The presence of vascular endothelial growth factor (VEGF) in the ovary has been reported in a number of species. The objective of the present study was to demonstrate the expression of VEGF, VEGF receptor (R)-1, and VEGFR-2 in detail by different methodological approaches in bovine corpora lutea (CL) obtained from different stages of the estrous cycle and during pregnancy. VEGF and VEGF receptor transcripts were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay. All components of the VEGF system were found in the bovine CL during the estrous cycle and pregnancy. Analysis of VEGF transcript by RT-PCR shows that CL tissues expressed predominantly the smallest isoforms (VEGF(121) and VEGF(165)). The highest mRNA expression for VEGF and VEGFR-2 mRNA was detected during the early luteal phase, followed by a significant decrease of expression during the mid and late luteal phase and a further decrease of VEGF mRNA after regression. During pregnancy, high levels of expression were always present. In contrast, no significant change in VEGFR-1 mRNA expression during the estrous cycle and pregnancy was found. The VEGF protein concentration in CL tissue was significantly higher (20.9-23.4 ng/g wet weight) during the early luteal phase (Days 1-7), followed by a decrease at the late luteal phase (14.3-18.7 ng/g wet weight) and, especially, after CL regression (2.8 ng/g wet weight). However, relatively high levels were found during pregnancy (10.1 ng/g wet weight). As achieved by immunohistochemistry, VEGF protein was localized predominantly in luteal cells. High VEGF protein and transcript concentrations and increased VEGFR-2 expression during the early luteal phase coincided with luteal vascularization. These results suggest an important role of VEGF in angiogenesis of the newly formed CL. The high VEGF mRNA expression and protein levels during matured vasculature in the mid-stage CL and pregnancy also suggest also a survival function for endothelial cells.

OBJECTIVEThe insulinotropic action of the incretin glucose-dependent insulinotropic polypeptide (GIP) is impaired in type 2 diabetes, while the effect of glucagon-like peptide-1 (GLP-1) is preserved. To evaluate the role of impaired GIP function in glucose homeostasis and development of the endocrine pancreas in a large animal model, we generated transgenic pigs expressing a dominant-negative GIP receptor (GIPRdn) in pancreatic islets.RESEARCH DESIGN AND METHODSGIPRdn transgenic pigs were generated using lentiviral transgenesis. Metabolic tests and quantitative stereological analyses of the different endocrine islet cell populations were performed, and β-cell proliferation and apoptosis were quantified to characterize this novel animal model.RESULTSEleven-week-old GIPRdn transgenic pigs exhibited significantly reduced oral glucose tolerance due to delayed insulin secretion, whereas intravenous glucose tolerance and pancreatic β-cell mass were not different from controls. The insulinotropic effect of GIP was significantly reduced, whereas insulin secretion in response to the GLP-1 receptor agonist exendin-4 was enhanced in GIPRdn transgenic versus control pigs. With increasing age, glucose control deteriorated in GIPRdn transgenic pigs, as shown by reduced oral and intravenous glucose tolerance due to impaired insulin secretion. Importantly, β-cell proliferation was reduced by 60% in 11-week-old GIPRdn transgenic pigs, leading to a reduction of β-cell mass by 35% and 58% in 5-month-old and 1- to 1.4-year-old transgenic pigs compared with age-matched controls, respectively.CONCLUSIONSThe first large animal model with impaired incretin function demonstrates an essential role of GIP for insulin secretion, proliferation of β-cells, and physiological expansion of β-cell mass.

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Over the past few years it has emerged that O-mannosyl glycans are not restricted to yeasts and fungi but are also present in higher eukaryotes, including humans. They play a substantial role in the onset of muscular dystrophy and neuronal migration disorders, like muscle-eye-brain disease. Protein O-mannosyltransferase genes (PMTs) are evolutionarily conserved from yeast to human; however, little is known about these enzymes in higher eukaryotes. In this study, we cloned the first PMT2 subfamily members from human (hPOMT2), mouse (mPomt2), and Drosophila (DmPOMT2). A detailed characterization of the mammalian POMT2, with emphasis on mouse Pomt2, shows that mammalian POMT2 is predominantly expressed in testis tissue. Due to differential transcription initiation of the mPomt2 gene, two distinct mRNA species that vary in length are formed. The shorter transcript is present in all somatic tissues examined. Expression of the corresponding hPOMT2 cDNA in mammalian cells identified POMT2 as an integral membrane protein of the endoplasmic reticulum with an apparent molecular weight of 83 kDa. The longer mPomt2 transcript is restricted to testis and encodes a testis-specific mPOMT2 protein isoform. Using in situ hybridization and immunolocalization, we demonstrate that in testis tissue mPOMT2 localizes to maturing spermatids and is abundant within the acrosome, a sperm-specific organelle essential for fertilization. Our data suggest a novel and specific role for the putative protein O-mannosyltransferase POMT2 in the maturation and/or function of sperm in mammals.

Differences in the distribution of CKs and AQPs in various species suggest species differences in the maintenance of structural integrity and fluid balance.