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Anterior determinants in embryos of Chironomus samoensis: characterization by rescue bioassay.

Embryos of Chironomus samoensis are programmed, by anterior u.v. irradiation, to form the abnormal body pattern 'double abdomen'. Most double abdomen embryos show a mirror-image duplication of abdominal segments in the absence of cephalic or thoracic segments. Such embryos can be 'rescued', i.e. restored to normal development, by microinjection of cytoplasm or RNA from unirradiated donor embryos. Most of the rescued embryos look completely normal and many of them hatch spontaneously. The rescuing activity decreases from the anterior to the posterior pole in the donor cytoplasm and must be delivered near the anterior pole of the recipient for maximum efficiency. Rescuing activity is present in total RNA extracted from whole, unirradiated embryos. Upon fractionation, the activity is associated with poly(A)+ RNA, with LiCl precipitate depleted of RNA smaller than 250 nucleotides (nt) and with a sucrose gradient fraction depleted of RNA larger than 500 nt. Corresponding fractions of RNA from Xenopus oocytes have no rescuing activity. The activity of Chironomus RNA is sensitive to u.v. irradiation with low fluence affecting less than 2% of the pyrimidine bases. Rescuing activity is present in cytoplasm until the blastoderm stage but disappears earlier from poly(A)+ RNA. Rescuing activity is also present, and localized, in cytoplasm of embryos from two related dipterans, Smittia sp. and Drosophila melanogaster, although the extent of rescue observed in Chironomus decreases with the phylogenetic distance between donor and recipient. The results of these and previous experiments indicate that dipteran embryos contain localized RNP particles acting as anterior determinants. In Chironomus, the activity of these particles seems to depend on the integrity of polyadenylated RNA of about 250 to 500 nt length.

Abdomen↗

Potentiation by the lithium ion of morphogenetic responses to a Xenopus inducing factor.

We have cultured explants of Xenopus blastular animal cap tissue from embryos that had received an earlier treatment with LiCl and from their untreated siblings, in various concentrations of XTC-cell-derived mesoderm-inducing factor (XTC-MIF, Smith, 1987; Smith et al. 1988). The pretreatment with lithium that we used transforms later morphogenesis in the whole embryo to give radialized body forms with anterior/dorsal levels of structure grossly over-represented. In addition, animal caps from 'Li+' embryos were allowed to develop without exposure to in vitro MIF (Li+ controls) and compared with normal uninduced control explants, and explants were made from normal early blastulae but given various initial treatments with LiCl in culture. The results confirm that the lithium ion itself will not induce mesoderm in competent, animal cap tissue of Xenopus. It does, however, enhance the responsiveness of this tissue to XTC-MIF, in a way that parallels its recently reported effect in the case of another mesoderm inducer of different character, bFGF (Slack et al. 1988). The effects observed are sufficient to imply that the altered body pattern that follows lithium treatment, in whole embryos, could be caused by modulation of the responses to an unaltered pattern of in situ inductive stimuli. We also observe evidence that appreciable inductive signals reach animal pole tissue beyond the limits of mesoderm formation in normal development. Relatively low concentrations of MIF prevent the development of an epidermis-specific marker in dissociated blastular animal cap cells (Symes et al. 1988). When such experiments are repeated in relation to the lithium pretreatment of embryos, such treatment is seen to have sensitized the cell population, so that the MIF concentration range that assures complete suppression of the marker is reduced. The results are discussed in relation to induction considered as pattern formation.

Animals↗

The biological effects of XTC-MIF: quantitative comparison with Xenopus bFGF.

Mesoderm in Xenopus and other amphibian embryos is induced by signals from the vegetal hemisphere acting on equatorial or animal hemisphere cells. These signals are diffusible and two classes of candidate signal molecule have been identified: the fibroblast growth factor (FGF) and transforming growth factor beta (TGF-beta) types. In this paper, we compare the effects of cloned Xenopus basic FGF (XbFGF) and electophoretically homogeneous XTC-MIF (a TGF-beta-like factor obtained from a Xenopus cell line) on animal pole explants. We find that they have a similar minimum active concentration (0.1-0.2 ng ml-1) but that, nonetheless, XTC-MIF is at least 40 times more active in inducing muscle. In general, we find that the two factors cause inductions of significantly different characters in terms of tissue type, morphology, gene expression and timing. At low concentrations (0.1-1.0 ng ml-1) both factors induce the differentiation of 'mesenchyme' and 'mesothelium' as well as blood-like cells. These latter cells do not, however, react with an antibody to Xenopus globin. This raised the possibility that the identification of red blood cells in other studies on mesoderm induction might have been mistaken, but combinations of animal pole regions with ventral vegetal pole regions confirmed that genuine erythrocytes are formed. The identity of the blood-like cells formed in response to the inducing factors remains unknown. At higher concentrations XTC-MIF induces neural tissue, notochord, pronephros and substantial and often segmented muscle. By contrast, XbFGF only induces significant amounts of muscle above 24 ng ml-1 and even then this is much less than that induced by XTC-MIF. For both factors an exposure of less than 30 min is effective. Competence of animal pole cells to respond to XbFGF is completely lost by the beginning of gastrulation (stage 10) while competence to XTC-MIF is detectable until somewhat later (stage 11). Since animal pole tissue is known to be able to respond to the natural inducer at least until stage 10, and perhaps until stage 10.5, this suggests that bFGF cannot be the sole inducer of mesoderm in vivo. Taken together, these results are consistent with XTC-MIF being a dorsoanterior inducer and XbFGF a ventroposterior inducer, suggesting that body pattern is established by the interaction of two types of inducing signal. This model is discussed in view of the qualitative and quantitative differences between the factors.

Animals↗

Control of segmental asymmetry in Drosophila embryos.

During Drosophila development, an important aspect of body patterning is the division of the embryo into repeating morphological units referred to as parasegments. The parasegmental domains are first defined at the blastoderm stage by alternating stripes of transcripts encoded by the pair-rule genes fushi tarazu (ftz) and even-skipped (eve) and later by stripes encoded by the segment polarity genes engrailed (en) and wingless. Here, we show that the runt gene (run) is required to generate asymmetries within these parasegmental domains. Using a heat-shock-inducible run transgene, we found that ectopic run expression leads to rapid repression of eve stripes and a somewhat delayed expansion of ftz stripes. Unexpectedly, we also found that ectopic run was a rapid and potent repressor of odd-numbered en stripes. Two remarkably different segmental phenotypes were generated as a consequence of these effects. In solving the mechanisms underlying these phenotypes, we discovered that the positioning of en stripes is largely determined by the actions of negative regulators. Our data indicate that run is required to limit the domains of en expression in the odd-numbered parasegments, while the odd-skipped gene is required to limit the domains of en expression in the even-numbered parasegments. Activation of en at the anterior margins of both sets of parasegments requires the repression of run and odd by the product of the eve gene. The spatial restriction of gene expression via negative and double negative pathways such as these is likely to be a common theme during development.

Animals↗

Mitotic delay dependent survival identifies components of cell cycle control in the Drosophila blastoderm.

The Drosophila body pattern is laid down by maternal and zygotic factors which act during the early phase of embryonic development. During this period, nascent zygotic transcripts longer than about 6 kilobases are aborted between the rapid mitotic cycles. Resurrector1 (Res1) and Godzilla1 (God1), two newly identified dominant zygotic suppressor mutations, and a heterozygous maternal deficiency of the cyclin B locus, complement the partial loss of function of the segmentation gene knirps (kni) by extending the length of mitotic cycles at blastoderm. The mitotic delay caused by Res1 and God1 zygotically and by the deficiency of the cyclin B locus maternally allows the expression of a much longer transcript of a kni cognate gene normally aborted between the short mitotic cycles and consequently allows survival of kni mutant progeny. In addition to the practical benefits of identifying mutations in Drosophila cell cycle regulatory genes as suppressors of kni, our results have evolutionary implications regarding the flexibility of the genome to meet sudden selective pressures by recruiting cognate genes to function.

Animals↗

Translational regulation of oskar mRNA occurs independent of the cap and poly(A) tail in Drosophila ovarian extracts.

Translational regulation plays a prominent role in Drosophila body patterning. Progress in elucidating the underlying mechanisms has been limited by the lack of a homologous in vitro system that supports regulation. Here we show that extracts prepared from Drosophila tissues are competent for translation. Ovarian extracts, but not embryonic extracts, support the Bruno response element- and Bruno-dependent repression of oskar mRNA translation, which acts in vivo to prevent protein synthesis from transcripts not localized to the posterior pole of the oocyte. Consistent with suggestive evidence from in vivo experiments, regulation in vitro does not involve changes in poly(A) tail length. Moreover, inhibition studies strongly suggest that repression does not interfere with the process of 5' cap recognition. Translational regulation mediated through the Bruno response elements is thus likely to occur via a novel mechanism.

Animals↗

Ypsilon Schachtel, a Drosophila Y-box protein, acts antagonistically to Orb in the oskar mRNA localization and translation pathway.

Subcellular localization of mRNAs within the Drosophila oocyte is an essential step in body patterning. Yps, a Drosophila Y-box protein, is a component of an ovarian ribonucleoprotein complex that also contains Exu, a protein that plays an essential role in mRNA localization. Y-box proteins are known translational regulators, suggesting that this complex might regulate translation as well as mRNA localization. Here we examine the role of the yps gene in these events. We show that yps interacts genetically with orb, a positive regulator of oskar mRNA localization and translation. The nature of the genetic interaction indicates that yps acts antagonistically to orb. We demonstrate that Orb protein is physically associated with both the Yps and Exu proteins, and that this interaction is mediated by RNA. We propose a model wherein Yps and Orb bind competitively to oskar mRNA with opposite effects on translation and RNA localization.

Animals↗

EGFR signalling inhibits Capicua-dependent repression during specification of Drosophila wing veins.

Localised activation of the Ras/Raf pathway by Epidermal Growth Factor Receptor (EGFR) signalling specifies the formation of veins in the Drosophila wing. However, little is known about how the EGFR signal regulates transcriptional responses during the vein/intervein cell fate decision. We provide evidence that EGFR signalling induces expression of vein-specific genes by inhibiting the Capicua (Cic) HMG-box repressor, a known regulator of embryonic body patterning. Lack of Cic function causes ectopic expression of EGFR targets such as argos, ventral veinless and decapentaplegic and leads to formation of extra vein tissue. In vein cells, EGFR signalling downregulates Cic protein levels in the nucleus and relieves repression of vein-specific genes, whereas intervein cells maintain high levels of Cic throughout larval and pupal development, repressing the expression of vein-specific genes and allowing intervein differentiation. However, regulation of some EGFR targets such as rhomboid appears not to be under direct control of Cic, suggesting that EGFR signalling branches out in the nucleus and controls different targets via distinct mediator factors. Our results support the idea that localised inactivation of transcriptional repressors such as Cic is a rather general mechanism for regulation of target gene expression by the Ras/Raf pathway.

Animals↗

Transcriptional control by Drosophila gap genes.

The segmented body pattern along the longitudinal axis of the Drosophila embryo is established by a cascade of specific transcription factor activities. This cascade is initiated by maternal gene products that are localized at the polar regions of the egg. The initial long-range positional information of the maternal factors, which are transcription factors (or are factors which activate or localize transcription factors), is transferred through the activity of the zygotic segmentation genes. The gap genes act at the top of this regulatory hierarchy. Expression of the gap genes occurs in discrete domains along the longitudinal axis of the preblastoderm and defines specific, overlapping sets of segment primordia. Their protein products, which are DNA-binding transcription factors mostly of the zinc finger type, form broad and overlapping concentration gradients which are controlled by maternal factors and by mutual interactions between the gap genes themselves. Once established, these overlapping gap protein gradients provide spatial cues which generate the repeated pattern of the subordinate pair-rule gene expression, thereby blue-printing the pattern of segmental units in the blastoderm embryo. Our results show different strategies by which maternal gene products, in combination with various gap gene proteins, provide position-dependent sets of transcriptional activator/repressor systems which regulate the spatial pattern of specific gap gene expression. Region-specific combinations of different transcription factors that derive from localized gap gene expression eventually generate the periodic pattern of pair-rule gene expression by the direct interaction with individual cis-acting "stripe elements" of particular pair-rule gene promoters. Thus, the developmental fate of blastoderm cells is programmed according to their position within the anterior-posterior axis of the embryo: maternal transcription factors regulate the region-specific expression of first zygotic transcription factors which, by their specific and unique combinations, control subordinate zygotic transcription factors, thereby subdividing the embryo into increasingly smaller units later seen in the larva.

Animals↗

Patterning a multi-headed mutant in Hydractinia: enhancement of head formation and its phenotypic normalization.

In a mutant strain of Hydractinia (Cnidaria: Hydrozoa), the polyps develop ectopic supernumerary tentacles and heads (hypostomes) after an initial phase of wild-type growth. In order to elucidate the molecular mechanisms implicated in the development of aberrant phenotypes, we tried to enhance or suppress the expressivity of this hypomorphic mutation by exposing subclones to factors supposedly influencing pattern formation. Upon iterated treatment with alsterpaullone, an inhibitor of GSK-3, the formation of additional, ectopic head structures and the budding of new polyps were dramatically accelerated and enhanced. The endogenous stolon-inducing factor (SIF) had opposite effects by reducing head forming potential while increasing stolon-forming potential. SIF could be used to rescue extremely aberrant phenotypes. In these mutant colonies, long polyps with multiple heads eventually detach from stolons and lose the ability to regenerate stolons. Upon exposure to SIF, such free-floating multi-headed polyps resumed production of stolons and acquired wild-type morphology. We conclude that a canonical WNT signaling cascade is involved in patterning the body axis of polyps and in the initiation of budding, and that SIF counteracts this signaling system.

Animals↗

Serotonergic and dopaminergic influence of the duration of embryogenesis and intracapsular locomotion of Lymnaea stagnalis L.

The role of the dopaminergic and serotonergic system was studied during the embryonic development of the pond snail Lymnaea stagnalis, with special attention to the effect of dopamine and serotonin as well as their agonists and antagonists on the rotation of the veliger larvae, and to the effect of precursors and inhibitors of the synthetizing enzymes on the duration of the embryonic life. Serotonin, D-lysergic acid diethylamide and N,N-dimethyltryptamine increased at a concentration of 1 microM the rotation by 50%, 90% and 87% respectively, and among them D-Lysergic acid diethylamide was found to be the most potent agonist. Other serotonergic agonists and antagonists enhanced the frequency of the rotation (from 165% to 355%) at higher threshold concentrations in the following rank order: methysergid > tryptamine > 2,5-dimethoxy-4-iodoamphetamine > 5-carboxyamidotryptamine > bromo-lysergic acid diethylamide > 7-methyltryptamine. Application of 1-(2-methoxyphenyl) piperazine decreased the rotation by 76%. The reuptake inhibitor desipramine completely blocked the rotation and killed the embryos. Dopaminergic agonists accelerated the rotation by 62% to 233%, and their effect was ranged as follows: dopamine > apomorphine > m-tyramine approximately equal to p-tyramine. Chlorpromazine at 100 microM concentration killed the embryos. At a concentration of 100 microg/ml, tyrosine, the precursor of DA, slowed down the embryonic development by increasing the duration of the embryonic life from 8 to 10 days. Decarboxylase inhibitors, alpha-methyl-3,4-dihydroxyphenyl-alanine (25 microg/ml) and m-hydroxybenzylhydrazin (5 microg/ml), killed 50% of the embryos, meanwhile the rest hatched ten days later, compared to the control animals. The development was partially blocked by the serotonin precusor L-tryptophane (50 microg/ml). Trytophan hydroxylase blocker, p-chlorphenylalanine (50 microg/ml) resulted in a distortion of the body pattern of the embryos, and prevented the hatching of most (95%) of the animals.

Amphetamines↗

Reproductive behavior in the squid Sepioteuthis australis from South Australia: interactions on the spawning grounds.

Squid behavior is synonymous with distinctive body patterns, postures, and movements that constitute a complex visual communication system. These communications are particularly obvious during reproduction. They are important for sexual selection and have been identified as a potential means of species differentiation. Here we present a detailed account of copulation, mating, and egg deposition behaviors from in situ observations of the squid Sepioteuthis australis from South Australia. We identified four mating types from 85 separate mating attempts: "Male-upturned mating" (64% of mating attempts); "Sneaker mating" (33%); "Male-parallel" (2%); and "Head-to-head" (1%). Intervals between successive egg deposition behaviors were clearly bimodal, with modes at 2.5 s and 70.0 s. Ninety-three percent of egg capsules contained 3 or 4 eggs (mean = 3.54), and each egg cluster contained between 218 and 1922 egg capsules (mean = 893.9). The reproductive behavior of S. australis from South Australia was different from that described for other cephalopod species. More importantly, comparison between these results and those for other populations of S. australis suggests that behavior may differ from one population to another.

Agonistic Behavior↗

Fasting does not impair insulin-stimulated glucose uptake but alters intracellular glucose metabolism in conscious rats.

Effects of 24-h and 48-h fasting on maximal insulin-stimulated whole-body and muscle glucose uptake, glycogen synthesis, and glycolysis were studied in conscious rats by combining the glucose clamp technique with tracer methods. Fasting decreased body weight and basal plasma glucose, plasma insulin, hepatic glucose output, and glucose clearance (P < 0.05 for all). However, maximal insulin-stimulated whole-body glucose uptake, normalized to body weight, was almost identical in fed, 24-h fasted, and 48-h fasted rats (191 +/- 8, 185 +/- 14, and 182 +/- 5 mumol.kg-1.min-1, respectively; P > 0.7). Similarly, rates of insulin-stimulated glucose uptake by four different skeletal muscles, estimated by the 2-deoxyglucose injection technique, were not different among the three groups. In contrast to glucose uptake, insulin-stimulated whole-body glycolysis was decreased significantly after fasting (36% after 48 h fasting; P < 0.05), whereas insulin-stimulated whole-body glycogen synthesis was increased (44% after 48 h fasting; P < 0.05). In fed rats, glycolysis was the major pathway for glucose metabolism during hyperinsulinemia, accounting for 60 +/- 5% of glucose uptake. This fraction was decreased significantly by fasting (P < 0.01), so that after a 48-h fast, glycolysis accounted for only 40 +/- 3% of insulin-stimulated glucose uptake and glycogen synthesis became predominant pathway, accounting for 60 +/- 3% of whole-body glucose utilization. Whole-body patterns of glucose metabolism during hyperinsulinemia were paralleled by glucose metabolism in individual muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

Projecting future medical care costs using four scenarios of lifestyle risk rates.

PURPOSE: This study predicts medical care expenditures over 10 years for Union Pacific Railroad (UPRR) under alternative health risk factor scenarios for the UPRR workforce. DESIGN: This paper describes the development of an economic forecasting model to predict medical care expenditures assuming four different scenarios of population risk. The variables used to predict medical care expenditures are employee demographics and health risk profiles. SETTING: UPRR is a transportation company with more than 56,000 employees in 25 states west and south of the Mississippi River. SUBJECTS: Employees of UPRR. MEASURES: Intermediate outcomes included health risk measures related to exercise patterns, body weight, eating habits, smoking, alcohol consumption, total cholesterol, blood glucose, blood pressure, stress, and depression. Major outcome measures included projected total annual payments by UPRR for medical care services for the decade following 1998. RESULTS: The UPRR work force is projected to grow by 500 employees per year over the 10-year study period. The average age is expected to increase from 44 to 48 years. Without further health promotion intervention, 7 of the 11 risk factors assessed would likely worsen among UPRR's workforce. Medical care cost increases are projected to range from $22.2 million to $99.6 million in constant 1998 dollars over the next decade, depending on the effectiveness of risk factor modification programs. With an expected health promotion budget averaging $1.9 million annually over 10 years, health risks must decline at least 0.09% per year for the program to pay for itself. CONCLUSIONS: Estimating various risk and cost scenarios can facilitate program planning and produce an economic justification for worksite health programs.

Adult↗

Behavioral assessment scale of oral functions in feeding.

When implementing therapeutic feeding programs for the multiply-handicapped developmentally disabled, it is imperative to establish a specific baseline of observable oral movement upon which management and change can be measured. The assessment reported provides an objective and graded method of documenting the major aspects of oral function in relation to feeding difficulties. It is designed to be used in conjunction with an assessment of overall muscle tone and body patterns and an evaluation of specific oral structures and deviations that might interfere with eating.

Adolescent↗

A C. elegans patched gene, ptc-1, functions in germ-line cytokinesis.

Patched (Ptc), initially identified in Drosophila, defines a class of multipass membrane proteins that control cell fate and cell proliferation. Biochemical studies in vertebrates indicate that the membrane proteins Ptc and Smoothened (Smo) form a receptor complex that binds Hedgehog (Hh) morphogens. Smo transduces the Hh signal to downstream effectors. The Caenorhabditis elegans genome encodes two Ptc homologs and one related pseudogene but does not encode obvious Hh or Smo homologs. We have analyzed ptc-1 by RNAi and mutational deletion and find that it is an essential gene, although the absence of ptc-1 has no detectable effect on body patterning or proliferation. Therefore, the C. elegans ptc-1 gene is functional despite the lack of Hh and Smo homologs. We find that the activity and expression of ptc-1 is essentially confined to the germ line and its progenitors. ptc-1 null mutants are sterile with multinucleate germ cells arising from a probable cytokinesis defect. We have also identified a surprisingly large family of PTC-related proteins containing sterol-sensing domains, including homologs of Drosophila dispatched, in C. elegans and other phyla. These results suggest that the PTC superfamily has multiple functions in animal development.

Amino Acid Sequence↗

New steps in the Wnt/beta-catenin signal transduction pathway.

Wnt regulates developmental and oncogenic processes through its downstream effector, beta-catenin, and a set of other intracellular regulators that are largely conserved among species. Wnt family genes encode secreted glycoproteins that act as ligands for membrane receptors belonging to the Frizzled family of proteins. Wnt-1 originally was found as a proto-oncogene that was upregulated in tumors caused by the mouse mammary tumor virus. The Drosophila homologue of Wnt-1, wingless, is a segment polarity gene that regulates body patterning of the fly embryo. In Xenopus, the Wnt pathway regulates formation of the ventral-dorsal axis. Although Wnt proteins are expressed widely in mammals, the function of the Wnt signaling pathway in normal adult mammalian tissues is not understood. Downstream components of the Wnt pathway, APC (adenomatous polyposis coli) and beta-catenin, clearly are involved in human cancer. There are also several reports that Wnt ligands are highly expressed in tumors. Wnt stabilizes cytoplasmic beta-catenin and activates beta-catenin/Lef-1 (lymphoid enhancer factor), Tcf (T-cell factor)-dependent gene transcription. This regulation of cytosolic beta-catenin is mediated by glycogen synthase kinase-3 (GSK-3) activity but in neither case is the mechanism known. The mechanism by which Wnt inhibits GSK-3 is unknown. Recent studies have shown that some of the intracellular signaling molecules that mediate the Wnt pathway are in complexes, including Dishevelled (Dsh or Dvl), GSK-3beta, and APC protein. However, little is known about how Wnt or other upstream stimuli regulate these complexes to stabilize beta-catenin. We took a variety of approaches to identify new components of the Wnt pathway. Using an expression-cloning technique, we isolated casein kinase I (CKI)epsilon as a positive regulator of beta-catenin in the Wnt pathway. Overexpression of CKIepsilon mimics Wnt by stabilizing beta-catenin, thereby increasing expression of beta-catenin-dependent genes. Inhibition of endogenous CKIepsilon attenuated gene transcription stimulated by Wnt or by Dsh. CKIepsilon forms a complex with Axin and the other downstream components of the Wnt pathway. CKIepsilon is a positive regulator of the Wnt pathway and a possible functional link between upstream signals and the intracellular Axin signaling complex that regulates beta-catenin. In separate experiments, we have identified a Dishevelled-associated kinase (DAK) that binds to Dsh and regulates its functions. Dsh is required for two different pathways, the Wnt pathway and planar polarity pathway in Drosophila. DAK dramatically enhances the function of Dsh in the Wnt pathway and inhibits its function in the planar polarity pathway. This chapter will discuss these newly identified components of the Wnt pathway.

Adaptor Proteins, Signal Transducing↗