A double-switch system regulates male courtship behavior in male and female Drosophila melanogaster

Current models describe male-specific fruitless (fruM) as a genetic 'switch' regulating sexual behavior in Drosophila melanogaster, and they postulate that female (F) and male (M) doublesex (dsx) products control body sexual morphology. In contradiction to this simple model, we show that dsx, as well as fruM and non-sex-specific retained (retn), affect both male and female sexual behaviors. In females, both retn and dsxF contribute to female receptivity, and both genes act to repress male-like courtship activity in the presence or absence of fruM. In males, consistent with the opposing functions of dsxM and dsxF, dsxM acts as a positive factor for male courtship. retn also acts counter to fruM in the development of the male-specific muscle of Lawrence. Molecularly, retn seems to regulate sexual behavior via a previously described complex that represses zerknullt. Thus, we show that fru and dsx together act as a 'switch' system regulating behavior in the context of other developmental genes, such as retn.     

On the mechanism of immunosympathectomy

Summary The effects in vivo and in vitro of the antiserum to mouse nerve growth factor (NGF) are independent of the presence of complement. These results are consistent with the view that the antiserum acts by neutralizing endogenous NGF.Acknowledgments. Financial support from the Whitehall Foundation, New York, The Wellcome Foundation, U.K. (to J.R.C.) and the Science Research Council (Studentship to M.E.) is gratefully acknowledged. We thank Professor J.H. Humphrey, National Institute for Medical, Research, Mill Hill, London, for discussion and determination of plasma C3 levels.     

Substrate-targeting gamma-secretase modulators

Selective lowering of Abeta42 levels (the 42-residue isoform of the amyloid-beta peptide) with small-molecule gamma-secretase modulators (GSMs), such as some non-steroidal anti-inflammatory drugs, is a promising therapeutic approach for Alzheimer's disease. To identify the target of these agents we developed biotinylated photoactivatable GSMs. GSM photoprobes did not label the core proteins of the gamma-secretase complex, but instead labelled the beta-amyloid precursor protein (APP), APP carboxy-terminal fragments and amyloid-beta peptide in human neuroglioma H4 cells. Substrate labelling was competed by other GSMs, and labelling of an APP gamma-secretase substrate was more efficient than a Notch substrate. GSM interaction was localized to residues 28-36 of amyloid-beta, a region critical for aggregation. We also demonstrate that compounds known to interact with this region of amyloid-beta act as GSMs, and some GSMs alter the production of cell-derived amyloid-beta oligomers. Furthermore, mutation of the GSM binding site in the APP alters the sensitivity of the substrate to GSMs. These findings indicate that substrate targeting by GSMs mechanistically links two therapeutic actions: alteration in Abeta42 production and inhibition of amyloid-beta aggregation, which may synergistically reduce amyloid-beta deposition in Alzheimer's disease. These data also demonstrate the existence and feasibility of 'substrate targeting' by small-molecule effectors of proteolytic enzymes, which if generally applicable may significantly broaden the current notion of 'druggable' targets.     

Rag mutations reveal robust alternative end joining

Mammalian cells repair DNA double-strand breaks (DSBs) through either homologous recombination or non-homologous end joining (NHEJ). V(D)J recombination, a cut-and-paste mechanism for generating diversity in antigen receptors, relies on NHEJ for repairing DSBs introduced by the Rag1-Rag2 protein complex. Animals lacking any of the seven known NHEJ factors are therefore immunodeficient. Nevertheless, DSB repair is not eliminated entirely in these animals: evidence of a third mechanism, 'alternative NHEJ', appears in the form of extremely rare V(D)J junctions and a higher rate of chromosomal translocations. The paucity of these V(D)J events has suggested that alternative NHEJ contributes little to a cell's overall repair capacity, being operative only (and inefficiently) when classical NHEJ fails. Here we find that removing certain portions of murine Rag proteins reveals robust alternative NHEJ activity in NHEJ-deficient cells and some alternative joining activity even in wild-type cells. We propose a two-tier model in which the Rag proteins collaborate with NHEJ factors to preserve genomic integrity during V(D)J recombination.     

Dating the origin of the Orchidaceae from a fossil orchid with its pollinator

Since the time of Darwin, evolutionary biologists have been fascinated by the spectacular adaptations to insect pollination exhibited by orchids. However, despite being the most diverse plant family on Earth, the Orchidaceae lack a definitive fossil record and thus many aspects of their evolutionary history remain obscure. Here we report an exquisitely preserved orchid pollinarium (of Meliorchis caribea gen. et sp. nov.) attached to the mesoscutellum of an extinct stingless bee, Proplebeia dominicana, recovered from Miocene amber in the Dominican Republic, that is 15-20 million years (Myr) old. This discovery constitutes both the first unambiguous fossil of Orchidaceae and an unprecedented direct fossil observation of a plant-pollinator interaction. By applying cladistic methods to a morphological character matrix, we resolve the phylogenetic position of M. caribea within the extant subtribe Goodyerinae (subfamily Orchidoideae). We use the ages of other fossil monocots and M. caribea to calibrate a molecular phylogenetic tree of the Orchidaceae. Our results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76-84 Myr ago), and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.     

Immunohistochemical and ultrastructural detection of the secretin cell in the pig intestinal mucosa

Riassunto Le cellule a secretina vengono identificate con l'immunofluorescenza nella mucosa duodenale e digiunale di maiale facendo uso di antisieri anti-secretina sintetica porcina. Parallele ricerche ultrastrutturali consentono di identificare in un tipo peculiare di cellular endocrina l'equivalente ultrastrutturale della cellular a secretina.

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We are much indebted to Dr.M. A. Ondetti (Squibb, New Brunswick) for his generous supply of synthetic secretin and to Dr.S. Ghielmi (Richter, Milano) for his valuable help in immunizing rabbits.