Control of the adipogenic differentiation of 3T3-F442A cells by retinoic acid, dexamethasone, and insulin: a topographic analysis

Differentiation of 3T3-F442A adipocytes, monitored by accumulation of neutral lipid and by using the sensitive marker glycerophosphate dehydrogenase, is inhibited by incubation of confluent 3T3-F442A fibroblasts in medium containing retinoic acid or dexamethasone. When added together, dexamethasone (0.25 microM) potentiates about 50-fold the inhibitory effect of retinoic acid (10 microM). Insulin cannot counteract the retinoic acid blockade; however, it can overcome the inhibition of differentiation elicited by dexamethasone. These differential effects of insulin are used for characterizing the adipose conversion cycle. We describe cell culture conditions where terminal differentiation of 3T3-F442A preadipocytes is achieved by low, physiological levels of insulin. They include the switch from a high-serum medium containing isobutyl methyl xanthine and dexamethasone to a serum-free, hormone-supplemented medium. The data reported establish the existence of two successive states for commitment to adipogenic differentiation: a first commitment point (CA) to differentiation which requires serum adipogenic factors, and a second commitment point (CH) controlled by lipogenic hormones, namely insulin, after which terminal maturation can resume. We demonstrate that retinoic acid can prevent and interrupt differentiation by blocking the cells within the early differentiation phase.     

The arthropod fauna of Quebec vineyards with particular reference to phytophagous arthropods

A 3-yr study using different sampling and trapping techniques showed that the arthropod pest fauna in two commercial vineyards in southwestern Quebec was qualitatively and quantitatively different than that of Ontario, Canada, and New York state. We hypothesize that a colder winter climate in addition to the agronomic activity of earthing up around the vines in autumn to protect the roots from freezing in winter contributed to low numbers of pests, such as the grape berry moth, Endopiza viteana Clemens (Lepidoptera, Tortricidae). Once in 3 yr, the density of this pest approached, in one of the vineyards, the action threshold recommended for New York. Therefore, it should be monitored on an annual basis. Another phytophagous arthropod that has the potential to cause sporadic economic damage is the potato leafhopper, Empoasca fabae (Harris). The Asiatic garden beetle, Maladera (= Autoserica) castanea (Arrow), was reported for the first time in Canada. The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was also captured by sampling. However, its status as a pest has yet to be clarified.     

DnaJA4 is a SREBP-regulated chaperone involved in the cholesterol biosynthesis pathway

Using subtractive hybridization technique in 3T3-L1 adipocytes overexpressing constitutively active SREBP2, we have identified a DnaJ/Hsp40 chaperone, DnaJA4, as a new SREBP-responsive gene. SREBP2 regulation was demonstrated by changes in DnaJA4 mRNA under conditions of altered sterol status that were strictly parallel to that of well-characterized SREBP targets (LDL receptor and HMG-CoA reductase). The role of SREBP2 was further established using adenoviral overexpression of a dominant negative SREBP2, which abolished cholesterol-regulated changes in DnaJA4 expression. To determine the functional significance of this regulation, DnaJA4 was overexpressed in COS cells, which induced a specific increase in the synthesis of cholesterol from acetate. We also observed that DnaJA4 overexpression increased the activity and the protein content of HMG-CoA reductase, the rate limiting enzyme in this pathway. At the molecular level, DnaJA4 overexpression did not alter HMG-CoA reductase stability or mRNA levels, suggesting a co-translational effect of the chaperone. In the DnaJ/Hsp40 family, DnaJA4 uniquely exhibited SREBP-regulated expression, and also responded to heat shock. Through its responsiveness to SREBP, and its stimulatory effect on cholesterol synthesis, the DnaJA4 chaperone can be viewed as a new player in cholesterol synthesis. These data suggest a link between molecular chaperones, heat stress and cholesterol synthesis.     

Characterization of the feeding behavior of three Erythroneura species on grapevine by histological and DC‐electrical penetration graph techniques

Feeding behavior of three leafhopper species – Erythroneura vitis (Harris), Erythroneura ziczac (Walsh), and Erythroneura elegantula (Say) (Hemiptera: Cicadellidae) – reared on grapevine, Vitis vinifera L. cv. ‘Seyval blanc’ (Vitaceae), was investigated using histological techniques and DC‐electrical penetration graphs (DC‐EPG). Histological studies revealed that the Erythroneura species induced white stipples on the leaves and that these leafhoppers produced thin salivary sheaths in grapevine leaf tissues. The DC‐EPG system allowed the characterization of five waveforms associated with stylet penetration and feeding in leaf tissues. These waveforms were characteristic of feeding phases corresponding to epidermis penetration pathway, salivation, and ingestion. We calculated 28 parameters (e.g., number of probes, duration of phases, and time spent in the various tissues) to describe and compare the feeding behavior of the Erythroneura species. We conclude that the three Erythroneura species are mainly mesophyll feeders but may probably also feed in other tissues such as xylem.     

Terbutaline stimulates alveolar fluid resorption in hyperoxic lung injury

Lasnier, Joseph M., O. Douglas Wangensteen, Laura S. Schmitz, Cynthia R. Gross, and David H. Ingbar. Terbutalinestimulates alveolar fluid resorption in hyperoxic lung injury.J. Appl. Physiol. 81(4):1723-1729, 1996.Alveolar fluid resorption occurs by active epithelial sodium transport and is accelerated by terbutaline inhealthy lungs. We investigated the effect of terbutaline on the rate ofalveolar fluid resorption from rat lungs injured by hyperoxia. Ratsexposed to >95% O₂ for 60 h,sufficient to increase wet-to-dry lung weight and cause alveolar edema,were compared with air-breathing control rats. After anesthesia, theanimals breathed 100% O₂ for 10 min through a tracheostomy. Ringer solution was instilled into thealveoli, and the steady-state rate of volume resorbed at 6 cmH₂O pressure was measured via apipette attached to the tracheostomy tubing. Ringer solution in someanimals contained terbutaline(10³ M), ouabain(10³ M), or both. Normoxicanimals resorbed 49 ± 6 µl ^· kg^{1 ·} min¹;ouabain reduced this by 39%, whereas terbutaline increased the rate by75%. The effect of terbutaline was blocked by ouabain. Hyperoxicanimals absorbed 78 ± 9 µl ^· kg^{1 ·} min¹;ouabain reduced this by 44%. Terbutaline increased the rate by a meanof 39 µl ^· kg^{1 ·} min¹,similar to the absolute effect seen in the normoxic group, and this wasblocked by ouabain. Terbutaline accelerates fluid resorption from bothnormal and injured rat lungs via its effects on active sodiumtransport.