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PubMed2004

Function of the Trithorax-like gene during Drosophila development.

Maintenance of homeotic gene expression during Drosophila development relies on the Polycomb and the trithorax groups of genes. Classically, the Polycomb proteins act as repressors of homeotic gene function, whereas trithorax proteins function as activators. However, recent investigation has indicated that some of these maintenance genes may act both as repressors and activators. One of those is the Drosophila Trithorax-like gene that codes for the GAGA factor. To investigate its dual activator/repressor role, we have studied the function of the Trithorax-like throughout Drosophila development. Embryos lacking both the maternal and the zygotic Trithorax-like function do not develop suggesting that Trithorax-like might be required in oogenesis. Homozygous Trithorax-like null mutant embryos show reduced expression levels of some of the homeotic proteins. Trithorax-like mutant larval clones, however, do not show phenotypes indicative of either activation or repression of homeotic gene function. These results suggest that Trithorax-like is required during embryogenesis but not throughout larval development for the regulation of homeotic gene expression. Moreover, this temporal requirement seems also to regulate MCP-mediated silencing. Finally, lack of Trithorax-like function modulates the gain of function phenotypes caused by over-expression of homeotic genes. To explain Trithorax-like gene function, we propose a model where very early in development, GAGA factor probably establishes a chromatin ground state for transcription. The differential "on/off" transcriptional state of the homeotic genes is then established and propagated by the action of the specific regulatory proteins independently of the GAGA factor. We also suggest that GAGA factor may not have a dual activator/repressor function. Rather, Trithorax-like mutations may produce dual loss of activation and loss of repression effects.

Animals↗
PubMed2006

mig-5/Dsh controls cell fate determination and cell migration in C. elegans.

Cell fate determination and cell migration are two essential events in the development of an organism. We identify mig-5, a Dishevelled family member, as a gene that regulates several cell fate decisions and cell migrations that are important during C. elegans embryonic and larval development. In offspring from mig-5 mutants, cell migrations are defective during hypodermal morphogenesis, QL neuroblast migration, and the gonad arm migration led by the distal tip cells (DTCs). In addition to abnormal migration, DTC fate is affected, resulting in either an absent or an extra DTC. The cell fates of the anchor cell in hermaphrodites and the linker cells in the male gonad are also defective, often resulting in the cells adopting the fates of their sister lineage. Moreover, 2 degrees vulval precursor cells occasionally adopt the 3 degrees vulval cell fate, resulting in a deformed vulva, and the P12 hypodermal precursor often differentiates into a second P11 cell. These defects demonstrate that MIG-5 is essential in determining proper cell fate and cell migration throughout C. elegans development.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Different mechanisms underlie phenotypic plasticity and interspecific variation for a reproductive character in drosophilids (Insecta: Diptera).

The insect ovary is a modular structure, the functional unit of which is the ovariole. Ovariole number is positively correlated with potential reproductive output. Among drosophilids (Insecta: Diptera), ovariole number shows both phenotypic plasticity and substantial interspecific and interpopulational variation. Here we examine the mechanistic connection between phenotypic plasticity and genetically fixed variation in ovariole number within the melanogaster species group. When a laboratory population of Drosophila melanogaster was reared under reduced food conditions, differences in ovariole number were entirely due to alterations in cell differentiation during the wandering stage at the very end of larval development. Cell growth and cell death were not affected. When these same flies were reared under a variety of temperatures, ovariole number differences arose during the latter half of the third (final) larval instar. Cell differentiation was affected, although cell number was not, and ovariole number differences were established before metamorphosis. In contrast, genetically fixed, interspecific and interpopulational variability in ovariole number was caused by alterations in the dynamics of cell differentiation and by cell number differences. Furthermore, the stages affected were different in different species and populations in the melanogaster species group, ranging from the first (D. sechellia) through the middle of the third (D. simulans and D. mauritiana) larval stage. Therefore, the mechanistic bases for plasticity-based variability are largely distinct from the mechanistic bases for interspecific and interpopulational variability. Our results suggest that phenotypic plasticity indicates evolutionary flexibility in underlying ontogenetic processes.

Animals↗
PubMed1996

Dpp receptors are autonomously required for cell proliferation in the entire developing Drosophila wing.

The mammalian growth factor TGFbeta negatively regulates cell proliferation in various systems. Here we provide evidence that another TGFbeta superfamily member, Drosophila Decapentaplegic (Dpp), stimulates cell proliferation. In the developing wing blade, somatic clones lacking the Dpp receptors Punt or Thick veins (Tkv), or lacking Schnurri, a transcription factor involved in Dpp signal interpretation, fail to grow when induced early in larval development. Furthermore the spatial requirement for these signaling components indicates that Dpp has to travel several cell diameters from its source in order to reach all cells that require its signal. The requirement for Tkv also depends on the distance of cells from the source of the Dpp signal. We propose that Dpp can act at a distance to positively control cell proliferation.

Animals↗
PubMed2005

Establishment of a sandwich ELISA system to detect diapause hormone, and developmental profile of hormone levels in egg and subesophageal ganglion of the silkworm, Bombyx mori.

In the silkworm Bombyx mori, diapause hormone (DH) is produced in the female subesophageal ganglion (SG) and induces embryonic diapause by targeting developing ovaries. DH is processed from a precursor protein consisting of DH, pheromone biosynthesis activating neuropeptide (PBAN) and three other neuropeptides (SGNPs). Because these five neuropeptides share a common sequence, FXPRLamide, at the C-terminus, a direct and specific assay for DH itself is required in order to understand the profile of concentration changes. In this study, we produced a mouse monoclonal antibody (anti-DH[N] mAb) against the N-terminal region of DH and developed a sandwich enzyme-linked immunosorbent assay using the anti-DH[N] mAb and a rabbit polyclonal antibody against the C-terminus of DH. This procedure enabled us to specifically quantify the DH molecule at femtomolar levels (equivalent to 1/10 of SG). We then plotted DH levels in eggs and SGs during embryonic and post-embryonic development. DH was present in late-stage embryos that had been destined for the production of both diapause and nondiapause eggs. DH levels in SG gradually increased in both types during larval development and peaked at the early pupal stage. At the middle pupal stage, DH levels in SG and SG-brain complex decreased markedly in the diapause-egg producing type, thus indicating active release of DH into the hemolymph. From 5th instar larva to adult, no sexual differences in DH levels were observed in SGs or SG-brain complexes from diapause and nondiapause egg-producing types.

Animals↗
PubMed2001

Temperature and myogenic factor transcript levels during early development determines muscle growth potential in rainbow trout (Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax).

The influence of changes in environmental temperature on the mRNA levels of myogenic regulatory factors (MRFs), i.e. MyoD and myogenin, as well as myosin heavy chain (MyHC) were studied during early larval development in rainbow trout and sea bass. Phosphoimager analysis of northern blots indicated that there is an optimum temperature for the RNA transcript levels of MRF and MyHC RNA in trout and in sea bass larvae. In the trout strain studied, the highest concentration for MRF and MyHC transcripts was found at 8 degrees C rather than 4 degrees C or 20 degrees C. In European sea bass, the highest concentrations of MRF and MyHC mRNA were observed at 15-20 degrees C rather than 13 degrees C. Raising sea bass larvae at 15 degrees C was associated with higher MyHC gene expression as well as a trend towards an increase in total muscle fibre number and higher growth rates after transfer at ambient temperature. Results suggest that mRNA levels of MRF and MyHC can be used to optimise early development. An experiment in which the temperature was changed illustrates the consequence of precise temporal expression of MRF genes in specifying muscle fibre number at critical stages during early development.

Animals↗
PubMed1975

Phenogenetics of the eyeless-dominant mutant of Drosophila melanogaster.

The eyeless-Dominant (eyD) mutation is a fourth chromosome insertional translocation which affects the eyes, antennae, ocelli, and sexcombs when heterozygous but is a larval-pupal lethal when homozygous. By use of a crowding technique, it was possible to separate eyD homozygotes and heterozygotes with 100% accuracy at an early stage of larval development. Under these conditions, the eyD homozygotes had a biphasic lethal period since 45% died as first or second instar larvae and 55% died as pupae. The eyDleyD pupal lethal, isolated by this technique, was able to form all the adult structures with the exception of the eye-antennal disc derivatives. The brain was present but abnormal. In testing the competence of the eyDleyD larval eye discs by means of transplantation experiments, it has been demonstrated that the mutant discs develop non-autonomously. Histological studies have revealed the existence of neurological defects in both eyD heterozygotes and homozygotes. The eyDleyD lethal larvae lacked detectable optic formation centers and showed an extreme reduction in the number of cells present in the cortex of the brain. The ey"dleyD lethal pupae possessed partial formation centers and also had severe reduction in the number of cortical cells. The eyD heterozygotes possessed normal appearing formation centers but they did exhibit a moderate reduction in the number of their cortical cells as compared to wild-type. These studies have shown that there is a direct correlation between the extent of neurological damage and the time of developmental arrest. It appears that the eyD mutation must adversely affect the neuroblasts at a very early stage of development. As a working hypothesis, it is suggested that the eyD mutation operates via the same basic mechanism of cell death in heterozygous and homozygous animals.

Animals↗
PubMed1999

Immunochemical localization of calretinin in the retina of the turbot (Psetta maxima) during development.

The expression of the calcium-binding protein calretinin was analysed by immunohistochemistry techniques in the retina of turbot (Psetta maxima) from embryonic to juvenile stages. Calretinin immunoreactivity was first detected in retinae from newly hatched larvae, in which the anlage of the inner plexiform layer and a subset of amacrine and ganglion cells displayed a faint immunolabelling. First appearance of photoreceptors during larval life coincided with an increase in the intensity of the labelling. During subsequent larval development, the expression of calretinin affected distinctive retinal components. The inner plexiform layer, optic fiber layer, and a population of amacrine and ganglion cells were invariably labelled. Occasional bipolar cells were labelled at the end of the larval period. By metamorphosis, calretinin is sequentially expressed in horizontal cells, and bipolar immunoreactive cells become numerous. The pattern of calretinin immunoreactivity of the inner plexiform layer changes from the larval to juvenile period. In all cases, calretinin immunoreactivity exhibited variations between the peripheral retina, which contains the most recently differentiated retinal components, and the remainder of the differentiated retina. Our results suggest that the progressive expression of calretinin in the turbot retina appears associated with some degree of neuronal differentiation. Once the definitive pattern of calretinin immunoreactivity is established in the turbot retina, both similarities and differences with the calretinin location in the retina of other vertebrates can be demonstrated.

Animals↗
PubMed2003

Temporally regulated expression of Lin-28 in diverse tissues of the developing mouse.

The gene lin-28 was originally identified through a mutant of the nematode Caenorhabditis elegans displaying defects in developmental timing. It is expressed stage-specifically in tissues throughout the animal and is required for cell fates to be expressed at the appropriate stage of larval development. lin-28 encodes a cytoplasmic protein with a unique pairing of RNA-binding motifs. Diverse animals possess Lin-28 homologues and mouse Lin-28 is expressed in embryos, embryonic stem cells and embryonal carcinoma cells, but not in some differentiated cell types. To assess whether mammalian Lin-28 may function as a developmental timing regulator, we examined adult and embryonic tissues of the mouse for its expression. We observed Lin-28 protein in many diverse tissues of the embryo through the period of organogenesis and that it persists in some tissues in the adult. In addition to an overall down-regulation during embryogenesis, in at least two tissues Lin-28 expression shows temporal regulation, as opposed to cell type or tissue-specific regulation: in the developing bronchial epithelium, where it is present in the developing lung and absent in the adult, and in a subset of cells developing along the crypt-villus axis of the intestine. Interestingly, unlike epithelia, cardiac and skeletal muscle continuously express Lin-28, suggesting an ongoing need for its activity there. We also observed that Lin-28 expression is repressed during the retinoic acid-induced differentiation of mouse P19 cells into neuronal cells, suggesting that down-regulation of Lin-28 in some tissues may occur in response to hormonal signals that govern development.

Animals↗
PubMed2000

MBF2 is a tissue- and stage-specific coactivator that Is regulated at the step of nuclear transport in the silkworm Bombyx mori.

Coactivators MBF1 and MBF2 mediate BmFTZ-F1-dependent transcriptional activation in vitro by interconnecting BmFTZ-F1, TATA binding protein TBP, and TFIIA. Here, we analyzed temporal and spatial expression patterns of MBF2 during embryonic and larval development of the silkworm Bombyx mori. MBF2 was detected in unfertilized eggs and embryos until stage 26. In stage 22 embryos, MBF1, MBF2, and BmFTZ-F1 colocalize in neural cells. During the larval stage, MBF2 was not expressed in the fat body and trachea. In the silk gland, MBF2 mRNA was constitutively expressed, but MBF2 protein appeared in the period between the second day and the molting D3 stage in both the third and the fourth instars and then disappeared. MBF2 was also detected on the second and third days of the fifth instar. Immunostaining during the fourth molt showed that MBF1, MBF2, and BmFTZ-F1 localize in the nucleus only at the D3 stage, while the two cofactors are present in the cytoplasm at other stages. Immunoprecipitation experiments suggested that MBF1, MBF2, and BmFTZ-F1 form a complex at the D3 stage. Transient expression of these factors in Schneider cell line 2 revealed that MBF1 and MBF2 localize to the nucleus and enhance BmFTZ-F1-dependent transcription only when all three factors are present. These data illustrate the functional regulation of MBF1 and MBF2 at the step of nuclear transport and implicate MBF2 in tissue- and stage-specific transcription.

Animals↗
PubMed2005

The ontogenic transcription of complement component C3 and Apolipoprotein A-I tRNA in Atlantic cod (Gadus morhua L.)--a role in development and homeostasis?

The complement system is important both in the innate and adaptive immune response, with C3 as the central protein of all three activation pathways. Apolipoprotein A-I (ApoLP A-I), a high-density lipoprotein (HDL), has been shown to have a regulatory role in the complement system by inhibiting the formation of the membrane attack complex (MAC). Complement has been associated with apoptotic functions, which are important in the immune response and are involved in organ formation and homeostasis. mRNA probes for cod C3 and ApoLP A-I were synthesized and in situ hybridisation used to monitor the ontogenic development of cod from fertilised eggs until 57 days after hatching. Both C3 and ApoLP A-I transcription was detected in the central nervous system (CNS), eye, kidney, liver, muscle, intestines, skin and chondrocytes at different stages of development. Using TUNEL staining, apoptotic cells were identified within the same areas from 4 to 57 days posthatching. The present findings may suggest a role for C3 and ApoLP A-I during larval development and a possible role in the homeostasis of various organs in cod.

Animals↗
PubMedDate not supplied

[Appearance of secondary melanophore reactions in the ontogeny of anuran amphibia].

The development of physiological reactions of the dermal melanophores has been studied in Rana temporaria, R. ridibunda and Xenopus laevis. In these species, the background (secondary) reactions of melanophores appeared at different stages of larval development but their appearance was always timed with the eye slit closure.

Animals↗
PubMed2002

A cellular memory module conveys epigenetic inheritance of hedgehog expression during Drosophila wing imaginal disc development.

In Drosophila, the Trithorax-group (trxG) and Polycomb-group (PcG) proteins interact with chromosomal elements, termed Cellular Memory Modules (CMMs). By modifying chromatin, this ensures a stable heritable maintenance of the transcriptional state of developmental regulators, like the homeotic genes, that is defined embryonically. We asked whether such CMMs could also control expression of genes involved in patterning imaginal discs during larval development. Our results demonstrate that expression of the hedgehog gene, once activated, is maintained by a CMM. In addition, our experiments indicate that the switching of such CMMs to an active state during larval stages, in contrast to embryonic stages, may require specific trans-activators. Our results suggest that the patterning of cells in particular developmental fields in the imaginal discs does not only rely on external cues from morphogens, but also depends on the previous history of the cells, as the control by CMMs ensures a preformatted gene expression pattern.

Animals↗
PubMed1998

Early development of the peripheral nervous system in a lancelet species.

The developmental pattern of the lancelet (amphioxus) peripheral nervous system from embryos to larvae has been studied by using wholemount immunostaining and transmission electron microscopy. The peripheral nerves first appeared on the anterior dorsal surface of the medulla at the middle neurula stage, when the anterior nerve cord was just closing. A single axon with a large growth cone was the progenitor of each nerve. The nerve roots adopted an asymmetric arrangement soon after. The first nerve, likely a pair of pure sensory nerves, sprouted from the anterior tip of the nerve cord. This nerve may be comparable topographically to the preoptic nerve (the posterior branch of the terminal nerve) in lungfishes. However, the neuron that first extends its axon was located in the medulla, as in the other posterior nerves. One of the extramedullary primary sensory neurons, the corpuscles of de Quatrefages, appeared in larvae with the mouth and two anterior gill pores. Their axons were seemingly fasciculated with the efferent axon of the first nerve. The second nerve, the most complex one to appear during embryonic and early larval development, innervated the preoral pit and the buccal region. The third and fourth nerves on the left side also innervated the buccal region. The larval innervation patterns in the anterior region differed from the adult organization, suggesting a segmental rearrangement of the nerve supply during development. There was no evidence to dichotomize the peripheral nerves into cranial and spinal nerves, as exist in vertebrates. These characteristics of the peripheral nervous system in the lancelet indicate that this animal has a rather derived or primitive developmental system of peripheral nerves, making the analysis of homology with vertebrates difficult.

Animals↗
PubMedDate not supplied

Ontogenetic evidence for the Paleozoic ancestry of salamanders.

The phylogenetic positions of frogs, salamanders, and caecilians have been difficult to establish. Data matrices based primarily on Paleozoic taxa support a monophyletic origin of all Lissamphibia but have resulted in widely divergent hypotheses of the nature of their common ancestor. Analysis that concentrates on the character states of the stem taxa of the extant orders, in contrast, suggests a polyphyletic origin from divergent Paleozoic clades. Comparison of patterns of larval development in Paleozoic and modern amphibians provides a means to test previous phylogenies based primarily on adult characteristics. This proves to be highly informative in the case of the origin of salamanders. Putative ancestors of salamanders are recognized from the Permo-Carboniferous boundary of Germany on the basis of ontogenetic changes observed in fossil remains of larval growth series. The entire developmental sequence from hatching to metamorphosis is revealed in an assemblage of over 600 specimens from a single locality, all belonging to the genus Apateon. Apateon forms the most speciose genus of the neotenic temnospondyl family Branchiosauridae. The sequence of ossification of individual bones and the changing configuration of the skull closely parallel those observed in the development of primitive living salamanders. These fossils provide a model of how derived features of the salamander skull may have evolved in the context of feeding specializations that appeared in early larval stages of members of the Branchiosauridae. Larvae of Apateon share many unique derived characters with salamanders of the families Hynobiidae, Salamandridae, and Ambystomatidae, which have not been recognized in any other group of Paleozoic amphibians.

Animals↗
PubMed1995

Very long-chain fatty acids change the ethanol tolerance of Drosophila melanogaster larvae.

This research tested the hypothesis that long-chain saturated fatty acids increase the order of cell membranes of an organism and minimize the detrimental fluidizing effects of ethanol. Unsaturated fatty acids increase membrane fluidity and are unlikely to increase the ethanol tolerance of the organism. Both a fatty acid-free medium and media supplemented with very long-chain fatty acids (20 or more carbons) were fed to wild-type larvae of Drosophila melanogaster; larvae were then transferred to media with or without ethanol to test for effects of the fatty acids on ethanol tolerance. Ethanol decreased the percent of larvae to pupate, and lengthened larval development time. However, the percentage of pupae to reach the adult stage and the weight of adult males increased when the larvae were fed ethanol. The very long-chain, unsaturated fatty acids, arachidonic acid [20:4(n-6)] and docosatetraenoic acid [22:4(n-6)], were associated with increased larval mortality when administered in a medium supplemented with ethanol. Arachidic acid (20:0) increased the percentage of larvae to pupate under ethanol stress, decreased the development time and increased the adult weight in the presence and absence of ethanol. Behenic acid (22:0) was not effectively incorporated into phospholipids and had little effect on growth traits. Thus, the experimental results were consistent with the hypothesis.

Alcohol Dehydrogenase↗
PubMed1999

Characterization of zebrafish primordial germ cells: morphology and early distribution of vasa RNA.

Research into germ line development is of conceptual and biotechnologic importance. In this study, we used morphology at the level of light and electron microscope to characterize the primordial germ cells (PGCs) of the zebrafish throughout embryonic and larval development. The study was complemented by the detailed analysis of mRNA expression of a putative germ line marker vasa. By morphology alone PGCs were identified at the earliest at the 5-somite stage in the peripheral endoderm in contact with the yolk syncytial layer. Subsequently, they move from lateral to medial positions into the median mesoderm and from there by means of the dorsal mesentery into the gonadal anlage at day 5 postfertilization (pf), to establish gonads with mesenchymal cells by day 9 pf. Ultrastructural analysis of the 4-day-old zebrafish larvae demonstrates the presence of the germ line-specific structures, nuage, and annulate lamellae. vasa RNA-positive cells can be followed during zebrafish embryogenesis from the 32-cell stage onward (Yoon et al., 1997). Upon completion of gastrulation, the RNA is exclusively present in the cells of the hypoblast, which as a consequence of convergence and extension movements first arrange themselves in a V-shaped string-like conformation to end up, by late somitogenesis, as a string of cells on each side of the midline. We show that the localization of maternal vasa RNA in the ovary changes from cytoplasmic, in the previtellogenic oocytes, to cortical in the vitellogenic oocytes, to concentrate at the boundary of the yolk and cytoplasm in the one cell stage zygote. These results demonstrate that the cortical vasa RNA localization precedes its cleavage furrow-associated localization in the embryos and is presumably cytoskeleton dependent. vasa RNA localization changes from asymmetric subcellular at the sphere stage, to become entirely cytoplasmic at the dome stage. These data suggest a close resemblance in modes of segregation of the germ plasma in the frog and vasa mRNA in the fish during cleavage stages. Based on the significantly larger size and the stereotype and similar position of morphologically distinct cells, presumed to be PGCs, and their vasa RNA-positive counterparts, we conclude that vasa RNA-positive cells are the PGCs and vasa RNA represents a definitive germ line marker in the fish. Dev Dyn 1999;216:153-167.

Animals↗
PubMed1975

Experimental studies on a lethal gene (1) in the Mexican axolotl, Ambystoma mexicanum.

1. Gene ł is a recessive lethal factor found in the white strain of axolotls. Animals heterozygous for the gene are phenotypically normal. When mated with each other they give offspring 25% of which exhibit the lethal effects of the gene. 2. The ł/ł homozygotes develop normally to an advanced embryonic stage (Harrison stage 40) before the effects of the gene are first manifested. They then come to display a characteristic combination of abnormalities, including a disproportionately small head, small and poorly developed eyes, abnormal poorly developed gills, undifferentiated limb buds, and reduced overall growth rate. They may feed briefly, but soon stop and invariably die within a few weeks of the time of hatching. 3. The action of gene ł has been analyzed by parabiosing mutant and normal embryos, and by grafting various organ primordia reciprocally between mutant and normal embryos. Parabiosis to normal embryos fails to correct the abnormalities of the mutants, although their survival may be somewhat prolonged. Grafts of mutant organ primordia (eye, limb, gill, pronephros, gonad, head) also invariably fail to show improved development or to survive on normal hosts; normal organ primordia develop normally on mutant hosts so long as the mutant survives. These experiments indicate that gene ł is a recessive autonomous cell lethal affecting all of the organ systems during late embryonic and early larval development.

Ambystoma↗