Glycogen breakdown in cleaving xenopus embryos is limited by ADP

Abstract

Xenopus eggs contain large stores of glycogen, but this glycogen is not glycolytically processed during cleavage. The Embden-Meyerhof pathway is inhibited by the absence of pyruvate kinase activity in vivo, and lactate and pyruvate are present at relatively low levels. In the late blastula, just preceding gastrulation, lactate levels increase, indicating the onset of glycogen breakdown and glycolytic flux. Glycolysis from microinjected [14C]glucose-6-phosphate could be transiently activated, however, by the coinjection of ADP into fertilized eggs, and constitutively activated by the injection of the ATPase potato apyrase, indicating the presence of all enzymes necessary for glycolytic activity. The isozyme profiles of pyruvate kinase and malic enzyme, two enzymes involved in carbon metabolism during cleavage or in the subsequent activation of glycogen breakdown, do not change between the egg and gastrula stages. These data suggest that the activation of glycogen breakdown and glycolysis in the late blastula is probably not a result of new gene activity but may be the metabolic consequence of increased free ADP that is then able to support the pyruvate kinase reaction.

The transcriptome of the newt Cynops orientalis provides new insights into evolution and function of sexual gene networks in sarcopterygians

“…the ribonucleotide reductases), oocyte maturation and early embryonic development. With this regard, the strong expression of perilipins (>1,500 TPM) and glycogenin-1 (>1,000 TPM) is consistent with the important role of these proteins in the formation of oocyte lipid droplets 48,49 and glycogen storage 50 , respectively. The strong female specificity of Cyclin A1 (expression level >1,000 TPM, nearly 3,000 folds higher than testis) is noteworthy, since it displayed a strikingly opposite trend compared to mammals.…”

O-Linked N-Acetylglucosaminyltransferase Inhibition Prevents G2/M Transition in Xenopus laevis Oocytes

“…From these considerations, it can be assumed that in Xenopus oocytes, glucose tends to be stored rather than being directed toward the hexosamine biosynthetic pathway. Because early cleavages in Xenopus embryos rely on the use of amino acids as its main source of carbon, glycolysis starts only at the onset of gastrulation (45). Taken together, these observations lead to the conclusion that oocytes glycosylate their proteins on an existing UDP-GlcNAc pool in a process that does not need UDP-GlcNAc production.…”

Metabolism of Preimplantation Embryo Development

“…Thus, glycolytic activity is suppressed during cleavage stage but can be metabolically induced by artificially manipulating ATP/ADP ratio such as by inhibiting OXPHOS (Dworkin & Dworkin-Rastl, 1990). It is likely that activation of glycolytic activity just prior to gastrulation observed in normally developing Xenopus embryos may be a result of changes in intermediary metabolism that influences ATP/ADP ratio or other metabolites (Dworkin & Dworkin-Rastl, 1992).…”