Cell-specific processing of preprosomatostatin in cultured neuroendocrine cells

We have previously found that preprosomatostatin is processed accurately to both somatostatin-14 and somatostatin-28 in pituitary gonadotrophs of transgenic mice. The foreign somatostatin peptides have been shown to enter the regulated secretory pathway of these cells. To determine whether accurate preprosomatostatin processing can occur in any neuroendocrine cell, we introduced preprosomatostatin cDNA expression vectors into several different neuroendocrine cell lines. We found that prosomatostatin was cleaved efficiently to somatostatin-14 and somatostatin-28 in RIN 5F and AtT20 cells, but not in GH4 or PC12 cells. The ability of a particular cell type to process prosomatostatin did not correlate with cellular storage capacity and was independent of the level of biosynthesis of the precursor. These data suggest that prosomatostatin processing requires specific pathways which are present in some neuroendocrine cells, but not in others.

Biosynthesis of pancreatic islet hormones

We have outlined the various strategies used to characterize the precursors of three pancreatic islet hormones--somatostatin, pancreatic polypeptide and VIP. In each case, isolation of the cDNA clones was facilitated by the use of gastrointestinal tissues that were extremely rich in specific mRNA. Characterization of the structures of the precursors is clearly only the first step in understanding the regulation of pancreatic hormone biosynthesis. It is likely that the availability of the cDNA clones will allow us to define the actual mechanisms underlying hormone production within the pancreas.

Somatostatin is targeted to the regulated secretory pathway of gonadotrophs in transgenic mice expressing a metallothionein-somatostatin gene

The pituitaries of transgenic mice that express a metallothionein-somatostatin fusion gene contain high concentrations of somatostatin-14 exclusively in the gonadotrophic cells. The purpose of this study was to determine whether somatostatin expressed from the foreign fusion gene enters the normal secretory pathway within these cells. Immuno-gold labeling of serial thin sections localized somatostatin to the secretory granules of gonadotropin-producing cells. The gonadotroph-specific hypophysiotropic factor, luteinizing hormone-releasing hormone caused a dose-dependent secretion of somatostatin when applied to primary pituitary cultures from these mice. Growth hormone-releasing hormone, thyrotropin-releasing hormone, corticotropin releasing factor, and dopamine did not affect somatostatin secretion. These experiments demonstrate that a neurosecretory peptide encoded by a foreign gene can enter the regulated secretory pathway of pituitary cells from transgenic mice.

Cyclic AMP regulates somatostatin mRNA accumulation in primary diencephalic cultures and in transfected fibroblast cells

Although the factors controlling the secretion of the neuropeptide somatostatin have been extensively studied, little is known about the mechanisms that control somatostatin biosynthesis. Somatostatin secretion is regulated by numerous agents that increase intracellular levels of cAMP. We sought to determine whether cAMP also regulates somatostatin mRNA accumulation. We found that forskolin elicited an increase in somatostatin secretion and mRNA levels in primary cultures of rat diencephalic cells. Another secretagogue, KCl, was as effective as forskolin in causing somatostatin secretion but had no effect on mRNA accumulation. Somatostatin expression in fibroblast cells transfected with the somatostatin gene was also regulated by forskolin. These results demonstrate that somatostatin mRNA accumulation can be regulated through a cAMP-dependent pathway, that this pathway is operative in heterologous cells transfected with the somatostatin gene, and that stimulation of somatostatin secretion and mRNA accumulation can be uncoupled from one another.

Gonadotroph-specific expression of metallothionein fusion genes in pituitaries of transgenic mice

Transgenic mice expressing a metallothionein-somatostatin fusion gene contain high concentrations of somatostatin in the anterior pituitary gland, a tissue that does not normally produce somatostatin. Immunoreactive somatostatin within the anterior pituitaries was found exclusively within gonadotrophs. Similarly, a metallothionein-human growth-hormone fusion gene was also expressed selectively in gonadotrophs. It is proposed that sequences common to the two fusion genes are responsible for the gonadotroph-specific expression.

Tissue-specific posttranslational processing of pre-prosomatostatin encoded by a metallothionein-somatostatin fusion gene in transgenic mice

The somatostatins are neuropeptides of 14 and 28 amino acids that inhibit the release of growth hormone and other hypophyseal and gastrointestinal peptides. These neuropeptides are cleaved posttranslationally from a common precursor, pre-prosomatostatin. We report here the production and processing of pre-prosomatostatin by transgenic mice carrying a metallothionein-somatostatin fusion gene. The most active site of somatostatin production, as determined by hormone concentrations in the tissues, is the anterior pituitary, a tissue that does not normally synthesize somatostatin-like peptides. Anterior pituitary processed pre-prosomatostatin almost exclusively to the two biologically active peptides, somatostatin-14 and somatostatin-28, whereas the liver and kidney synthesized much smaller quantities of predominantly a 6000 dalton somatostatin-like peptide. The growth of the transgenic mice was normal despite high plasma levels of the somatostatin-like peptides. These studies indicate that proteases which cleave prosomatostatin to somatostatin-28 and somatostatin-14 are not specific to tissues that normally express somatostatin.

Biosynthesis of rat preprosomatostatin

The biologically active forms of somatostatin, somatostatin-14 (SS-14) and somatostatin-28 (SS-28) arise by post-translational cleavage of prosomatostatin. Prosomatostatin in turn is derived from a larger precursor, preprosomatostatin. We have previously reported the structure of a complementary DNA molecule encoding rat preprosomatostatin. The nucleotide sequence of this cDNA indicated that SS-14 and SS-28 are located at the carboxy-terminus of a 116 amino acid precursor. At the amino-terminus of the precursor is a hydrophobic region characteristic of a leader or pre-sequence. Sequential Edman degradations of cell-free translation products synthesized in the presence of microsomal membranes indicate that preprosomatostatin is cleaved within the endoplasmic reticulum to form prosomatostatin, a precursor of 92 amino acids. To begin to elucidate the factors which regulate the expression of the rat somatostatin gene, we have determined the sequence of the gene isolated from recombinant bacteriophage libraries. The gene spans 1.2 kilobases in length and is interrupted within the coding sequence of prosomatostatin by a single intron of 630 bases. A variant of the Goldberg-Hogness promotor, TTTAAA, is located 31 bases upstream from the transcriptional start point. A repetitive sequence was identified in the 5' region of the gene within 650 bases of the promoter. The nucleotide sequence of this region reveals an alternating GT sequence 42 bases in length characteristic of DNA with Z-forming potential. Such sequences are thought to influence the expression of other eukaryotic genes.

Effects of immunizing rabbits against oestradiol-6-oxime-BSA on ovarian follicular development

Female rabbits were actively immunized either against bovine serum albumin (BSA) or oestradiol-6-oxime BSA. When the antibody titres were elevated they were sacrificed and various parameters measured. Uterine weights were significantly lower, and a large number of haemorrhagic and some cystic follicles were present in the ovaries of the oestradiol immunized group. Increased serum gonadotrophins, testosterone, oestradiol, and progesterone levels as well as greater serum binding of oestradiol were also noted. Examination of the response of isolated follicles to gonadotrophin treatment in vitro indicated that oestradiol immunization decreased the ability of isolated follicles to form androgen and oestrogen following gonadotrophin treatment; however, progesterone levels were high regardless of the presence or absence of gonadotrophins. These data suggest that oestradiol plays an important role in follicular development.

Measurement of the infrared spectral reflection of some common minerals and rocks using multiple-scan interferometry

Infrared reflection spectra (2500-250 cm(-1)) of some minerals and rocks were recorded with a multiplescan interference spectrometer. Samples were small, irregular, and unpolished. Spectra were obtained with some samples approximately 1 mm in diameter. Emission of samples was obviated by using the interferometer as chopper.

Measurement of the spectral emission of infrared radiation of minerals and rocks using multiple-scan interferometry

The ir spectral emission of a variety of minerals and rocks was measured at a specimen temperature of 20 degrees C. A multiple-scan interference spectrometer was used. The samples were located within a cold-box during the measurements, the experimental arrangement thus simulating the conditions to be found in the field.