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PubMed1993

Characterization of mannose 6-phosphate receptors (MPRs) from opossum liver: opossum cation-independent MPR binds insulin-like growth factor-II.

Bovine, human, and rat cation-independent mannose 6-phosphate receptors (CI-MPRs) are capable of binding both mannose 6-phosphate and insulin-like growth factor-II (IGF-II). However, the receptor isolated from either chicken or frog lacks the high affinity IGF-II-binding site. To determine whether CI-MPRs isolated from a species that is closely related to placental mammals can bind IGF-II, the MPRs were purified from a marsupial, the American opossum (Didelphis virginiana), by phosphomannan-Sepharose affinity chromatography and then tested for their ability to bind IGF-II. Opossum liver expressed both the CI-MPR and the cation-dependent MPR (CD-MPR). Both receptors contained Asn-linked oligosaccharides. In contrast to CD-MPRs isolated from other species, the opossum CD-MPR displayed heterogeneity with respect to the number of Asn-linked oligosaccharide chains it contains. The CI-MPR isolated from opossum liver, like the CI-MPR from bovine liver, bound iodinated human recombinant IGF-II. However, Scatchard analysis revealed that the opossum CI-MPR bound IGF-II with a lower affinity (Kd = 14.5 nM) than the bovine receptor (Kd = 0.2 nM). The addition of excess IGF-II, but not IGF-I or insulin, inhibited binding to [125I]IGF-II, indicating that the opossum CI-MPR exhibits specificity for IGF-II. These results suggest that the emergence of a high affinity IGF-II-binding site in the CI-MPR occurred in evolution before the divergence of marsupials and placental mammals from their last common ancestor.

Animals↗

PubMed1993

Cloning and characterization of the opossum kidney cell D1 dopamine receptor: expression of identical D1A and D1B dopamine receptor mRNAs in opossum kidney and brain.

Opossum kidney cells are an established epithelial cell line which is often studied as a physiological model system of renal proximal tubule function, and which has also been shown to possess dopamine receptors. To identify dopamine receptor subtypes present in renal tissue, as well as to explore the usefulness of opossum kidney cells for the study of D1 dopamine receptors and renal dopaminergic physiology, we have undertaken the cloning and characterization of the dopamine receptor expressed in this cell line. In the brains of rats and humans, two different subtypes of D1 dopamine receptors, D1A and D1B, have recently been characterized. The OK cell D1 receptor message is 4500 bp long and exhibits extensive homology with the rat and human D1A subtypes of dopamine receptors. Pharmacological experiments were performed on COS-7 cell membranes transiently transfected with this cDNA. Binding properties were compared with those reported for OK cell membranes, and comparison experiments were performed in parallel with the human D1A expressed transiently in the same system. Molecular techniques including Northern blotting, in situ hybridization, and RNase protection analysis were used to study the expression pattern of the OK cell D1 receptor message. Expression of both D1A and D1B subtypes was detected in both the opossum brain and the opossum kidney, however, the OK cell line expresses exclusively the D1A receptor subtype.

Amino Acid Sequence↗

PubMed1988

Studies on the energy metabolism of opossum Didelphis virginiana erythrocytes--III. Metabolic depletion with 2-deoxyglucose markedly accelerates methemoglobin reduction in opossum but not in human erythrocytes.

1. Glucose-depleted, nitrite-treated erythrocytes reduce ferriheme in vitro in an environment 100 mM to 2-deoxy-D-glucose at a rate of 2.4 microM/ml cells/hr (opossum) and 0.37 microM/ml cells/hr (human). 2. During the process of methemoglobin reduction the breakdown of adenine ribonucleotides is more rapid in opossum (0.9 microM/g hg/hr) than in human (0.36 microM/g hg/hr) erythrocytes. 3. Radiolabelled ribose from [U-14C] ATP is catabolized exclusively to [14C] lactate in opossum, and to [14C] pyruvate and [14C] lactate in human red cells.

Adenosine Triphosphate↗

PubMed2000

Experimental transmission of Sarcocystis speeri Dubey and Lindsay, 1999 from the South American opossum (Didelphis albiventris) to the North American opossum (Didelphis virginiana).

Sarcocystis speeri Dubey and Lindsay, 1999 from the South American opossum Didelphis albiventris was successfully transmitted to the North American opossum Didelphis virginiana. Sporocysts from a naturally infected D. albiventris from Argentina were fed to 2 gamma-interferon knockout (KO) mice. The mice were killed 64 and 71 days after sporocyst feeding (DAF). Muscles containing sarcocysts from the KO mouse killed 71 DAF were fed to a captive D. virginiana; this opossum shed sporocysts 11 days after ingesting sarcocysts. Sporocysts from D. virginiana were fed to 9 KO mice and 4 budgerigars (Melopsittacus undulatus). Schizonts, sarcocysts, or both of S. speeri were found in tissues of all 7 KO mice killed 29-85 DAF; 2 mice died 39 and 48 DAF were not necropsied. Sarcocystis stages were not found in tissues of the 4 budgerigars fed S. speeri sporocysts and killed 35 DAE These results indicate that S. speeri is distinct from Sarcocystis falcatula and Sarcocystis neurona, and that S. speeri is present in both D. albiventris and D. virginiana.

Animals↗

PubMed1985

Neurohypophyseal hormones as evolutionary tracers: identification of oxytocin, lysine vasopressin, and arginine vasopressin in two South American opossums (Didelphis marsupialis and Philander opossum).

The neurohypophyseal hormones of two South American opossums (Didelphis marsupialis and Philander opossum) were isolated by molecular sieving and preparative high-pressure liquid chromatography (HPLC). One oxytocin-like and two vasopressin-like peptides were found in each species. These peptides have been identified by their amino acid composition and by their retention time in HPLC. Oxytocin, lysine vasopressin, and arginine vasopressin have been characterized in both species. Lysine vasopressin is roughly as abundant as arginine vasopressin. Comparison is made with Australian marsupials Macropodidae and Phalangeridae, and possible evolutionary mechanisms are discussed.

Amino Acids↗

PubMed1988

Studies on the energy metabolism of opossum Didelphis virginiana erythrocytes--II. Comparative aspects of 2-deoxy-D-glucose catabolism in opossum and human red cells in vitro.

1. G-6-P, F-6-P, F-1, 6-P, DHAP and GA-3-P in opossum erythrocytes were found at levels above those reported in human red cells. 2. About 1% of the radioactivity provided as [1-14C] DOG to red cells of both species was recovered as 14CO2 in 1 hr. 3. Unlike [1-14C] DOG, radiochromatography of extracts of cells incubated DOG revealed two diffusible radiolabelled compounds in the supernatant of cell suspensions. 4. The catabolism of DOG was quantitatively and qualitatively similar in opossum and human erythrocytes under the conditions of this study.

Animals↗

PubMed1985

Histology and carbohydrate histochemistry of the prostate gland of the Brazilian four-eyed opossum (Philander opossum Linnaeus, 1758).

The histology as well as glycogen and mucosubstances were described in the cranial, middle and caudal segments of the disseminate prostate of the Philander opossum. The prostate tubuli show external, medium and internal zones. The stroma presents few thin colagenous fibers while the reticular fibers form a well developed network around the glands. The elastic fibers are scant and only observed amidst the excretory ducts (internal zones). The cranial segment is formed by the narrowest tubuli of the gland. The external and medium zones are formed by cubic or cuboidal epithelium with acidophilic granules in the cytoplasm. The internal zone is lined by slightly acidophilic columnar cells. Several excretory ducts join to each other, before emptying in the urethral lumen. The middle segment is formed by largest and longest tubuli of the gland. The secretory epithelium of the external zone shows 2 morphologically distinct types of cells. The medium zone is formed by cells showing strong acidophilia at basal part and slightly basophilia in the apical part. The caudal segment is formed by cuboidal acidophilic epithelium and show the largest lumen of the gland. The luminal secretion of the gland is constituted by acidophilic fluid and numerous globules. Neutral mucosubstances were demonstrated in epithelium and lumen secretion of the 3 prostatic segments; epithelial glycogen was not found in the medium zone of the middle segment. Sialomucins were detected in the cranial and middle segments. Sulfomucins were not found in the prostate of the Philander opossum.

Animals↗

PubMed1999

Receptor selectivity of the cloned opossum G protein-coupled receptor kinase 2 (GRK2) in intact opossum kidney cells: role in desensitization of endogenous alpha2C-adrenergic but not serotonin 1B receptors.

To characterize the specificity of endogenously expressed G protein-coupled receptor kinases (GRKs) for endogenous Gi-coupled alpha2C-adrenergic and serotonin 1B (5-HT1B) receptors in the opossum kidney (OK) cell line, we have isolated a 3.073-kb OK-GRK2 clone encoding a 689-amino acid protein that shares 94.2% amino acid identity with rat GRK2. Northern blot analysis revealed the presence of GRK2 mRNA transcripts of 5.0 and 3.0 kb in OK cells. In intact OK cells, preincubation (45 min) with agonist (5-HT or UK 14304, 1 microM) reduced the maximal inhibition of forskolin-induced cAMP accumulation mediated by endogenous 5-HT1B and alpha2C-adrenergic receptors by 12 +/- 2% or 17 +/- 4%, respectively. In transfected OK cells overexpressing OK-GRK2, agonist-induced desensitization of the alpha2C-adrenergic receptor, but not the 5-HT1B receptor, was enhanced by 2- to 4-fold. Conversely, in cells overexpressing the kinase-inactive mutant OK-GRK2-K220R, alpha2C-adrenergic receptor desensitization was selectively abolished, whereas desensitization of the 5-HT1B receptor was slightly enhanced. Similarly, depletion of GRK-2 protein by stable transfection of full-length antisense OK-GRK2 cDNA blocked the desensitization of alpha2C-adrenergic receptors but not of 5-HT1B receptors. These results represent the first evidence of the coexistence of GRK2-dependent (for alpha2C receptors) and GRK2-independent (for 5-HT1B receptors) mechanisms of desensitization in intact cells and demonstrate the selectivity of GRK2 for distinct Gi-coupled receptors.

Adrenergic alpha-Agonists↗

PubMed1990

The penis morphology of the four-eyed opossum Philander opossum.

The penis of the Philander opossum is found in post-scrotal position and attached to the schiatic arch by means of a suspensory ligament. The bulk of the penile musculature is formed by the ischio-cavernosus (IC) and bulbo-spongiosus (BS) muscles, which converge caudo-medially to join the radix penis. The paired levator penis muscles are encaised in the radix and fuse to each other ventrally to the urethra forming a long tendon. The erectile tissue arisen from the BS forms the corpus spongiosum of the urethra and the corpus cavernosum starts within the IC. The urethral mucosa is longitudinally folded and lined with transitional epithelium. The body of the penis shows a pronounced sigmoid flexure which runs ventro-dorsally, with ventral, intermediate and dorsal segments. The retractor penis (RP) muscles insert in both sides of the penile dorsal curvature. The fascia of the penis is thick and surrounds the corpus cavernosum, the corpus spongiosum of the urethra and the final part of the levator penis muscles. The body-glans transition initiates with the formation of a mid- ventral groove which progressively reaches the urethral lumen; the mid-dorsal groove initiates farther distally and also reaches the urethra. The transition of urethra into urethral grooves is characterized by the modification of transitional into stratified squamous epithelium. The glans penis is bifid and has slender tips. Each urethral groove are situated on the medial-ventral surface of each glands tip. The penis in the non-erect state is partially situated in the preputial cavity; when erected, projects through the cloaca, unfolding the sigmoid flexure. The preputial sac is formed by the lamina externa (without hair follicles but having preputial glands), the lamina interna (which shows cornified areas and delimit externally the opening of the preputial cavity) and the visceral lamina, very folded and with numerous cornified spicules.

Animals↗

PubMed1969