Regulation of DAF-2 receptor signaling by human insulin and ins-1, a member of the unusually large and diverse C. elegans insulin gene family.

The activity of the DAF-2 insulin-like receptor is required for Caenorhabditis elegans reproductive growth and normal adult life span. Informatic analysis identified 37 C. elegans genes predicted to encode insulin-like peptides. Many of these genes are divergent insulin superfamily members, and many are clustered, indicating recent diversification of the family. The ins genes are primarily expressed in neurons, including sensory neurons, a subset of which are required for reproductive development. Structural predictions and likely C-peptide cleavage sites typical of mammalian insulins suggest that ins-1 is most closely related to insulin. Overexpression of ins-1, or expression of human insulin under the control of ins-1 regulatory sequences, causes partially penetrant arrest at the dauer stage and enhances dauer arrest in weak daf-2 mutants, suggesting that INS-1 and human insulin antagonize DAF-2 insulin-like signaling. A deletion of the ins-1 coding region does not enhance or suppress dauer arrest, indicating a functional redundancy among the 37 ins genes. Of five other ins genes tested, the only other one bearing a predicted C peptide also antagonizes daf-2 signaling, whereas four ins genes without a C peptide do not, indicating functional diversity within the ins family.

A screen for modifiers of decapentaplegic mutant phenotypes identifies lilliputian, the only member of the Fragile-X/Burkitt's Lymphoma family of transcription factors in Drosophila melanogaster.

The decapentaplegic (dpp) gene directs numerous developmental events in Drosophila melanogaster. dpp encodes a member of the Transforming Growth Factor-beta family of secreted signaling molecules. At this time, mechanisms of dpp signaling have not yet been fully described. Therefore we conducted a genetic screen for new dpp signaling pathway components. The screen exploited a transvection-dependent dpp phenotype: heldout wings. The screen generated 30 mutations that appear to disrupt transvection at dpp. One of the mutations is a translocation with a recessive lethal breakpoint in cytological region 23C1-2. Genetic analyses identified a number of mutations allelic to this breakpoint. The 23C1-2 complementation group includes several mutations in the newly discovered gene lilliputian (lilli). lilli mutations that disrupt the transvection-dependent dpp phenotype are also dominant maternal enhancers of recessive embryonic lethal alleles of dpp and screw. lilli zygotic mutant embryos exhibit a partially ventralized phenotype similar to dpp embryonic lethal mutations. Phylogenetic analyses revealed that lilli encodes the only Drosophila member of a family of transcription factors that includes the human genes causing Fragile-X mental retardation (FMR2) and Burkitt's Lymphoma (LAF4). Taken together, the genetic and phylogenetic data suggest that lilli may be an activator of dpp expression in embryonic dorsal-ventral patterning and wing development.

Molecular evolution of a developmental pathway: phylogenetic analyses of transforming growth factor-beta family ligands, receptors and Smad signal transducers.

Intercellular signaling by transforming growth factor-beta (TGF-beta) proteins coordinates developmental decisions in many organisms. A receptor complex and Smad signal transducers are required for proper responses to TGF-beta signals. We have taken a phylogenetic approach to understanding the developmental evolutionary history of TGF-beta signaling pathways. We were interested in detecting evolutionary influences among the physically interacting multigene families encoding TGF-beta ligands, receptors, and Smads. Our analyses included new ligands and Smads identified from genomic sequence as well as the newest published family members. From an evolutionary perspective we find that (1) TGF-beta pathways do not predate the divergence of animals, plants, and fungi; (2) ligands of the TGF-beta/activin subfamily likely originated after the divergence of nematodes and arthropods; (3) type I receptors from Caenorhabditis elegans are distinct from other receptors and may reflect an ancestral transitional state between type I and type II receptors; and (4) the Smad family appears to be evolving faster than, and independently of, ligands and receptors. From a developmental perspective we find (1) numerous phylogenetic associations not previously detected in each multigene family; (2) that there are unidentified pathway components that discriminate between type I and type II receptors; (3) that there are more Smads to be discovered in Drosophila and mammals; and (4) that the number of C-terminal serines is the best predictor of a Smad's role in TGF-beta signal transduction. We discuss these findings with respect to the coevolution of physically interacting genes.

Medea is a Drosophila Smad4 homolog that is differentially required to potentiate DPP responses.

Mothers against dpp (Mad) mediates Decapentaplegic (DPP) signaling throughout Drosophila development. Here we demonstrate that Medea encodes a MAD-related protein that functions in DPP signaling. MEDEA is most similar to mammalian Smad4 and forms heteromeric complexes with MAD. Like dpp, Medea is essential for embryonic dorsal/ventral patterning. However, Mad is essential in the germline for oogenesis whereas Medea is dispensable. In the wing primordium, loss of Medea most severely affects regions receiving low DPP signal. MEDEA is localized in the cytoplasm, is not regulated by phosphorylation, and requires physical association with MAD for nuclear translocation. Furthermore, inactivating MEDEA mutations prevent nuclear translocation either by preventing interaction with MAD or by trapping MAD/MEDEA complexes in the cytosol. Thus MAD-mediated nuclear translocation is essential for MEDEA function. Together these data show that, while MAD is essential for mediating all DPP signals, heteromeric MAD/MEDEA complexes function to modify or enhance DPP responses. We propose that this provides a general model for Smad4/MEDEA function in signaling by the TGF-beta family.

Biogeographic analysis of the Uhu and LOA elements in the Hawaiian Drosophila.

Two transposable elements have been isolated from the Hawaiian Drosophila, the Uhu and LOA elements. The Uhu element has been shown to be present in a group of closely related species, the planitibia subgroup of the picture-winged Drosophila. This study examines the distribution of the Uhu element in several other subgroups of the picture-winged Drosophila, as well as the modified-mouthparts and antopocerus groups of the Hawaiian Drosophila. The LOA element has a much more limited distribution, having only been found in representatives of the planitibia and grimshawi subgroups of the picture-winged Drosophila. For both the Uhu and LOA elements there is an inverse correlation between the copy number of the element and the age of the island on which the species is endemic, i.e., species endemic to the Island of Hawaii, the youngest island, have the highest copy number, while species endemic to Kauai, the oldest island, have the lowest copy number of the element. The correlation suggests there is a relationship between speciation and the activity of transposable elements.

Genetic effects on various measures of ethanol dependence in mice: a diallel analysis.

A complete 5 X 5 diallel cross was performed using mice from 5 highly inbred strains. Five hundred and fifty-five offspring were fed ethanol in a liquid diet for 9 days, then tested during a withdrawal period using a battery of tests designed to measure physical dependence on ethanol ( McClearn et al., Sub. Alcohol Use/Abuse, 3 (1982) 135; Allen et al., Alcohol Clin. Exp. Res., 7 (1983) 443). The analyses were done separately for each sex. The results show significant, but low genetic effects for most of the measures and no maternal effects for any measure. There was also evidence for a sex-by-genotype interaction that was not due to sex-linkage, i.e., the same autosomal genes are acting differently in the two sexes during withdrawal from ethanol. Males tended to exhibit more genetic influence than females for most of the traits measured. The results are discussed in terms of the use of these measures for creating genetically defined models of physical dependence on ethanol.