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ABSTRACT

Insulin is important for optimal fetal and neonatal growth and development. Its continued availability is due, in part, to ongoing islet cell growth within the pancreas. IGFs and IGF-binding proteins (IGFBPs) have been implicated as paracrine regulators of islet cell growth within the developing pancreas. The purpose of this study was to determine whether the intact rat pancreas expresses mRNAs for IGF-I, IGF-II and IGFBPs, and how these might change with development. Liver was studied as a control tissue. Pancreas and liver were taken from fetal rats at 20–22 days of gestation, from postnatal rats at 1–21 days and from adult animals, and mRNAs for IGFs-I and -II and IGFBPs-1 to -6 were detected by Northern blot hybridization. The amount of IGF-II mRNA was greatest in the liver and pancreas of the fetal rat, and declined in both tissues during the neonatal period. Conversely, IGF-I mRNA levels were low but detectable in fetal life, and rose to adult levels within 2 weeks of birth. Both IGFBP-1 and IGFBP-2 mRNAs were present in fetal rat liver, increasing in amount over the first week of life, and declining in the adult. However, within the pancreas, IGFBP-1 mRNA was undetectable and IGFBP-2 mRNA was very low in the fetus and neonate. Both IGFBP-1 and IGFBP-2 mRNAs transiently appeared in the pancreas between postnatal weeks 2 and 3 and declined in the adult. IGFBP-3 and IGFBP-4 mRNAs were detected in both the liver and pancreas throughout the developmental period studied. IGFBP-3 mRNA increased in amount immediately following birth, while the quantity of IGFBP-4 mRNA increased sharply in liver from postnatal day 21, but declined in the pancreas. mRNA for IGFBP-5 or -6 was undetectable in either tissue.

The results show that both IGF-I and IGF-II are expressed by rat pancreas from at least 20 days of gestation, the latter being predominant in fetal life and the former during postnatal development. In addition, at least four IGFBP mRNAs (IGFBPs-1, -2, -3 and -4) were expressed within the pancreas with distinct developmental patterns. IGFBP-3 and -4 were predominant in the fetal and neonatal periods, while increased expression of IGFBPs-1 and -2 occurred 2–3 weeks after birth. The ontogeny of IGFBP mRNA expression in pancreas differed from that in liver. The temporal and spatially specific pattern of IGF and IGFBP gene expression within the developing pancreas supports a paracrine role for the IGF—IGFBP axis during pancreatic development in the rat.

ABSTRACT

We have isolated ovine follistatin cDNA from an ovarian follicle cDNA library and determined its sequence. The deduced amino acid sequence of the ovine follistatin precursor is highly homologous (>97%) to the porcine, human and rat follistatins.

Northern analysis was used to characterize follistatin gene expression in ovaries of adult ewes, collected from days 11 to 13 of the oestrous cycle. Two major (about 2.7kb and 1.5 kb) and one minor (about 0.5 kb) transcripts were detected in polyadenylated RNA extracted from ovarian follicles and corpora lutea. The degree of expression of the transcripts varied in the two ovarian compartments, with the 2.7kb species predominating in the follicles and the 1.5kb species being more abundant in the corpora lutea. No transcripts were detected in stromal tissue containing preantral follicles of <1 mm.

ABSTRACT

Insulin-like growth factors (IGFs) are expressed by, and are biologically active on, human fetal cells. The mitogenic actions of IGF-I are modulated by the 21–41 kDa class of IGF-binding proteins (IGF-BPs). Using a rabbit anti-human IGF-BP antibody raised against a highly pure 26 kDa IGF-BP derived from amniotic fluid, we have compared the cellular location of IGF-BP and IGF peptides in tissue sections from prostaglandin-induced human abortuses of 14–16 weeks of gestation. The monoclonal and polyclonal antibodies used were raised against human IGF-I, but did not distinguish between IGF-I and IGF-II. Positive staining for IGF-BP was seen in every tissue except brain, spleen and thyroid. With the exception of skin, the cellular distribution of IGF-BP was similar to that of IGF peptides. Strong immunostaining was found in hepatocytes, hepatic erythropoietic cells, pulmonary epithelium, the tubular epithelium of kidney, intestinal epithelia, the fetal adrenal cortex and cardiac and skeletal muscle fibres. In skin, IGF-BP was located throughout the dermis and in the germinal layer of the epidermis. IGF peptide in skin was restricted to the deeper dermal layers. In the tibial epiphyseal growth plate both IGF-BP and IGF peptide were located in chondrocytes throughout the proliferation and hypertrophic zones. The similarity in distribution of IGF-BP and IGF peptides in fetal tissues suggests that the latter may exist predominantly complexed to IGF-BP in or on the surfaces of cells in vivo. The distribution of IGF-BP may define the sites of biological action of IGF peptides.