Expression patterns of hedgehog, wingless, and decapentaplegic during gut formation of Gryllus bimaculatus (cricket)

A conserved role for arrow in posterior axis patterning across Arthropoda

Segmentation is a key characteristic of Arthropoda that is linked to the evolutionary success of this lineage. It has previously been shown in both vertebrates and short germ insects that posterior segmentation requires canonical Wnt (cWnt) signaling, which maintains the expression of Caudal and the posterior growth zone; disruption of cWnt signaling incurs posterior truncations in these lineages due to the loss of the tail bud. However, comparable datasets for Wnt signaling are limited outside of holometabolous insects, due to incomparable phenotypic spectra and inefficacy of gene misexpression methods in certain model species. We applied RNA interference (RNAi) against the Wnt co-receptor arrow (arr), a key member of the cWnt signaling pathway in holometabolous insects and vertebrates, to examine posterior axis elongation of the cobweb spider Parasteatoda tepidariorum (short germ embryogenesis; one Wnt8 homolog), the cricket Gryllus bimaculatus (intermediate germ; one Wnt8 homolog), and the milkweed bug Oncopeltus fasciatus (short germ; two Wnt8 homologs). Knockdown of arr in insects resulted in posterior truncations affecting the gnathos through the abdomen in O. fasciatus, whereas posterior truncations only affected the T3 segment through the abdomen in G. bimaculatus. Spider embryos with disrupted arr expression exhibited defects along the entire axis, including segmentation defects throughout the germband. RNA-Seq-based differential gene expression analysis of severe Ptep-arr loss-of-function phenotypes at two developmental stages was used to confirm that knockdown of Ptep-arr results in systemic disruption of the Wnt pathway. Intriguingly, we found that knockdown of arr did not abrogate Wnt8 expression in any of the three species, with cad expression additionally retained in severe loss-of-function phenotypes in the cricket and the spider. Together with data from a holometabolous insect, our results suggest that cWnt signaling is not required for maintenance of Wnt8 expression across Arthropoda. These outcomes underscore the diagnostic power of differential gene expression analyses in characterizing catastrophic phenotypes in emerging model species.

Molecular control of gut formation in the spider Parasteatoda tepidariorum

The development of a digestive system is an essential feature of bilaterians. Studies of the molecular control of gut formation in arthropods have been studied in detail in the fruit fly Drosophila melanogaster. However, little is known in other arthropods, especially in noninsect arthropods. To better understand the evolution of arthropod alimentary system, we investigate the molecular control of gut development in the spider Parasteatoda tepidariorum (Pt), the primary chelicerate model species for developmental studies. Orthologs of the ectodermal genes Pt-wingless (Pt-wg) and Pt-hedgehog (Pt-hh), of the endodermal genes, Pt-serpent (Pt-srp) and Pt-hepatocyte-nuclear factor-4 (Pt-hnf4) and of the mesodermal gene Pt-twist (Pt-twi) are expressed in the same germ layers during spider gut development as in D. melanogaster. Thus, our expression data suggest that the downstream molecular components involved in gut development in arthropods are conserved. However, Pt-forkhead (Pt-fkh) expression and function in spiders is considerably different from its D. melanogaster ortholog. Pt-fkh is expressed before gastrulation in a cell population that gives rise to endodermal and mesodermal precursors, suggesting a possible role for this factor in specification of both germ layers. To test this hypothesis, we knocked down Pt-fkh via RNA interference. Pt-fkh RNAi embryos not only fail to develop a proper gut, but also lack the mesodermal Pt-twi expressing cells. Thus, in spiders Pt-fkh specifies endodermal and mesodermal germ layers. We discuss the implications of these findings for the evolution and development of gut formation in Ecdysozoans.

A genes eye view of ontogeny: de novo assembly and profiling of the Gryllus rubens transcriptome

Crickets (Orthoptera:Gryllidae) are widely used model organisms for developmental, evolutionary, neurobiological and behavioural research. Here, we developed a de novo transcriptome from pooled RNA-seq Illumina data spanning seven stages in the life cycle of Gryllus rubens. Approximately 705 Mbp of data was assembled and filtered to form 27 312 transcripts. We were able to annotate 52% of our transcripts using BLAST and assign at least one gene ontology term to 41%. Pooled samples from three different ontogenetic stages were used for transcriptomic profiling revealing patterns of differential gene expression that highlight processes in the different life stages. Embryonic and early instar development was enriched for ecdysteroid metabolism, cytochrome P450s and glutathione production. Late instar development was enriched for regulation of gene expression and many of the genes highly expressed during this stage were involved in conserved developmental signalling pathways suggesting that these developmental pathways are active beyond embryonic development. Adults were enriched for fat transport (mostly relating to egg production) and production of octopamine, an important neurohormone. We also identified genes involved in conserved developmental pathways (Hedgehog, Hippo, Wnt, JAK/STAT, TGF-beta, Notch, and MEK/ERK). This is the first transcriptome spanning ontogeny in Gryllus rubens and a valuable resource for future work on development and evolution in Orthoptera.

Embryonic development of the cricket Gryllus bimaculatus

Extensive research into Drosophila melanogaster embryogenesis has improved our understanding of insect developmental mechanisms. However, Drosophila development is thought to be highly divergent from that of the ancestral insect and arthropod in many respects. We therefore need alternative models for arthopod development that are likely to be more representative of basally-branching clades. The cricket Gryllus bimaculatus is such a model, and currently has the most sophisticated functional genetic toolkit of any hemimetabolous insect. The existing cricket embryonic staging system is fragmentary, and it is based on morphological landmarks that are not easily visible on a live, undissected egg. To address this problem, here we present a complementary set of "egg stages" that serve as a guide for identifying the developmental progress of a cricket embryo from fertilization to hatching, based solely on the external appearance of the egg. These stages were characterized using a combination of brightfield timelapse microscopy, timed brightfield micrographs, confocal microscopy, and measurements of egg dimensions. These egg stages are particularly useful in experiments that involve egg injection (including RNA interference, targeted genome modification, and transgenesis), as injection can alter the speed of development, even in control treatments. We also use 3D reconstructions of fixed embryo preparations to provide a comprehensive description of the morphogenesis and anatomy of the cricket embryo during embryonic rudiment assembly, germ band formation, elongation, segmentation, and appendage formation. Finally, we aggregate and schematize a variety of published developmental gene expression patterns. This work will facilitate further studies on G. bimaculatus development, and serve as a useful point of reference for other studies of wild type and experimentally manipulated insect development in fields from evo-devo to disease vector and pest management.

Developmental gene discovery in a hemimetabolous insect: de novo assembly and annotation of a transcriptome for the cricket Gryllus bimaculatus

Most genomic resources available for insects represent the Holometabola, which are insects that undergo complete metamorphosis like beetles and flies. In contrast, the Hemimetabola (direct developing insects), representing the basal branches of the insect tree, have very few genomic resources. We have therefore created a large and publicly available transcriptome for the hemimetabolous insect Gryllus bimaculatus (cricket), a well-developed laboratory model organism whose potential for functional genetic experiments is currently limited by the absence of genomic resources. cDNA was prepared using mRNA obtained from adult ovaries containing all stages of oogenesis, and from embryo samples on each day of embryogenesis. Using 454 Titanium pyrosequencing, we sequenced over four million raw reads, and assembled them into 21,512 isotigs (predicted transcripts) and 120,805 singletons with an average coverage per base pair of 51.3. We annotated the transcriptome manually for over 400 conserved genes involved in embryonic patterning, gametogenesis, and signaling pathways. BLAST comparison of the transcriptome against the NCBI non-redundant protein database (nr) identified significant similarity to nr sequences for 55.5% of transcriptome sequences, and suggested that the transcriptome may contain 19,874 unique transcripts. For predicted transcripts without significant similarity to known sequences, we assessed their similarity to other orthopteran sequences, and determined that these transcripts contain recognizable protein domains, largely of unknown function. We created a searchable, web-based database to allow public access to all raw, assembled and annotated data. This database is to our knowledge the largest de novo assembled and annotated transcriptome resource available for any hemimetabolous insect. We therefore anticipate that these data will contribute significantly to more effective and higher-throughput deployment of molecular analysis tools in Gryllus.

The function and evolution of Wnt genes in arthropods

Wnt signalling is required for a wide range of developmental processes, from cleavage to patterning and cell migration. There are 13 subfamilies of Wnt ligand genes and this diverse repertoire appeared very early in metazoan evolution. In this review, we first summarise the known Wnt gene repertoire in various arthropods. Insects appear to have lost several Wnt subfamilies, either generally, such as Wnt3, or in lineage specific patterns, for example, the loss of Wnt7 in Anopheles. In Drosophila and Acyrthosiphon, only seven and six Wnt subfamilies are represented, respectively; however, the finding of nine Wnt genes in Tribolium suggests that arthropods had a larger repertoire ancestrally. We then discuss what is currently known about the expression and developmental function of Wnt ligands in Drosophila and other insects in comparison to other arthropods, such as the spiders Achaearanea and Cupiennius. We conclude that studies of Wnt genes have given us much insight into the developmental roles of some of these ligands. However, given the frequent loss of Wnt genes in insects and the derived development of Drosophila, further studies of these important genes are required in a broader range of arthropods to fully understand their developmental function and evolution.

Evolution of insect development: to the hemimetabolous paradigm

Mechanisms of insect development have been extensively studied in Drosophila melanogaster, a holometabolous insect. However, recent studies on other insects have gradually revealed that there exist new developmental paradigms. In this review, we focus on the new hemimetabolous paradigm. We highlight how hemimetabolous short-germ or intermediate-germ embryos establish the anterior/posterior (A/P) pattern and the importance of dynamic cell movement during germband formation. In hemimetabolous insects, orthodenticle, encoding a homeodomain-containing transcription factor, and wingless/Wnt signaling could play crucial roles in the A/P pattern formation. We also discuss recent evidence suggesting that insect developmental modes may have evolved by heterochronic shifts, while retaining certain universal metazoan features.

Hedgehog: functions and mechanisms

The Hedgehog (Hh) family of proteins control cell growth, survival, and fate, and pattern almost every aspect of the vertebrate body plan. The use of a single morphogen for such a wide variety of functions is possible because cellular responses to Hh depend on the type of responding cell, the dose of Hh received, and the time cells are exposed to Hh. The Hh gradient is shaped by several proteins that are specifically required for Hh processing, secretion, and transport through tissues. The mechanism of cellular response, in turn, incorporates multiple feedback loops that fine-tune the level of signal sensed by the responding cells. Germline mutations that subtly affect Hh pathway activity are associated with developmental disorders, whereas somatic mutations activating the pathway have been linked to multiple forms of human cancer. This review focuses broadly on our current understanding of Hh signaling, from mechanisms of action to cellular and developmental functions. In addition, we review the role of Hh in the pathogenesis of human disease and the possibilities for therapeutic intervention.

The Hedgehog gene family of the cnidarian, Nematostella vectensis, and implications for understanding metazoan Hedgehog pathway evolution

Hedgehog signaling is an important component of cell-cell communication during bilaterian development, and abnormal Hedgehog signaling contributes to disease and birth defects. Hedgehog genes are composed of a ligand ("hedge") domain and an autocatalytic intein ("hog") domain. Hedgehog (hh) ligands bind to a conserved set of receptors and activate downstream signal transduction pathways terminating with Gli/Ci transcription factors. We have identified five intein-containing genes in the anthozoan cnidarian Nematostella vectensis, two of which (NvHh1 and NvHh2) contain definitive hedgehog ligand domains, suggesting that to date, cnidarians are the earliest branching metazoan phylum to possess definitive Hh orthologs. Expression analysis of NvHh1 and NvHh2, the receptor NvPatched, and a downstream transcription factor NvGli (a Gli3/Ci ortholog) indicate that these genes may have conserved roles in planar and trans-epithelial signaling during gut and germline development, while the three remaining intein-containing genes (NvHint1,2,3) are expressed in a cell-type-specific manner in putative neural precursors. Metazoan intein-containing genes that lack a hh ligand domain have previously only been identified within nematodes. However, we have identified intein-containing genes from both Nematostella and in two newly annotated lophotrochozoan genomes. Phylogenetic analyses suggest that while nematode inteins may be derived from an ancestral true hedgehog gene, the newly identified cnidarian and lophotrochozoan inteins may be orthologous, suggesting that both true hedgehog and hint genes may have been present in the cnidarian-bilaterian ancestor. Genomic surveys of N. vectensis suggest that most of the components of both protostome and deuterostome Hh signaling pathways are present in anthozoans and that some appear to have been lost in ecdysozoan lineages. Cnidarians possess many bilaterian cell-cell signaling pathways (Wnt, TGFbeta, FGF, and Hh) that appear to act in concert to pattern tissues along the oral-aboral axis of the polyp. Cnidarians represent a diverse group of animals with a predominantly epithelial body plan, and perhaps selective pressures to pattern epithelia resulted in the ontogeny of the hedgehog pathway in the common ancestor of the Cnidaria and Bilateria.

brachyenteron is necessary for morphogenesis of the posterior gut but not for anteroposterior axial elongation from the posterior growth zone in the intermediate-germband cricket Gryllus bimaculatus

In the long-germband insect Drosophila, all body segments and posterior terminal structures, including the posterior gut and anal pads, are specified at the blastoderm stage. In short- and intermediate-germband insects, however, posterior segments are sequentially produced from the posterior growth zone, a process resembling somitogenesis in vertebrates, and invagination of the posterior gut starts after anteroposterior (AP) axial elongation from the growth zone. The mechanisms underlying posterior segmentation and terminal patterning in these insects are poorly understood. In order to elucidate these mechanisms, we have investigated the roles of the Brachyury/brachyenteron (Bra/byn) homolog in the intermediate-germband cricket Gryllus bimaculatus. Loss-of-function analysis by RNA interference (RNAi) revealed that Gryllus byn (Gb'byn) is not required for AP axial elongation or normal segment formation, but is required for specification of the posterior gut. We also analyzed Gryllus caudal (Gb'cad) RNAi embryos using in situ hybridization with a Gb'byn probe, and found that Gb'cad is required for internalization of the posterior gut primordium, in addition to AP axial elongation. These results suggest that the functions of byn and cad in posterior terminal patterning are highly conserved in Gryllus and Drosophila despite their divergent posterior patterning. Moreover, because it is thought that the progressive growth of the AP axis from the growth zone, controlled by a genetic program involving Cdx/cad and Bra/byn, might be ancestral to bilaterians, our data suggest that the function of Bra/byn in this process might have been lost in insects.

The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence

Understanding the head is one of the great challenges in the fields of comparative anatomy, developmental biology, and palaeontology of arthropods. Numerous conflicting views and interpretations are based on an enormous variety of descriptive and experimental approaches. The interpretation of the head influences views on phylogenetic relationships within the Arthropoda as well as outgroup relationships. Here, we review current hypotheses about head segmentation and the nature of head structures from various perspectives, which we try to combine to gain a deeper understanding of the arthropod head. Though discussion about arthropod heads shows some progress, unquestioned concepts (e.g., a presegmental acron) are still a source of bias. Several interpretations are no longer tenable based on recent results from comparative molecular developmental studies, improved morphological investigations, and new fossils. Current data indicate that the anterior arthropod head comprises three elements: the protocerebral/ocular region, the deutocerebral/antennal/cheliceral segment, and the tritocerebral/pedipalpal/second antennal/intercalary segment. The labrum and the mouth are part of the protocerebral/ocular region. Whether the labrum derives from a former pair of limbs remains an open question, but a majority of data support its broad homology across the Euarthropoda. From the alignment of head segments between onychophorans and euarthropods, we develop the concept of "primary" and "secondary antennae" in Recent and fossil arthropods, posit that "primary antennae" are retained in some fossil euarthropods below the crown group level, and propose that Trilobita are stem lineage representatives of the Mandibulata.

Krüppel acts as a gap gene regulating expression of hunchback and even-skipped in the intermediate germ cricket Gryllus bimaculatus

In Drosophila, a long germ insect, segmentation occurs simultaneously across the entire body. In contrast, in short and intermediate germ insects, the anterior segments are specified during the blastoderm stage, while the remaining posterior segments are specified during later stages. In Drosophila embryos, the transcriptional factors coded by gap genes, such as Krüppel, diffuse in the syncytial environment and regulate the expression of other gap, pair-rule, and Hox genes. To understand the segmentation mechanisms in short and intermediate germ insects, we investigated the role of Kr ortholog (Gb'Kr) in the development of the intermediate germ insect Gryllus bimaculatus. We found that Gb'Kr is expressed in a gap pattern in the prospective thoracic region after cellularization of the embryo. To determine the function of Gb'Kr in segmentation, we analyzed knockdown phenotypes using RNA interference (RNAi). Gb'Kr RNAi depletion resulted in a gap phenotype in which the posterior of the first thoracic through seventh abdominal segments were deleted. Analysis of the expression patterns of Hox genes in Gb'Kr RNAi embryos indicated that regulatory relationships between Hox genes and Kr in Gryllus differ from those in Oncopeltus, another intermediate germ insect. Furthermore, we found that Gb'Kr regulates expression minimally of hunchback and even-skipped, directly or indirectly, in the prospective thoracic region. Our findings suggest that Gb'Kr is a gap gene that acts in the cellular environment and is required for segmentation in the thoracic and abdominal regions through the regulation of gap and pair-rule gene expression.

The characteristics of karyotype and telomeric satellite DNA sequences in the cricket, Gryllus bimaculatus (Orthoptera, Gryllidae)

The chromosomes derived from the Japanese population of Gryllus bimaculatus were characterized by C-banding and Ag-NOR staining. The chromosome number, 2n = 28 + XX (female)/XO (male), corresponded with that of other populations of G. bimaculatus, but the chromosome configuration in idiograms varied between the populations. NORs were carried on one pair of autosomes and appeared polymorphous. The positive C-bands located at the centromere of all chromosomes and the distal regions of many chromosome pairs, and the size and the distribution pattern of the distal C-heterochromatin showed differences among the chromosomes. In addition, this paper reports on the characteristics of HindIII satellite DNA isolated from the genome of G. bimaculatus. The HindIII repetitive fragments were about 0.54 kb long, and localized at the distal C-bands of the autosomes and the interstitial C-bands of the X chromosome. Molecular analysis showed two distinct satellite DNA sequences, named the GBH535 and GBH542 families, with high AT contents of about 67 and 66%, respectively. The two repetitive families seem to be derived from a common ancestral sequence, and both families possessed the same 13-bp palindrome sequence. The results of Southern blot hybridization suggest that the sequence of the GBH535 family is conserved in the genomic DNAs of Gryllus species, whereas the GBH542 family is a species-specific sequence.

caudal is required for gnathal and thoracic patterning and for posterior elongation in the intermediate-germband cricket Gryllus bimaculatus

Although the molecular mechanisms directing anteroposterior patterning of the Drosophila embryo (long-germband mode) are well understood, how these mechanisms were evolved from an ancestral mode of insect embryogenesis remains largely unknown. In order to gain insight into mechanisms of evolution in insect embryogenesis, we have examined the expression and function of the orthologue of Drosophila caudal (cad) in the intermediate-germband cricket Gryllus bimaculatus. We observed that a posterior (high) to anterior (low) gradient in the levels of Gryllus bimaculatus cad (Gb' cad) transcript was formed in the early-stage embryo, and then Gb' cad was expressed in the posterior growth zone until the posterior segmentation was completed. Reduction of Gb' cad expression level by RNA interference resulted in deletion of the gnathum, thorax, and abdomen in embryos, remaining only anterior head. We found that the gnathal and thoracic segments are formed by Gb' cad probably through the transcriptional regulation of gap genes including Gb' hunchback and Gb' Kruppel. Furthermore, Gb' cad was found to be involved in the posterior elongation, acting as a downstream gene in the Wingless/Armadillo signalling pathways. These findings indicate that Gb' cad does not function as it does in Drosophila, suggesting that regulatory and functional changes of cad occurred during insect evolution. Since Wnt/Cdx pathways are involved in the posterior patterning of vertebrates, such mechanisms may be conserved in animals that undergo sequential segmentation from the posterior growth zone.

hedgehog is a segment polarity gene in a crustacean and a chelicerate

The evolution of arthropod segmentation has been studied by comparing expression patterns of pair-rule and segment polarity genes in various species. In Drosophila, the formation and maintenance of the parasegmental boundaries depend on the interactions between the wingless (wg), engrailed (en) and hedgehog (hh) genes. Until now, the expression pattern of hh has not been analysed to such a great extent as en or wg. We report the cloning and expression analysis of hh genes from Euscorpius flavicaudis, a chelicerate, and Artemia franciscana, a branchiopod crustacean. Our data provide evidence that hh, being expressed in the posterior part of every segment, is a segment polarity gene in both organisms. Additional hh expression sites were observed in the rostrum and appendages of Euscorpius and in the gut of Artemia. From the available data on hh expression in various bilaterians, we review the various hypotheses on the evolution of hh function and we suggest an ancestral role of hh in proctodeum specification and gut formation.

piggyBac-mediated somatic transformation of the two-spotted cricket, Gryllus bimaculatus

Transgenic insects have been artificially produced to study functions of interesting developmental genes, using insect transposons such as piggyBac. In the case of the cricket, however, transgenic animals have not yet been successfully artificially produced. In the present study, we examined whether the piggyBac transposon functions as a tool for gene delivery in embryos of Gryllus bimaculatus. We used either a piggyBac helper plasmid or a helper RNA synthesized in vitro as a transposase source. An excision assay revealed that the helper RNA was more effective in early Gryllus eggs to transpose a marker gene of eGFP than the helper plasmid containing the piggyBac transposase gene driven by the G. bimaculatus actin3/4 promoter. Further, only when the helper RNA was used, somatic transformation of the embryo with the eGFP gene was observed. These results suggest that the piggyBac system with the helper RNA may be effective for making transgenic crickets.

Gene expression suggests decoupled dorsal and ventral segmentation in the millipede Glomeris marginata (Myriapoda: Diplopoda)

Diplopods (millipedes) are known for their irregular body segmentation. Most importantly, the number of dorsal segmental cuticular plates (tergites) does not match the number of ventral structures (e.g., sternites). Controversial theories exist to explain the origin of this so-called diplosegmentation. We have studied the embryology of a representative diplopod, Glomeris marginata, and have analyzed the segmentation genes engrailed (en), hedgehog (hh), cubitus-interruptus (ci), and wingless (wg). We show that dorsal segments can be distinguished from ventral segments. They differ not only in number and developmental history, but also in gene expression patterns. engrailed, hedgehog, and cubitus-interruptus are expressed in both ventral and dorsal segments, but at different intrasegmental locations, whereas wingless is expressed only in the ventral segments, but not in the dorsal segments. Ventrally, the patterns are similar to what has been described from Drosophila and other arthropods, consistent with a conserved role of these genes in establishing parasegment boundaries. On the dorsal side, however, the gene expression patterns are different and inconsistent with a role in boundary formation between segments, but they suggest that these genes might function to establish the tergite borders. Our data suggest a profound and rather complete decoupling of dorsal and ventral segmentation leading to the dorsoventral discrepancies in the number of segmental elements. Based on gene expression, we propose a model that may resolve the hitherto controversial issue of the correlation between dorsal tergites and ventral leg pairs in basal diplopods (e.g., Glomeris) and is suggestive also for derived, ring-forming diplopods (e.g., Juliformia).

Involvement of Wingless/Armadillo signaling in the posterior sequential segmentation in the cricket, Gryllus bimaculatus (Orthoptera), as revealed by RNAi analysis

In insects, there are two different modes of segmentation. In the higher dipteran insects (like Drosophila), their segmentation takes place almost simultaneously in the syncytial blastoderm. By contrast, in the orthopteran insects (like Schistocerca (grasshopper)), the anterior segments form almost simultaneously in the cellular blastoderm and then the remaining posterior part elongates to form segments sequentially from the posterior proliferative zone. Although most of their orthologues of the Drosophila segmentation genes may be involved in their segmentation, little is known about their roles. We have investigated segmentation processes of Gryllus bimaculatus, focusing on its orthologues of the Drosophila segment-polarity genes, G. bimaculatus wingless (Gbwg), armadillo (Gbarm) and hedgehog (Gbhh). Gbhh and Gbwg were observed to be expressed in the each anterior segment and the posterior proliferative zone. In order to know their roles, we used RNA interference (RNAi). We could not observed any significant effects of RNAi for Gbwg and Gbhh on segmentation, probably due to functional replacement by another member of the corresponding gene families. Embryos obtained by RNAi for Gbarm exhibited abnormal anterior segments and lack of the abdomen. Our results suggest that GbWg/GbArm signaling is involved in the posterior sequential segmentation in the G. bimaculatus embryos, while Gbwg, Gbarm and Gbhh are likely to act as the segment-polarity genes in the anterior segmentation similarly as in Drosophila.

Developmental roles and clinical significance of hedgehog signaling

Cell signaling plays a key role in the development of all multicellular organisms. Numerous studies have established the importance of Hedgehog signaling in a wide variety of regulatory functions during the development of vertebrate and invertebrate organisms. Several reviews have discussed the signaling components in this pathway, their various interactions, and some of the general principles that govern Hedgehog signaling mechanisms. This review focuses on the developing systems themselves, providing a comprehensive survey of the role of Hedgehog signaling in each of these. We also discuss the increasing significance of Hedgehog signaling in the clinical setting.

Extrachromosomal transposition of the transposable element Minos in embryos of the cricket Gryllus bimaculatus

Effective germline transformation of insects has been shown to depend on the right choice of transposon system and selection marker. In this study the promoter region of a Gryllus cytoplasmic actin (GbA3/4) gene was isolated and characterized, and was used to drive the expression of Minos transposase in embryos of the cricket Gryllus bimaculatus. Active Minos transposase was produced in these embryos as monitored through established transposon excision and interplasmid transposition assays. In contrast, Drosophila melanogaster hsp70 promoter, previously used to express Minos transposase in a number of insect species and insect cell lines, failed to produce any detectable Minos transposase activity, as recorded by using the very sensitive transposon excision assay. In addition, the GbA3/4 promoter was found to drive expression of enhanced green fluorescent protein (eGFP) predominantly in vitellophages of the developing Gryllus eggs when a plasmid carrying a GbA3/4 promoter-eGFP fusion gene was transiently injected into embryos. These results strongly support the use of Minos transposons marked with the GbA3/4 promoter-eGFP for the genetic transformation of this emerging model insect species.