Medically Assisted Conception An Agenda for Research (1989) / Chapter Skim
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Glycolytic Pathway in Preimplantation Mammalian Embryos
Glycolytic Pathway in Preimplantation Mammalian Embryos
Pages 282-303
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From page 282... ...
Pioneering studies by Whitten (1956, 1957) on media for the culture of preimplantation mouse embryos found that 2-cell stages that would not develop if glucose alone was the only energy source would develop if lactate was present.
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. In this paper I wish to revisit particularly the glycolytic pathway, whose function seems to account for the original observations on the nutritional requirements.of the preimplantation mouse embryo.
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Nutritional studies with chemicaliv defined media The early results obtained on the nutritional requirements of the preimplantation mouse embryo are summarized in Fig.
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. Second, rabbit preimplantation embryos are able to use as energy sources a variety of long- and short-chain fatty acids that contaminate many samples of bovine serum albumin (Kane, 1979)
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From page 286... ...
Both of these sets of results are consistent with the earlier nutritional studies on the mouse which suggested that metabolic fluxes of preimplantation mouse embryos change with development. Recently it has been possible to measure the uptake of pyruvate by single human oocytes and spare human embryos obtained from an IVFET Program (Leese et al., 1986~.
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Similar results on the production of CO2 from glucose have recently been reported by Wales (1986) using single mouse preimplantation embryos.
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An example has recently come to light in studies on the breakdown of glycogen by mouse preimplantation embryos. The concentrations of glycogen in the mouse preimplantation embryo analyzed immediately after flushing from the female genital tract are shown in Fig.
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From page 289... ...
Then it can be used through either the glycolytic pathway, the pentose phosphate pathway or the glycogen synthesis/degradation shuttle. A simplistic interpretation of the experiments on the fate of glucose and pyruvate at different stages of preimplantation development in the mouse is that the glycolytic pathway is shut down during oogenesis while the citric acid cycle and the respiratory pathways are left intact.
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The evidence, in fact, suggested that the g~ycolytic pathway in the mouse oocyte and preimplantation embryo operates at a low'leve] throughout development, and that the citric acid cycle is also not operating to full capacity.
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have re-examined the relative fluxes of the glycolytic pathway and the pentose-phosphate pathway in the preimplantation mouse embryo using the methods described by Katz et al. in their studies of rat adipose tissue.
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These results provide strong evidence that phosphofructokinase is a rate-limiting enzyme that controls the utilization of glucose by the i preimplantation mouse embryo. In a further study, Barbehenn et al.
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From page 293... ...
. The two interconvertible enzymes, glycogen phosphorylase and pyruvate dehydrogenase, are placed at the beginning and end of the chain.
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From page 294... ...
Two cooperative enzymes phosphofructokinase and pyruvate kinase - are also located at either end of the glycolytic pathway. The activites of these cooperative enzymes, in contrast to the interconvertible enzymes, are modified at fast rates through allosteric control mechanisms.' They also regulate the exit of metabolites from the glycolytic pathway.
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From page 295... ...
in the regulation of the glycolytic pathway in mouse preimplantation embryos-has been discussed in terms of Atkinson's energy charge (Atkinson, i968; Biggers, 1976; Biggers and Borland, 1976)
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From page 296... ...
The high energy charge at the beginning of development may allosterical~y inhibit phosphofructokinase and cause a restriction in the use of glucose by early mouse embryos. It is also known that citrate is present in high concentrations in preimplantation mouse embryos (Barbehenn et al., 1974)
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From page 297... ...
and early cleavage stages is limited and explanations are sought in terms of the well known control points. These explanations, however, may not be the final answer, since recent work has emphasized other mechanisms which may control glycolysis.
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1978. Measurement of metabolizes in single preimplantation embryos: a new means to study metabolic control in early embryos.
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1967. The pattern of utilization of respiratory metabolic intermediates by preimplantation mammalian rabbit embryos in vitro.
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1979. Enzymes of g~ycogen metabolism and related metabolizes in preimpJantation mouse embryos.
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1986. Quantitative determination of the pentose phosphate pathway in preimplantation mouse embryos.
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1971. Adenosine triphosphate content of preimplantation mouse embryos.
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1986. Measurement of metabolic turnover in single mouse embryos.
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