The solution structure of the forkhead box-O DNA binding domain of Brugia malayi DAF-16a

Brugia malayi is a parasitic nematode that causes lymphatic filariasis in humans. Here the solution structure of the forkhead DNA binding domain of Brugia malayi DAF-16a, a putative ortholog of Caenorhabditis elegans DAF-16, is reported. It is believed to be the first structure of a forkhead or winged helix domain from an invertebrate. C. elegans DAF-16 is involved in the insulin/IGF-I signaling pathway and helps control metabolism, longevity, and development. Conservation of sequence and structure with human FOXO proteins suggests that B. malayi DAF-16a is a member of the FOXO family of forkhead proteins.

Using clickers in nonmajors- and majors-level biology courses: student opinion, learning, and long-term retention of course material

Student response systems (clickers) are viewed positively by students and instructors in numerous studies. Evidence that clickers enhance student learning is more variable. After becoming comfortable with the technology during fall 2005-spring 2006, we compared student opinion and student achievement in two different courses taught with clickers in fall 2006. One course was an introductory biology class for nonmajors, and the other course was a 200 level genetics class for biology majors. Students in both courses had positive opinions of the clickers, although we observed some interesting differences between the two groups of students. Student performance was significantly higher on exam questions covering material taught with clickers, although the differences were more dramatic for the nonmajors biology course than the genetics course. We also compared retention of information 4 mo after the course ended, and we saw increased retention of material taught with clickers for the nonmajors course, but not for the genetics course. We discuss the implications of our results in light of differences in how the two courses were taught and differences between science majors and nonmajors.

Orthologues of the Drosophila melanogaster E75 molting control gene in the filarial parasites Brugia malayi and Dirofilaria immitis

Filarial parasites cause debilitating diseases in humans and domesticated animals. Brugia malayi and Dirofilaria immitis are transmitted by mosquitoes and infect humans and dogs, respectively. Their life cycle is punctuated by a series of cuticular molts as they move between different hosts and tissues. An understanding of the genetic basis for these developmental transitions may suggest potential targets for vaccines or chemotherapeutics. Nuclear receptor (NR) proteins have been implicated in molting in the free-living nematode Caenorhabditis elegans and have well characterized roles in molting during larval development of Drosophila melanogaster. For example, the D. melanogaster E75 (NR1D3) NR gene is required for molting and metamorphosis, as well as egg chamber development in adult females. We have identified Bm-nhr-11and Di-nhr-6, B. malayi and D. immitis orthologues of E75. Both genes encode canonical nuclear receptor proteins, are developmentally regulated, and are expressed in a sex-specific manner in adults.

Expression and function of conserved nuclear receptor genes in Caenorhabditis elegans

The Caenorhabditis elegans genome encodes 284 nuclear receptor (NR) genes. Among these 284 NR genes are 15 genes conserved among the Metazoa. Here, we analyze the expression and function of eight heretofore uncharacterized conserved C. elegans NR genes. Reporter gene analysis demonstrates that these genes have distinct expression patterns and that a majority of the C. elegans cell types express a conserved NR gene. RNA interference with NR gene function resulted in visible phenotypes for three of the genes, revealing functions in various processes during postembryonic development. Five of the conserved NR genes are orthologs of NR genes that function during molting and metamorphosis in insects. Functional studies confirm a role for most of these 'ecdysone cascade' NR orthologs during the continuous growth and dauer molts. Transcript levels for these genes fluctuate in a reiterated pattern during the molting cycles, reminiscent of the expression hierarchy observed in the insect ecdysone response. Together, these analyses provide a foundation for further dissecting the role of NRs in nematode development as well as for evaluating conservation of NR functions among the Metazoa.

Dirofilaria immitis encodes Di-nhr-7, a putative orthologue of the Drosophila ecdysone-regulated E78 gene

Filarial parasites are responsible for several serious human diseases with symptoms such as lymphoedema, elephantiasis, and blindness. An understanding of how these parasites pass through developmental checkpoints may elucidate the general mechanisms of these illnesses and suggest potential targets for intervention. A useful model system for the study of human filariasis is the related nematode Dirofilaria immitis, the causative agent of dog heartworm disease. In D. immitis, molting from the third to the fourth larval stage can be induced in vitro by the insect hormone 20-OH ecdysone, suggesting that ecdysone, or some related hormone, may play a similar role in the development of D. immitis. Ecdysone has a well-characterized developmental role in insects, where it is involved in the control of molting and metamorphosis. We have identified a D. immitis orthologue of the Drosophila ecdysone response early gene E78, a member of the nuclear receptor (NR) superfamily. The D. immitis gene, Di-nhr-7 (NR1E1) encodes at least three isoforms, including two potential negative regulatory isoforms, and is expressed in a sex-specific manner. An MBP/Di-NHR-7 fusion protein is able to bind to DNA response elements that are recognized by the closely related mammalian NR Rev-erb(alpha).

The Drosophila Broad-Complex early gene directly regulates late gene transcription during the ecdysone-induced puffing cascade

The ensemble of tissue-specific changes that drives Drosophila metamorphosis is initiated by the steroid hormone ecdysone and proceeds through a transcriptional cascade comprised of primary response transcriptional regulators and secondary response structural genes. The Broad-Complex (BR-C) primary response early gene is composed of several distinct genetic functions and encodes a family of related transcription factor isoforms. Our objective in this study was to determine whether individual BR-C isoforms directly regulate secondary response target genes. A cluster of 10 salivary gland-specific secondary response L71 late genes are dependent on the BR-C rbp+ genetic function. Transgenic animals expressing individual BR-C isoforms were tested for their ability to provide the BR-C rbp+ genetic function by monitoring the transcriptional activation of the L71 genes. We found that the BR-C Z1 isoforms could complement the transcriptional defects seen in rbp mutants but the Z2, Z3, and Z4 isoforms could not. We conclude that the BR-C rbp+ function is provided by the BR-C Z1 isoform in prepupal salivary glands. L71 gene rescue was restricted to the prepupal salivary gland, suggesting the involvement of additional factors in L71 gene regulation. Interestingly, we found that the overexpression of Z3 or Z4 isoforms in BR-C+ salivary glands repressed L71 expression, indicating that BR-C proteins might also function as transcriptional repressors. Molecular mapping and characterization of the regulatory sequences that control L71-6 expression revealed several Z1 isoform binding sites. Mutagenesis of these Z1 binding sites resulted in the failure to activate late gene expression in vivo when measured by transgenic reporter genes. We conclude that the BR-C early gene directly activates late gene transcription by interacting with late gene cis-acting regulatory elements and that this interaction is responsible for the temporal linkage of early and late ecdysone-induced gene expression.

Hormonal induction of Dopa decarboxylase in the epidermis of Drosophila is mediated by the Broad-Complex

The 2B5 early puff locus corresponds to the Broad-Complex BR-C) and encodes a family of transcription factors whose members are induced by the molting hormone ecdysone. Mutations in the br subcomplementation group substantially reduce the levels of Dopa decarboxylase (DDC) in the epidermis of mature third instar larvae but not in mature second instar organisms. Enzyme levels are normal in the central nervous system of the two mutants examined. The specificity of these effects suggests that a product of the BR-C locus mediates the rapid appearance of DDC in mature third instar larvae experiencing an elevated titer of ecdysone. The likely identity of this protein has been confirmed by pursuing the observation that the br28 allele caused by the insertion of a Pelement into the Z2 DNA-binding domain. Both the transcript and a protein carrying this domain are present in the epidermis and a BR-C recombinant protein carrying the Z2 finger binds to the first intron of the Ddc gene. Five binding sites have been identified within the intron by DNAase I footprinting and a core consensus sequence has been derived which shares some identity with the consensus binding site of the Z2 protein to the Sgs-4 regulatory region. Our demonstration that Ddc is a target of BR-C in the epidermis is the first direct evidence of a role for this early gene in a tissue other than the salivary glands. The data reinforce the idea that BR-C, which clearly mediates a salivary gland-specific response to ecdysone, may play a widespread role in the hormone's activation of gene cascades in other target tissues.

The Broad-Complex directly controls a tissue-specific response to the steroid hormone ecdysone at the onset of Drosophila metamorphosis

In Drosophila, all of the major metamorphic transitions are regulated by changes in the titer of the steroid hormone ecdysone. Here we examine how a key regulator of metamorphosis and primary ecdysone response gene, the Broad-Complex, transmits the hormonal signal to one of its targets, the Sgs-4 glue gene. We show that Broad-Complex RNAs accumulate in mid third instar larval salivary glands prior to Sgs-4 induction, as expected for the products of a gene that regulates the timing of Sgs-4 activation. The Broad-Complex codes for a family of zinc finger transcriptional regulators. We have identified a number of binding sites for these proteins in sequences known to regulate the timing of Sgs-4 induction, and have used these sites to derive a binding consensus for each protein. Some of these binding sites are required in vivo for Sgs-4 activity. In addition, rbp+, a genetically defined Broad-Complex function that is required for Sgs-4 induction, acts through these Broad-Complex binding sites. Thus, the Broad-Complex directly mediates a temporal and tissue-specific response to ecdysone as larvae become committed to metamorphosis.