Sequential expression of maternally inherited phosphoglycerate kinase-1 in the early mouse embryo.
Enzyme activities of X-linked phosphoglycerate kinase (PGK-1) and autosomal glucose phosphate isomerase (GPI-1) were determined in intact mouse blastocysts and isolated inner cell masses (ICMs). Blastocysts were recovered from the uterus on day 4 of gestation and cultured overnight in vitro. ICMs were isolated by treatment with calcium ionophore A23187. On day 4, approximately 35% of the total activity of both PGK-1 and GPI-1 was located in the ICM. After overnight culture, the PGK-1 activity of the whole blastocyst nearly doubled, due to the activation of only the maternally derived gene coding for PGK-1. In the ICM, however, a pronounced decrease of PGK-1 activity was measured: only 10% of the total PGK-1 activity was measured in the ICM on day 5. In contrast to PGK-1, GPI-1 activity of the intact blastocyst remained stable from day 4 to day 5. In the ICM, the GPI-1 activity did decline, but to a lesser extent than PGK-1 activity: 20% of total GPI-1 activity was found in the ICM on day 5. These results, when compared with the data of Handyside and Hunter, suggest that the decline in GPI-1 activity in the ICM is due to a change in the ratio of trophectoderm (TE) to ICM cells. The greater reduction of PGK-1 activity in the ICM cannot, however, be explained solely by this mechanism. To explain the observed additional decrease, we postulate that Pgk-1 is not activated in the ICM prior to day 6. This implies that on day 4 maternal Pgk-1 is activated in the TE exclusively.
Fundele
R
R
Laboratoire de Différenciation cellulaire, Ecole de Médecine, Genève 4, Switzerland.
Illmensee
K
K
Jägerbauer
E M
EM
Fehlau
M
M
Krietsch
W K
WK
D000818:Animals; D001755:Blastocyst / Q000201:enzymology*; D003433:Crosses, Genetic; D004622:Embryo, Mammalian / Q000201:enzymology; D005260:Female; D005796:Genes; D005956:Glucose-6-Phosphate Isomerase / Q000096:biosynthesis / Q000235:genetics; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D010735:Phosphoglycerate Kinase / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic; D014960:X Chromosome
D010735:Phosphoglycerate Kinase; D005956:Glucose-6-Phosphate Isomerase