Developmentally regulated synthesis of p8, a stress-associated transcription cofactor, in diapause-destined embryos of Artemia franciscana

Integrating ATAC-Seq and RNA-Seq Reveals the Signal Regulation Involved in the Artemia Embryonic Reactivation Process

Embryonic diapause is a common evolutionary adaptation observed across a wide range of organisms. Artemia is one of the classic animal models for diapause research. The current studies of Artemia diapause mainly focus on the induction and maintenance of the embryonic diapause, with little research on the molecular regulatory mechanism of Artemia embryonic reactivation. The first 5 h after embryonic diapause breaking has been proved to be most important for embryonic reactivation in Artemia. In this work, two high-throughput sequencing methods, ATAC-seq and RNA-seq, were integrated to study the signal regulation process in embryonic reactivation of Artemia at 5 h after diapause breaking. Through the GO and KEGG enrichment analysis of the high-throughput datasets, it was showed that after 5 h of diapause breaking, the metabolism and regulation of Artemia cyst were quite active. Several signal transduction pathways were identified in the embryonic reactivation process, such as G-protein-coupled receptor (GPCR) signaling pathway, cell surface receptor signaling pathway, hormone-mediated signaling pathway, Wnt, Notch, mTOR signaling pathways, etc. It indicates that embryonic reactivation is a complex process regulated by multiple signaling pathways. With the further protein structure analysis and RT-qPCR verification, 11 GPCR genes were identified, in which 5 genes function in the embryonic reactivation stage and the other 6 genes contribute to the diapause stage. The results of this work reveal the signal transduction pathways and GPCRs involved in the embryonic reactivation process of Artemia cysts. These findings offer significant clues for in-depth research on the signal regulatory mechanisms of the embryonic reactivation process and valuable insights into the mechanism of animal embryonic diapause.

Effect of Different Culture Conditions on Gene Expression Associated With Cyst Production in Populations of Artemia franciscana

Artemia franciscana inhabits hypersaline environments in the Americas and has a well-adapted reproductive system that allows it to survive in these extreme conditions, represented by the production of diapause cysts (oviparous reproduction). This reproduction mode is controlled by numerous genes that are expressed in response to different environmental stressors, enabling this species to avoid population extinction. However, to date, the expression of these genes has not been sufficiently studied to clarify their levels in response to a combination of different environmental factors under controlled conditions. We analyzed the expression of eight genes related to oviparous reproduction (SGEG, Arp-CBP, artemin, BRCA1, p8, ArHsp21, ArHsp22, and p26) to determine their association with cyst production in two populations of A. franciscana with contrasting phenotypes, one with high (Barro Negro, BNE, Chile) and one with low (San Francisco Bay, SFB, United States) cyst production. Populations were cultured under controlled conditions of salinity (SAL, 35 and 75 ppt), photoperiod (PHO, 12L:12D and 24L:00D), iron concentration (IC, 0[Fe] and 5[Fe]), and microalgae diet (DIE; Dunaliella tertiolecta (DUN) and Tetraselmis suecica (TETRA)). Sixteen treatments were performed by combining the two conditions of each of the four factors. Data on nine reproductive parameters per female were recorded, including the percent of offspring encysted (%) (POE). The gene expression levels were analyzed by semiquantitative RT-PCR. The mean POE was significantly greater in BNE than in SFB (32.40 versus 12.74%, Mann-Whitney's test, p < 0.05). Significantly upregulated expression of seven genes in BNE (more than twofold, p < 0.05) was observed in 38.28% of the treatments (e.g., DUN-75ppt-12L:12D-5[Fe] and TETRA-35ppt-12L:12D-5[Fe]). In SFB, seven genes showed significant differential expression, but most were downregulated in 29.69% of the treatments (e.g., DUN-75ppt-12L:12D-0[Fe] and DUN-75ppt-24L:00D-0[Fe]). Multiple regression analyses indicated that in BNE, five genes (SGEG, artemin, Arp-CBP, p8, and BRCA1) and three environmental factors (DIE, SAL, and IC) were important predictor variables for the POE response variable given that all of them were included in the highest-ranking models. In SFB, only two genes (ArHsp21 and artemin) and one environmental factor (SAL) were important explanatory variables in the highest-ranking models. It was concluded that the BNE population presented a characteristic gene expression pattern that differed from that of the SFB population. This pattern might be related to the marked oviparous reproduction of the BNE population. This gene expression pattern could be useful for monitoring the reproductive mode leading to diapause in Artemia and to assist with intensive cyst production in pond systems.

Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades

Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts.

ArHsp40 and ArHsp40-2 contribute to stress tolerance and longevity in Artemia franciscana, but only ArHsp40 influences diapause entry

Embryos of the crustacean Artemia franciscana develop either ovoviviparously or oviparously, yielding swimming larvae (nauplii) or encysted gastrulae (cysts), respectively. Nauplii moult several times and become adults whereas cysts enter diapause, a state of dormancy characterized by exceptionally low metabolism and high stress tolerance. Synthesis of molecular chaperones such as the J-domain proteins ArHsp40 and ArHsp40-2 occurs during embryo development and post-diapause growth of A. franciscana and they influence development and stress tolerance. To further investigate J-domain protein function, ArHsp40 and ArHsp40-2 were each knocked down by RNA interference. Reductions in ArHsp40 and ArHsp40-2 had no effect on adult survival, time to release of cysts and nauplii from females and first-brood size. However, knockdown of both A. franciscana J-domain proteins reduced the longevity and heat tolerance of nauplii, with the loss of ArHsp40 having a greater effect. The knockdown of ArHsp40, but not of ArHsp40-2, caused approximately 50% of cysts to abort diapause entry and hatch without exposure to an exogenous signal such as low temperature and/or desiccation. Cysts lacking ArHsp40 that entered diapause exhibited decreased stress tolerance as did cysts with reduced ArHsp40-2, the latter to a lesser degree. The longevity of nauplii hatching prematurely from cysts was less than for nauplii arising by other means. The results expand our understanding of Hsp40 function in A. franciscana stress tolerance and development, especially during diapause, and they provide the first example of a molecular chaperone that influences diapause entry.

The transcription factor p8 regulates autophagy during diapause embryo formation in Artemia parthenogenetica

Autophagy is an essential homeostatic process by which cytoplasmic components, including macromolecules and organelles, are degraded by lysosome. Increasing evidence suggests that phosphorylated AMP-activated protein kinase (p-AMPK) and target of rapamycin (TOR) play key roles in the regulation of autophagy. However, the regulation of autophagy in quiescent cells remains unclear, despite the fact that autophagy is known to be critical for normal development, regeneration, and degenerative diseases. Here, crustacean Artemia parthenogenetica was used as a model system because they produced and released encysted embryos that enter a state of obligate dormancy in cell quiescence to withstand various environmental threats. We observed that autophagy was increased before diapause stage but dropped to extremely low level in diapause cysts in Artemia. Western blot analyses indicated that the regulation of autophagy was AMPK/TOR independent during diapause embryo formation. Importantly, the level of p8 (Ar-p8), a stress-inducible transcription cofactor, was elevated at the stage just before diapause and was absent in encysted embryos, indicating that Ar-p8 may regulate autophagy. The results of Ar-p8 knockdown revealed that Ar-p8 regulated autophagy during diapause formation in Artemia. Moreover, we observed that activating transcription factors 4 and 6 (ATF4 and ATF6) responded to Ar-p8-regulated autophagy, indicating that autophagy targeted endoplasmic reticulum (ER) during diapause formation in Artemia. Additionally, AMPK/TOR-independent autophagy was validated in human gastric cancer MKN45 cells overexpressing Ar-p8. The findings presented here may provide insights into the role of p8 in regulating autophagy in quiescent cells.

Study of model systems to test the potential function of Artemia group 1 late embryogenesis abundant (LEA) proteins

Embryos of the brine shrimp, Artemia franciscana, are genetically programmed to develop either ovoviparously or oviparously depending on environmental conditions. Shortly upon their release from the female, oviparous embryos enter diapause during which time they undergo major metabolic rate depression while simultaneously synthesize proteins that permit them to tolerate a wide range of stressful environmental events including prolonged periods of desiccation, freezing, and anoxia. Among the known stress-related proteins that accumulate in embryos entering diapause are the late embryogenesis abundant (LEA) proteins. This large group of intrinsically disordered proteins has been proposed to act as molecular shields or chaperones of macromolecules which are otherwise intolerant to harsh conditions associated with diapause. In this research, we used two model systems to study the potential function of the group 1 LEA proteins from Artemia. Expression of the Artemia group 1 gene (AfrLEA-1) in Escherichia coli inhibited growth in proportion to the number of 20-mer amino acid motifs expressed. As well, clones of E. coli, transformed with the AfrLEA-1 gene, expressed multiple bands of LEA proteins, either intrinsically or upon induction with isopropyl-β-thiogalactoside (IPTG), in a vector-specific manner. Expression of AfrLEA-1 in E. coli did not overcome the inhibitory effects of high concentrations of NaCl and KCl but modulated growth inhibition resulting from high concentrations of sorbitol in the growth medium. In contrast, expression of the AfrLEA-1 gene in Saccharomyces cerevisiae did not alter the growth kinetics or permit yeast to tolerate high concentrations of NaCl, KCl, or sorbitol. However, expression of AfrLEA-1 in yeast improved its tolerance to drying (desiccation) and freezing. Under our experimental conditions, both E. coli and S. cerevisiae appear to be potentially suitable hosts to study the function of Artemia group 1 LEA proteins under environmentally stressful conditions.

Expression and roles of As-NUPR1 protein from Artemia sinica during embryo development and in response to salinity stress

As-NUPR1, a stress-related protein, plays an important role in post-diapause during embryonic development in the brine shrimp Artemia sinica. In the present study, successful expression of As-NUPR1 from the cDNA sequence isolated from A. sinica was demonstrated using a prokaryotic expression system. The recombinant protein consisted of 132 amino acids with a molecular weight of 15 kDa, and a predicted isoelectric point of 7.17. As-NUPR1 polyclonal antibodies were prepared by immunization of Balb/c mice with purified recombinant As-NUPR1 protein as an antigen, and immunological studies were carried out. Expression of As-NUPR1 during different developmental stages of the embryo and in response to salinity stress was analyzed in A. sinica using Western blots. The experimental results showed that the expression of As-NUPR1 is widely distributed at different developmental stages in A. sinica, and there was no tissue or organ specificity. Expression of As-NUPR1 decreased gradually during the diapause termination stage of embryo development, after which there was a general increase in expression after breaking the shell. In addition, As-NUPR1 expression was highly upregulated under conditions of high salinity. These results suggest that the As-NUPR1 protein is a stress-related protein that plays a role in protecting embryos from high salt damage in different embryonic developmental stages, especially during the post-diapause period.

Identification of the glycerol kinase gene and its role in diapause embryo restart and early embryo development of Artemia sinica

Glycerol kinase (GK) catalyzes the rate-limiting step in glycerol utilization by transferring a phosphate from ATP to glycerol, yielding glycerol 3-phosphate, which is an important intermediate for both energy metabolism and glycerolipid production. Artemia sinica has an unusual diapause process under stress conditions of high salinity, low temperature and lack of food. In the process, diapause embryos of A. sinica (brine shrimp) accumulate high concentrations of glycerol as a cryoprotectant to prevent low temperature damage to embryos. Upon embryo restart, glycerol is converted into glucose and other carbohydrates. Therefore, GK plays an important role in the diapause embryo restart process. However, the role of GK in diapause termination of embryo development in A. sinica remains unknown. In the present study, a 2096 bp full-length cDNA of gk from A. sinica (As-gk) was obtained, encoding putative 551 amino acids, 60.6 kDa protein. As a crucial enzyme in glycerol uptake and metabolism, GK has been conserved structurally and functionally during evolution. The expression pattern of As-gk was investigated by quantitative real-time PCR and Western blotting. Expression locations of As-gk were analyzed using in situ hybridization. As-gk was widely distributed in the early embryo and several main parts of Artemia after differentiation. The expression of As-GK was also induced by stresses such as cold exposure and high salinity. This initial research into the expression pattern and stress response of GK in Artemia provides a sound basis for further understanding of the function and regulation of genes in early embryonic development in A. sinica and the stress response.

Biotic acts of antibiotics

Biological functions of antibiotics are not limited to killing. The most likely function of antibiotics in natural microbial ecosystems is signaling. Does this signaling function of antibiotics also extend to the eukaryotic – in particular mammalian – cells? In this review, the host modulating properties of three classes of antibiotics (macrolides, tetracyclines, and β-lactams) will be briefly discussed. Antibiotics can be effective in treatment of a broad spectrum of diseases and pathological conditions other than those of infectious etiology and, in this capacity, may find widespread applications beyond the intended antimicrobial use. This use, however, should not compromise the primary function antibiotics are used for. The biological background for this inter-kingdom signaling is also discussed.

Functional differentiation of small heat shock proteins in diapause-destined Artemia embryos

Encysted embryos of Artemia franciscana cease development and enter diapause, a state of metabolic suppression and enhanced stress tolerance. The development of diapause-destined Artemia embryos is characterized by the coordinated synthesis of the small heat shock proteins (sHsps) p26, ArHsp21 and ArHsp22, with the latter being stress inducible in adults. The amounts of sHsp mRNA and protein varied in Artemia cysts, suggesting transcriptional and translational regulation. By contrast to p26, knockdown of ArHsp21 by RNA interference had no effect on embryo development. ArHsp21 provided limited protection against stressors such as desiccation and freezing but not heat. ArHsp21 may have a non-essential or unidentified role in cysts. Injection of Artemia adults with amounts of ArHsp22 double-stranded RNA less than those used for other sHsps killed females and males, curtailing the analysis of ArHsp22 function in developing embryos and cysts. The results indicate that diapause-destined Artemia embryos synthesize varying amounts of sHsps as a result of differential gene expression and mRNA translation and also suggest that these sHsps have distinctive functions.

Localization, developmental regulation and stress induction of p8-L1 and p8-L2 in zebrafish

The transcription cofactor, p8, has a basic helix-loop-helix motif and is involved in several metabolic processes. It has previously been reported that p8 plays an important role in stress response in zebrafish. We expanded on these studies to further investigate the roles of two p8-like cDNAs found in zerbrafish, p8-L1 and p8-L2. Zebrafish p8-L1 and p8-L2 cDNAs consist of 742 bp and 813 bp, respectively. Both have the same open reading frame despite different genomic structures and encode a 76 amino acid polypeptide with conserved a Phospho_p8 domain. These two cDNA’s were abundant in different tissues in the zebrafish: p8-L1 was high in intestine and muscle tissue and in low abundance in the backbone, whereas the highest amount of p8-L2 was found in the backbone, similar to p8. During embryogenesis, both p8-L1 and p8-L2 were abundant at the cleavage stage and decreased gradually in abundance from blastula to pharyngula stage. However, p8-L1 abundance increased during hatching as observed in p8. Quantitative real-time PCR assay suggested that p8-L1 and p8-L2 were both up-regulated significantly under osmotic pressure and pH value challenges, suggesting an important role of p8-L1 and p8-L2 genes in stress response.

Molecular characterization and expression of As-nurp1 gene from Artemia sinica during development and in response to salinity and temperature stress

Nuclear protein 1 (NURP1) is a stress-related protein and closely related to diapause in the development of Artemia. In the present paper, the full-length 568-bp cDNA sequence of the nurp1 homolog of Artemia sinica (As-nurp1) was isolated by RACE technology for the first time. The putative As-nurp1 protein consists of 66 amino acids with a basic helix-loop-helix (bHLH) motif and a bipartite nuclear localization signal (NLS). Multiple sequence alignments revealed that the putative As-nurp1 protein sequence was relatively conserved across species, especially in the bHLH domain. The expression of As-nurp1 is widely distributed during A. sinica development. This is followed by a dramatic downregulation after diapause and is newly upregulated from the larval nauplius stage. Furthermore, As-nurp1 transcripts are highly upregulated under conditions of high salinity and low temperature. These findings suggest that As-nurp1 is stress-related and may act as a protective factor in embryonic development.

Diapause specific gene expression in the eggs of multivoltine silkworm Bombyx mori, identified by suppressive subtractive hybridization

Molecular mechanism controlling egg diapause remains obscure in silkworm, Bombyx mori. An attempt is made to decipher various molecular events occurring during embryonic diapause in multivoltine silkworm, B. mori. Using suppressive subtractive hybridization (SSH), 186 cDNA clones isolated from both diapause and nondiapause eggs were sequenced. Of the sequenced clones, 29 matched with silkbase entries and these identified putative genes were classified into six functional groups such as regulatory, food utilization, stress response, metabolic, ribosomal and transposable elements. Among these genes, twelve belonged to regulatory group while, one taste receptor type 2 member 117 gene was related to food utilization. One heat shock cognate 70 kDa protein and 3 of the ubiquitin family were identified under stress response category. Similarly, four genes were identified as metabolic genes, 3 belonging to chitin family and one propanediol utilization protein. Of the seven genes identified in ribosomal groups, most of them were 60s ribosomal protein subunits. However, one negative regulation of transcription gene identified was a transposable element. The qPCR analysis confirmed the expression of 21 of the above genes, wherein, 6 were upregulated during diapause, 12 during non-diapause, while, 3 remained unchanged.

Stress-related proteins compared in diapause and in activated, anoxic encysted embryos of the animal extremophile, Artemia franciscana

Previous work indicated similarities between diapause and anoxic quiescence in encysted embryos (cysts) of the brine shrimp Artemia franciscana. That possibility was examined further in the present study through an immunochemical study of the following stress-related proteins in low speed supernatants and pellets: hsc70, artemin, p26, hsp21, LEA Group 1 protein and p8. Changes in the amounts and locations of these proteins occurred during the initial period after release of diapause cysts from females, and after activated (diapause-terminated) cysts were made anoxic. However, with the passage of incubation time the patterns seen in both kinds of cysts were more similar than different, lending further support to the possibility that activated anoxic embryos retain many of the mechanisms operative in the previous diapause condition.

Comparative studies on sorting cells from Artemia sinica at different developmental stages for in vitro cell culture

Cell growth in primary cell culture of the brine shrimp (Artemia sinica) embryo at 12 and 20 h after rehydration at 25°C was examined comparatively in modified Leibovitz-15 medium. The cells from A. sinica embryo at 12 h after rehydration were dispersed, and the cells disseminated but did not attach to the surface of wells and multiply at 2 d of culture, and 12 d later, the cells were degenerated and dead. The best growth of the brine shrimp cells was obtained from the prenauplii of A. sinica at 20 h after dormant embryo rehydration. The fibroblast-like cells attached to the well surface and multiplied at 15 d after the primary culture was set up. Confluent monolayer was formed at 50 d. The prenauplii cells have been subcultured up to passage 3 and maintained for approximately 200 d. The reasons for cell growth potential at the different developmental stages of Artemia embryo were discussed.

Determination in oocytes of the reproductive modes for the brine shrimp Artemia parthenogenetica

The brine shrimp, Artemia, reproduces either oviparously, producing encysted embryos (diapause cysts), or ovoviviparously, producing free-swimming nauplii. Environmental factors, such as photoperiod, have been applied to control the reproduction mode of Artemia, but when the determination of a reproductive mode occurs remains unknown. We analysed the differential gene expression between oocytes from oviparous and ovoviviparous Artemia reared under different photoperiods. A total of 692 qualified cDNA clones were obtained by subtractive hybridization, 327 of which matched GenBank® Nucleotide Sequence Database entries. Gene expressions of 44 cDNAs (representing 56 clones) were analysed in oocytes using real-time PCR. Among these genes, 11 (21 clones) were significantly (P<0.05) up-regulated and 7 (9 clones) down-regulated in Artemia oocytes that subsequently enter diapause. Remarkably, known diapause-related proteins such as ArHsp22 (Artemia heat-shock protein 22) and chitin-binding proteins are found to be already differentially expressed. Furthermore, RNAi (RNA interference) knockdown of a differentially expressed gene, polo-like kinase 1, in oocyte of ovoviviparous Artemia led to the production of white embryos rather than free-swimming nauplii. In summary, our results provide evidence at the molecular level that the reproductive mode of Artemia is already determined at the oocyte stage of their life cycle.

Diapause termination and development of encysted Artemia embryos: roles for nitric oxide and hydrogen peroxide

Encysted embryos (cysts) of the brine shrimp Artemia undergo diapause, a state of profound dormancy and enhanced stress tolerance. Upon exposure to the appropriate physical stimulus diapause terminates and embryos resume development. The regulation of diapause termination and post-diapause development is poorly understood at the molecular level, prompting this study on the capacity of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) to control these processes. Exposure to H(2)O(2) and NO, the latter generated by the use of three NO generators, promoted cyst development, emergence and hatching, effects nullified by catalase and the NO scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The maximal effect of NO and H(2)O(2) on cyst development was achieved by 4 h of exposure to either chemical. NO was effective at a lower concentration than H(2)O(2) but more cysts developed in response to H(2)O(2). Promotion of development varied with incubation conditions, indicating for the first time a population of Artemia cysts potentially arrested in post-diapause and whose development was activated by either H(2)O(2) or NO. A second cyst sub-population, refractory to hatching after prolonged incubation, was considered to be in diapause, a condition broken by H(2)O(2) but not NO. These observations provide clues to the molecular mechanisms of diapause termination and development in Artemia, while enhancing the organism's value in aquaculture by affording a greater understanding of its growth and physiology.

Cloning and characterization of p8 homolog cDNA in the Atlantic halibut (Hippoglossus hippoglossus)

The p8 gene encodes a transcription factor known to modulate cell growth, division, and apoptosis and influences gene expression. In this study, an Atlantic halibut (Hippoglossus hippoglossus) homolog of the p8 gene was cloned, sequenced, and characterized. The full-length p8 cDNA consists of 601 bp and encodes 76 amino acids with a molecular mass of 9 kD. The bHLH region is well conserved between Atlantic halibut and other animals. Analysis by RT-PCR showed that the p8 transcript is constitutively expressed in 9 of the 12 tissues tested: pancreas, intestine, stomach, gill, head kidney, heart, liver, ovary, and spleen. A predicted microRNA target site was found in the 3'UTR of Atlantic halibut p8 mRNA. We speculate that the target site may pair to microRNA molecules because the target site resides in a big loop, a space large enough for the binding of microRNA molecules.

Tissue distribution, developmental expression and up-regulation of p8 transcripts on stress in zebrafish

The p8 is a transcription factor with a basic helix-loop-helix motif and a nuclear localization signal. A zebrafish p8 cDNA, which consists of 732 bp and encodes 75 amino acids, was identified in this paper. Sequence alignment showed that the bHLH region of p8 was well-conserved during the evolution. Phylogenetic analysis revealed that zebrafish p8 was close to its homologous protein in frog, together clustering to the clade of vertebrates. The zebrafish p8 mRNA expression levels varied much among the detected adult tissues, with the obvious higher expression in backbone and liver. During embryogenesis, the expression of zebrafish p8 mRNA was in higher levels in cleavage stage, decreased from blastula to segmentation stage, but sharply elevated at hatching stage. Quantitative real-time PCR assay suggested up-regulation expressions of zebrafish p8 on a wide range of cellular stressors such as starvation, temperature, osmotic pressure and pH value, implying an important role of p8 gene in response to stress.

Embryonic diapause highlighted by differential expression of mRNAs for ecdysteroidogenesis, transcription and lipid sparing in the cricket Allonemobius socius

Embryos of the ground cricket, Allonemobius socius, enter diapause 4-5 days post-oviposition and overwinter in this dormant state that is characterized by developmental arrest. Suppressive subtractive hybridization and quantitative real-time PCR reveal eight candidate genes in pre-diapause embryos that show promise as regulators of diapause entry, when compared with embryos not destined for diapause. Identifications are based both on the magnitude/consistency of differential mRNA abundances and the predicted functions of their products when placed in context of the physiological and biochemical events of diapause characterized in our companion paper. The proteins CYP450, AKR and RACK1 (associated with ecdysteroid synthesis and signaling) are consistently upregulated in pre-diapause, followed by major downregulation later in diapause. The pattern suggests that elevated ecdysone may facilitate onset of diapause in A. socius. Upregulation seen for the transcription factors Reptin and TFDp2 may serve to depress transcription and cell cycle progression. Cathpesin B-like protease, ACLY and MSP are three downregulated genes associated with yolk mobilization and/or metabolism that we predict may promote lipid sparing. Finally, embryos that have been in diapause for 10 days show a substantially different pattern of mRNA expression compared with either pre-diapause or embryos not destined for diapause, with the majority of mRNAs examined being downregulated. These transcript levels in later diapause suggest that a number of upregulated genes in pre-diapause are transiently expressed and are less essential as diapause progresses.

Thermotolerance and gene expression following heat stress in the whitefly Bemisia tabaci B and Q biotypes

The whitefly Bemisia tabaci (Gennadius) causes tremendous losses to agriculture by direct feeding on plants and by vectoring several families of plant viruses. The B. tabaci species complex comprises over 10 genetic groups (biotypes) that are well defined by DNA markers and biological characteristics. B and Q are amongst the most dominant and damaging biotypes, differing considerably in fecundity, host range, insecticide resistance, virus vectoriality, and the symbiotic bacteria they harbor. We used a spotted B. tabaci cDNA microarray to compare the expression patterns of 6000 ESTs of B and Q biotypes under standard 25 degrees C regime and heat stress at 40 degrees C. Overall, the number of genes affected by increasing temperature in the two biotypes was similar. Gene expression under 25 degrees C normal rearing temperature showed clear differences between the two biotypes: B exhibited higher expression of mitochondrial genes, and lower cytoskeleton, heat-shock and stress-related genes, compared to Q. Exposing B biotype whiteflies to heat stress was accompanied by rapid alteration of gene expression. For the first time, the results here present differences in gene expression between very closely related and sympatric B. tabaci biotypes, and suggest that these clear-cut differences are due to better adaptation of one biotype over another and might eventually lead to changes in the local and global distribution of both biotypes.

Characterization, expression, and response to stress of p8 gene in amphioxus

The amphioxus Branchiostoma belcheri tsingtaunese homolog of p8, Bbp8, was identified from the gut cDNA library. The full-length Bbp8 cDNA consists of 1032 bp, which is clearly longer than those of p8 in human, mouse, rat, frog, zebrafish and fruit fly. The genomic DNA sequences of amphioxus p8 contain three exons and two introns, which is similar to the exon/intron organization of p8 homologues in vertebrates such as human, mouse and zebrafish, while it is sharply different to the organization of p8 gene in fruit fly, which has only one exon. Sequence alignment and phylogenetic analysis showed that the basic helix-loop-helix (bHLH) region of p8 is well conserved during the long process of evolution, and Bbp8 is more close to its homologous proteins in the invertebrates than to those in the vertebrates. RT-PCR and In situ hybridization histochemistry demonstrated the expression of Bbp8 in all the tissues assayed, with relatively higher expression in the gut, gill and ovaries. Quantitative real-time PCR assay revealed quick up-regulation of Bbp8 transcripts on lipopolysaccharide (LPS) challenge and starvation, implying a stress-related function for Bbp8.

Activation of an AMP-activated protein kinase is involved in post-diapause development of Artemia franciscana encysted embryos

Background

Cysts of Artemia can remain in a dormant state for long periods with a very low metabolic rate, and only resume their development with the approach of favorable conditions. The post-diapause development is a very complicated process involving a variety of metabolic and biochemical events. However, the intrinsic mechanisms that regulate this process are unclear.

Results

Herein we report the specific activation of an AMP-activated protein kinase (AMPK) in the post-diapause developmental process of Artemia. Using a phospho-AMPKα antibody, AMPK was shown to be phosphorylated in the post-diapause developmental process. Results of kinase assay analysis showed that this phosphorylation is essential for AMPK activation. Using whole-mount immunohistochemistry, phosphorylated AMPK was shown to be predominantly located in the ectoderm of the early developed embryos in a ring shape; however, the location and shape of the activation region changed as development proceeded. Additionally, Western blotting analysis on different portions of the cyst extracts showed that phosphorylated AMPKα localized to the nuclei and this location was not affected by intracellular pH. Confocal microscopy analysis of immunofluorescent stained cyst nuclei further showed that AMPKα localized to the nuclei when activated. Moreover, cellular AMP, ADP, and ATP levels in developing cysts were determined by HPLC, and the results showed that the activation of Artemia AMPK may not be associated with cellular AMP:ATP ratios, suggesting other pathways for regulation of Artemia AMPK activity.

Conclusion

Together, we report evidence demonstrating the activation of AMPK in Artemia developing cysts and present an argument for its role in the development-related gene expression and energy control in certain cells during post-diapause development of Artemia.

ArHsp21, a developmentally regulated small heat-shock protein synthesized in diapausing embryos of Artemia franciscana

Embryos of the crustacean, Artemia franciscana, undergo alternative developmental pathways, producing either larvae or encysted embryos (cysts). The cysts enter diapause, characterized by exceptionally high resistance to environmental stress, a condition thought to involve the sHSP (small heat-shock protein), p26. Subtractive hybridization has revealed another sHSP, termed ArHsp21, in diapause-destined Artemia embryos. ArHsp21 shares sequence similarity with p26 and sHSPs from other organisms, especially in the α-crystallin domain. ArHsp21 is the product of a single gene and its synthesis occurred exclusively in diapause-destined embryos. Specifically, ArHsp21 mRNA appeared 2 days post-fertilization, followed 1 day later by the protein, and then increased until embryo release at day 5. No ArHsp21 protein was detected in embryos developing directly into larvae, although there was a small amount of mRNA at 3 days post-fertilization. The protein was degraded during post-diapause development and had disappeared completely from second instar larvae. ArHsp21 formed large oligomers in encysted embryos and transformed bacteria. When purified from bacteria, ArHsp21 functioned as a molecular chaperone in vitro, preventing heat-induced aggregation of citrate synthase and reduction-driven denaturation of insulin. Sequence characteristics, synthesis patterns and functional properties demonstrate clearly that ArHsp21 is an sHSP able to chaperone other proteins and contribute to stress tolerance during diapause. As such, ArHsp21 would augment p26 chaperone activity and it may also possess novel activities that benefit Artemia embryos exposed to stress.