for Dilantin during the preimplantation stages of development. Some of the postimplantation effects include congenital malformations and the potential'loss of the fetus. Our lab has proposed that in preimplantation mouse embryos the drug may be altering the timing of expression of cell cycle regulatory proteins and therefore, we have begun to examine the expression of these proteins. Thus, it was the goal of this study to characterize and localize various cell cycle proteins at specific time points in normal in vivo preimplantation mouse embryos, as this will provide important baseline information for studies on how anticonvulsant drugs may alter cell cycle regulation in embryos.Western blotting has confirmed the presence of cyclin BI in G1 of the first cell cycle. Both cyclin E and CDK2 were not detected in GI or G2/M of the first cell cycle or GI of the second cell cycle.From the immunogold TEM experiments, the density of cyclin B1 staining was observed to be the highest at G1 of the first cell cycle and declined at S and G2/M. Cyclin B 1 was detected in all regions of the embryo including the microvilli, cortical cytoplasm, interior cytoplasm, and was observed to be associated with vesicles and some filaments. The gold particles at GI, S, and G2/N4 of the first cell cycle and G1 of the second cell cycle appear to be associated with filamentous and membraneous structures and not free in the cytoplasmic spaces. Cyclin B 1 expression was more concentrated around vesicles at G1 of the first cell cycle and in general, was more concentrated around vesicles than in microvilli and cortical cytoplasm, interior cytoplasm, or around filaments at each cell cycle stage tested. / Department of Biology