Molecular identification and characterization of two new Lepidoptera chemoreceptors belonging to the Drosophila melanogaster OR83b family

In insect antennae, olfaction depends on olfactory receptors (ORs) that function through heterodimerization with an unusually highly conserved partner orthologue to the Drosophila melanogaster DOR83b. Here, we report the identification of two cDNAs encoding new DOR83b orthologues that represent the first members, although nonconventional, of the OR families of two noctuid crop pests, the cotton leafworm Spodoptera littoralis and the cabbage armyworm Mamestra brassicae. They both displayed high protein sequence conservation with previously identified DOR83b orthologues. Transcripts were abundantly detected in adult chemosensory organs as well as in fifth instar larvae heads. In adult antennae, the expression patterns of both genes revealed common features with other members of the OR83b subfamily: they appeared to be expressed at the bases of numerous olfactory sensilla belonging to different functional categories, suggesting that both receptors may be co-expressed with yet unidentified conventional ORs. Bioinformatic analyses predicted the occurrence of seven transmembrane domains and an unusual topology with intracellular N-termini and extracellular C-termini, extending to Lepidoptera the hypothesis of an inverted topology for DOR83b orthologues, demonstrated to date only in D. melanogaster.

Regulation of retinoic acid signaling during lung morphogenesis

Little is known about how retinoic acid (RA) synthesis, utilization and metabolism are regulated in the embryonic lung and how these activities relate to lung pattern formation. Here we report that early lung bud formation and subsequent branching morphogenesis are characterized by distinct stages of RA signaling. At the onset of lung development RA signaling is ubiquitously activated in primary buds, as shown by expression of the major RA-synthesizing enzyme, RALDH-2 and activation of a RARE-lacZ transgene. Nevertheless, further airway branching appears to require downregulation of RA pathways by decreased synthesis, increased RA degradation in the epithelium via P450RAI-mediated metabolism, and inhibition of RA signaling in the mesenchyme by COUPTF-II expression. These mechanisms controlling local RA signaling may be critical for normal branching, since we show that manipulating RA levels in vitro to maintain RA signaling activated as in the initial stage, leads to an immature lung phenotype characterized by failure to form typical distal buds. We show that this phenotype likely results from RA interfering with the establishment of a distal signaling center, altering levels and distribution of Fgf10 and Bmp4, genes that are essential for distal lung formation. Furthermore, RA upregulates P450RAI expression, suggesting the presence of feedback mechanisms controlling RA availability. Our study illustrates the importance of regional mechanisms that control RA availability and utilization for correct expression of pattern regulators and normal morphogenesis during lung development.

Fibroblast growth factor interactions in the developing lung

Cellular activities that lead to organogenesis are mediated by epithelial-mesenchymal interactions, which ultimately result from local activation of complex gene networks. Fibroblast growth factor (FGF) signaling is an essential component of the regulatory network present in the embryonic lung, controlling proliferation, differentiation and pattern formation. However, little is known about how FGFs interact with other signaling molecules in these processes. By using cell and organ culture systems, we provide evidence that FGFs, Sonic hedgehog (Shh), bone morphogenetic protein 4 (BMP-4), and TGFbeta-1 form a regulatory circuit that is likely relevant for lung development in vivo. Our data show that FGF-10 and FGF-7, important for patterning and growth of the lung bud, are differentially regulated by FGF-1, -2 and Shh. In addition, we show that FGFs regulate expression of Shh, BMP-4 and other FGF family members. Our data support a model in which Shh, TGFbeta-1 and BMP-4 counteract the bud promoting effects of FGF-10, and where FGF levels are maintained throughout lung development by other FGFs and Shh.

PCR based targeted genomic and cDNA differential display

We previously described a targeted genomic differential display method (TGDD: Broude NE, Chandra A, Smith CL. Differential display of genomic subsets containing specific interspersed repeats. Proc. Natl. Acad. Sci. USA 1997;94:4548-53). In that method, presently characterized as method I, targeting was accomplished by capturing DNA fragments containing specific a sequence by hybridization with complementary single-stranded DNA. The captured fragments were amplified by PCR. Here, we describe method II where targeting is accomplished by PCR using primers specific to the target sequence. Method II takes advantage of PCR suppression to eliminate fragments not containing the target sequence (Siebert PDA, Chenchik A, Kellogg DE, Lukyanov KA and Lukyanov SA. An improved PCR method for walking in uncloned genomic DNA. Nucleic Acids Res 1995;23:1087-1088). Targeting focuses analysis on and around interesting areas and additionally serves to reduce the complexity of the amplified subset. These approaches are useful to amplify genome subsets containing a variety of targets including various conserved sequences coding for cis-acting elements or protein motifs.