Uptake and salvage of hypoxanthine mediates developmental arrest in preimplantation mouse embryos.
Preimplantation mouse embryos become arrested after first or second cleavage when cultured in hypoxanthine-supplemented Whitten's medium. We present evidence that the hypoxanthine-induced arrest is dependent on uptake and salvage of hypoxanthine and depletion of phosphoribosylpyrophosphate (PRPP) levels. Hypoxanthine uptake increased during the 2-cell stage and was augmented by glucose. HPLC analysis of [14C]hypoxanthine metabolism revealed that hypoxanthine was salvaged and converted to ATP and guanosine triphosphate (GTP), with a shift to more guanyl nucleotide production at the 3- to 4-cell stage. In embryos from mice with a null mutation for the salvage enzyme hypoxanthine-guanine phosphoribosyltransferase, hypoxanthine did not block development nor was it taken up by the embryos. Glucose, which is required for the hypoxanthine-induced arrest, produced a 5.3-fold increase in PRPP levels at the 2-cell stage, which was eliminated by hypoxanthine. We conclude that metabolism of hypoxanthine to nucleotides mediates its inhibitory action on preimplantation mouse embryos via negative feedback on PRPP synthetase, ultimately resulting in decreased PRPP availability and arrest of other PRPP-dependent pathways. Finally, reversal of the block by EDTA and cAMP-elevating agents may be mediated by alterations in hypoxanthine or glucose uptake, or by changes in the relative metabolism of hypoxanthine.
Dienhart
M K
MK
Marquette University, Department of Biology, Milwaukee, Wisconsin 53210-1881, USA.
O'Brien
M J
MJ
Downs
S M
SM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001755:Blastocyst / Q000187:drug effects / Q000502:physiology; D002452:Cell Count; D046508:Culture Techniques; D004624:Embryo Transfer; D004622:Embryo, Mammalian / Q000187:drug effects / Q000502:physiology*; D047108:Embryonic Development; D005314:Embryonic and Fetal Development / Q000187:drug effects; D005260:Female; D005947:Glucose / Q000494:pharmacology; D019271:Hypoxanthine / Q000378:metabolism* / Q000494:pharmacology; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009028:Morula / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D015053:Zygote / Q000378:metabolism
D019271:Hypoxanthine; D000255:Adenosine Triphosphate; D007041:Hypoxanthine Phosphoribosyltransferase; D005947:Glucose; D015056:1-Methyl-3-isobutylxanthine