Postembryonic Stages Research Articles

Ability of 4-Poster Passive Topical Treatment Devices for Deer to Sustain Low Population Levels of <I>Ixodes scapularis</I> (Acari: Ixodidae) After Integrated Tick Management in a Residential Landscape

In a recent study, the combined use of 4-Posters and Maxforce TMS bait boxes along with a barrier application of deltamethrin resulted in accelerated control of Ixodes scapularis Say by sequentially attacking each postembryonic life stage. We report the results of a follow-up study to test the ability of 4-Posters used alone to sustain the high levels of control achieved through the integrated tick management (ITM) approach after withdrawal of the bait boxes. In the first year after withdrawal, we observed declines in the level of control of larvae on small mammals, as well as of numbers of host-seeking larvae in the treatment area. There was no difference in the level of control of host-seeking adults in the treatment area after 2 yr. Within 2 yr, we observed a decline in control of subadult ticks infesting small mammals, but continued to see significant control of both host-seeking nymphs (85.9%) and larvae (89.0%) in the treatment area. The inconsistency that we observed between the apparent ability of 4-Posters to sustain high levels of control of host-seeking ticks, although having less effect on tick burdens on small mammal hosts, may be explained by the host-seeking ecology of immature I. scapularis.

Reproductive tables of predatory phytoseiid mites (Phytoseiulus persimilis, Galendromus occidentalis, and Neoseiulus cucumeris)

Feeding of predatory mites (Phytoseiulus persimilis, Galendromus occidentalis, and Neoseiulus cucumeris) on different life stages of Tetranychus atlanticus under optimal conditions was studied. Daily and total consumption of prey by predators and selection of prey of different life stages were studied for 5 days and for the entire feeding period. Average daily food consumption [number of individuals] for the entire life period of mature mite females constituted 0.43 females + 5.0 [nymphs and males] + 3.4 eggs of Tetranychus atlanticus in P. persimilis; 0.12 females + 3.70 [nymphs and males] + 3.10 eggs in G. occidentalis; and 0.19 females + 4.10 [nymphs and males] + 3.50 eggs in N. cucumeris. During the entire period of feeding, P. persimilis preferred large individuals and at the postembryonic stages selected prey to a greater extent than G. occidentalis and N. cucumeris (61.8 and 55.1%, respectively). The use of a 5-day express-method is possible for estimation of some biological characteristics of phytoseiids that previously consumed the same food for a long period. In other cases, analysis of characteristics for the entire life period is necessary.

Variability of some blood serum β-globulins in life cycle of sturgeons (Acipenseridae)

Blood proteins of sturgeons of two genera Acipenser and Pseudoscaphirhynchus preserving unidirectional variability in ontogenesis regardless of peculiarities of the fish ecology have heterochronic character. The slowest ontogenetic development lasting for 4–6 years is peculiar to one of antigens of β-globulins. Analysis of the variability of β-globulins in the age range beginning from the 4-month juveniles and including adult spawned individuals indicates different functional significance of their individual components. The βA-globulin absent at early postembryonic stages becomes the second, after albumin, quantitatively predominant antigen in the adult fish blood. The amount of βB-globulin, like antigens of α1and α2-globulins preserving relative ontogenetic stability, can decrease significantly in freshwater sturgeons due to their preparation for spawning.

Notch signalling is required for both dauer maintenance and recovery inC. elegans

The Notch signalling pathway is conserved among higher metazoans and is used repeatedly throughout development to specify distinct cell fates among populations of equipotent cells. Mounting evidence suggests that Notch signalling may also be crucial in neuronal function in postmitotic, differentiated neurons. Here, we demonstrate a novel role for the canonical Notch signalling pathway in postmitotic neurons during a specialised ;diapause-like' post-embryonic developmental stage in C. elegans called dauer. Our data suggest that cell signalling downstream of the developmental decision to enter dauer leads to the activation of Notch-responding genes in postmitotic neurons. Consistent with this, we demonstrate that glp-1, one of the two C. elegans Notch receptors, and its ligand lag-2 are expressed in neurons during the dauer stage, and both genes are required to maintain this stage in a daf-7/TGFbeta dauer constitutive background. Our genetic data also suggest that a second Notch receptor, lin-12, functions upstream of, or in parallel with, insulin-like signalling components in response to replete growth conditions to promote dauer recovery. Based on our findings, cues associated with the onset of dauer ultimately trigger a glp-1-dependent Notch signalling cascade in neurons to maintain this developmental state. Then, as growth conditions improve, activation of the LIN-12 Notch receptor cooperates with the insulin-like signalling pathway to signal recovery from the dauer stage.

Canonical Wnt Signaling Controls Proliferation of Retinal Stem/Progenitor Cells in Postembryonic Xenopus Eyes

Vertebrate retinal stem cells, which reside quiescently within the ciliary margin, may offer a possibility for treatment of degenerative retinopathies. The highly proliferative retinal precursor cells in Xenopus eyes are confined to the most peripheral region, called the ciliary marginal zone (CMZ). Although the canonical Wnt pathway has been implicated in the developing retina of different species, little is known about its involvement in postembryonic retinas. Using a green fluorescent protein-based Wnt-responsive reporter, we show that in transgenic Xenopus tadpoles, the canonical Wnt signaling is activated in the postembryonic CMZ. To further investigate the functional implications of this, we generated transgenic, hormone-inducible canonical Wnt pathway activating and repressing systems, which are directed to specifically intersect at the nuclear endpoint of transcriptional Wnt target gene activation. We found that postembryonic induction of the canonical Wnt pathway in transgenic retinas resulted in increased proliferation in the CMZ compartment. This is most likely due to delayed cell cycle exit, as inferred from a pulse-chase experiment on 5-bromo-2'-deoxyuridine-labeled retinal precursors. Conversely, repression of the canonical Wnt pathway inhibited proliferation of CMZ cells. Neither activation nor repression of the Wnt pathway affected the differentiated cells in the central retina. We conclude that even at postembryonic stages, the canonical Wnt signaling pathway continues to have a major function in promoting proliferation and maintaining retinal stem cells. These findings may contribute to the eventual design of vertebrate, stem cell-based retinal therapies. Disclosure of potential conflicts of interest is found at the end of this article.

Perspectivas para a criação massal de Iphiseiodes zuluagai Denmark & Muma (Acari: Phytoseiidae)

Iphiseiodes zuluagai Denmark & Muma is an important predator of Brevipalpus phoenicis (Geijskes) on citrus in Brazil. The suitability of Tyrophagus putrescentiae (Schrank) as a food source of I. zuluagai in laboratory rearing was investigated at 25.5 +/- 0.5 masculineC, 88 +/- 7% RU and photophase of 12h. Initially, levels of oviposition of the predator fed on eggs were evaluated, as well as the dead or live post-embryonic stages of T. putrescentiae, in a period of 10 days. The daily oviposition rate was 1.3 egg per female when they were fed on eggs on T. putrescentiae, 0.7 egg per female when they were fed on dead post embryonic stages and about 0.3 egg per female when they were fed on live post-embryonic stages. Later, the life table of I. zuluagai was constructed, when eggs of T. putrescentiae were offered to the predators as prey. The immature stages were observed every 8h, to determine the corresponding durations. In the adult phase, the mites were observed every 24h, to determine the reproductive parameters. The intrinsic rate of natural increase (r m) was 0.11 female/ female/day; resulting in a finite rate of increase of 1.11 (l). The net reproductive rate (R0) was 7.1 females/generation, with a mean generation time (T) 18.6 days. The results show that T. putrescentiae is a favorable food source for the development of I. zuluagai.

Developmental trajectories in geographically separated populations of non-marine ostracods: morphometric applications for palaeoecological studies

Developmental trajectories refer here to patterns of size and shape changes in ostracod valves during the sequence of post-embryonic growth stages. The information obtained from the study of such patterns has significant applications for evolutionary biology and/or (palaeo) ecology. Using geometric morphometrics methods, we describe the developmental trajectories of three ostracod species with valves retrieved from the sediments of lakes Mondsee (Austria), Hancza (Poland) and Iseo (Italy). Size and shape data result in distinct developmental trajectories. Ontogenetic changes agree with predictions of Prizbram’s and Brooks’ laws. Patterns of valve shape change provide information which might be of use to the taxonomic definition of evolutionary lineages and to the development of studies of allometry and heterochrony in non-marine ostracods.

Involvement of HMG-12 and CAR-1 in the cdc-48.1 expression of Caenorhabditis elegans

Caenorhabditis elegans possesses two p97/VCP/Cdc48p homologues, named CDC-48.1 (C06A1.1) and CDC-48.2 (C41C4.8), and their expression patterns and levels are differently regulated. To clarify the regulatory mechanisms of differential expression of two p97 proteins of C. elegans, we performed detailed deletion analysis of their promoter regions. We found that the promoter of cdc-48.1 contains two regions necessary for embryonic and for post-embryonic expression, while the promoter of cdc-48.2 contains the single region necessary for embryonic expression. In particular, two elements (Element A and Element B) and three conserved boxes (Box a, Box b and Box c) were essential for cdc-48.1 expression in embryos and at post-embryonic stages, respectively. By using South-Western blotting and MALDI-TOF MS analysis, we identified HMG-12 and CAR-1 as proteins that bind to Element A and Element B, respectively, from the embryonic nuclear extract. Importantly, we found the decreased expression of p97 in embryos prepared from hmg-12(RNAi) or car-1(RNAi) worms. These results indicate that both HMG-12 and CAR-1 play important roles in embryonic expression of cdc-48.1.

Characterization of Rickettsial Infection in Amblyomma americanum (Acari: Ixodidae) by Quantitative Real-Time Polymerase Chain Reaction

Several species of the spotted fever group Rickettsia (SFGR), with considerable variation in vertebrate host pathogenicity, are present in ticks in the United States. In this study, quantitative real-time PCR (qPCR) was used to characterize the growth and the distribution of Rickettsia amblyommii in selected tissues (salivary glands, gut, and ovaries) of naturally infected Amblyomma americanum (L.) (Acari: Ixodidae), during bloodmeal acquisition and throughout vertical transmission to eggs and postembryonic life cycle stages (larvae and nymphs). R. amblyommii was identified in the samples at ratios of ≤1 rickettsiae per tick cell. Significant variability in the ratio of rickettsial to tick gene copy numbers between the tissues was identified; however, no single tissue was consistently observed to have the greatest rickettsial burden throughout the feeding event. Furthermore, the ratio of rickettsial to tick gene copy numbers did not significantly differ between eggs, immature ticks, and feeding events. This is the first study to use qPCR to enumerate rickettsial growth and distribution in the tick host during bloodmeal acquisition. Deciphering SFGR tissue distribution and transmission mechanisms is necessary for the development of novel approaches to control tick-borne rickettsial diseases.

Characterization of Rickettsial Infection in <I>Amblyomma americanum</I> (Acari: Ixodidae) by Quantitative Real-Time Polymerase Chain Reaction

Several species of the spotted fever group Rickettsia (SFGR), with considerable variation in vertebrate host pathogenicity, are present in ticks in the United States. In this study, quantitative real-time PCR (qPCR) was used to characterize the growth and the distribution of Rickettsia amblyommii in selected tissues (salivary glands, gut, and ovaries) of naturally infected Amblyomma americanum (L.) (Acari: Ixodidae), during bloodmeal acquisition and throughout vertical transmission to eggs and postembryonic life cycle stages (larvae and nymphs). R. amblyommii was identified in the samples at ratios of < or = 1 rickettsiae per tick cell. Significant variability in the ratio of rickettsial to tick gene copy numbers between the tissues was identified; however, no single tissue was consistently observed to have the greatest rickettsial burden throughout the feeding event. Furthermore, the ratio of rickettsial to tick gene copy numbers did not significantly differ between eggs, immature ticks, and feeding events. This is the first study to use qPCR to enumerate rickettsial growth and distribution in the tick host during bloodmeal acquisition. Deciphering SFGR tissue distribution and transmission mechanisms is necessary for the development of novel approaches to control tick-borne rickettsial diseases.

Phenology and descriptions of two sympatric native whiteflies (Hemiptera: Aleyrodidae) with a high degree of niche overlap

Aleuroplatus coronata (Quaintance 1900) and A. gelatinosus (Cockerell 1898) are native, sympatric whiteflies (Hemiptera: Aleyrodidae) that develop on live oaks, Quercus spp. (Fagaceae) in California. This study provides characters to separate them in all postembryonic stages. The phenology of these whiteflies was studied in Riverside County, California on one tree each of Quercus agrifolia Née and Q. engelmannii Greene. Their phenology was almost identical. Both species are univoltine. Adult emergence and oviposition are synchronized with the flush of new foliage in late March and April; however, egg hatch does not occur until late May or early June, and nymphal development occurs primarily after leaf maturation and hardening. Both species attain the final (fourth) nymphal instar by late summer and remain in this stage until adult emergence the following Spring. Both species were abundant on Q. agrifolia, but on the adjacent Q. engelmannii tree, only A. coronata was abundant. On Q. agrifolia, eggs of both species were laid on both the new flush and on the previous year's foliage, whereas on Q. engelmannii, oviposition was almost exclusively on the new flush. This corresponds to the longevity of the foliage; leaves of Q. agrifolia apparently survive two years, allowing development of a second generation of whiteflies, whereas leaves of Q. engelmannii last little over one year, and thus would be unsuitable for a second generation. The sympatric distribution, shared hosts and almost identical phenology give these whitefly species a very high degree of niche overlap. A. coronata usually dominates numerically over A. gelatinosus, but this varies among trees and among seasons.

Involvement of p90 Ribosomal S6 Kinase in Termination of Cell Cycle Arrest during Development of Artemia-encysted Embryos

Artemia has evolved a unique developmental pattern of encysted embryos to cope with various environmental threats. Cell divisions totally cease during the preemergence developmental stage from gastrula to prenauplius. The molecular mechanism of this, however, remains unknown. Our study focuses on the involvement of p90 ribosomal S6 kinase (RSK), a family of serine/threonine kinase-mediating signal transduction downstream of mitogen-activated protein kinase cascades, in the termination of cell cycle arrest during the post-embryonic development of Artemia-encysted gastrula. With immunochemistry, morphology, and cell cycle analysis, the identified Artemia RSK was established to be specifically activated during the post-embryonic and early larval developmental stages when arrested cells of encysted embryos resumed mitoses. In vivo knockdown of RSK activity by RNA interference, kinase inhibition, and antibody neutralization consistently induced defective larvae with distinct gaps between the exoskeleton and internal tissues. In these abnormal individuals, mitoses were detected to be largely inhibited in the affected regions. These results display the requirement of RSK activity during Artemia development and suggest its role in termination of cell cycle (G(2)/M phase) arrest and promotion of mitogenesis. Our findings may, thus, provide insights into the regulation of cell division during Artemia post-embryonic development and reveal further aspects of RSK functions.

Regulation of rnt-1 expression mediated by the opposing effects of BRO-1 and DBL-1 in the nematode Caenorhabditis elegans

During development of Caenorhabditis elegans, expression of the RUNX homolog, rnt-1, is tightly regulated both spatially and temporally. In this study, we investigated the mechanism underlying the temporal regulation of rnt-1. We found that rnt-1 contained evolutionarily conserved consensus RUNX binding sequences within one of its introns, and that RNT-1 bound to these intronic sequences both in vitro and in vivo in the presence of BRO-1, suggesting that RNT-1 together with BRO-1 represses its own transcription. Fine deletion and substitution experiments revealed a binding site within the intron that was critical for rnt-1 regulation. Importantly, we found that the TGFβ homolog, DBL-1, was required for counteracting the repressive activity of BRO-1 at postembryonic stages. Accordingly, ectopic expression of DBL-1 induced transcription of rnt-1 in the lateral hypodermis and other tissues even at the postembryonic stages. Taken together, our data suggest that rnt-1 expression is regulated by the balance between DBL-1-mediated activation and BRO-1-mediated repression at the postembryonic stages.

Epimorphosis and repair processes of schistomelic pedipalps and walking appendages in Tegenaria atrica (Araneae, Agelenidae)

Experimental studies of regeneration and repair processes of schistomelic walking legs and pedipalps in the early postembryonal stages of Tegenaria atrica were carried out in two parts. In the first part changes in the structure of appendages were produced by exposing the developing embryos to alternating temperatures (14 and 32°C, changing every 12 hours) as teratogenic factor. In the second, principal, part of studies after amputating a given fragment of a larval schistomelic appendage the appearance, then the growth and development of the external regenerates were observed. The completion of epimorphosis of the pedipalps followed at nymph IV stage (after four post-larval moults) that of the walking appendages in most cases at nymph V stage (after five post-larval moults). In control spiders repair processes were noted, which proceeded at a rate comparable to regeneration processes.

Adult honeybees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity

Hemocytes and the (prophenol-) phenoloxidase system constitute the immediate innate immune system in insects. These components of insect immunity are present at any post-embryonic life stage without previous infection. Differences between individuals and species in these immune parameters can reflect differences in infection risk, life expectancy, and biological function. In honeybees which show an age-related division of labor within the worker caste, previous studies demonstrated that foragers show a strongly reduced number of hemoctyes compared to the younger nurse bees. This loss of immune competence has been regarded advantageous with respect to an already high mortality rate due to foraging and to redistribution of energy costs at the colony level. Based on the idea that abandoning hemocytes in all adults would be a reasonably direct regulatory mechanism, we posed the hypothesis that abandoning hemocytic immunity is not restricted to worker honeybees. We tested our hypotheses by performing a comprehensive analysis of hemocyte number and phenoloxidase (PO)-activity levels in immunologically naive workers, queens, and drones. We found that in all three adult phenotypes hemocyte number is dramatically reduced in early adult life. In contrast, we found that the dynamics of PO-activity levels have sex and caste-specific characteristics. In workers, PO activity reached a plateau within the first week of adult life, and in queens enzyme levels continuously increased with age and reached levels twice as high as those found in workers. PO-activity levels slightly declined with age in drones. These data support our hypothesis, from which we infer that the previously reported reduction of hemocyte in foragers is not worker specific but represents a general phenomenon occurring in all honeybee adult phenotypes.

Gene expression analysis in post-embryonic pericardial cells of Drosophila

Increasing evidence suggests conservation of cardiovascular molecules between vertebrates and invertebrates. Vertebrate Rudhira, an evolutionary conserved WD40 protein is expressed during primitive erythropoiesis, neoangiogenesis and tumors. We report here the expression profile of the Drosophila ortholog of Rudhira (DRudh) in the fly life cycle. DRudh is expressed specifically in all post-embryonic pericardial cells (PCs) and garland cells (GCs). This is the first report of a cytoplasmic marker highly specific to post-embryonic PCs. Embryonic PCs belong to three distinct genetic classes based on Odd-skipped (Odd), Even-skipped (Eve) and Tinman (Tin) expression. To identify which among these three classes of PCs expresses DRudh in post-embryonic stages, we analyzed expression of embryonic PC markers in the post-embryonic stages. Unlike in the embryo all larval PCs show an identical gene expression profile. While Odd and Eve expression is mutually exclusive in the embryonic PCs, these two markers are co-expressed in larval PCs but show a distinct subcellular localization. Tin is not expressed in any post-embryonic PC. Additionally larval PCs also express the GATA factor, Serpent (Srp) and the extracellular matrix protein, Pericardin (Prc). While PC number is known to decrease post-embryogenesis, which of the Odd or Eve lineage embryonic PCs persists is not known. Co-expression of the two distinct lineage markers only in post-embryonic stages indicates a complex temporal regulation of gene expression in PCs.

An olig2 reporter gene marks oligodendrocyte precursors in the postembryonic spinal cord of zebrafish

Continuous production of new neurons and glia in adult mammals occurs within specialized proliferation zones of the forebrain. Neural cell proliferation and neurogenesis is more widespread in adult amphibians, reptiles, and fish but the identity of neural stem cell populations in these organisms has not been fully described. We investigated expression of a reporter gene driven by olig2 regulatory DNA at postembryonic stages in zebrafish. We show that olig2 expression marks a discrete population of spinal cord radial glia in larvae and adults that divide continuously. olig2(+) radial glia have hallmarks of stem cells and their divisions appear to be asymmetric, producing new oligodendrocytes but not neurons or astrocytes.

Exposure of the eggs to 17α-methyl testosterone reduced hatching success and growth and elicited teratogenic effects in postembryonic life stages of crayfish

Testosterone is regularly found in the tissues of decapod crustaceans. Although this vertebrate-type sex hormone is not the principal factor of sex differentiation in crustaceans, it was shown to be capable of acting on the reproductive organs of shrimps and crabs. In the present study I have exposed developing eggs and stage 5 juveniles of the parthenogenetic all female marbled crayfish to 17α-methyl testosterone in order to test whether in freshwater crayfish sex can be changed from female to male by this androgen. MT did not elicit sex change, neither when administered during embryonic development nor during juvenile stage 5, the main period of proliferation of the oocytes. However, exposure to 100 μg/L MT from 64% to 84% embryonic development resulted in prolonged embryonic development, reduced hatching success, reduced growth of the juveniles, and severe malformations of the appendages in the juveniles. The marbled crayfish is recommended to be considered for toxicity tests due to its easy culture in the laboratory and its genotypical uniformity.

Specification and development of the germline in Caenorhabditis elegans.

Maternal-effect sterile (mes) genes encode maternal components that are required for establishment and development of the germline. Five such genes have been identified in the nematode Caenorhabditis elegans. Mutations in one of the genes result in defects in the asymmetric division and cytoplasmic partitioning that generate the primordial germ cell P4 at the 16-24-cell stage of embryogenesis. As a result of these defects, the P4 cell is transformed into a muscle progenitor and mutant embryos develop into sterile adults with extra body muscles. Mutations in the other four mes genes do not affect formation of the germline during embryogenesis, but result in drastically reduced proliferation of the germline during post-embryonic stages and in an absence of gametes in adults. The failure to form gametes may reflect a defect in germline specification or may be a consequence of reduced germline proliferation. We are currently testing these two possibilities. In addition to the mes gene products, wild-type function of the zygotic gene glp-4 is required for normal post-embryonic proliferation of the germline. Germ cells in glp-4 mutant worms are arrested in prophase of the mitotic cell cycle and are unable to enter meiosis and form gametes. Thus, following establishment of the germ lineage in the early embryo, both maternal and zygotic gene products work in concert to promote the extensive proliferation of the germline and to enable germ cells to generate functional gametes.

Oxidative stress inCaenorhabditis elegans: protective effects of the Omega class glutathione transferase (GSTO‐1)

To elucidate the function of Omega class glutathione transferases (GSTs) (EC 2.5.1.18) in multicellular organisms, the GSTO-1 from Caenorhabditis elegans (GSTO-1; C29E4.7) was investigated. Disc diffusion assays using Escherichia coli overexpressing GSTO-1 provided a test of resistance to long-term exposure under oxidative stress. After affinity purification, the recombinant GSTO-1 had minimal catalytic activity toward classic GST substrates but displayed significant thiol oxidoreductase and dehydroascorbate reductase activity. Microinjection of the GSTO-1-promoter green fluorescent protein construct and immunolocalization by electron microscopy localized the protein exclusively in the intestine of all postembryonic stages of C. elegans. Deletion analysis identified an approximately 300-nucleotide sequence upstream of the ATG start site necessary for GSTO-1 expression. Site-specific mutagenesis of a GATA transcription factor binding motif in the minimal promoter led to the loss of reporter expression. Similarly, RNA interference (RNAi) of Elt-2 indicated the involvement of this gut-specific transcription factor in GSTO-1 expression. Transcriptional up-regulation under stress conditions of GSTO-1 was confirmed by analyzing promoter-reporter constructs in transgenic C. elegans strains. To investigate the function of GSTO-1 in vivo, transgenic animals overexpressing GSTO-1 were generated exhibiting an increased resistance to juglone-, paraquat-, and cumene hydroperoxide-induced oxidative stress. Specific silencing of the GSTO-1 by RNAi created worms with an increased sensitivity to several prooxidants, arsenite, and heat shock. We conclude that the stress-responsive GSTO-1 plays a key role in counteracting environmental stress.