Two major-effect loci influence interspecific mating in females of the sibling species, Drosophila simulans and D. sechellia.

Secondary contact between incompletely isolated species can produce a wide variety of outcomes. The vinegar flies Drosophila simulans and D. sechellia diverged on islands in the Indian Ocean and are currently separated by partial pre- and postzygotic barriers.

The genetic determination of alternate stages in polyphenic insects.

Molt-based transitions in form are a central feature of insect life that have enabled adaptation to diverse and changing environments. The endocrine regulation of these transitions is well established, but an understanding of their genetic regulation has only recently emerged from insect models. The pupal and adult stages of metamorphosing insects are determined by the stage specifying transcription factors broad-complex (br) and Ecdysone inducible protein 93 (E93), respectively.

The Genetics of Resistance to Morinda Fruit Toxin During the Postembryonic Stages in Drosophila sechellia.

Although a great deal has been learned regarding the genetic changes that give rise to adaptation in bacteria and yeast, an understanding of how new complex traits arise in multicellular organisms is far less complete. Many phytophagous insect species are ecological specialists that have adapted to utilize a single host plant. Drosophila sechellia is a specialist that utilizes the ripe fruit of Morinda citrifolia, which is toxic to its sibling species, D.

Expression of the pupal determinant broad during metamorphic and neotenic development of the strepsipteran Xenos vesparum Rossi.

Derived members of the endoparasitic order Strepsiptera have acquired an extreme form of sexual dimorphism whereby males undergo metamorphosis and exist as free-living adults while females remain larviform, reaching sexual maturity within their hosts. Expression of the transcription factor, broad (br) has been shown to be required for pupal development in insects in which both sexes progress through metamorphosis. A surge of br expression appears in the last larval instar, as the epidermis begins pupal development.

Pupariation site preference within and between Drosophila sibling species.

Holometabolous insects pass through a sedentary pupal stage and often choose a location for pupation that is different from the site of larval feeding. We have characterized a difference in pupariation site choice within and between sibling species of Drosophila. We found that, in nature, Drosophila sechellia pupariate within their host fruit, Morinda citrifolia, and that they perform this behavior in laboratory assays.

Morphological evolution caused by many subtle-effect substitutions in regulatory DNA.

Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby (svb), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called 'trichomes'. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression.

Multiplexed shotgun genotyping for rapid and efficient genetic mapping.

We present a new approach to genotyping based on multiplexed shotgun sequencing that can identify recombination breakpoints in a large number of individuals simultaneously at a resolution sufficient for most mapping purposes, such as quantitative trait locus (QTL) mapping and mapping of induced mutations. We first describe a simple library construction protocol that uses just 10 ng of genomic DNA per individual and makes the approach accessible to any laboratory with standard molecular biology equipment. Sequencing this library results in a large number of sequence reads widely distributed across the genomes of multiplexed bar-coded individuals.

The role of the pupal determinant broad during embryonic development of a direct-developing insect.

Metamorphosis is one of the most common, yet dramatic of life history strategies. In insects, complete metamorphosis with morphologically distinct larval stages arose from hemimetabolous ancestors that were more direct developing. Over the past century, several ideas have emerged that suggest the holometabolous pupa is developmentally homologous to the embryonic stages of the hemimetabolous ancestor.

The nuclear receptor E75A has a novel pair-rule-like function in patterning the milkweed bug, Oncopeltus fasciatus.

Genetic studies of the fruit fly Drosophila have revealed a hierarchy of segmentation genes (maternal, gap, pair-rule and HOX) that subdivide the syncytial blastoderm into sequentially finer-scale coordinates. Within this hierarchy, the pair-rule genes translate gradients of information into periodic stripes of expression. How pair-rule genes function during the progressive mode of segmentation seen in short and intermediate-germ insects is an ongoing question.

Imperfect eggs and oviform nymphs: a history of ideas about the origins of insect metamorphosis.

The problem of insect metamorphosis has inspired naturalists for centuries. One question that often arises is why some insects, such as butterflies and bees, undergo a fairly radical metamorphosis while others, such as crickets and lice, do not. Even before the concept of homology emerged scientists speculated which stage found in more direct-developing insects would correspond with the pupal stage of metamorphosing insects.

What is metamorphosis?

Metamorphosis (Gr. meta- "change" + morphe "form") as a biological process is generally attributed to a subset of animals: most famously insects and amphibians, but some fish and many marine invertebrates as well. We held a symposium at the 2006 Society for Integrative and Comparative Biology (SICB) annual meeting in Orlando, FL (USA) to discuss metamorphosis in a comparative context.

Juvenile hormone acts at embryonic molts and induces the nymphal cuticle in the direct-developing cricket.

During embryogenesis of hemimetabolous insects, the sesquiterpenoid hormone, juvenile hormone (JH), appears late in embryogenesis coincident with formation of the first nymphal cuticle. We tested the role of embryonic JH by treating cricket embryos with JH III, or the JH-mimic (JHM) pyriproxifen, during early embryogenesis. We found two discrete windows of JH sensitivity.

Detection and quantitation of perlecan mRNA levels in Alzheimer's disease and normal aged hippocampus by competitive reverse transcription-polymerase chain reaction.

Our previous studies have implicated perlecan, a specific heparan sulfate proteoglycan, in the pathogenesis of fibrillar beta-amyloid protein (A beta) accumulation and persistence in Alzheimer's disease (AD) brain. In the present investigation, we determined if perlecan mRNA was present in rodent and human brain tissue and whether perlecan persistence in A beta amyloid deposits in AD hippocampus may be partly due to increased perlecan expression and/or decreased perlecan degradation. To detect and to quantify low-abundance perlecan mRNA in rodent and postmortem human brain tissue, regions of perlecan domain I (503 and 366 bp) containing the unique heparan sulfate glycosaminoglycan attachment sites were analyzed by reverse transcription (RT) and polymerase chain reaction (PCR).

Induction of a secondary embryonic axis in zebrafish occurs following the overexpression of beta-catenin.

Formation of the vertebrate axis may involve a Wnt signaling cascade similar to the Drosophila wingless pathway. Zebrafish wnt8 is a candidate for involvement in axis specification insofar as it is expressed maternally and when overexpressed it can induce goosecoid, a transcription factor normally expressed in the embryonic shield. In this study we demonstrate that beta-catenin, a cadherin associated protein in the Wnt pathway, is expressed maternally in zebrafish and is widely distributed in the early embryo.

Zebrafish wnt8 and wnt8b share a common activity but are involved in distinct developmental pathways.

The specification of the vertebrate body plan is dependent on numerous signaling molecules, including members of the Wnt family. We have identified two zebrafish wnt8 paralogs related to Xwnt-8B and Xwnt-8, respectively. A RT-PCR assay demonstrated that wnt8 is expressed maternally, with transcripts detected throughout embryogenesis, whereas wnt8b transcripts were first detected during late gastrulation.