Late ovarian chambers of Drosophila melanogaster have been examined by ultrastructural cytochemistry in an attempt to characterize some of the transformations which precede the completion of oogenesis. From stage 11 onward peroxidase activity is present in the endoplasmic reticulum of both nurse cells and oocyte, as well as in the egg-covering precursors of the columnar follicle cells. Catalase activity is restricted to the very last stages of oogenesis (stage 13-14) and appears to be located in membrane-bound organelles of the ooplasm which are continuous with the endoplasmic reticulum. Because of the presence of catalase as well as by their structural appearance, these organelles are to be identified as microperoxisomes. Catalase activity becomes cytochemically detectable in the ooplasm somehow in coincidence with the formation of glycogen. Furthermore, glycogen is first formed in intimate association with alpha-1 yolk platelets. On the basis of these findings it is suggested that glycogen synthesis occurs by a process of gluconeogenesis.

ZAM is an env-containing member of the gypsy family of retrotransposons that represents a possible retrovirus of invertebrates. In this paper, we traced ZAM mobilization to get information about a potential path a retroelement may take to reach the germ line of its host. In situ hybridization on whole-mount tissues and immunocytochemistry analyses with antibodies raised against ZAM Gag and Env proteins have shown that all components necessary to assemble ZAM viral particles, i.e., ZAM full-length RNAs and Gag and Env polypeptides, are coexpressed in a small set of follicle cells surrounding the oocyte. By electron microscopy, we have shown that ZAM viral particles are indeed detected in this somatic lineage of cells, which they leave and enter the closely apposed oocyte. Our data provide evidence that the vesicular traffic and yolk granules in the process of vitellogenesis play an important role in ZAM transfer to the oocyte. Our data support the possibility that vitellogenin transfer to the oocyte may help a retroelement pass to the germ line with no need of its envelope product.ZAM is a 8.4-kb retroelement that resides within the genome of Drosophila melanogaster (11). On the basis of sequence similarity and gene organization, ZAM is a member of a group of retrotransposons that bears a striking resemblance to the vertebrate retroviruses. These elements are flanked by long terminal repeats (LTRs) that direct the transcription of fulllength RNAs representing potential templates for reverse transcription during mobilization. The LTRs flank three open reading frames (ORFs) analogous in position and coding potential to the retroviral gag, pol, and env genes ( Fig. 1). Among the diverse classes of eukaryotic retrotransposons, the presence of a third env-like ORF (ORF3) is unique to ZAM and a small group of other members of this family, including gypsy, 297, 17.6, Idefix, and nomad in D. melanogaster (3,8,14,19,26), tom in Drosophila ananassae (25), Osvaldo in Drosophila buzzatii (15), TED in the lepidopteran Trichoplusia ni (5), and Yoyo in the medfly Ceratitis capitata (28). An envelope protein expressed in vivo has been identified for only three of these elements (gypsy, tom, and TED) (16,21,24,25), and only one of them, gypsy, has been shown to date to have infectious properties (9,22). Although retroviral Env proteins are known to be involved in viral infectivity through host cell receptor recognition and fusion of viral and cellular membranes, the role of the Env glycoproteins encoded by these elements is still unclear since no budding has ever been visualized for any of them.ZAM was first identified as a spontaneous insertion at the white locus, giving rise to the w IR6RevI allele in a line of D. melanogaster subsequently called RevI (11). This mutation occurred in the course of a massive amplification of ZAM elements in this line due to their mobilization, which remains active in this stock of flies (3). The existence of RevI and its parental line, w IR6 , which displays a low copy number of stable ZAM elemen...

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In this study, we aimed at establishing whether two previously identified thyroid disruptors, the insecticide 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and Aroclor 1254 (a complex mixture of polychlorinated water), may inhibit thyrotropin (TSH) receptor (TSHr) activity. DDT and Aroclor 1254 were shown to inhibit both the basal and bovine TSH (bTSH)-stimulated accumulation of cAMP in Chinese hamster ovary (CHO)-K1 cells stably transfected with the TSHr. Furthermore, both DDT and Aroclor 1254 did indeed prevent cAMP accumulation, as induced by the constitutive activity of a point mutant TSHr(I486M) transiently transfected in African green monkey kidney fibroblast (COS)-7 cells. Neither trypsin digestion of the extracellular domain (ECD) nor deletion of the ECD in a mutant TSHr trunk transiently transfected in COS-7 cells counteracted the inhibitory activity of DDT and Aroclor 1254. DDT exerted a weak inhibitory activity against forskolin in both CHO-K1 and COS-7 cells, whereas it was nil against the agonists dopamine and 5Ј-(N-ethyl-carboxamido)-adenosine (NECA) in CHO cells stably transfected with the dopamine D 1 receptor and in COS-7 cells transiently transfected with the adenosine type 2a receptor (A 2 a) receptor. Furthermore, DDT was inactive against the stimulation by isoproterenol of the endogenously expressed ␤ 2 adrenergic receptor in COS-7 cells. Conversely, Aroclor 1254 inhibited completely forskolin activity in CHO-K1 cells but not in COS-7 cells. Furthermore, it did not prevent accumulation of cAMP as induced by NECA in A 2 a transfected cells. The analog of DDT, diphenylethylene, was inactive against bTSH-induced increase in cAMP in CHO-K1 cells stably transfected with the TSHr. We interpreted these results as indicating that DDT and possibly Aroclor 1254 may have an uncompetitive inverse agonist activity for the TSHr.

The aim of this study was to compare the capacity of the collagen products Biopad (Euroresearch, Milano, Italy), Promogran (Systagenix Wound Management, Quincy, Massachusetts), Colactive (Smith & Nephew, St Petersburg, Florida), and Puracol (Medline Industries, Mundelein, Illinois) to interact with biological tissues and to start restoring the healing process. These results demonstrate how these products can interact differently with enzymes and cells that characterize the environment of a healing wound.

␤-Arrestins regulate the functioning of G protein-coupled receptors in a variety of cellular processes including receptor-mediated endocytosis and activation of signaling molecules such as ERK. A key event in these processes is the G protein-coupled receptor-mediated recruitment of ␤-arrestins to the plasma membrane. However, despite extensive knowledge in this field, it is still disputable whether activation of signaling pathways via ␤-arrestin recruitment entails paired activation of receptor dimers. To address this question, we investigated the ability of different muscarinic receptor dimers to recruit ␤-arrestin-1 using both co-immunoprecipitation and fluorescence microscopy in COS-7 cells. Experimentally, we first made use of a mutated muscarinic M 3 receptor, which is deleted in most of the third intracellular loop (M 3 -short). Although still capable of activating phospholipase C, this receptor loses almost completely the ability to recruit ␤-arrestin-1 following carbachol stimulation in COS-7 cells. Subsequently, M 3 -short was co-expressed with the M 3 receptor. Under these conditions, the M 3 /M 3 -short heterodimer could not recruit ␤-arrestin-1 to the plasma membrane, even though the control M 3 /M 3 homodimer could. We next tested the ability of chimeric adrenergic muscarinic ␣ 2 /M 3 and M 3 /␣ 2 heterodimeric receptors to co-immunoprecipitate with ␤-arrestin-1 following stimulation with adrenergic and muscarinic agonists. ␤-Arrestin-1 co-immunoprecipitation could be induced only when carbachol or clonidine were given together and not when the two agonists were supplied separately. Finally, we tested the reciprocal influence that each receptor may exert on the M 2 /M 3 heterodimer to recruit ␤-arrestin-1. Remarkably, we observed that M 2 /M 3 heterodimers recruit significantly greater amounts of ␤-arrestin-1 than their respective M 3 /M 3 or M 2 /M 2 homodimers. Altogether, these findings provide strong evidence in favor of the view that binding of ␤-arrestin-1 to muscarinic M 3 receptors requires paired stimulation of two receptor components within the same receptor dimer.Over the past several years, receptor dimerization has become an established concept in the field of G protein-coupled receptors (1, 2). Although the mechanism(s) by which receptors may undergo dimerization has yet to be elucidated in detail, it is becoming ever more clear that the phenomenon is playing a key role in receptor maturation, G protein coupling, and downstream signaling besides regulating such processes as internalization and desensitization. One of the most critical issues in receptor homodimerization and heterodimerization is whether signal transduction may require pair activation of receptor dimers. Many of the recent reports on G protein coupling consider separate stimulation of receptor dimers to be sufficient for activating G proteins in co-transfected cells (3-7). Accordingly, heterodimerization would not necessarily interfere with G protein coupling and the receptor monomer should be sufficient by itself to ac...

Background: Retroviruses have evolved various mechanisms to optimize their transfer to new target cells via late endosomes. Here, we analyzed the transfer of ZAM, a retroelement from Drosophila melanogaster, from ovarian follicle cells to the oocyte at stage 9-10 of oogenesis, when an active yolk transfer is occurring between these two cell types.

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