Establishment of CRISPR/Cas9-based knock-in in a hemimetabolous insect: targeted gene tagging in the cricket Gryllus bimaculatus

Studies of traditional model organisms such as the fruit fly Drosophila melanogaster have contributed immensely to our understanding of the genetic basis of developmental processes. However, the generalizability of these findings cannot be confirmed without functional genetic analyses in additional organisms. Direct genome editing using targeted nucleases has the potential to transform hitherto poorly understood organisms into viable laboratory organisms for functional genetic study. To this end, we present a method to induce targeted genome knockout and knock-in of desired sequences in an insect that serves as an informative contrast to Drosophila, the cricket Gryllus bimaculatus. The efficiency of germline transmission of induced mutations is comparable with that reported for other well-studied laboratory organisms, and knock-ins targeting introns yield viable, fertile animals in which knock-in events are directly detectable by visualization of a fluorescent marker in the expression pattern of the targeted gene. Combined with the recently assembled and annotated genome of this cricket, this knock-in/knockout method increases the viability of G. bimaculatus as a tractable system for functional genetics in a basally branching insect.

Two transcriptional cascades orchestrate cockroach leg regeneration

The mystery of appendage regeneration has fascinated humans for centuries, while the underlying regulatory mechanisms remain unclear. In this study, we establish a transcriptional landscape of regenerating leg in the American cockroach, Periplaneta americana, an ideal model in appendage regeneration studies showing remarkable regeneration capacity. Through a large-scale in vivo screening, we identify multiple signaling pathways and transcription factors controlling leg regeneration. Specifically, zfh-2 and bowl contribute to blastema cell proliferation and morphogenesis in two transcriptional cascades: bone morphogenetic protein (BMP)/JAK-STAT-zfh-2-B-H2 and Notch-drm/bowl-bab1. Notably, we find zfh-2 is working as a direct target of BMP signaling to promote cell proliferation in the blastema. These mechanisms might be conserved in the appendage regeneration of vertebrates from an evolutionary perspective. Overall, our findings reveal that two crucial transcriptional cascades orchestrate distinct cockroach leg regeneration processes, significantly advancing the comprehension of molecular mechanism in appendage regeneration.

ERK-activated CK-2 triggers blastema formation during appendage regeneration

Appendage regeneration relies on the formation of blastema, a heterogeneous cellular structure formed at the injury site. However, little is known about the early injury-activated signaling pathways that trigger blastema formation during appendage regeneration. Here, we provide compelling evidence that the extracellular signal-regulated kinase (ERK)-activated casein kinase 2 (CK-2), which has not been previously implicated in appendage regeneration, triggers blastema formation during leg regeneration in the American cockroach, Periplaneta americana. After amputation, CK-2 undergoes rapid activation through ERK-induced phosphorylation within blastema cells. RNAi knockdown of CK-2 severely impairs blastema formation by repressing cell proliferation through down-regulating mitosis-related genes. Evolutionarily, the regenerative role of CK-2 is conserved in zebrafish caudal fin regeneration via promoting blastema cell proliferation. Together, we find and demonstrate that the ERK-activated CK-2 triggers blastema formation in both cockroach and zebrafish, helping explore initiation factors during appendage regeneration.

Molecular aspects of regeneration in insects

Regeneration is a fascinating phenomenon observed in various organisms across the animal kingdom. Different orders of class Insecta are reported to possess comprehensive regeneration abilities. Several signalling molecules, such as morphogens, growth factors, and others trigger a cascade of events that promote wound healing, blastema formation, growth, and repatterning. Furthermore, epigenetic regulation has emerged as a critical player in regulating the process of regeneration. This report highlights the major breakthrough research on wound healing and tissue regeneration. Exploring and reviewing the molecular basis of regeneration can be helpful in the area of regenerative medicine advancements. The understanding gathered from this framework can potentially contribute to hypothesis designing with implications in the field of synthetic biology and human health.

Regenerative growth is constrained by brain tumor to ensure proper patterning in Drosophila

Some animals respond to injury by inducing new growth to regenerate the lost structures. This regenerative growth must be carefully controlled and constrained to prevent aberrant growth and to allow correct organization of the regenerating tissue. However, the factors that restrict regenerative growth have not been identified. Using a genetic ablation system in the Drosophila wing imaginal disc, we have identified one mechanism that constrains regenerative growth, impairment of which also leads to erroneous patterning of the final appendage. Regenerating discs with reduced levels of the RNA-regulator Brain tumor (Brat) exhibit enhanced regeneration, but produce adult wings with disrupted margins that are missing extensive tracts of sensory bristles. In these mutants, aberrantly high expression of the pro-growth factor Myc and its downstream targets likely contributes to this loss of cell-fate specification. Thus, Brat constrains the expression of pro-regeneration genes and ensures that the regenerating tissue forms the proper final structure.

Physiological and molecular mechanisms of insect appendage regeneration

Regeneration, as a fascinating scientific field, refers to the ability of animals replacing lost tissue or body parts. Many metazoan organisms have been reported with the regeneration phenomena, but showing evolutionarily variable abilities. As the most diverse metazoan taxon, hundreds of insects show strong appendage regeneration ability. The regeneration process and ability are dependent on many factors, including macroscopic physiological conditions and microscopic molecular mechanisms. This article reviews research progress on the physiological conditions and internal underlying mechanisms controlling appendage regeneration in insects.

Integrative biology of injury in animals

Mechanical injury is a prevalent challenge in the lives of animals with myriad potential consequences for organisms, including reduced fitness and death. Research on animal injury has focused on many aspects, including the frequency and severity of wounding in wild populations, the short- and long-term consequences of injury at different biological scales, and the variation in the response to injury within or among individuals, species, ontogenies, and environmental contexts. However, relevant research is scattered across diverse biological subdisciplines, and the study of the effects of injury has lacked synthesis and coherence. Furthermore, the depth of knowledge across injury biology is highly uneven in terms of scope and taxonomic coverage: much injury research is biomedical in focus, using mammalian model systems and investigating cellular and molecular processes, while research at organismal and higher scales, research that is explicitly comparative, and research on invertebrate and non-mammalian vertebrate species is less common and often less well integrated into the core body of knowledge about injury. The current state of injury research presents an opportunity to unify conceptually work focusing on a range of relevant questions, to synthesize progress to date, and to identify fruitful avenues for future research. The central aim of this review is to synthesize research concerning the broad range of effects of mechanical injury in animals. We organize reviewed work by four broad and loosely defined levels of biological organization: molecular and cellular effects, physiological and organismal effects, behavioural effects, and ecological and evolutionary effects of injury. Throughout, we highlight the diversity of injury consequences within and among taxonomic groups while emphasizing the gaps in taxonomic coverage, causal understanding, and biological endpoints considered. We additionally discuss the importance of integrating knowledge within and across biological levels, including how initial, localized responses to injury can lead to long-term consequences at the scale of the individual animal and beyond. We also suggest important avenues for future injury biology research, including distinguishing better between related yet distinct injury phenomena, expanding the subjects of injury research to include a greater variety of species, and testing how intrinsic and extrinsic conditions affect the scope and sensitivity of injury responses. It is our hope that this review will not only strengthen understanding of animal injury but will contribute to building a foundation for a more cohesive field of 'injury biology'.

CRISPR/Cas9-Mediated genomic knock out of tyrosine hydroxylase and yellow genes in cricket Gryllus bimaculatus

Gryllus bimaculatus is an emerging model organism in various fields of biology such as behavior, neurology, physiology and genetics. Recently, application of reverse genetics provides an opportunity of understanding the functional genomics and manipulating gene regulation networks with specific physiological response in G. bimaculatus. By using CRISPR/Cas9 system in G. bimaculatus, we present an efficient knockdown of Tyrosine hydroxylase (TH) and yellow-y, which are involved in insect melanin and catecholamine-biosynthesis pathway. As an enzyme catalyzing the conversion of tyrosine to 3,4-dihydroxyphenylalanine, TH confines the first step reaction in the pathway. Yellow protein (dopachrome conversion enzyme, DCE) is also involved in the melanin biosynthetic pathway. The regulation system and molecular mechanism of melanin biogenesis in the pigmentation and their physiological functions in G. bimaculatus hasn't been well defined by far for lacking of in vivo models. Deletion and insertion of nucleotides in target sites of both TH and Yellow are detected in both F0 individuals and the inheritable F1 progenies. We confirm that TH and yellow-y are down-regulated in mutants by quantitative real-time PCR analysis. Compared with the control group, mutations of TH and yellow-y genes result in defects in pigmentation. Most F0 nymphs with mutations of TH gene die by the first instar, and the only adult had significant defects in the wings and legs. However, we could not get any homozygotes of TH mutants for all the F2 die by the first instar. Therefore, TH gene is very important for the growth and development of G. bimaculatus. When the yellow-y gene is knocked out, 71.43% of G. bimaculatus are light brown, with a slight mosaic on the abdomen. The yellow-y gene can be inherited stably through hybridization experiment with no obvious phenotype except lighter cuticular color. The present loss of function study indicates the essential roles of TH and yellow in pigmentation, and TH possesses profound and extensive effects of dopamine synthesis in embryonic development in G. bimaculatus.

Toll signalling promotes blastema cell proliferation during cricket leg regeneration via insect macrophages

Hemimetabolous insects, such as the two-spotted cricket Gryllus bimaculatus, can recover lost tissues, in contrast to the limited regenerative abilities of human tissues. Following cricket leg amputation, the wound surface is covered by the wound epidermis, and plasmatocytes, which are insect macrophages, accumulate in the wound region. Here, we studied the function of Toll-related molecules identified by comparative RNA sequencing during leg regeneration. Of the 11 Toll genes in the Gryllus genome, expression of Toll2-1, Toll2-2 and Toll2-5 was upregulated during regeneration. RNA interference (RNAi) of Toll, Toll2-1, Toll2-2, Toll2-3 or Toll2-4 produced regeneration defects in more than 50% of crickets. RNAi of Toll2-2 led to a decrease in the ratio of S- and M-phase cells, reduced expression of JAK/STAT signalling genes, and reduced accumulation of plasmatocytes in the blastema. Depletion of plasmatocytes in crickets using clodronate also produced regeneration defects, as well as fewer proliferating cells in the regenerating legs. Plasmatocyte depletion also downregulated the expression of Toll and JAK/STAT signalling genes in the regenerating legs. These results suggest that Spz-Toll-related signalling in plasmatocytes promotes leg regeneration through blastema cell proliferation by regulating the Upd-JAK/STAT signalling pathway.

Genomics and genome editing techniques of crickets, an emerging model insect for biology and food science

Most tools available for manipulating gene function in insects have been developed for holometabolous species. In contrast, functional genetics tools for the Hemimetabola are highly underdeveloped. This is a barrier both to understanding ancestral insect biology, and to optimizing contemporary study and manipulation of particular large hemimetabolous orders of crucial economic and agricultural importance like the Orthoptera. For orthopteran insects, including crickets, the rapid spread of next-generation sequencing technology has made transcriptome data available for a wide variety of species over the past decade. Furthermore, whole genome sequences of orthopteran insects with relatively large genome sizes are now available. With these new genome assemblies and the development of genome editing technologies such as the CRISPR-Cas9 system, it has become possible to create gene knock-out and knock-in strains in orthopteran insects. As a result, orthopteran species should become increasingly feasible for laboratory study not only in research fields that have traditionally used insects, but also in agricultural fields that use them as food and feed. In this review, we summarize these recent advances and their relevance to such applications.

Dissecting cricket genomes for the advancement of entomology and entomophagy

Significant advances in biophysical methods such as next-generation sequencing technologies have now opened the way to conduct evolutionary and applied research based on the genomic information of greatly diverse insects. Crickets belonging to Orthoptera (Insecta: Polyneoptera), one of the most flourishing groups of insects, have contributed to the development of multiple scientific fields including developmental biology and neuroscience and have been attractive targets in evolutionary ecology for their diverse ecological niches. In addition, crickets have recently gained recognition as food and feed. However, the genomic information underlying their biological basis and application research toward breeding is currently underrepresented. In this review, we summarize the progress of genomics of crickets. First, we outline the phylogenetic position of crickets in insects and then introduce recent studies on cricket genomics and transcriptomics in a variety of fields. Furthermore, we present findings from our analysis of polyneopteran genomes, with a particular focus on their large genome sizes, chromosome number, and repetitive sequences. Finally, how the cricket genome can be beneficial to the food industry is discussed. This review is expected to enhance greater recognition of how important the cricket genomes are to the multiple biological fields and how basic research based on cricket genome information can contribute to tackling global food security.

JAK/STAT signaling regulates the Harmonia axyridis leg regeneration by coordinating cell proliferation

Harmonia axyridis presents remarkable appendage regeneration capacity and can therefore be considered as an emerging regeneration research model. Amino acid sequences of the Janus kinase Hopscotch (Hahop) and the transcription factor STAT (HaStat), the main components of the JAK/STAT signaling pathway, conserved with their homologs in other models. The expression levels of these two genes were continuously up-regulated during the appendage regeneration process. To identify the functions of JAK/STAT signaling, we performed RNAi experiments of Hahop and HaStat in H. axyridis, and found regeneration defects following in Hahop^RNAi and HaStat^RNAi treatments at different regeneration stages. Additionally, we confirmed that regeneration defects caused by the low-level of JAK/STAT activity were due to the inhibition of cell proliferation. The results of the current study suggest that JAK/STAT signaling regulates the entire regeneration process by coordinating cell proliferation of regenerating appendages.

Insights into the genomic evolution of insects from cricket genomes

Most of our knowledge of insect genomes comes from Holometabolous species, which undergo complete metamorphosis and have genomes typically under 2 Gb with little signs of DNA methylation. In contrast, Hemimetabolous insects undergo the presumed ancestral process of incomplete metamorphosis, and have larger genomes with high levels of DNA methylation. Hemimetabolous species from the Orthopteran order (grasshoppers and crickets) have some of the largest known insect genomes. What drives the evolution of these unusual insect genome sizes, remains unknown. Here we report the sequencing, assembly and annotation of the 1.66-Gb genome of the Mediterranean field cricket Gryllus bimaculatus, and the annotation of the 1.60-Gb genome of the Hawaiian cricket Laupala kohalensis. We compare these two cricket genomes with those of 14 additional insects and find evidence that hemimetabolous genomes expanded due to transposable element activity. Based on the ratio of observed to expected CpG sites, we find higher conservation and stronger purifying selection of methylated genes than non-methylated genes. Finally, our analysis suggests an expansion of the pickpocket class V gene family in crickets, which we speculate might play a role in the evolution of cricket courtship, including their characteristic chirping.

Ylla, Extavour et al. use genomic data from crickets to investigate the evolution of large genome sizes and DNA methylation events in insects. Their findings indicate that transposable element activity drove genome expansion in hemimetabolous insects, such as crickets and grasshoppers, and that DNA methylation is predominant in conserved genes.

Animal regeneration in the era of transcriptomics

Animal regeneration, the ability to restore a lost body part, is a process that has fascinated scientists for centuries. In this review, we first present what regeneration is and how it relates to development, as well as the widespread and diverse nature of regeneration in animals. Despite this diversity, animal regeneration includes three common mechanistic steps: initiation, induction and activation of progenitors, and morphogenesis. In this review article, we summarize and discuss, from an evolutionary perspective, the recent data obtained for a variety of regeneration models which have allowed to identify key shared mechanisms that control these main steps of animal regeneration. This review also synthesizes the wealth of high-throughput mRNA sequencing data (bulk mRNA-seq) concerning regeneration which have been obtained in recent years, highlighting the major advances in the regeneration field that these studies have revealed. We stress out that, through a comparative approach, these data provide opportunities to further shed light on the evolution of regeneration in animals. Finally, we point out how the use of single-cell mRNA-seq technology and integration with epigenomic approaches may further help researchers to decipher mechanisms controlling regeneration and their evolution in animals.

The Ras/MAPK pathway is required for regenerative growth of wing discs in the black cutworm Agrotis ypsilon

Regeneration is a common phenomenon in various organisms by which tissues restore the damaged or naturally detached parts. In insects, appendage regeneration takes place during the embryonic, larval and pupal stages for individual survival. The wing disc of black cutworm Agrotis ypsilon has the capacity of regeneration after ablation, but understanding of molecular mechanisms in wing disc regeneration is still limited. After ablation of partial or whole wing discs before the fifth instar larval stage, the adult wings appeared to be normal. In the last two larval stages, ablation of the left wing disc led to smaller corresponding adult wing. Cell proliferation was reduced in the ablated wing disc but was gradually recovered two days post ablation. Transcriptome analysis found that genes in the mitogen-activated protein kinase (MAPK) pathway were upregulated. Repression of gene expression in this pathway, including Ras oncogene at 64B (Ras64B), Downstream of raf1 (Dsor1), and cAMP-dependent protein kinase catalytic subunit 3 (Pka-C3) by RNA interference after ablation, led to diminishment of both adult wings, suggesting that the MAPK signaling is essential for wing growth. Additionally, cell proliferation was still decelerated by injecting Ras64B, Dsor, or Pka-C3 dsRNA two days after ablation, indicating that the MAPK signaling-regulated cell proliferation is essential for growth. These results provide molecular clues to the regulation of cell proliferation during regeneration in lepidopteran insects.

Striking parallels between dorsoventral patterning in Drosophila and Gryllus reveal a complex evolutionary history behind a model gene regulatory network

Dorsoventral pattering relies on Toll and BMP signalling in all insects studied so far, with variations in the relative contributions of both pathways. Drosophila and the beetle Tribolium share extensive dependence on Toll, while representatives of more distantly related lineages like the wasp Nasonia and bug Oncopeltus rely more strongly on BMP signalling. Here, we show that in the cricket Gryllus bimaculatus, an evolutionarily distant outgroup, Toll has, like in Drosophila, a direct patterning role for the ventral half of the embryo. In addition, Toll polarises BMP signalling, although this does not involve the conserved BMP inhibitor Sog/Chordin. Finally, Toll activation relies on ovarian patterning mechanisms with striking similarity to Drosophila. Our data suggest two surprising hypotheses: (1) that Toll's patterning function in Gryllus and Drosophila is the result of convergent evolution or (2) a Drosophila-like system arose early in insect evolution and was extensively altered in multiple independent lineages.

Hedgehog signaling regulates regenerative patterning and growth in Harmonia axyridis leg

Appendage regeneration has been widely studied in many species. Compared to other animal models, Harmonia axyridis has the advantage of a short life cycle, is easily reared, has strong regeneration capacity and contains systemic RNAi, making it a model organism for research on appendage regeneration. Here, we performed transcriptome analysis, followed by gene functional assays to reveal the molecular mechanism of H. axyridis leg regenerative growth process. Signaling pathways including Decapentaplegic (Dpp), Wingless (Wg), Ds/Ft/Hippo, Notch, Egfr, and Hedgehog (Hh) were all upregulated during the leg regenerative patterning and growth. Among these, Hh and its auxiliary receptor Lrp2 were required for the proper patterning and growth of the regenerative leg. The targets of canonical Hh signaling were required for the regenerative growth which contributes to the leg length, but were not essential for the pattern formation of the regenerative leg. dpp, wg and leg developmental-related genes including rn, dac and Dll were all regulated by hh and lrp2 and may play an essential role in the regenerative patterning of the leg.

Transcriptome analysis of life stages of the house cricket, Acheta domesticus, to improve insect crop production

To develop genetic resources for the improvement of insects as food, we sequenced transcripts from embryos, one-day hatchlings, three nymphal stages, and male and female adults of the house cricket, Acheta domesticus. A draft transcriptome was assembled from more than 138 million sequences combined from all life stages and sexes. The draft transcriptome assembly contained 45,866 contigs, and more than half were similar to sequences at NCBI (e value < e⁻³). The highest sequence identity was found in sequences from the termites Cryptotermes secundus and Zootermopsis nevadensis. Sequences with identity to Gregarina niphandrodes suggest that these crickets carry the parasite. Among all life stages, there were 5,042 genes with differential expression between life stages (significant at p < 0.05). An enrichment analysis of gene ontology terms from each life stage or sex highlighted genes that were important to biological processes in cricket development. We further characterized genes that may be important in future studies of genetically modified crickets for improved food production, including those involved in RNA interference, and those encoding prolixicin and hexamerins. The data represent an important first step in our efforts to provide genetically improved crickets for human consumption and livestock feed.

An Overview of Embryogenesis: External Morphology and Transcriptome Profiling in the Hemipteran Insect Nilaparvata lugens

During embryogenesis of insects, the morphological and transcriptional changes are important signatures to obtain a better understanding of insect patterning and evolution. The brown planthopper Nilaparvata lugens is a serious insect pest of rice plants, but its embryogenesis has not uncovered. Here, we described embryonic development process of the pest and found it belongs to an intermediate-germ mode. The RNA-seq data from different times (6, 30, 96, and 150 h, after egg laying) of embryogenesis were then analyzed, and a total of 10,895 genes were determined as differentially expressed genes (DEGs) based on pairwise comparisons. Afterward, 1,898 genes, differentially expressed in at least two comparisons of adjacent embryonic stages were divided into 10 clusters using K means cluster analysis (KMCA). Eight-gene modules were established using a weighted gene co-expression network analysis (WGCNA). Gene expression patterns in the different embryonic stages were identified by combining the functional enrichments of the stage-specific clusters and modules, which displayed the expression level and reprogramming of multiple developmental genes during embryogenesis. The "hub" genes at each embryonic stage with possible crucial roles were identified. Notably, we found a "center" set of genes that were related to overall membrane functions and might play important roles in the embryogenesis process. After parental RNAi of the MSTRG.3372, the hub gene, the embryo was observed as abnormal. Furthermore, some homologous genes in classic embryonic development processes and signaling pathways were also involved in embryogenesis of this insect. An improved comprehensive finding of embryogenesis within the N. lugens reveals better information on genetic and genomic studies of embryonic development and might be a potential target for RNAi-based control of this insect pest.

Honokiol inhibits breast cancer cell metastasis by blocking EMT through modulation of Snail/Slug protein translation

Honokiol (HNK), an active compound isolated from traditional Chinese medicine Magnolia officinalis, has shown potent anticancer activities. In the present study, we investigated the effects of HNK on breast cancer metastasis in vitro and in vivo, as well as the underlying molecular mechanisms. We showed that HNK (10-70 μmol/L) dose-dependently inhibited the viability of human mammary epithelial tumor cell lines MCF7, MDA-MB-231, and mouse mammary tumor cell line 4T1. In the transwell and scratch migration assays, HNK (10, 20, 30 μmol/L) dose-dependently suppressed the invasion and migration of the breast cancer cells. We demonstrated that HNK (10-50 μmol/L) dose-dependently upregulated the epithelial marker E-cadherin and downregulated the mesenchymal markers such as Snail, Slug, and vimentin at the protein level in breast cancer cells. Using a puromycin incorporation assay, we showed that HNK decreased the Snail translation efficiency in the breast cancer cells. In a mouse model of tumor metastasis, administration of HNK (50 mg/kg every day, intraperitoneal (i.p.), 6 times per week for 30 days) significantly decreased the number of metastatic 4T1 cell-derived nodules and ameliorated the histological alterations in the lungs. In addition, HNK-treated mice showed decreased Snail expression and increased E-cadherin expression in metastatic nodules. In conclusion, HNK inhibits EMT in the breast cancer cells by downregulating Snail and Slug protein expression at the mRNA translation level. HNK has potential as an integrative medicine for combating breast cancer by targeting EMT.

winged eye Induces Transdetermination of Drosophila Imaginal Disc by Acting in Concert with a Histone Methyltransferase, Su(var)3-9

Drosophila imaginal disc cells exhibit a remarkable ability to convert cell fates in response to various perturbations, a phenomenon called transdetermination (TD). We previously identified winged eye (wge) as a factor that induces eye-to-wing TD upon overexpression in eye imaginal discs, but the molecular mechanisms underlying TD have remained largely unclear. Here, we found that wge induces various histone modifications and enhances the methylation of Lys9 on histone H3 (H3K9), a feature of heterochromatin. A histone methyltransferase, Su(var)3-9, is required for wge-mediated H3K9 methylation and eye-to-wing TD. Su(var)3-9 is also required for classical wound-induced TD but not for normal development, suggesting its involvement in several types of imaginal disc TDs. Transcriptome analysis revealed that wge represses eye identity genes independently of Su(var)3-9 and activates TD-related genes by acting together with Su(var)3-9. These findings provide new insights into diverse types of chromatin regulation at progressive steps of cell-fate conversions.

JAK/STAT signaling in stem cells and regeneration: from Drosophila to vertebrates

The JAK/STAT pathway is a conserved metazoan signaling system that transduces cues from extracellular cytokines into transcriptional changes in the nucleus. JAK/STAT signaling is best known for its roles in immunity. However, recent work has demonstrated that it also regulates critical homeostatic processes in germline and somatic stem cells, as well as regenerative processes in several tissues, including the gonad, intestine and appendages. Here, we provide an overview of JAK/STAT signaling in stem cells and regeneration, focusing on Drosophila and highlighting JAK/STAT pathway functions in proliferation, survival and cell competition that are conserved between Drosophila and vertebrates.

Evolution and Regulation of Limb Regeneration in Arthropods

Regeneration has fascinated both scientists and non-scientists for centuries. Many organisms can regenerate, and arthropod limbs are no exception although their ability to regenerate is a product shaped by natural and sexual selection. Recent studies have begun to uncover cellular and molecular processes underlying limb regeneration in several arthropod species. Here we argue that an evo-devo approach to the study of arthropod limb regeneration is needed to understand aspects of limb regeneration that are conserved and divergent. In particular, we argue that limbs of different species are comprised of cells at distinct stages of differentiation at the time of limb loss and therefore provide insights into regeneration involving both stem cell-like cells/precursor cells and differentiated cells. In addition, we review recent studies that demonstrate how limb regeneration impacts the development of the whole organism and argue that studies on the link between local tissue damage and the rest of the body should provide insights into the integrative nature of development. Molecular studies on limb regeneration are only beginning to take off, but comparative studies on the mechanisms of limb regeneration across various taxa should not only yield interesting insights into development but also answer how this remarkable ability evolved across arthropods and beyond.

The Cricket Gryllus bimaculatus: Techniques for Quantitative and Functional Genetic Analyses of Cricket Biology

All extant species are an outcome of nature's "experiments" during evolution, and hence multiple species need to be studied and compared to gain a thorough understanding of evolutionary processes. The field of evolutionary developmental biology (evo-devo) aspires to expand the number of species studied, because most functional genetic studies in animals have been limited to a small number of "traditional" model organisms, many of which belong to the same phylum (Chordata). The phylum Arthropoda, and particularly its component class Insecta, possesses many important characteristics that are considered favorable and attractive for evo-devo research, including an astonishing diversity of extant species and a wide disparity in body plans. The development of the most thoroughly investigated insect genetic model system to date, the fruit fly Drosophila melanogaster (a holometabolous insect), appears highly derived with respect to other insects and indeed with respect to most arthropods. In comparison, crickets (a basally branching hemimetabolous insect lineage compared to the Holometabola) are thought to embody many developmental features that make them more representative of insects. Here we focus on crickets as emerging models to study problems in a wide range of biological areas and summarize the currently available molecular, genomic, forward and reverse genetic, imaging and computational tool kit that has been established or adapted for cricket research. With an emphasis on the cricket species Gryllus bimaculatus, we highlight recent efforts made by the scientific community in establishing this species as a laboratory model for cellular biology and developmental genetics. This broad toolkit has the potential to accelerate many traditional areas of cricket research, including studies of adaptation, evolution, neuroethology, physiology, endocrinology, regeneration, and reproductive behavior. It may also help to establish newer areas, for example, the use of crickets as animal infection model systems and human food sources.

Bone morphogenetic protein signaling in distal patterning and intercalation during leg regeneration of the cricket, Gryllus bimaculatus

The cricket, Gryllus bimaculatus, is a classic model of leg regeneration following amputation. We previously demonstrated that Gryllus decapentaplegic (Gb'dpp) is expressed during leg regeneration, although it remains unclear whether it is essential for this process. In this study, double-stranded RNA targeting the Smad mathers-against-dpp homolog, Gb'mad, was used to examine the role of bone morphogenetic protein (BMP) signaling in the leg regeneration process of Gryllus bimaculatus. RNA interference (RNAi)-mediated knockdown of Gb'mad led to a loss of tarsus regeneration at the most distal region of regenerating leg segments. Moreover, we confirmed that the phenotype obtained by knockdown of Dpp type I receptor, Thick veins (Gb'tkv), closely resembled that observed for Gb'mad RNAi crickets, thereby suggesting that the BMP signaling pathway is indispensable for the initial stages of tarsus formation. Interestingly, knockdown of Gb'mad and Gb'tkv resulted in significant elongation of regenerating tibia along the proximodistal axis compared with normal legs. Moreover, our findings indicate that during the regeneration of tibia, the BMP signaling pathway interacts with Dachsous/Fat (Gb'Ds/Gb'Ft) signaling and dachshund (Gb'dac) to re-establish positional information and regulate determination of leg size. Based on these observations, we discuss possible roles for Gb'mad in the distal patterning and intercalation processes during leg regeneration in Gryllus bimaculatus.

De novo assembly of a transcriptome for the cricket Gryllus bimaculatus prothoracic ganglion: An invertebrate model for investigating adult central nervous system compensatory plasticity

The auditory system of the cricket, Gryllus bimaculatus, demonstrates an unusual amount of anatomical plasticity in response to injury, even in adults. Unilateral removal of the ear causes deafferented auditory neurons in the prothoracic ganglion to sprout dendrites across the midline, a boundary they typically respect, and become synaptically connected to the auditory afferents of the contralateral ear. The molecular basis of this sprouting and novel synaptogenesis in the adult is not understood. We hypothesize that well-conserved developmental guidance cues may recapitulate their guidance functions in the adult in order to facilitate this compensatory growth. As a first step in testing this hypothesis, we have generated a de novo assembly of a prothoracic ganglion transcriptome derived from control and deafferented adult individuals. We have mined this transcriptome for orthologues of guidance molecules from four well-conserved signaling families: Slit, Netrin, Ephrin, and Semaphorin. Here we report that transcripts encoding putative orthologues of most of the candidate developmental ligands and receptors from these signaling families were present in the assembly, indicating expression in the adult G. bimaculatus prothoracic ganglion.

De Novo Assembly and Characterization of the Xenocatantops brachycerus Transcriptome

Grasshoppers are common pests but also have high nutritional and commercial potential. Xenocatantops brachycerus Willemse (Orthoptera: Acrididae) is an economically important grasshopper species that is reared in China. Using the IlluminaHiSeqTM 4000 platform, three transcriptomes of the adult male, adult female, and nymph of X. brachycerus were sequenced. A total of 133,194,848 clean reads were obtained and de novo assembled into 43,187 unigenes with an average length of 964 bp (N50 of 1799 bp); of these, 24,717 (57.23%) unigenes matched known proteins. Based on these annotations, many putative transcripts related to X. brachycerus growth, development, environmental adaptability, and metabolism of nutritional components and bioactive components were identified. In addition, the expression profiles of all three transcriptome datasets were analyzed, and many differentially expressed genes were detected using RSEM and PossionDis. Unigenes. Unigenes with functions associated with growth and development exhibited higher transcript levels at the nymph stage, and unigenes associated with environmental adaptability showed increased transcription in the adults. These comprehensive X. brachycerus transcriptomic data will provide a useful molecular resource for gene prediction, molecular marker development, and studies on signaling pathways in this species and will serve as a reference for the efficient use of other grasshoppers.

EvoRegen in animals: Time to uncover deep conservation or convergence of adult stem cell evolution and regenerative processes

How do animals regenerate specialised tissues or their entire body after a traumatic injury, how has this ability evolved and what are the genetic and cellular components underpinning this remarkable feat? While some progress has been made in understanding mechanisms, relatively little is known about the evolution of regenerative ability. Which elements of regeneration are due to lineage specific evolutionary novelties or have deeply conserved roots within the Metazoa remains an open question. The renaissance in regeneration research, fuelled by the development of modern functional and comparative genomics, now enable us to gain a detailed understanding of both the mechanisms and evolutionary forces underpinning regeneration in diverse animal phyla. Here we review existing and emerging model systems, with the focus on invertebrates, for studying regeneration. We summarize findings across these taxa that tell us something about the evolution of adult stem cell types that fuel regeneration and the growing evidence that many highly regenerative animals harbor adult stem cells with a gene expression profile that overlaps with germline stem cells. We propose a framework in which regenerative ability broadly evolves through changes in the extent to which stem cells generated through embryogenesis are maintained into the adult life history.

The Drosophila Duox maturation factor is a key component of a positive feedback loop that sustains regeneration signaling

Regenerating tissue must initiate the signaling that drives regenerative growth, and sustain that signaling long enough for regeneration to complete. How these key signals are sustained is unclear. To gain a comprehensive view of the changes in gene expression that occur during regeneration, we performed whole-genome mRNAseq of actively regenerating tissue from damaged Drosophila wing imaginal discs. We used genetic tools to ablate the wing primordium to induce regeneration, and carried out transcriptional profiling of the regeneration blastema by fluorescently labeling and sorting the blastema cells, thus identifying differentially expressed genes. Importantly, by using genetic mutants of several of these differentially expressed genes we have confirmed that they have roles in regeneration. Using this approach, we show that high expression of the gene moladietz (mol), which encodes the Duox-maturation factor NIP, is required during regeneration to produce reactive oxygen species (ROS), which in turn sustain JNK signaling during regeneration. We also show that JNK signaling upregulates mol expression, thereby activating a positive feedback signal that ensures the prolonged JNK activation required for regenerative growth. Thus, by whole-genome transcriptional profiling of regenerating tissue we have identified a positive feedback loop that regulates the extent of regenerative growth.

Regenerating tissue must initiate the signaling that drives regenerative growth, and then sustain that signaling long enough for regeneration to complete. Drosophila imaginal discs, the epithelial structures in the larva that will form the adult animal during metamorphosis, have been an important model system for tissue repair and regeneration for over 60 years. Here we show that damage-induced JNK signaling leads to the upregulation of a gene called moladietz, which encodes a co-factor for an enzyme, NADPH dual oxidase (Duox), that generates reactive oxygen species (ROS), a key tissue-damage signal. High expression of moladietz induces continuous production of ROS in the regenerating tissue. The sustained production of ROS then continues to activate JNK signaling throughout the course of regeneration, ensuring maximal tissue regrowth.

Comparison of Leg Regeneration Potency Between Holometabolous Helicoverpa armigera (Lepidoptera: Noctuidae) and Hemimetabolous Locusta migratoria manilensis (Orthoptera: Acrididae)

After injury many insects could regenerate lost limb. In this study, Helicoverpa armigera Hubner and Locusta migratoria manilensis (Meyen, 1835) were chosen to compare the regeneration potency of holometabolous and hemimetabolous insects. We employed the classical approach of surgical excision to verify the regeneration ability and to investigate the factors that affect the extent of regeneration. The results found that H. armigera could regenerate intact legs when the larval legs were excised at the first and second instar and that legs of adult H. armigera had a close relationship with their larval counterparts. However, the adult legs became malformed or disappeared when excised at other older instars. For the L. migratoria, we found the legs have weak partial regeneration ability when amputation was conducted at the joint of two segments. The regeneration potency might be stronger the more proximal the operation. Regeneration process had a negative impact on the larval development. This is the first report of complete leg regeneration capacity having a strong correlation with the instar but not with the position where amputation occurred for H. armigera, while for the L. migratoria, partial regenerative ability had a close relationship with the position where amputation occurred but not with instars.

Characterization and analysis of a de novo transcriptome from the pygmy grasshopper Tetrix japonica

The pygmy grasshopper Tetrix japonica is a common insect distributed throughout the world, and it has the potential for use in studies of body colour polymorphism, genomics and the biology of Tetrigoidea (Insecta: Orthoptera). However, limited biological information is available for this insect. Here, we conducted a de novo transcriptome study of adult and larval T. japonica to provide a better understanding of its gene expression and develop genomic resources for future work. We sequenced and explored the characteristics of the de novo transcriptome of T. japonica using Illumina HiSeq 2000 platform. A total of 107 608 206 paired-end clean reads were assembled into 61 141 unigenes using the trinity software; the mean unigene size was 771 bp, and the N50 length was 1238 bp. A total of 29 225 unigenes were functionally annotated to the NCBI nonredundant protein sequences (Nr), NCBI nonredundant nucleotide sequences (Nt), a manually annotated and reviewed protein sequence database (Swiss-Prot), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. A large number of putative genes that are potentially involved in pigment pathways, juvenile hormone (JH) metabolism and signalling pathways were identified in the T. japonica transcriptome. Additionally, 165 769 and 156 796 putative single nucleotide polymorphisms occurred in the adult and larvae transcriptomes, respectively, and a total of 3162 simple sequence repeats were detected in this assembly. This comprehensive transcriptomic data for T. japonica will provide a usable resource for gene predictions, signalling pathway investigations and molecular marker development for this species and other pygmy grasshoppers.

Enhancer of zeste plays an important role in photoperiodic modulation of locomotor rhythm in the cricket, Gryllus bimaculatus

INTRODUCTION

Insects show daily behavioral rhythms controlled by an endogenous oscillator, the circadian clock. The rhythm synchronizes to daily light-dark cycles (LD) and changes waveform in association with seasonal change in photoperiod.

RESULTS

To explore the molecular basis of the photoperiod-dependent changes in circadian locomotor rhythm, we investigated the role of a chromatin modifier, Enhancer of zeste (Gb'E(z)), in the cricket, Gryllus bimaculatus. Under a 12 h:12 h LD (LD 12:12), Gb'E(z) was constitutively expressed in the optic lobe, the site of the biological clock; active phase (α) and rest phase (ρ) were approximately 12 h in duration, and α/ρ ratio was approximately 1.0. When transferred to LD 20:4, the α/ρ ratio decreased significantly, and the Gb'E(z) expression level was significantly reduced at 6 h and 10 h after light-on, as was reflected in the reduced level of trimethylation of histone H3 lysine 27. This change was associated with change in clock gene expression profiles. The photoperiod-dependent changes in α/ρ ratio and clock gene expression profiles were prevented by knocking down Gb'E(z) by RNAi.

CONCLUSIONS

These results suggest that histone modification by Gb'E(z) is involved in photoperiodic modulation of the G. bimaculatus circadian rhythm.

JAK/STAT signalling mediates cell survival in response to tissue stress

Tissue homeostasis relies on the ability of tissues to respond to stress. Tissue regeneration and tumour models in Drosophila have shown that JNK is a prominent stress-response pathway promoting injury-induced apoptosis and compensatory proliferation. A central question remaining unanswered is how both responses are balanced by activation of a single pathway. JAK/STAT signalling, a potential JNK target, is implicated in promoting compensatory proliferation. While we observe JAK/STAT activation in imaginal discs upon damage, our data demonstrates that JAK/STAT and its downstream effector Zfh2 promote survival of JNK-signalling cells instead. The JNK component fos and the pro-apoptotic gene hid are regulated in a JAK/STAT-dependent manner. This molecular pathway restrains JNK-induced apoptosis and spatial propagation of JNK-signalling, thereby limiting the extent of tissue damage, as well as facilitating systemic and proliferative responses to injury. We find that the pro-survival function of JAK/STAT also drives tumour growth under conditions of chronic stress. Our study defines JAK/STAT function in tissue stress and illustrates how crosstalk between conserved signalling pathways establishes an intricate equilibrium between proliferation, apoptosis and survival to restore tissue homeostasis.

During Drosophila disc regeneration, JAK/STAT coordinates cell proliferation with Dilp8-mediated developmental delay

Regeneration of fragmented Drosophila imaginal discs occurs in an epimorphic manner involving local cell proliferation at the wound site. After disc fragmentation, cells at the wound site activate a restoration program through wound healing, regenerative cell proliferation, and repatterning of the tissue. However, the interplay of signaling cascades driving these early reprogramming steps is not well-understood. Here, we profiled the transcriptome of regenerating cells in the early phase within 24 h after wounding. We found that JAK/STAT signaling becomes activated at the wound site and promotes regenerative cell proliferation in cooperation with Wingless (Wg) signaling. In addition, we showed that the expression of Drosophila insulin-like peptide 8 (dilp8), which encodes a paracrine peptide to delay the onset of pupariation, is controlled by JAK/STAT signaling in early regenerating discs. Our findings suggest that JAK/STAT signaling plays a pivotal role in coordinating regenerative disc growth with organismal developmental timing.

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.

Regenerated leg segment patterns are regulated epigenetically by histone H3K27 methylation in the cricket Gryllus bimaculatus

Hemimetabolous insects such as the cricket Gryllus bimaculatus regenerate lost tissue parts using blastemal cells, which is a population of dedifferentiated-proliferating cells. The gene expression of several epigenetic factors is upregulated in the blastema compared with the expression in differentiated tissue, suggesting that epigenetic changes in gene expression may control the differentiation status of blastema cells during regeneration. To clarify the molecular basis of epigenetic regulation during regeneration, we focused on the function of the Gryllus Enhancer of zeste (Gb’E(z)) and Ubiquitously-transcribed tetratricopeptide repeat gene on the X chromosome (Gb’Utx) homologues that regulate the methylation and demethylation on histone H3 27th lysine residue (H3K27), respectively. Methylated histone H3K27 in the regenerating leg was diminished by Gb’E(z)RNAi and was increased by Gb’UtxRNAi. Regenerated Gb’E(z)RNAi cricket legs exhibited extra leg segment formation between the tibia and tarsus, and regenerated Gb’UtxRNAi cricket legs showed leg joint formation defects in the tarsus. In the Gb’E(z)RNAi-regenerating leg, the Gb’dac expression domain expanded in the tarsus. In contrast, in the Gb’UtxRNAi-regenerating leg, Gb’Egfr expression in the middle of the tarsus was diminished. These results suggest that regulation of the histone H3K27 methylation state is involved in the repatterning process during leg regeneration among cricket species via the epigenetic regulation of leg patterning gene expression.

Genome-wide expression profile of the response to spinal cord injury in Xenopus laevis reveals extensive differences between regenerative and non-regenerative stages

Background

Xenopus laevis has regenerative and non-regenerative stages. As a tadpole, it is fully capable of functional recovery after a spinal cord injury, while its juvenile form (froglet) loses this capability during metamorphosis. We envision that comparative studies between regenerative and non-regenerative stages in Xenopus could aid in understanding why spinal cord regeneration fails in human beings.

Results

To identify the mechanisms that allow the tadpole to regenerate and inhibit regeneration in the froglet, we obtained a transcriptome-wide profile of the response to spinal cord injury in Xenopus regenerative and non-regenerative stages. We found extensive transcriptome changes in regenerative tadpoles at 1 day after injury, while this was only observed by 6 days after injury in non-regenerative froglets. In addition, when comparing both stages, we found that they deployed a very different repertoire of transcripts, with more than 80% of them regulated in only one stage, including previously unannotated transcripts. This was supported by gene ontology enrichment analysis and validated by RT-qPCR, which showed that transcripts involved in metabolism, response to stress, cell cycle, development, immune response and inflammation, neurogenesis, and axonal regeneration were regulated differentially between regenerative and non-regenerative stages.

Conclusions

We identified differences in the timing of the transcriptional response and in the inventory of regulated transcripts and biological processes activated in response to spinal cord injury when comparing regenerative and non-regenerative stages. These genes and biological processes provide an entry point to understand why regeneration fails in mammals. Furthermore, our results introduce Xenopus laevis as a genetic model organism to study spinal cord regeneration.

Cell proliferation dynamics in regeneration of the operculum head appendage in the annelid Pomatoceros lamarckii

Regeneration of lost or damaged appendages is a widespread and ecologically important ability in the animal kingdom, and also of great significance to developing regenerative medicine. The operculum of serpulid polychaetes is one among the many diverse appendages found in the lophotrochozoan superphylum, a clade hitherto understudied with respect to the mechanisms of appendage regeneration. In this study, we establish the normal time course of opercular regeneration in the serpulid Pomatoceros lamarckii and describe cell proliferation patterns in the regenerating opercular filament. The P. lamarckii operculum regenerates through a rapid and consistent series of morphogenetic events. Based on 5-bromo-2'-deoxyuridine (BrdU) labeling and anti-phosphohistone H3 immunohistochemistry, opercular regeneration appears to be a mixture of an early morphallactic stage, and a later phase characterized by widespread proliferative activity within the opercular filament. Tracking residual pigmentation suggests that the distal part of the stump gives rise to the most distal structures of the operculum via morphallactic remodeling, whereas more proximal structures are derived from the proximal stump. Our work underscores the diversity of regenerative strategies employed by animals and introduces P. lamarckii as an emerging model of appendage regeneration.

A bioinformatics expert system linking functional data to anatomical outcomes in limb regeneration

Amphibians and molting arthropods have the remarkable capacity to regenerate amputated limbs, as described by an extensive literature of experimental cuts, amputations, grafts, and molecular techniques. Despite a rich history of experimental efforts, no comprehensive mechanistic model exists that can account for the pattern regulation observed in these experiments. While bioinformatics algorithms have revolutionized the study of signaling pathways, no such tools have heretofore been available to assist scientists in formulating testable models of large-scale morphogenesis that match published data in the limb regeneration field. Major barriers preventing an algorithmic approach are the lack of formal descriptions for experimental regenerative information and a repository to centralize storage and mining of functional data on limb regeneration. Establishing a new bioinformatics of shape would significantly accelerate the discovery of key insights into the mechanisms that implement complex regeneration. Here, we describe a novel mathematical ontology for limb regeneration to unambiguously encode phenotype, manipulation, and experiment data. Based on this formalism, we present the first centralized formal database of published limb regeneration experiments together with a user-friendly expert system tool to facilitate its access and mining. These resources are freely available for the community and will assist both human biologists and artificial intelligence systems to discover testable, mechanistic models of limb regeneration.

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.