Genes encoding receptors for insulin and insulin-like growth factor I are expressed in Xenopus oocytes and embryos.

Abstract

Insulin and insulin-like growth factor I (IGF-I) initiate their metabolic, growth, and differentiation effects through binding to the insulin receptor and the IGF-I receptor, two members of the tyrosine kinase family of receptors. To study the role of these peptides and receptors in early development, we used the polymerase chain reaction and embryo-derived RNA to generate partial cDNA sequences of the insulin receptor and IGF-I receptor from the amphibian Xenopus laevis. Three unique tyrosine kinase-related sequences were obtained. Two of the nucleotide sequences, XTK la and XTK lb, corresponded to peptides that share 92% amino acid identity, and each is 89% identical to the human insulin receptor. The third sequence, XTK 2, corresponds to a peptide that has 92% amino acid identity with the human IGF-I receptor but only 80% identity with XTK la and XTK lb. On the basis of these similarities, the pattern of conserved amino acids, and the tetraploid nature of the Xenopus genome, we suggest that XTK la and XTK lb most likely represent the product of two different nonallelic insulin receptor genes, while XTK2 may be one of the probable two Xenopus IGF-I receptor genes. By reverse transcription-polymerase chain reaction and gene-specific hybridization, expression of the three XTK sequences was detected in the oocyte, unfertilized egg, and embryos through gastrulation, neurulation, and tailbud stages. Competition binding assays with Xenopus membrane preparations demonstrated insulin receptors and IGF-I receptors in older tadpoles. IGF-I receptors were also present in oocytes, eggs, and gastrula embryos. By contrast, insulin binding was present but atypical in oocytes and was barely detected in eggs and gastrula embryos. The expression of receptors for insulin and IGF-I in early Xenopus embryos and their apparent distinct developmental regulation suggest that these molecules and their ligands may be important in early Xenopus development.

Acute Suppression of Inwardly Rectifying Kir2.1 Channels by Direct Tyrosine Kinase Phosphorylation

“…This analysis demonstrated that, in tsA-201 cells under basal conditions, the activity of endogenous TKs was dominated by the action of PTPs. When measured 48 h after transfection, Kir2.1 cDNA gave rise to inwardly rectifying I Kir2.1 currents with large amplitudes that averaged 1.97 Ϯ 1.12 nA (n ϭ 10) measured in the patch-clamp-whole cell configuration at Ϫ120 mV and in elevated (25 Fig. 1).…”

Molecular Cloning of an Amphibian Insulin Receptor Substrate 1-Like cDNA and Involvement of Phosphatidylinositol 3-Kinase in Insulin-Induced Xenopus Oocyte Maturation

“…The mobilities of a set of prestained protein markers (in thousands) are indicated. Although Xenopus oocytes resume meiosis in response to either insulin or IGF-1, circumstantial evidence has suggested that an endogenous IGF-1 receptor mediates this response (6,27). Recent evidence has indicated that mammalian IRS-1 is a major substrate for the IGF-1 receptor as well as the insulin receptor and hence may mediate the cellular response to IGF-1 (20,33).…”

Xenopus laevis insulin receptor substrate IRS‐1 is important for eye development

“…However, at the end of neurulation and during organogenesis IR is also restricted to ectodermal and mesodermal tissues, such as optic vesicles, brain, otic vesicles, branchial arches, somites, and pronephros. IGF-1R transcripts can be detected at all stages of embryogenesis (Scavo et al, 1991;Zhu et al, 1998). However, IR and IGF-1R differ in posttranscriptional regulation as binding assays suggest a biphasic pattern of expression: IGF-1R is expressed at high levels in the oocyte and during embryogenesis, whereas the expression level of IR is higher in tadpole stages.…”