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Transcriptome analysis of zebrafish embryogenesis using microarrays.

Zebrafish (Danio rerio) is a well-recognized model for the study of vertebrate developmental genetics, yet at the same time little is known about the transcriptional events that underlie zebrafish embryogenesis. Here we have employed microarray analysis to study the temporal activity of developmentally regulated genes during zebrafish embryogenesis. Transcriptome analysis at 12 different embryonic time points covering five different developmental stages (maternal, blastula, gastrula, segmentation, and pharyngula) revealed a highly dynamic transcriptional profile. Hierarchical clustering, stage-specific clustering, and algorithms to detect onset and peak of gene expression revealed clearly demarcated transcript clusters with maximum gene activity at distinct developmental stages as well as co-regulated expression of gene groups involved in dedicated functions such as organogenesis. Our study also revealed a previously unidentified cohort of genes that are transcribed prior to the mid-blastula transition, a time point earlier than when the zygotic genome was traditionally thought to become active. Here we provide, for the first time to our knowledge, a comprehensive list of developmentally regulated zebrafish genes and their expression profiles during embryogenesis, including novel information on the temporal expression of several thousand previously uncharacterized genes. The expression data generated from this study are accessible to all interested scientists from our institute resource database (http://giscompute.gis.a-star.edu.sg/~govind/zebrafish/data_download.html).

Journal Article↗

A cis-acting element, T alpha-1, in the upstream region of rod alpha-transducin gene that binds a developmentally regulated retina-specific nuclear factor.

The G protein transducin (T) is an integral component of the signal transduction pathway in photoreceptors. We have identified a cis-acting element, T alpha-1, in the upstream region of the mouse rod alpha-T (Tr alpha) gene that may be important for tissue-specific expression. T alpha-1 binds a retina-specific nuclear factor of apparent molecular mass of 90 kDa. Binding to the T alpha-1 site is developmentally regulated and peaks between postnatal days 6 and 9. This corresponds to the time of rod photoreceptor maturation and the rise in Tr alpha gene expression. The sequence of T alpha-1 shows homology with RET-1, a cis-acting element in the proximal promoter of opsin gene that binds a distinct retina-specific factor. T alpha-1 and RET-1 sequences may have been derived from a prototype T alpha-1/RET-1 sequence, evolved to confer photoreceptor specificity on retina-specific genes.

Animals↗

Isolation of Aspergillus nidulans Mutants That Overcome brlA-Induced Growth Arrest

The Aspergillus nidulans brlA gene is a primary regulator of development-specific gene expression during conidiation. Forced activation of brlA in vegetative cells leads to inappropriate induction of conidiophore formation and causes growth to stop. In fact, when conidia containing a nutritionally inducible brlA gene fusion are placed on inducing medium, they fail to germinate. We used this phenotype to select 174 mutants that continue growing following such forced brlA activation. Forty-six of these mutants also produced abnormal developmental structures during air-induced conidiation as expected if the mutations resulted in an altered response to BrlA (designated sbr mutants for suppressors of brlA response). The predominant mutant class identified was defective in a known developmental regulatory gene, abaA. We also identified mutants with defects in the previously characterized early acting developmental regulatory genes flbB and flbD and in four previously undescribed loci designated sbrA-D. sbrA mutants represent the second largest group and are characterized by production of conidiophore stalks that lack a normal vesicle and form branching sterigmata that rarely make spores. Because abaA expression could not be detected in sbrA mutants following brlA activation we propose that sbrA functions as a developmental modifier, participating in brlA-dependent activation of other developmental regulators.

Journal Article↗

Developmental and stress regulation of gene expression for plastid and cytosolic isoprenoid pathways in pepper fruits.

Plant cells synthesize a myriad of isoprenoid compounds in different subcellular compartments, which include the plastid, the mitochondria, and the endoplasmic reticulum cytosol. To start the study of the regulation of these parallel pathways, we used pepper (Capsicum annuum) fruit as a model. Using different isoprenoid biosynthetic gene probes from cloned cDNAs, we showed that only genes encoding the plastid enzymes (geranylgeranyl pyrophosphate synthase, phytoene synthase, phytoene desaturase, and capasanthin-capsorubin synthase) are specifically triggered during the normal period of development, at the ripening stage. This pattern of expression can be mimicked and precociously induced by a simple wounding stress. Concerning the cytosol-located enzymes, we observed that the expression of the gene encoding farnesyl pyrophosphate synthase is constitutive, whereas that of farnesyl pyrophosphate cyclase (5-epi-aristolochene synthase) is undetectable during the normal development of the fruit. The expression of these later genes are, however, only selectively triggered after elicitor treatment. The results provide evidence for developmental control of isoprenoid biosynthesis occurring in plastids and that cytoplasmic isoprenoid biosynthesis is regulated, in part, by environmental signals.

Amino Acid Sequence↗

Six post-implantation lethal knockouts of genes for lipophilic MAPK pathway proteins are expressed in preimplantation mouse embryos and trophoblast stem cells.

Mitogen-activated protein kinase (MAPK) signaling pathways play an important role in controlling embryonic proliferation and differentiation. It has been demonstrated that sequential lipophilic signal transduction mediators that participate in the MAPK pathway are null post-implantation lethal. It is not clear why the lethality of these null mutants arises after implantation and not before. One hypothesis is that the gene product of these post-implantation lethal null mutants are not present before implantation in normal embryos and do not have function until after implantation. To test this hypothesis, we selected a set of lipophilic genes mediating MAPK signal transduction pathways whose null mutants result in early peri-implantation or placental lethality. These included FRS2alpha, GAB1, GRB2, SOS1, Raf-B, and Raf1. Products of these selected genes were detected and their locations and functions indicated by indirect immunocytochemistry and Western blotting for proteins and RT-polymerase chain reaction (PCR) for mRNA transcription. We report here that all six signal mediators are detected at the protein level in preimplantation mouse embryo, placental trophoblasts, and in cultured trophoblast stem cells (TSC). Proteins are all detected in E3.5 embryos at a time when the first known mitogenic intercellular communication has been documented. mRNA transcripts of two post-implantation null mutant genes are expressed in mouse preimplantation embryos and unfertilized eggs. These mRNA transcripts were detected as maternal mRNA in unfertilized eggs that could delay the lethality of null mutants. All of the proteins were detected in the cytoplasm or in the cell membrane. This study of spatial and temporal expression revealed that all of these six null mutants post-implantation genes in MAPK pathway are expressed and, where tested, phosphorylated/activated proteins are detected in the blastocyst. Studies on RNA expression using RT-PCR suggest that maternal RNA could play an important role in delaying the presence of the lethal phenotype of null mutations.

Adaptor Proteins, Signal Transducing↗

Mutations in the clk-1 gene of Caenorhabditis elegans affect developmental and behavioral timing.

We have identified three allelic, maternal-effect mutations that affect developmental and behavioral timing in Caenorhabditis elegans. They result in a mean lengthening of embryonic and postembryonic development, the cell cycle period and life span, as well as the periods of the defecation, swimming and pumping cycles. These mutants also display a number of additional phenotypes related to timing. For example, the variability in the length of embryonic development is several times larger in the mutants than in the wild type, resulting in the occasional production of mutant embryos developing more rapidly than the most rapidly developing wild-type embryos. In addition, the duration of embryonic development of the mutants, but not of the wild type, depends on the temperature at which their parents were raised. Finally, individual variations in the severity of distinct mutant phenotypes are correlated in a counterintuitive way. For example, the animals with the shortest embryonic development have the longest defecation cycle and those with the longest embryonic development have the shortest defecation cycle. Most of the features affected by these mutations are believed to be controlled by biological clocks, and we therefore call the gene defined by these mutations clk-1, for "abnormal function of biological clocks."

Alleles↗

Altered mRNA expression patterns in bovine blastocysts after fertilisation in vitro using flow-cytometrically sex-sorted sperm.

Sperm-sexing has been used to produce embryos and offspring of a pre-determined sex in a number of species. However, the fertility of sex-sorted sperm is reduced and the full effects of sperm-sexing remain to be elucidated. The purpose of the present study was to investigate the potential effects of sex-sorted sperm on mRNA expression patterns of developmentally important genes employing in vitro produced bovine embryos. Bovine embryos were produced in vitro with unsorted and sex-sorted sperm and mRNA expression patterns were determined for glucose-3 transporter (Glut-3), glucose-6-phosphate dehydrogenase (G6PD), X-inactive specific transcript (X-ist) and Heat shock protein 70.1 (Hsp) using semi-quantitative endpoint reverse transcriptase-PCR in male and female, day-7 and 8 embryos. The relative abundance (RA) of Glut-3 was higher for day-7 male than female embryos, and day-7 embryos derived from unsorted compared with sex-sorted sperm. The RA of G6PD was higher for embryos derived from unsorted than sex-sorted sperm, and for day-8 female compared with male embryos. The RA of Xist was higher for female than male embryos, and for day-7 female embryos derived from unsorted than sex-sorted sperm. Hsp RA was higher for female compared with male embryos, was similar for day-7 and 8 embryos, and unsorted and sex-sorted sperm derived embryos. These results demonstrate differential expression of developmentally important genes between male and female embryos, and embryos derived from unsorted and sex-sorted sperm.

Animals↗

Developmental control of lymphokine gene expression in fetal thymocytes during T-cell ontogeny.

We have used the technique of in situ hybridization to investigate the expression of lymphokine genes by immature thymocytes during intrathymic development. In 13-day fetal thymocytes a population of cells constitutively produces low levels of interleukin 2 (IL-2) and interleukin 4 (IL-4) mRNAs. A second phase of lymphokine gene expression occurs in the majority of 15-day thymocytes, and a population of cells constitutively produces both IL-2 and IL-4 mRNAs. Thymocytes at 14 days of gestation and after 16 days up until birth do not express detectable lymphokine mRNA. By contrast, the population of IL-2 receptor mRNA-producing thymocytes increases progressively up to 15 days of gestation, and expression thereafter decreases up to birth. In addition, thymocytes expressing interferon gamma mRNA were not present until just prior to birth. Our findings indicate developmental control of lymphokine and lymphokine receptor gene expression in fetal thymocytes during ontogeny.

Animals↗

Carotenoid biosynthesis during tomato fruit development: regulatory role of 1-deoxy-D-xylulose 5-phosphate synthase.

Plant isoprenoids represent a heterogeneous group of compounds which play essential roles not only in growth and development, but also in the interaction of plants with their environment. Higher plants contain two pathways for the biosynthesis of isoprenoids: the mevalonate pathway, located in the cytosol/endoplasmic reticulum, and the recently discovered mevalonate-independent pathway (Rohmer pathway), located in the plastids. In order to evaluate the function of the Rohmer pathway in the regulation of the synthesis of plastidial isoprenoids, we have isolated a tomato cDNA encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS), the first enzyme of the pathway. We demonstrate in vivo activity and plastid targeting of plant DXS. Expression analysis of the tomato DXS gene indicates developmental and organ-specific regulation of mRNA accumulation and a strong correlation with carotenoid synthesis during fruit development. 1-Deoxy-D-xylulose feeding experiments, together with expression analysis of DXS and PSY1 (encoding the fruit-specific isoform of phytoene synthase) in wild-type and yellow flesh mutant fruits, indicate that DXS catalyses the first potentially regulatory step in carotenoid biosynthesis during early fruit ripening. Our results change the current view that PSY1 is the only regulatory enzyme in tomato fruit carotenogenesis, and point towards a coordinated role of both DXS and PSY1 in the control of fruit carotenoid synthesis.

Alkyl and Aryl Transferases↗

Expression of the granule-bound starch synthase I (Waxy) gene from snapdragon is developmentally and circadian clock regulated

The granule-bound starch synthase I (GBSSI or waxy) enzyme catalyzes one of the enzymatic steps of starch synthesis. This enzyme is responsible for the synthesis of amylose and is also involved in building the final structure of amylopectin. Little is known about expression of GBSSI genes in tissues other than storage organs, such as seeds, endosperm, and tuber. We have isolated a gene encoding the GBSSI from snapdragon (Antirrhinum majus). This gene is present as a single copy in the snapdragon genome. There is a precise spatial and developmental regulation of its expression in flowers. GBSSI expression was observed in all floral whorls at early developmental stages, but it was restricted to carpel before anthesis. These results give new insights into the role of starch in later reproductive events such as seed filling. In leaves the mRNA level of GBSSI is regulated by an endogenous circadian clock, indicating that the transition from day to night may be accompanied by abolition of expression of starch synthesis genes. This mechanism does not operate in sink tissues such as roots when grown in the dark.

Journal Article↗

P25 gene regulation in Bombyx mori silk gland: two promoter-binding factors have distinct tissue and developmental specificities.

The gene encoding the silk protein P25 is expressed in the posterior silk gland of Bombyx mori with strict territorial and developmental specificities. The cis-acting regulatory elements previously located within the 441-bp 5' proximal sequence of the gene were examined for protein-binding capacities. We identified two factors, BMFA and SGFB, that lead to prominent band shifts and the target sites for which are included in a region homologous to the fibroin gene enhancer sequence. Analysis of the tissue-specific incidence of both factors showed that BMFA is ubiquitous, whereas SGFB is restricted to the silk gland cells. However, SGFB was found in both posterior and middle silk gland cells and therefore likely directs organ-specific, but not territory-specific, expression. Developmental studies throughout the fourth larval molt, at which the P25 gene status changes from derepressed to repressed, revealed that BMFA is reversibly modified at the transition from intermolt to molt. Indeed, the preexisting BMFA is replaced by a structurally related factor, BMFA', during the 2 h following head capsule apolysis. The exact temporal coincidence of this conversion with the onset of gene repression suggests that BMFA' is involved in transcription inactivation and likely results from a transduction process initiated by the hormonal change at molting.

Animals↗

Analysis and expression of a cloned pre-T cell receptor gene.

The T cell antigen receptor (TCR) beta chain regulates early T cell development in the absence of the TCR alpha chain. The developmentally controlled gene described here encodes the pre-TCR alpha (pT alpha) chain, which covalently associates with TCR beta and with the CD3 proteins forms a pre-TCR complex that transduces signals in immature thymocytes. Unlike the lambda 5 pre-B cell receptor protein, the pT alpha chain is a type I transmembrane protein whose cytoplasmic tail contains two potential phosphorylation sites and a Src homology 3 (SH3)-domain binding sequence. Pre-TCR alpha transfection experiments indicated that surface expression of the pre-TCR is controlled by additional developmentally regulated proteins. Identification of the pT alpha gene represents an essential step in the structure-function analysis of the pre-TCR complex.

Amino Acid Sequence↗

Separate elements cause lineage restriction and specify boundaries of Hox-1.1 expression.

The Hox genes are a class of putative developmental control genes that are thought to be involved in the specification of positional identity along the anteroposterior axis of the vertebrate embryo. It is apparent from their expression pattern that their regulation is dependent upon positional information. In a previous analysis of the Hox-1.1 promoter in transgenic mice, we identified sequences that were sufficient to establish transgene expression in a specific region of the embryo. The construct used, however, did not contain enough regulatory sequences to reproduce all aspects of Hox-1.1 expression. In particular, neither a posterior boundary nor a restriction of expression to prevertebrae was achieved. Here we show correct regulation by Hox-1.1 sequences in transgenic mice and identify the elements responsible for different levels of control. Concomitant with the subdivision of mesodermal cells into different lineages during gastrulation and organogenesis, Hox-1.1 expression is restricted to successively smaller sets of cells. Distinct elements are required at different stages of development to execute this developmental programme. One position-responsive element (130 bp nontranslated leader) was shown to be crucial for the restriction of expression not only along the anteroposterior axis of the embryo, setting the posterior border, but also along the dorsoventral axis of the neural tube and to the lineage giving rise to the prevertebrae. Thus, Hox-1.1 expression is established in a specific region of the embryo and in a specific lineage of the mesoderm by restricting the activity of the promoter by the combined effect of several regulatory elements.

Animals↗

A developmentally regulated cysteine protease gene family in Haemonchus contortus.

The nucleotide sequence of a gene encoding a 35-kDa thiol protease of the parasitic nematode Haemonchus contortus has been determined. The gene, designated AC-2, shares 97% nucleotide sequence identity and 98% amino acid identity with previously characterized AC-1 cDNAs encoding the thiol protease. The AC-2 gene spans 8 kb and appears to contain 11 introns, ranging in size from 57 bp to over 5.2 kb. One of the introns interrupts the proposed active site region that is conserved between the H. contortus protease and the related thiol proteases cathepsin B and papain. Southern blot hybridization experiments indicate that the protease is encoded by a small gene family in H. contortus. Rabbit antisera prepared against the recombinant protein react on Western blots with 35 and 37-kDa proteins of adult worms. These proteins were not detectable by Western blot analysis in three larval parasitic developmental stages of H. contortus. Northern blot hybridizations indicate that mRNA transcripts for the gene family are present at low levels in a mixed population of third- and fourth-stage larvae but highly abundant in adult worms. Expression of the protease correlates with blood-feeding and suggests a role for the protease in blood digestion.

Amino Acid Sequence↗

Dysregulation of gene expression in mouse trisomy 16, an animal model of Down syndrome.

In humans, trisomy 21 results in a specific phenotype known as Down syndrome (DS). The mechanism by which an extra copy of normal genes leads to the DS phenotype is unknown. Most studies in DS and other aneuploid organisms have shown that gene dose is proportional to gene expression. To date, most genes examined have encoded either metabolic enzymes or constitutively expressed products. In the trisomy 16 mouse, an animal model of DS, we found marked dysregulation of two developmentally regulated genes, App and Prn-p. Dysregulation varied from tissue to tissue and during development in the same tissue. We conclude that abnormal phenotypes seen in aneuploid conditions may result in part from disordered expression of developmentally regulated genes.

Aneuploidy↗

The glyceraldehyde-3-phosphate dehydrogenase homologue is differentially regulated in phases of Paracoccidioides brasiliensis: molecular and phylogenetic analysis.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays important roles in various cellular processes. Here we report the sequence and analysis of a novel developmentally regulated gene and cDNA (Pbgadph), encoding a GAPDH homologue (PbGAPDH), of the pathogenic dimorphic fungus Paracoccidioides brasiliensis. We have analyzed the protein, the cDNA and genomic sequences to provide insights into the structure, function, and potential regulation of PbGAPDH. That Pbgapdh encodes PbGAPDH was demonstrated by micro-sequencing of the native protein homologue isolated from the fungus proteome. The deduced amino acid sequence of Pbgapdh showed identity to those of from other species (88-76%). Phylogenetic analysis indicated that GAPDH could be useful for the determination of evolutionary relationships. Expression of the Pbgapdh gene and the cognate protein were developmentally regulated in phases of P. brasiliensis, with a higher expression in the yeast parasitic phase and was induced during the transition from mycelium to yeast and decreased during the reverse process, transition from yeast to mycelium.

Amino Acid Sequence↗

Expression of the preoptic regulatory factor-1 and -2 genes in rat testis. Developmental and hormonal regulation.

Hormone-responsive peptides play a vital role in development and regulation of testicular function. The preoptic regulatory factors, porf-1 and porf-2, were originally discovered in the rat brain, but are also expressed in the rat and human testis. In the brain expression is age-related, hormone-responsive, region- specific, and gender-related, suggesting that porf-1 and porf-2 are involved in gender-specific brain development and function. Tissue-specific porf-1 and porf-2 mRNAs are also found in the testis and hypophysectomy may alter testicular porf-2 expression. It was thus of interest to further examine porf-1 and porf-2 expression in the testis to evaluate their potential as hormone-responsive peptides that regulate testicular development and function. Testicular expression of both porf-1 and -2 was analyzed as a function of maturational stage, aging and hypophysectomy by the solution hybridization/nuclease protection assay, and cellular location determined by in situ hybridization histochemistry. Expression was quantitatively compared in normal male rats at 15, 30 and 60 d (n = 4) and at 2, 6, 12, and 24 mo of age (n = 5). During development porf-1 is expressed at a constant level at 15, 30 and 60 d, then declines significantly with advancing age; levels at 24 mo are only 20% of those seen at 2 mo (p < 0.05). In contrast, porf-2 expression is highest at 15 d of age and steadily declines at 30 and 60 d, plateaus in the mature adult (6 and 12 mo), then exhibits an additional significant decline in the aged 24 mo animals (6 vs 24 mo, p < 0.05). Hypophysectomy of young adult rats at day 42 results in increased testicular expression 12 d later of both porf-1 (p < 0.05) and porf-2(p < 0.005) compared to intact 54-d-old rats (n = 5). In situ hybridization histochemistry confirms that both porf-1 and porf-2 are expressed in the mature testis at 60 d of age. Porf-2 mRNA is localized to immature germ cells including spermatogonia and primary spermatocytes. Porf-1 mRNA is associated with mature sperm and at low levels in the Sertoli cell cytoplasm surrounding spermatocytes. These data suggest that porf-2 is a pituitary hormone-responsive factor in the developing testis and that both porf-1 and porf-2 have cell-type specific functions in the germ cell compartment of the mature testis

Aging↗