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PubMed2006

Multiple layers of temporal and spatial control regulate accumulation of the fruiting body-specific protein APP in Sordaria macrospora and Neurospora crassa.

During fungal fruiting body development, specialized cell types differentiate from vegetative mycelium. We have isolated a protein from the ascomycete Sordaria macrospora that is not present during vegetative growth but accumulates in perithecia. The protein was sequenced by mass spectrometry and the corresponding gene was termed app (abundant perithecial protein). app transcript occurs only after the onset of sexual development; however, the formation of ascospores is not a prerequisite for APP accumulation. The transcript of the Neurospora crassa ortholog is present prior to fertilization, but the protein accumulates only after fertilization. In crosses of N. crassa Deltaapp strains with the wild type, APP accumulates when the wild type serves as female parent, but not in the reciprocal cross; thus, the presence of a functional female app allele is necessary and sufficient for APP accumulation. These findings highlight multiple layers of temporal and spatial control of gene expression during fungal development.

Alleles↗
PubMed2004

Spatial complexity of mechanisms controlling a bacterial cell cycle.

Cell cycle progression in Caulobacter is governed by a multilayered regulatory network linking chromosome replication with polar morphogenesis and cell division. Temporal and spatial regulation have emerged as the central themes, with the abundance, activity and subcellular location of key structural and regulatory proteins changing over the course of the cell cycle. An additional layer of complexity was recently uncovered, showing that each segment of the chromosome is located at a specific cellular position both during and after the completion of DNA replication, raising the possibility that this positioning contributes to temporal and spatial control of gene expression.

Bacterial Proteins↗
PubMed2004

Requirement for fibroblast growth factor 10 or fibroblast growth factor receptor 2-IIIb signaling for cecal development in mouse.

Epithelial-mesenchymal interactions are critical for the formation of gastrointestinal buds such as the cecum from the midgut, but the mechanisms regulating this process remain unclear. To investigate this problem, we have studied the temporal and spatial expression of key genes known to orchestrate branching morphogenesis. At E10.5, Fibroblast growth factor 10 (Fgf10) is specifically expressed in the mesenchyme above the future cecal epithelial bud, whereas Fgfr2b is found throughout the gut epithelium. From E11.5 onwards, Fgf10 expression is found throughout the cecum mesenchyme. Other relevant signaling molecules such as Sonic hedgehog, Wnt2b, and Tbx4 transcripts are found throughout the gut epithelium, including the cecum. Epithelial expression is also seen for Sprouty2, but only from E14.5 onwards. By contrast, Bone morphogenetic 4 (Bmp4) and Pitx2 are specifically expressed in the mesenchyme of the cecal bud at E11.5. Abrogation of either Fgf10 or Fgfr2b leads to similar phenotypes characterized by an arrest of epithelial invasion into the cecal mesenchymal tissue. However, a bud of undifferentiated cecal mesenchymal tissue is maintained throughout development. Our results further indicate that mesenchymal FGF10 acts mostly through the epithelial FGFR2b receptor; thereby triggering invasion of the midgut epithelium into the adjacent mesenchyme via an increased rate of epithelial proliferation at the tip of the cecum. Thus, FGF10 signaling via FGFR2b appears to be critical in the extension of the epithelium into the mesenchyme during cecal development.

Actins↗
PubMed2004

Identification and analysis of genes from the mouse otic vesicle and their association with developmental subprocesses through in situ hybridization.

The otic vesicle (otocyst) occupies a pivotal position in inner ear development, bridging the gap between otic placode determination, and morphogenesis of vestibular and auditory compartments. The molecular mechanisms underlying the progressive subdivision of the developing inner ear into different compartments, and the molecular control and execution of the different developmental processes involved, are largely unknown. Since relatively few genes have been implicated in these processes, we have undertaken this study to identify genes involved in these early embryonic stages. We have used cDNA subtractions of mouse otic vesicle against adult liver cDNA, and describe a set of 280 candidate genes. We have also performed otic vesicle RNA hybridizations against DNA chips to not only confirm the efficacy of the library approach, but also to investigate the utility of DNA array alternatives. To begin to dissect potential developmental roles, we investigated the spatial pattern of gene expression for a selected set of 80 genes in developing mouse embryos at mid-gestation by whole-mount in situ hybridization. These data illustrate the compartmentalisation of gene expression in the otic vesicle for the majority of genes tested, and furthermore, implicate many of the genes tested with distinct developmental subprocesses.

Animals↗
PubMed2005

TAF4b, a TBP associated factor, is required for oocyte development and function.

Development of a fertilizable oocyte is a complex process that relies on the precise temporal and spatial expression of specific genes in germ cells and in surrounding somatic cells. Since female mice null for Taf4b, a TBP associated factor, are sterile, we sought to determine when during follicular development this phenotype was first observed. At postnatal day 3, ovaries of Taf4b null females contained fewer (P < 0.01) oocytes than ovaries of wild type and heterozygous Taf4b mice. However, expression of only one somatic cell marker Foxl2 was reduced in ovaries at day 15. Despite the reduced number of follicles, many proceed to the antral stage, multiple genes associated with granulosa cell differentiation and oocyte maturation were expressed in a normal pattern, and immature Taf4b null females could be hormonally primed to ovulate and mate. However, the ovulated cumulus oocyte complexes from the Taf4b null mice had fewer (P < 0.01) cumulus cells, and the oocytes were functionally abnormal. GVBD and polar body extrusion were reduced significantly (P < 0.01). The few oocytes that were fertilized failed to progress beyond the two-cell stage of development. Thus, infertility in Taf4b null female mice is associated with defects in early follicle formation, oocyte maturation, and zygotic cleavage following ovulation and fertilization.

Animals↗
PubMed2006

Delta and Hairy establish a periodic prepattern that positions sensory bristles in Drosophila legs.

In vertebrates and invertebrates, spatially defined proneural gene expression is an early and essential event in neuronal patterning. In this study, we investigate the mechanisms involved in establishing proneural gene expression in the primordia of a group of small mechanosensory bristles (microchaetae), which on the legs of the Drosophila adult are arranged in a series of longitudinal rows along the leg circumference. In prepupal legs, the proneural gene achaete (ac) is expressed in longitudinal stripes, which comprise the leg microchaete primordia. We have previously shown that periodic ac expression is partially established by the prepattern gene, hairy, which represses ac expression in four of eight interstripe domains. Here, we identify Delta (Dl), which encodes a Notch (N) ligand, as a second leg prepattern gene. We show that Hairy and Dl function concertedly and nonredundantly to define periodic ac expression. We also explore the regulation of periodic hairy expression. In prior studies, we have found that expression of two hairy stripes along the D/V axis is induced in response to the Hedgehog (Hh), Decapentaplegic (Dpp) and Wingless (Wg) morphogens. Here, we show that expression of two other hairy stripes along the orthogonal A/P axis is established through a distinct mechanism which involves uniform activation combined with repressive influences from Dpp and Wg. Our findings allow us to formulate a general model for generation of periodic pattern in the adult leg. This process involves broad and late activation of ac expression combined with refinement in response to a prepattern of repression, established by Hairy and Dl, which unfolds progressively during larval and early prepupal stages.

Animals↗
PubMed2003

Mechanisms of insulator function in gene regulation and genomic imprinting.

Correct temporal and spatial patterns of gene expression are required to establish unique cell types. Several levels of genome organization are involved in achieving this intricate regulatory feat. Insulators are elements that modulate interactions between other cis-acting sequences and separate chromatin domains with distinct condensation states. Thus, they are proposed to play an important role in the partitioning of the genome into discrete realms of expression. This review focuses on the roles that insulators have in vivo and reviews models of insulator mechanisms in the light of current understanding of gene regulation.

Animals↗
PubMed2002

How to pattern an epithelium: lessons from achaete-scute regulation on the notum of Drosophila.

The notum of Drosophila is a good model system for the study of two-dimensional pattern formation. Attention has mainly focused on the regulation of the spatial expression of the genes of the achaete-scute complex (AS-C) that results in a stereotyped bristle pattern. Expression of AS-C genes has traditionally been viewed as a consequence of the activity of a group of factors that constitute a prepattern [Stern, 1954. Am. Sci. 42, 213]. The prepattern is thought to be composed of a mosaic of transcription factors that act in combination, through discrete cis-regulatory sequences, to activate expression of genes of the AS-C in small clusters of cells at the sites of each future bristle. Recent results challenge this view and suggest a hierarchy of activity amongst prepattern genes. It is suggested that in the medial notum, the selector-like gene pannier regulates the entire pattern, and is the only factor to directly activate AS-C genes. Other factors may play subsidiary roles. On the lateral notum genes of the iroquois complex appear to regulate the lateral pattern. Regulation of pannier and iroquois depends upon the signalling molecule Decapentaplegic. The majority of genes are expressed in either longitudinal or transverse domains on the notum and we discuss the possibility that pattern formation may rely on these two axial coordinates. We also discuss preliminary results suggesting that prepattern factors also regulate genes required for other, little studied, aspects of notal morphology, such as the muscle attachment sites and pigment distribution. Thus there may be a common prepattern for the entire structure.

Animals↗
PubMed2001

Ci-IPF1, the pancreatic homeodomain transcription factor, is expressed in neural cells of Ciona intestinalis larva.

We describe the cloning and the expression pattern of insulin promoter factor 1 in the ascidian Ciona intestinalis (Ci-IPF1). Northern blot analysis showed that transcripts appeared at the late tailbud stage and increased at the larval stage. We have raised a specific antibody against the Ci-IPF1-GST fusion protein to determine the spatial expression of this gene. The protein is immunodetected at the larval stage in the sensory vesicle, in the visceral ganglion and in the mesenchymal cells. Our results support the hypothesis that IPF1/IDX1 might have extrapancreatic functions during animal development, particularly in neural cells.

Amino Acid Sequence↗
PubMed1991

The initiation of pair-rule stripes in the Drosophila blastoderm.

The interactions between the products of gap genes and pair-rule promoters results in the single most dramatic increase in the spatial complexity of gene expression during the segmentation process. We attempt to relate recent findings on the regulation of striped patterns of gene expression in the early Drosophila embryo to general strategies of gene expression and development employed by higher organisms.

Animals↗
PubMed2001

A Rho-dependent signaling pathway operating through myosin localizes beta-actin mRNA in fibroblasts.

BACKGROUND: The sorting of mRNA is a determinant of cell asymmetry. The cellular signals that direct specific RNA sequences to a particular cellular compartment are unknown. In fibroblasts, beta-actin mRNA has been shown to be localized toward the leading edge, where it plays a role in cell motility and asymmetry. RESULTS: We demonstrate that a signaling pathway initiated by extracellular receptors acting through Rho GTPase and Rho-kinase regulates this spatial aspect of gene expression in fibroblasts by localizing beta-actin mRNA via actomyosin interactions. Consistent with the role of Rho as an activator of myosin, we found that inhibition of myosin ATPase, myosin light chain kinase (MLCK), and the knockout of myosin II-B in mouse embryonic fibroblasts all inhibited beta-actin mRNA from localizing in response to growth factors. CONCLUSIONS: We therefore conclude that the sorting of beta-actin mRNA in fibroblasts requires a Rho mediated pathway operating through a myosin II-B-dependent step and postulate that polarized actin bundles direct the mRNA to the leading edge of the cell.

Actins↗
PubMed2001

[Development of the central nervous system in mammals].

In humans, the nervous system is induced during the third gestational week by molecular signals coming from the mesoderm, which modulate the temporal and spatial expression of specific genes in the cells of the dorsal ectoderm. The induced neural plate closes to form the neural tube where the cells actively proliferate in the germinal zone. The neuroblasts which have completed their last division migrate along the fibers of the radial glia to which they adhere, and this movement is essential to establish the normal cerebral organization. The regional identity of the developing brain is governed by the expression of homeobox genes, and the main central structures are clearly delineated by the end of the fifth week. The cerebral cortex begins to form on the seventh week, and the early specification of the cortical areas, which is under genetic control, would be modulated later on by environmental influences. When the neurons have reached their final position, they extend an axon, using surface molecules or diffusible molecules present along its pathway as cues to reach the appropriate target and form a synapse, and this process is a critical step for the establishment of neuronal relationships. The maturation and stabilization of neural networks is characterized by the apoptotic death of roughly 50% of the neurons, due to insufficient neurotrophic support, and by the remodeling of the initial synaptic connections in the surviving neurons. These regressive events occur late in development and depend on both the interactions with the environment and the resulting neuronal activity.

Animals↗
PubMed1998

Software implementation of statistical methods for the analysis of structure and patterns in neuroanatomical objects.

Neuroanatomical research has greatly benefited from the availability of a large number of cell-specific and region-specific molecular markers. In fact, the analysis of spatial patterns of gene expression in individual cells or patterns within cell populations often provides an inroad into understanding the functional significance of distinct structures. However, it can be difficult to discern whether the arrangement of different morphologically or biochemically defined structures represents a defined pattern. To address this issue, we adapted a series of established statistical procedures for the analysis of uni- and bivariate point patterns in histological specimens. We implemented these statistical procedures in an easy-to-use computer program. The methods are scale independent and easy to expand for various applications. The utility of this approach is demonstrated with examples from tissue sections and cultured cells at the light and electron microscopical levels.

Actins↗
PubMed1988

Transgenes as probes for active chromosomal domains in mouse development.

Embryonic development entails a well defined temporal and spatial programme of gene expression, which may be influenced by active chromosomal domains. These chromosomal domains can be detected using transgenes which integrate randomly throughout the genome, as their expression can be affected by chromosomal position. Position effects are probably exerted most strongly on transgenes that do not contain strong promoters, enhancers or other modulating sequences. Here we have systematically explored position effects using a transgene with the weak herpes-simplex-virus thymidine-kinase promoter, linked to the readily visualized lacZ indicator gene (HSV-TK-lacZ). Each transgenic fetus with detectable expression displayed a unique lacZ staining pattern. Thus expression of this construct is apparently dictated entirely by its chromosomal position, without any construct specificity. Furthermore the transgene is faithfully transmitted to subsequent generations, allowing for systematic mapping of changes in expression during development and in adult life. These results demonstrate that transgenes can indeed be powerful tools to probe the genome for active chromosomal regions, with the potential for identifying endogenous genes involved in organogenesis and pattern formation.

Animals↗
PubMed2000

Control of neurulation by the nucleosome assembly protein-1-like 2.

Neurulation is a complex process of histogenesis involving the precise temporal and spatial organization of gene expression. Genes influencing neurulation include proneural genes determining primary cell fate, neurogenic genes involved in lateral inhibition pathways and genes controlling the frequency of mitotic events. This is reflected in the aetiology and genetics of human and mouse neural tube defects, which are of both multifactorial and multigenic origin. The X-linked gene Nap1l2, specifically expressed in neurons, encodes a protein that is highly similar to the nucleosome assembly (NAP) and SET proteins. We inactivated Nap1l2 in mice by gene targeting, leading to embryonic lethality from mid-gestation onwards. Surviving mutant chimaeric embryos showed extensive surface ectoderm defects as well as the presence of open neural tubes and exposed brains similar to those observed in human spina bifida and anencephaly. These defects correlated with an overproduction of neuronal precursor cells. Protein expression studies showed that the Nap1l2 protein binds to condensing chromatin during S phase and in apoptotic cells, but remained cytoplasmic during G1 phase. Nap1l2 therefore likely represents a class of tissue-specific factors interacting with chromatin to regulate neuronal cell proliferation.

Animals↗
PubMed2003

Regulation of endospore formation in Bacillus subtilis.

Spore formation in bacteria poses a number of biological problems of fundamental significance. Asymmetric cell division at the onset of sporulation is a powerful model for studying basic cell-cycle problems, including chromosome segregation and septum formation. Sporulation is one of the best understood examples of cellular development and differentiation. Fascinating problems posed by sporulation include the temporal and spatial control of gene expression, intercellular communication and various aspects of cell morphogenesis.

Bacillus subtilis↗
PubMed2026

Mechanisms and functional implications of long-range enhancer-dependent gene regulation.

Metazoan development relies on the coordinated establishment of diverse gene regulatory programs that drive the formation of specific cell types, tissues and organs. The temporal and spatial control of gene expression is achieved through the concerted activity of multiple classes of cis-regulatory elements encoded in the genome. Among these, enhancers enable the establishment of specific and precise gene expression patterns and control gene expression over long linear distances, a property often referred to as distance-independent regulatory activity. However, enhancer activity is, in fact, inversely correlated with linear genomic distance, and target gene expression and transcriptional precision decrease with increasing enhancer-promoter linear distances. Here, we highlight emerging insights into multiple mechanisms that enable enhancers to precisely and robustly activate gene expression across large genomic distances. Finally, we provide a more speculative perspective on the potential advantages that long-range regulation might confer during the establishment of developmental gene expression programs.

Enhancer Elements, Genetic↗
PubMed2002

The olfactory bulb as an independent developmental domain.

The olfactory system is a good model to study the mechanisms underlying guidance of growing axons to their appropriate targets. The formation of the olfactory bulb involves differentiation of several populations of cells and the initiation of the central projections, all under the temporal and spatial patterns of gene expression. Moreover, the nature of interactions between the olfactory epithelium, olfactory bulb and olfactory cortex at early developmental stages is currently of great interest. To explore these questions more fully, the present review aims to correlate recent data from different developmental studies, to gain insight into the mechanisms involved in the specification and development of the olfactory system. From our studies in the pax6 mutant mice (Sey(Neu)/Sey(Neu)), it was concluded that the initial establishment of the olfactory bulb central projections is able to proceed independently of the olfactory sensory axons from the olfactory epithelium. The challenge that now remains is to consider the validity of the olfactory bulb as an independent development domain. In the course of evaluating these ideas, we will review the orchestra of molecular cues involved in the formation of the projection from the OB to the olfactory cortex.

Animals↗