Effect of inducers and inhibitors on the expression of bcs genes involved in cypris larval attachment and metamorphosis of the barnacles Balanus amphitrite.
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We examined the expression of six barnacle cypris larva-specific gene (bcs) cDNAs (bcs-1, -2, -3, -4,- 5, and -6), the bcs genes, by using Northern blot analysis under various conditions that induced or inhibited cypris larval attachment and metamorphosis. Inducers of larval attachment and metamorphosis, such as a neurotransmitter, tended to increase the expression of bcs mRNAs. All inhibitors of larval attachment and metamorphosis, such as G protein-coupled receptor agonists/antagonists, inhibitors of tyrosine kinase-linked receptors and inhibitors of their signal transduction, suppressed the expression of bcs-6 mRNA alone, but affected differentially other bcs genes. These results strongly suggest that the bcs-6 product plays a key role in triggering the attachment and metamorphosis of cypris larvae into juvenile barnacles. The roles of four late bcs genes (bcs-3,-4, -5 and -6) are discussed. (+info)
Induction of segmentation in polyps of Aurelia aurita (Scyphozoa, Cnidaria) into medusae and formation of mirror-image medusa anlagen.
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Polyps of Aurelia aurita can transform into several medusae (jellyfish) in a process of sequential subdivision. During this transformation, two processes take place which are well known to play a key role in the formation of various higher metazoa: segmentation and metamorphosis. In order to compare these processes in bilaterians and cnidarians we studied the control and the kinetics of these processes in Aurelia aurita. Segmentation and metamorphosis visibly start at the polyp's head and proceed down the body column but do not reach the basal disc. The small piece of polyp which remains will develop into a new polyp. The commitment to the medusa stage moves down the body column and precedes the visible onset of segmentation by about one day. Segmentation and metamorphosis can start at the cut surface of transversely cut body columns, leading to a mirror-image pattern of sequentially developing medusae. (+info)
Temporally restricted expression of transcription factor betaFTZ-F1: significance for embryogenesis, molting and metamorphosis in Drosophila melanogaster.
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FTZ-F1, a member of the nuclear receptor superfamily, has been implicated in the activation of the segmentation gene fushi tarazu during early embryogenesis of Drosophila melanogaster. We found that an isoform of FTZ-F1, betaFTZ-F1, is expressed in the nuclei of almost all tissues slightly before the first and second larval ecdysis and before pupation. Severely affected ftz-f1 mutants display an embryonic lethal phenotype, but can be rescued by ectopic expression of betaFTZ-F1 during the period of endogenous betaFTZ-F1 expression in the wild type. The resulting larvae are not able to molt, but this activity is rescued again by forced expression of betaFTZ-F1, allowing progression to the next larval instar stage. On the other hand, premature expression of betaFTZ-F1 in wild-type larvae at mid-first instar or mid-second instar stages causes defects in the molting process. Sensitive periods were found to be around the time of peak ecdysteroid levels and slightly before the start of endogenous betaFTZ-F1 expression. A hypomorphic ftz-f1 mutant that arrests in the prepupal stage can also be rescued by ectopic, time-specific expression of betaFTZ-F1. Failure of salivary gland histolysis, one of the phenotypes of the ftz-f1 mutant, is rescued by forced expression of the ftz-f1 downstream gene BR-C during the late prepupal period. These results suggest that betaFTZ-F1 regulates genes associated with ecdysis and metamorphosis, and that the exact timing of its action in the ecdysone-induced gene cascade is important for proper development. (+info)
Mutational analysis of endothelin receptor b1 (rose) during neural crest and pigment pattern development in the zebrafish Danio rerio.
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Pigment patterns of fishes are a tractable system for studying the genetic and cellular bases for postembryonic phenotypes. In the zebrafish Danio rerio, neural crest-derived pigment cells generate different pigment patterns during different phases of the life cycle. Whereas early larvae exhibit simple stripes of melanocytes and silver iridophores in a background of yellow xanthophores, this pigment pattern is transformed at metamorphosis into that of the adult, comprising a series of dark melanocyte and iridophore stripes, alternating with light stripes of iridophores and xanthophores. Although several genes have been identified in D. rerio that contribute to the development of both early larval and adult pigment patterns, comparatively little is known about genes that are essential for pattern formation during just one or the other life cycle phase. In this study, we identify the gene responsible for the rose mutant phenotype in D. rerio. rose mutants have wild-type early larval pigment patterns, but fail to develop normal numbers of melanocytes and iridophores during pigment pattern metamorphosis and exhibit a disrupted pattern of these cells. We show that rose corresponds to endothelin receptor b1 (ednrb1), an orthologue of amniote Ednrb genes that have long been studied for their roles in neural crest and pigment cell development. Furthermore, we demonstrate that D. rerio ednrb1 is expressed both during pigment pattern metamorphosis and during embryogenesis, and cells of melanocyte, iridophore, and xanthophore lineages all express this gene. These analyses suggest a phylogenetic conservation of roles for Ednrb signaling in the development of amniote and teleost pigment cell precursors. As murine Ednrb is essential for the development of all neural crest derived melanocytes, and D. rerio ednrb1 is required only by a subset of adult melanocytes and iridophores, these analyses also reveal variation among vertebrates in the cellular requirements for Ednrb signaling, and suggest alternative models for the cellular and genetic bases of pigment pattern metamorphosis in D. rerio. (+info)
FTZ-F1alpha is expressed in the developing gonad of frogs.
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Fushi tarazu transcription factor-1 (FTZ-F1), a member of the nuclear hormone receptor superfamily, is a regulator for fushi tarazu gene expression in Drosophila. Its expression pattern during organogenesis in vertebrates, however, is not known yet. In this study, we cloned a frog FTZ-F1 homologue (rrFTZ-F1alpha) and analyzed its expression and localization during gonadal development of the frog Rana rugosa. Cloned rrFTZ-F1alpha cDNA encoded a protein of 501 amino acids including the regions I-III and FTZ-F1 box that are evolutionally conserved in the FTZ-F1 superfamily. rrFTZ-F1alpha shared high similarity at the amino acid level with mouse LRH-1 (76%), human FTF (92%), chicken OR2.0 (92%), Xenopus laevis FF1rA (94%) and zebrafish FF1A (82%). Northern blot analysis showed that the rrFTZ-F1alpha mRNA at a size of 7.4 kb was the most prominent in the testis among various tissues of adult frogs examined. The RT-PCR analysis revealed that the expression of rrFTZ-F1alpha was weak in the gonad of tadpoles before stage XVI, but it became stronger in the testis of froglets at stage XXV and much higher in the testis of frogs 2 months after metamorphosis. In addition, in situ hybridization analysis revealed that the rrFTZ-F1alpha gene was transcribed in germ cells except for sperm in the testis, and in oocytes at stage A in the ovary of frogs 2 months after metamorphosis. Together, these results suggest that FTZ-F1alpha probably plays an important role in differentiation of germ cells in the gonad of frogs in both sexes. (+info)
Incorporation of lipid into the epicuticle of Rhodnius (Hemiptera).
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The incorporation of lipid into both the outer and inner epicuticle during deposition is described. Waterproofing of the epicuticle by secretion of the wax layer, and sclerotization with or without melanization, are controlled from a distance by the epidermal cells by way of the pore canals. The pore canals gradually narrow as they approach the epicuticle. On reaching the inner epicuticle the canal ends in a conical projection from the apex of which a permeable lipophilic channel about 20-25 nm in diameter runs vertically to the apex of which a permeable lipophilic channel about 20-25 nm in diameter runs vertically to the surface. Shortly before ecdysis, silver-binding material (perhaps protein rich in tyrosine, or other precursors concerned in sclerotization) spreads radially from a point in the cuticular channels just below the outer epicuticle, and gradually impregnates the outer two thirds or more of the inner epicuticle. The precise pattern varies in different cuticular structures. Argentaffin materials (polyphenols) first appear in these same sites at the time of ecdysis and increase rapidly during the next 24 h. Lipid appears in the lumen of the distal parts of the pore canals (with a patchy distribution) shortly before ecdysis. When digestion and absorption of the old endocuticle are almost complete, minute lipid droplets appear on the surface of the epicuticle, apparently exuded from the epicuticular channels, and spread to make a uniform layer. When first formed this layer strains readily with Sudan B, but the lipid becomes incorporated in a delicate non-lipid silver-binding membrane (also exuded from the epicuticular channels) and hardens just before ecdysis, to form the so-called 'wax layer' which then no longer stains with Sudan B. Within half an hour after ecdysis the alcian blue-staining cement layer is poured out by the dermal glands, and forms a continuous but somewhat irregular covering over the 'wax layer'. Changes in the epicticle that accompany the repair of abrasions are described. (+info)
Dynamic expression of broad-complex isoforms mediates temporal control of an ecdysteroid target gene at the onset of Drosophila metamorphosis.
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Metamorphosis in Drosophila melanogaster is orchestrated by the steroid hormone ecdysone, which triggers a cascade of primary-response transcriptional regulators and secondary effector genes during the third larval instar and prepupal periods of development. The early ecdysone-response Broad-Complex (BR-C) gene, a key regulator of this cascade, is defined by three complementing functions (rbp, br, and 2Bc) and encodes several distinct zinc-finger-containing isoforms (Z1 to Z4). Using isoform-specific polyclonal antibodies we observe in the fat body a switch in BR-C isoform expression from the Z2 to the other three isoforms during the third instar. We show that the 2Bc(+) function that corresponds presumably to the Z3 isoform is required for the larval fat body-specific expression of a transgenic construct (AE) in which the lacZ gene is under the control of the ecdysone-regulated enhancer and minimal promoter of the fat body protein 1 (Fbp1) gene. Using hs(BR-C) transgenes, we demonstrate that overexpression of Z1, Z3, or Z4, but not Z2, is able to rescue AE activity with faithful tissue specificity in a BR-C null (npr1) genetic context, demonstrating a partial functional redundancy between Z1, Z3, and Z4 isoforms. We also show that continuous overexpression of Z2 during the third instar represses AE, while conversely, expression of Z3 earlier than its normal onset induces precocious expression of the construct. This finding establishes a tight correlation between the dynamic pattern of expression of the BR-C isoforms and their individual repressive or inductive roles in AE regulation. Altogether our results demonstrate that the balance between BR-C protein isoforms in the fat body mediates, in part, the precise timing of the ecdysone activation of the AE construct but does not modulate its tissue specificity. (+info)
Targeted chromatin binding and histone acetylation in vivo by thyroid hormone receptor during amphibian development.
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Amphibian metamorphosis is marked by dramatic, thyroid hormone (TH)-induced changes involving gene regulation by TH receptor (TR). It has been postulated that TR-mediated gene regulation involves chromatin remodeling. In the absence of ligand, TR can repress gene expression by recruiting a histone deacetylase complex, whereas liganded TR recruits a histone acetylase complex for gene activation. Earlier studies have led us to propose a dual function model for TR during development. In premetamorphic tadpoles, unliganded TR represses transcription involving histone deacetylation. During metamorphosis, endogenous TH allows TR to activate gene expression through histone acetylation. Here using chromatin immunoprecipitation assay, we directly demonstrate TR binding to TH response genes constitutively in vivo in premetamorphic tadpoles. We further show that TH treatment leads to histone deacetylase release from TH response gene promoters. Interestingly, in whole animals, changes in histone acetylation show little correlation with the expression of TH response genes. On the other hand, in the intestine and tail, where TH response genes are known to be up-regulated more dramatically by TH than in most other organs, we demonstrate that TH treatment induces gene activation and histone H4 acetylation. These data argue for a role of histone acetylation in transcriptional regulation by TRs during amphibian development in some tissues, whereas in others changes in histone acetylation levels may play no or only a minor role, supporting the existence of important alternative mechanisms in gene regulation by TR. (+info)