Cell lineage-specific signaling of insulin and insulin-like growth factor I in rabbit blastocysts.
The insulin/IGF system plays a critical role in embryo growth and development. We have investigated the expression of insulin receptor (IR) and IGF-I receptor (IGF-IR) and the activation of their downstream pathways in rabbit 6-d-old blastocysts. IR was expressed in embryoblast (Em, inner cell mass) and trophoblast (Tr) cells, whereas IGF-IR was localized mainly in Em. Isoform A (IR-A) represents the main insulin isoform in blastocysts and was found in Em and Tr cells. IR-B was detectable only in Tr. IR/IGF-IR signaling pathways were analyzed after stimulation with insulin (17 nm) or IGF-I (1.3 nm) in cultured blastocysts. Insulin stimulated Erk1/2 in Em and Tr and Akt in Tr but not in Em. IGF-I activated both kinases exclusively in Em. The target genes c-fos (for MAPK kinase-1/Erk signaling) and phosphoenolpyruvate carboxykinase (PEPCK, for PI3K/Akt signaling) were also specifically regulated. Insulin down-regulated PEPCK RNA amounts in Tr by activation of the phosphatidylinositol 3-kinase/Akt pathway. Expression of c-fos by insulin and IGF-I was different with respect to time and fortitude of expression, mirroring again the specific IR and IGF-IR expression patterns in Em and Tr. Taken together, we show that IGF-I acts primarily mitogenic, an effect that is cell lineage-specifically restricted to the Em. By contrast, insulin is the growth factor of the Tr stimulating mitogenesis and down-regulating metabolic responses. As soon as blastocyst differentiation in Em and Tr has been accomplished, insulin and IGF-I signaling is different in both cell lineages, implying a different developmental impact of both growth factors.
Navarrete Santos
Anne
A
Department of Anatomy and Cell Biology, Martin Luther University Faculty of Medicine, Grosse Steinstrasse 52, D-06108, Halle (Saale), Germany. a.navarrete-santos@medizin.uni-halle.de
Ramin
Nicole
N
Tonack
Sarah
S
Fischer
Bernd
B
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001755:Blastocyst / Q000166:cytology* / Q000378:metabolism; D019070:Cell Lineage / Q000502:physiology*; D046149:Embryo Culture Techniques; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D011817:Rabbits; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism
D007328:Insulin; D016760:Proto-Oncogene Proteins c-fos; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases