A mouse pluripotent embryonal stem cell line stage-specifically regulates expression of homeo-box containing DNA sequences during differentiation in vitro.

Mouse embryonal stem (ES) cells have been shown to provide a new model system suitable for the analysis of different aspects of murine development. This report gives evidence that ES cell lines are also most useful for the study of developmentally regulated gene expression in vitro. Homeo-box containing genes which are suggested to play a key role in the regulation of differentiation steps occurring during embryogenesis are stage-specifically transcribed in differentiating murine ES cells: (i) A mouse embryonal stem cell line (ES-12957) was isolated and characterized with respect to its differentiation potential. When injected subcutaneously into syngeneic mice, ES-12957 cells formed fully differentiated teratomas representing derivatives of all three germ layers. When allowed to grow in suspension cultures in vitro, the cells followed a reproducible developmental pathway forming complex organized 'embryoid bodies' which resembled mouse early postimplantation embryos. (ii) A mouse DNA sequence with homeo-box homology (MH-121) was isolated and structurally analyzed. Transcription of a 1.7 kb RNA species from this DNA sequence was demonstrated in ES-12957 cells which were differentiated in vitro. A second, previously described homeo-box gene (Mo-10) was also shown to be expressed in ES-12957 cells in a stage-specific manner. A 4-kb transcript could be identified exclusively in RNA of cells which were allowed to differentiate for 9 days. These findings support the suggestion that the homeo-box genes of mammals, like those of Drosophila, may have important functions during embryonic development.

Transcriptional activity of the neuron-specific enolase (NSE) promoter in murine embryonic stem (ES) cells and preimplantation embryos.

Mouse embryonic stem (ES) cells were transfected with a plasmid composed of an E. coli lacZ gene fused to 1.8 kb of rat neuron-specific enolase (NSE) promoter sequences. While this reporter construct had been shown previously to function exclusively in postmitotic neurons and neuro-endocrine cells of transgenic mice, stably transfected ES cell clones unexpectedly displayed beta-galactosidase (beta-Gal) activity in the undifferentiated state. This transcriptional activity of the heterologous NSE promoter was confirmed by the identification of endogenous NSE mRNA in undifferentiated ES cells, mouse morulae and blastocysts. NSE protein, however, could not be found in undifferentiated ES cells. Interestingly, in ES cells which were cultured for 7 days under differentiation conditions in vitro, beta-Gal activity decreased to basal levels consistent with the parallel down-regulation of endogenous NSE mRNA. In contrast, prolonged culture of ES cells under differentiation conditions led to the reappearance of NSE mRNA and beta-Gal activity after 17 days. Significant increases in beta-Gal activity were also observed in ES cells which were cultured either on dishes coated with attachment factors such as laminin and gelatin or in the presence of nerve growth factor (NGF). These results suggest that i) transcriptional control mechanisms regulating neuronal gene expression are present at early developmental stages in the mouse and ii) ES cells provide a useful in vitro model system for the analysis of developmentally regulated cellular and molecular events coupled to neuron-specific enolase promoter activity.

Signal transduction mechanisms of recombinant bovine neurokinin-2 receptor stably expressed in baby hamster kidney cells.

The bovine neurokinin-2 (NK-2) receptor gene was stably transfected into Baby hamster kidney (BHK-21) fibroblasts and one recombinant clone expressing 17,700 high-affinity [125I]neurokinin A (NKA) binding sites/cell characterized further. [125I]NKA binding was displaced by unlabeled NKA with an IC50 of 8.26 +/- 2 nM (n = 5) and with the rank order of potency NKA > neurokinin B (NKB) > Substance P (SP) confirming pharmacological characteristics of an NK-2 receptor subtype. Stimulation with NKA resulted in a rapid and dose-dependent increase in inositol 1,4,5-trisphosphate (IP3) levels (EC50 = 32 +/- 10 nM; n = 7) which was paralleled by a transient biphasic rise in intracellular free calcium concentration [Ca2+]i (EC50 = 35 +/- 20 nM; n = 3). In addition to phosphoinositide (PI) hydrolysis and Ca2+ mobilization, NKA was found to stimulate both cyclic AMP formation (EC50 = 1.02 +/- 0.26 microM; n = 7) and [3H]arachidonic acid mobilization (EC50 = 0.65 +/- 0.45 microM; n = 4). Interestingly, cyclic AMP levels also rose after addition of an exogenous arachidonic acid metabolite, prostaglandin E2 (PGE2) (EC50 = 11.5 +/- 2 microM). Similar observations of NKA-induced IP3 production, Ca2+ mobilization, arachidonic acid liberation, and cAMP formation have been made previously following expression of the bovine NK-2 receptor in Chinese hamster ovary (CHO) epithelial cells. The present results suggest that activation of NK-2 receptors leads to characteristic and reproducible intracellular second messenger responses in a subclass of cell types which includes fibroblasts and epithelial cells irrespective of their genetic and phenotypic background.

Functional characterization of neurokinin-1 receptors on human U373MG astrocytoma cells.

The neurokinin-1 (NK-1, substance P) receptor belongs to the class of seven transmembrane domain (7-TM) receptors that interact with cellular effector systems via guanine nucleotide binding regulatory proteins (G-proteins). In this study, coupling mechanisms of functional NK-1 receptors endogenously expressed in a human astrocytoma cell line (U373MG) were analyzed. Stimulation with substance P (SP) resulted in 1) a rapid increase in inositol 1,4,5-trisphosphate (IP3) synthesis; 2) a rise in cytosolic free calcium concentration ([Ca2+]i); 3) induction of immediate early gene transcription as monitored by c-fos and c-jun expression; and 4) a significant increase in de novo DNA synthesis. Thus, the functional responses induced by stimulation of NK-1 receptors on U373MG strongly correlate with those observed after treatment of primary astrocytes with SP and make U373MG cells a useful in vitro model system for the analysis of NK-1 receptor function on astrocytes in vivo.

The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein.

Human pulmonary-surfactant-associated protein C (SP-C) is an extremely hydrophobic peptide comprising 34-35 amino acids. It is involved in the reduction of surface tension at the air/liquid in the lung. In order to understand the mechanism by which this molecule is generated from its 197-amino-acid-residues-long precursor and secreted into the alveolar space, we analysed the biosynthesis and processing of this precursor in an 'in vitro' system. Our results show that the SP-C precursor is a 21 kDa integral membrane protein. It is anchored in the membrane by a hydrophobic domain that comprises the 20-amino-acid-residues-long hydrophobic core of the mature SP-C peptide. The N-terminus remains in the cytoplasm, which leads to a type II transmembrane orientation of the precursor. Membrane integration occurs in a signal-peptidase-independent manner. The hydrophobic domain acts as both signal sequence and membrane-anchoring domain. We suggest that correct membrane insertion of the SP-C precursor, which is strictly dependent on the hydrophobic-amino-acid sequence represented by the hydrophobic core of the mature SP-C, is itself a prerequisite for further processing and intracellular transport of the mature SP-C.

Chromosomal mapping of the structural gene coding for the mouse cell adhesion molecule uvomorulin.

The gene coding for the mouse cell adhesion molecule uvomorulin has been mapped to chromosome 8. Uvomorulin cDNA clone F5H3 identified restriction fragment length polymorphisms in Southern blots of genomic DNA from mouse species Mus musculus domesticus and Mus spretus. By analyzing the segregation pattern of the gene in 75 offspring from an interspecific backcross a single genetic locus, Um, was defined on chromosome 8. Recombination frequency between Um and the co-segregating loci serum esterase 1 (Es-1) and tyrosine aminotransferase (Tat) places Um about 14 centimorgan (cM) distal to Es-1, and 5 cM proximal to Tat. In situ hybridization of uvomorulin [3H]cDNA to mouse metaphase chromosomes located the Um locus close to the distal end of chromosome 8 (bands C3-E1). Since uvomorulin is evolutionarily highly conserved, its chromosomal assignment adds an important marker to the mouse genetic map.

Recombinant bovine neurokinin-2 receptor stably expressed in Chinese hamster ovary cells couples to multiple signal transduction pathways.

Neurokinins are a family of neuropeptides with widespread distribution mediating a broad spectrum of physiological actions through three distinct receptor subtypes: NK-1, NK-2, and NK-3. We investigated some of the second messenger and cellular processes under control by the recombinant bovine NK-2 receptor stably expressed in Chinese hamster ovary cells. In this system the NK-2 receptor displays its expected pharmacological characteristics, and the physiological agonist neurokinin A stimulates several cellular responses. These include 1) transient inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ mobilization, 2) increased out put of arachidonic acid and prostaglandin E2 (PGE2), 3) enhanced cyclic AMP (cAMP) generation, 4) increased de novo DNA synthesis, and 5) an induction of the "immediate early" genes c-fos and c-jun. Although NK-2 receptor-mediated IP3 formation involves activation of a pertussis toxin-insensitive G-protein, increased cAMP production is largely a secondary response and can be at least partially attributed to autocrine stimulation by endogenously generated eicosanoids, particularly PGE2. This is the first demonstration that a single recombinant neurokinin receptor subtype can regulate, either directly or indirectly, multiple signal transduction pathways and suggests several potential important mediators of neurokinin actions under physiological conditions.