Isolation and characterization of the cDNA coding for the 216-residue Xenopus laevis prion protein is reported. Existence of this protein in amphibians was suggested by an EST fragment (accession number BG813008), while a conclusive demonstration is presented here. This protein exhibits a higher identity level to avian and turtle prion (more than 44%) than to mammalian prion (about 28%). Although most of the structural motifs common to known prion proteins are conserved in X. laevis, the lack of repeats represents a substantial difference. Other features worth noting are the presence of not perfectly conserved hydrophobic stretch, which is considered the prion signature, as well as the complete absence of histidine residues. ß

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We were interested in whether central nervous system progenitor cells possess the signal transduction machinery necessary to mediate cytokine functions and whether this machinery can become activated upon stable expression of a particular cytokine receptor. For this purpose we utilized a previously obtained conditionally immortalized striatum-derived nestin-positive cell line (ST14A). We found that ST14A cells express Jak2, but not Jak1 or Tyk2. An identical pattern of expression was found in embryonic striatal tissue. To evaluate the susceptibility of these cytokine specific cytoplasmic transducers to activation, ST14A cells were stably transfected with the ␣ and ␤ (AIC2A) chains of the murine interleukin-3 receptor. Four independent lines expressing both the ␣ and ␤ receptor subunits were obtained. We found that cells from each of these lines were induced to proliferate upon exposure to interleukin-3. Dose response curve, antibody blocking experiments and binding studies revealed that the response was mediated by the reconstituted high affinity interleukin-3 receptor. Immunoprecipitation studies on these cells showed that Jak2 and Stat5 were being phosphorylated after stimulation of the reconstituted receptor. These results indicate that members of the JAK/STAT family of proteins are expressed in central nervous system progenitor cells and are susceptible to activation through stimulation of an exogenously expressed cytokine receptor, ultimately leading to cell proliferation.

When isolated salmon gills were perfused under simulated in vivo conditions, norepinephrine increased and calcitonin decreased the rate of flow of perfusate and the influx of calcium and phosphate through the gill. Only the increased water flow was mediated by f-adrenergic receptors.Differences in sensitivity to both hormones were observed with gills from prespawning and postspawning salmon; gills from freshwater-adapted fish were relationships for norepinephrine and calcitonin were clearly evident. Three rates were directly determined through the gill preparation: (a) rate of flow of perfusate, (b) calcium influx, and (c) phosphate influx. The mediation of these responses by ,3-adrenergic receptors was investigated using propranolol as f-adrenergic blocking agent. The difference in sensitivity to calcitonin and norepinephrine was assessed between gills from fishes in pre-and postspawning conditions. MATERIALS AND METHODSWe have adapted the gill preparation of Rankin and Maetz (6). Pacific salmon (Oncorhynchus gorbuscha, 0. keta, and 0. kisutch) were captured in purse seines and maintained in large tanks of flowing seawater. Twenty gills obtained from the same number of animals weighing from 2 to 5.4 kg in prespawning conditions and from 0.7 to 1.1 kg in postspawning conditions were perfused by cannulating afferent and efferent arteries with polythene tubing. The Ringer's solution used for seawater salmon differed from that for freshwater salmon (Table 1). All perfusion solutions were filtered through a 0.22-,um Millipore filter to remove small particles and gassed with 95% 02/5% CO2 throughout the experiments, resulting in a final pH of 7.3. Heparin (2500 international units) was injected intravenously 10 min before salmon were killed by decapitation posterior to the operculum.Depending on the pre-and postspawning condition of the fish, the gill was suspended by the cannulae in a bath of stirred and aerated seawater or freshwater (250-350 ml) containing, respectively, ACi of 45CaCl2 or [32P]phosphate. The two cannulae were fitted tightly into cannulae of larger diameter filled with Ringer's solution. The gill was perfused under hydrostatic pressure from a reservoir at a variable height (40 cm above the bath water level). The outlet cannulae terminated in an electronic drop counter connected to a potentiometric chart recorder. To test for leakage in some experiments, bovine serum albumin labeled with 125I was added to the Ringer's solution used for perfusion. Fractions of the perfusate were collected at regular time intervals, usually every 2 min. The radioactivity of the samples (0.5 ml) was measured in a Beckman LS-100 liquid scintillation counter after addition of 7 ml of scintillation fluid (toluene/Triton X-100; 2/1, and 5.5 g of 2,5-diphenyloxazole per liter). Norepinephrine and synthetic salmon calcitonin (Sandoz) were injected as 10-ml pulses into the inlet cannula at increasing concentrations; the pH of calcitonin/Ringer's solution was 7.2. Propranolol was added to the Ringer's solution used...