Distinct developmental mechanisms influence sexual dimorphisms in the milkweed bug Oncopeltus fasciatus.

Sexual dimorphism is common in animals. The most complete model of sex determination comes from Drosophila melanogaster, where the relative dosage of autosomes and X chromosomes leads indirectly to sex-specific transcripts of doublesex (dsx). Female Dsx interacts with a mediator complex protein encoded by intersex (ix) to activate female development. In males, the transcription factor encoded by fruitless (fru) promotes male-specific behaviour. The genetics of sex determination have been examined in a small number of other insects, yet several questions remain about the plesiomorphic state. Is dsx required for female and male development? Is fru conserved in male behaviour or morphology? Are other components such as ix functionally conserved? To address these questions, we report expression and functional tests of dsx, ix and fru in the hemipteran Oncopeltus fasciatus, characterizing three sexual dimorphisms. dsx prevents ix phenotypes in all sexes and dimorphic traits in the milkweed bug. ix and fru are expressed across the body, in females and males. fru and ix also affect the genitalia of both sexes, but have effects limited to different dimorphic structures in different sexes. These results reveal roles for ix and fru distinct from other insects, and demonstrate distinct development mechanisms in different sexually dimorphic structures.

Theme and variation in the evolution of insect sex determination.

The development of dimorphic adult sexes is a critical process for most animals, one that is subject to intense selection. Work in vertebrate and insect model species has revealed that sex determination mechanisms vary widely among animal groups. However, this variation is not uniform, with a limited number of conserved factors. Therefore, sex determination offers an excellent context to consider themes and variations in gene network evolution. Here we review the literature describing sex determination in diverse insects. We have screened public genomic sequence databases for orthologs and duplicates of 25 genes involved in insect sex determination, identifying patterns of presence and absence. These genes and a 3.5 reference set of 43 others were used to infer phylogenies and compared to accepted organismal relationships to examine patterns of congruence and divergence. The function of candidate genes for roles in sex determination (virilizer, female-lethal-2-d, transformer-2) and sex chromosome dosage compensation (male specific lethal-1, msl-2, msl-3) were tested using RNA interference in the milkweed bug, Oncopeltus fasciatus. None of these candidate genes exhibited conserved roles in these processes. Amidst this variation we wish to highlight the following themes for the evolution of sex determination: (1) Unique features within taxa influence network evolution. (2) Their position in the network influences a component's evolution. Our analyses also suggest an inverse association of protein sequence conservation with functional conservation.

Social Justice, Community Engagement, and Undergraduate STEM Education: Participatory Science as a Teaching Tool.

Social justice is increasingly being seen as relevant to the science curriculum. We examine the intersection of participatory science, social justice, and higher education in the United States to investigate how instructors can teach about social justice and enhance collaborations to work toward enacting social justice. Participatory science approaches, like those that collect data over large geographic areas, can be particularly useful for teaching students about social justice. Conversely, local-scale approaches that integrate students into community efforts can create powerful collaborations to help facilitate social justice. We suggest a variety of large-scale databases, platforms, and portals that could be used as starting points to address a set of learning objectives about social justice. We also describe local-scale participatory science approaches with a social justice focus, developed through academic and community partnerships. Considerations for implementing participatory science with undergraduates are discussed, including cautions about the necessary time investment, cultural competence, and institutional support. These approaches are not always appropriate but can provide compelling learning experiences in the correct circumstances.

Conserved chromatin and repetitive patterns reveal slow genome evolution in frogs.

Frogs are an ecologically diverse and phylogenetically ancient group of anuran amphibians that include important vertebrate cell and developmental model systems, notably the genus Xenopus. Here we report a high-quality reference genome sequence for the western clawed frog, Xenopus tropicalis, along with draft chromosome-scale sequences of three distantly related emerging model frog species, Eleutherodactylus coqui, Engystomops pustulosus, and Hymenochirus boettgeri. Frog chromosomes have remained remarkably stable since the Mesozoic Era, with limited Robertsonian (i.e., arm-preserving) translocations and end-to-end fusions found among the smaller chromosomes. Conservation of synteny includes conservation of centromere locations, marked by centromeric tandem repeats associated with Cenp-a binding surrounded by pericentromeric LINE/L1 elements. This work explores the structure of chromosomes across frogs, using a dense meiotic linkage map for X. tropicalis and chromatin conformation capture (Hi-C) data for all species. Abundant satellite repeats occupy the unusually long (~20 megabase) terminal regions of each chromosome that coincide with high rates of recombination. Both embryonic and differentiated cells show reproducible associations of centromeric chromatin and of telomeres, reflecting a Rabl-like configuration. Our comparative analyses reveal 13 conserved ancestral anuran chromosomes from which contemporary frog genomes were constructed.

Developing Scientific Communication Skills Using Primary Literature in an Undergraduate Cell Biology Course.

Being able to communicate scientifically is an important skill for students graduating with a science degree. Skills used in future graduate school and careers for science majors include oral and written communication, as well as science literacy and being able to create figures to display information. There is a consensus that these skills should be taught throughout an undergraduate science curriculum; however, many instructors have cited insufficient time to cover skills and develop materials to effectively incorporate these skills, especially into lower-level content-focused courses. Here, we present an active curriculum that can easily be incorporated into any content-focused undergraduate Cell Biology course. The curriculum is designed around scientific literature that engages students in a multitude of active learning activities to develop different types of scientific communication skills. This curriculum not only develops student skills and self-efficacy in scientific communication, it also engages them in course content and stimulates their interest in research. While making changes to a course to include scientific communication can be difficult, making small changes, such as addition of this curriculum to an already-existing content-focused course, could make a big difference in the skills and attitudes of early undergraduate science students.

The big potential of the small frog Eleutherodactylus coqui.

The Puerto Rican coquí frog Eleutherodactylus coqui is both a cultural icon and a species with an unusual natural history that has attracted attention from researchers in a number of different fields within biology. Unlike most frogs, the coquí frog skips the tadpole stage, which makes it of interest to developmental biologists. The frog is best known in Puerto Rico for its notoriously loud mating call, which has allowed researchers to study aspects of social behavior such as vocal communication and courtship, while the ability of coquí to colonize new habitats has been used to explore the biology of invasive species. This article reviews existing studies on the natural history of E. coqui and discusses opportunities for future research.

Evolutionary Conservation of Thyroid Hormone Receptor and Deiodinase Expression Dynamics in ovo in a Direct-Developing Frog, Eleutherodactylus coqui.

Direct development is a reproductive mode in amphibians that has evolved independently from the ancestral biphasic life history in at least a dozen anuran lineages. Most direct-developing frogs, including the Puerto Rican coquí, Eleutherodactylus coqui, lack a free-living aquatic larva and instead hatch from terrestrial eggs as miniature adults. Their embryonic development includes the transient formation of many larval-specific features and the formation of adult-specific features that typically form postembryonically-during metamorphosis-in indirect-developing frogs. We found that pre-hatching developmental patterns of thyroid hormone receptors alpha (thra) and beta (thrb) and deiodinases type II (dio2) and type III (dio3) mRNAs in E. coqui limb and tail are conserved relative to those seen during metamorphosis in indirect-developing frogs. Additionally, thra, thrb, and dio2 mRNAs are expressed in the limb before formation of the embryonic thyroid gland. Liquid-chromatography mass-spectrometry revealed that maternally derived thyroid hormone is present throughout early embryogenesis, including stages of digit formation that occur prior to the increase in embryonically produced thyroid hormone. Eleutherodactylus coqui embryos take up much less 3,5,3'-triiodothyronine (T3) from the environment compared with X. tropicalis tadpoles. However, E. coqui tissue explants mount robust and direct gene expression responses to exogenous T3 similar to those seen in metamorphosing species. The presence of key components of the thyroid axis in the limb and the ability of limb tissue to respond to T3 suggest that thyroid hormone-mediated limb development may begin prior to thyroid gland formation. Thyroid hormone-dependent limb development and tail resorption characteristic of metamorphosis in indirect-developing anurans are evolutionarily conserved, but they occur instead in ovo in E. coqui.

Environmental Oxygen Exposure Allows for the Evolution of Interdigital Cell Death in Limb Patterning.

Amphibians form fingers without webbing by differential growth between digital and interdigital regions. Amniotes, however, employ interdigital cell death (ICD), an additional mechanism that contributes to a greater variation of limb shapes. Here, we investigate the role of environmental oxygen in the evolution of ICD in tetrapods. While cell death is restricted to the limb margin in amphibians with aquatic tadpoles, Eleutherodactylus coqui, a frog with terrestrial-direct-developing eggs, has cell death in the interdigital region. Chicken requires sufficient oxygen and reactive oxygen species to induce cell death, with the oxygen tension profile itself being distinct between the limbs of chicken and Xenopus laevis frogs. Notably, increasing blood vessel density in X. laevis limbs, as well as incubating tadpoles under high oxygen levels, induces ICD. We propose that the oxygen available to terrestrial eggs was an ecological feature crucial for the evolution of ICD, made possible by conserved autopod-patterning mechanisms.

Melanization in response to wounding is ancestral in arthropods and conserved in albino cave species.

Many species adapted to aphotic subterranean habitats have lost all body pigmentation. Yet, melanization is an important component of wound healing in arthropods. We amputated appendages in a variety of cave-adapted and surface-dwelling arthropods. A dark clot formed at the site of injury in most species tested, including even albino cave-adapted species. The dark coloration of the clots was due to melanin deposition. The speed of wound melanization was uncorrelated with a difference in metabolic rate between surface and cave populations of an amphipod. The chelicerate Limulus polyphemus, all isopod crustaceans tested, and the cave shrimp Troglocaris anophthalmus did not melanize wounds. The loss of wound melanization in T. anophthalmus was an apomorphy associated with adaptation to subterranean habitats, but in isopods it appeared to be a symplesiomorphy unrelated to colonization of subterranean habitats. We conclude that wound melanization i) is an important part of innate immunity because it was present in all major arthropod lineages, ii) is retained in most albino cave species, and iii) has been lost several times during arthropod evolution, indicating melanization is not an indispensable component of wound healing in arthropods.

A mitochondrial ATP synthase subunit interacts with TOR signaling to modulate protein homeostasis and lifespan in Drosophila.

Diet composition is a critical determinant of lifespan, and nutrient imbalance is detrimental to health. However, how nutrients interact with genetic factors to modulate lifespan remains elusive. We investigated how diet composition influences mitochondrial ATP synthase subunit d (ATPsyn-d) in modulating lifespan in Drosophila. ATPsyn-d knockdown extended lifespan in females fed low carbohydrate-to-protein (C:P) diets but not the high C:P ratio diet. This extension was associated with increased resistance to oxidative stress; transcriptional changes in metabolism, proteostasis, and immune genes; reduced protein damage and aggregation, and reduced phosphorylation of S6K and ERK in TOR and mitogen-activated protein kinase (MAPK) signaling, respectively. ATPsyn-d knockdown did not extend lifespan in females with reduced TOR signaling induced genetically by Tsc2 overexpression or pharmacologically by rapamycin. Our data reveal a link among diet, mitochondria, and MAPK and TOR signaling in aging and stresses the importance of considering genetic background and diet composition in implementing interventions for promoting healthy aging.

Cranberry interacts with dietary macronutrients to promote healthy aging in Drosophila.

Botanicals possess numerous bioactivities, and some promote healthy aging. Dietary macronutrients are major determinants of life span. The interaction between botanicals and macronutrients that modulates life span is not well understood. Here, we investigated the effect of a cranberry-containing botanical on life span and the influence of macronutrients on the longevity-related effect of cranberry in Drosophila. Flies were supplemented with cranberry on three dietary conditions: standard, high sugar-low protein, and low sugar-high protein diets. We found that cranberry slightly extended life span in males fed with the low sugar-high protein diet but not with other diets. Cranberry extended life span in females fed with the standard diet and more prominently the high sugar-low protein diet but not with the low sugar-high protein diet. Life-span extension was associated with increased reproduction and higher expression of oxidative stress and heat shock response genes. Moreover, cranberry improved survival of sod1 knockdown and dfoxo mutant flies but did not increase wild-type fly's resistance to acute oxidative stress. Cranberry slightly extended life span in flies fed with a high-fat diet. These findings suggest that cranberry promotes healthy aging by increasing stress responsiveness. Our study reveals an interaction of cranberry with dietary macronutrients and stresses the importance of considering diet composition in designing interventions for promoting healthy aging.

A botanical containing freeze dried açai pulp promotes healthy aging and reduces oxidative damage in sod1 knockdown flies.

Superoxide dismutase 1 (SOD1), a critical enzyme against oxidative stress, is implicated in aging and degenerative diseases. We previously showed that a nutraceutical containing freeze-dried açai pulp promotes survival of flies fed a high-fat diet or sod1 knockdown flies fed a standard diet. Here, we investigated the effect of açai supplementation initiated at the early or late young adulthood on lifespan, physiological function, and oxidative damage in sod1 knockdown flies. We found that Açai supplementation extended lifespan even when started at the age of 10 days, which is the time shortly before the mortality rate of flies accelerated. Life-long açai supplementation increased lifetime reproductive output in sod1 knockdown flies. Our molecular studies indicate that açai supplementation reduced the protein levels of genes involved in oxidative stress response, cellular growth, and nutrient metabolism. Açai supplementation also affected the protein levels of ribosomal proteins. In addition, açai supplementation decreased the transcript levels of genes involved in oxidative stress response and gluconeogenesis, while increasing the transcript levels of mitochondrial biogenesis genes. Moreover, açai supplementation reduced the level of 4-hydroxynonenal-protein adducts, a lipid peroxidation marker. Our findings suggest that açai supplementation promotes healthy aging in sod1-deficient flies partly through reducing oxidative damage, and modulating nutrient metabolism and oxidative stress response pathways. Our findings provide a foundation to further evaluate the viability of using açai as an effective dietary intervention to promote healthy aging and alleviate symptoms of diseases with a high level of oxidative stress.

The effect of resveratrol on lifespan depends on both gender and dietary nutrient composition in Drosophila melanogaster.

Resveratrol, a polyphenolic compound, has been shown to extend lifespan in different organisms. Emerging evidence suggests that the prolongevity effect of resveratrol depends on dietary composition. However, the mechanisms underlying the interaction of resveratrol and dietary nutrients in modulating lifespan remain elusive. Here, we investigated the effect of resveratrol on lifespan of Drosophila melanogaster fed diets differing in the concentrations of sugar, yeast extract, and palmitic acid representing carbohydrate, protein, and fat, respectively. Resveratrol at up to 200 µM in diets did not affect lifespan of wild-type female flies fed a standard, restricted or high sugar-low protein diet, but extended lifespan of females fed a low sugar-high protein diet. Resveratrol at 400 µM extended lifespan of females fed a high-fat diet. Lifespan extension by resveratrol was associated with downregulation of genes in aging-related pathways, including antioxidant peroxiredoxins, insulin-like peptides involved in insulin-like signaling and several downstream genes in Jun-kinase signaling involved in oxidative stress response. Furthermore, resveratrol increased lifespan of superoxide dismutase 1 (sod1) knockdown mutant females fed a standard or high-fat diet. No lifespan extension by resveratrol was observed in wild-type and sod1 knockdown males under the culture conditions in this study. Our results suggest that the gender-specific prolongevity effect of resveratrol is influenced by dietary composition and resveratrol promotes the survival of flies by modulating genetic pathways that can reduce cellular damage. This study reveals the context-dependent effect of resveratrol on lifespan and suggests the importance of dietary nutrients in implementation of effective aging interventions using dietary supplements.

Nutrient-dependent requirement for SOD1 in lifespan extension by protein restriction in Drosophila melanogaster.

Reactive oxygen species (ROS) modulate aging and aging-related diseases. Dietary composition is critical in modulating lifespan. However, how ROS modulate dietary effects on lifespan remains poorly understood. Superoxide dismutase 1 (SOD1) is a major cytosolic enzyme responsible for scavenging superoxides. Here we investigated the role of SOD1 in lifespan modulation by diet in Drosophila. We found that a high sugar-low protein (HS-LP) diet or low-calorie diet with low-sugar content, representing protein restriction, increased lifespan but not resistance to acute oxidative stress in wild-type flies, relative to a standard base diet. A low sugar-high protein diet had an opposite effect. Our genetic analysis indicated that SOD1 overexpression or dfoxo deletion did not alter lifespan patterns of flies responding to diets. However, sod1 reduction blunted lifespan extension by the HS-LP diet but not the low-calorie diet. HS-LP and low-calorie diets both reduced target of rapamycin (TOR) signaling and only the HS-LP diet increased oxidative damage. sod1 knockdown did not affect phosphorylation of S6 kinase, suggesting that SOD1 acts in parallel with or downstream of TOR signaling. Surprisingly, rapamycin decreased lifespan in sod1 mutant but not wild-type males fed the standard, HS-LP, and low-calorie diets, whereas antioxidant N-acetylcysteine only increased lifespan in sod1 mutant males fed the HS-LP diet, when compared to diet-matched controls. Our findings suggest that SOD1 is required for lifespan extension by protein restriction only when dietary sugar is high and support the context-dependent role of ROS in aging and caution the use of rapamycin and antioxidants in aging interventions.

Nectarine promotes longevity in Drosophila melanogaster.

Fruits containing high antioxidant capacities and other bioactivities are ideal for promoting longevity and health span. However, few fruits are known to improve the survival and health span in animals, let alone the underlying mechanisms. Here we investigate the effects of nectarine, a globally consumed fruit, on life span and health span in Drosophila melanogaster. Wild-type flies were fed standard, dietary restriction (DR), or high-fat diet supplemented with 0-4% nectarine extract. We measured life span, food intake, locomotor activity, fecundity, gene expression changes, and oxidative damage indicated by the level of 4-hydroxynonenal-protein adduct in these flies. We also measured life span, locomotor activity, and oxidative damage in sod1 mutant flies on the standard diet supplemented with 0-4% nectarine. Supplementation with 4% nectarine extended life span, increased fecundity, and decreased expression of some metabolic genes, including a key gluconeogenesis gene, PEPCK, and oxidative stress-response genes, including peroxiredoxins, in female wild-type flies fed the standard, DR, or high-fat diet. Nectarine reduced oxidative damage in wild-type females fed the high-fat diet. Moreover, nectarine improved the survival of and reduced oxidative damage in female sod1 mutant flies. Together, these findings suggest that nectarine promotes longevity and health span partly by modulating glucose metabolism and reducing oxidative damage.