bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative autoregulation by Ultrabithorax controls the level and pattern of its expression
Authors: Irvine Kenneth D. , Botas Juan , Jha Sanjaya , Mann Richard S. , Hogness David S. 
Published: April 2021

ABSTRACT
The Drosophila homeotic gene Ultrabithorax (Ubx) encodes transcriptional regulatory proteins (UBX) that specify thoracic and abdominal segmental identities. Ubx autoregulation was examined by manipulating UBX levels, both genetically and with an inducible transgene, and monitoring the effect of these manipulations on the expression of Ubx and Ubx-lacZ reporter genes. Positive autoregulation by Ubx is restricted to the visceral meso-derm, while in other tissues Ubx negatively autoregu-lates. In some cases, negative autoregulation stabilizes UBX levels, while in others it modulates the spatial and temporal patterns of UBX expression. This modulation of UBX expression may enable Ubx to specify distinct identities in different segments. The upstream control region of Ubx contains multiple autoregulatory elements for both positive and negative autoregulation.
Perpendicular contact guidance of CNS neuroblasts on artificial microstructures
Authors: Nagata Isao , Kawana Akio , Nakatsuji Norio 
Published: April 2021

ABSTRACT
Rodent CNS neuroblasts show parallel and perpendic-ular contact guidance behaviors on aligned neurite bun-dles in microexplant cultures (Nakatsuji, N. and Nagata, I. (1989) Development, 106, 441-447; N. I. and N. N. (1991) ibid., 112, 581-590). To test the hypothesis that the physical surface structure of the neurite bundle causes the perpendicular contact guidance, we cultured dissociated neuroblasts on quartz plates on which grat-ing-like microstructures were fabricated by lithographic techniques. Various types of CNS neuroblasts, but not PNS neurons, oriented their processes and migrated both perpendicular and parallel to the axis of the microstructure. Perpendicular orientation was fre-quently observed when the microstructured grooves had depths between 0.3 m and 0.8 m and a width of 1 m, which roughly mimics a tightly aligned neurite bundle. Thus, CNS neuroblasts have the ability to extend their processes and migrate perpendicular to aligned surface microstructures.
Origins, migration and differentiation of glial cells in the insect enteric nervous system from a discrete set of glial precursors
Authors: Copenhaver Philip F. 
Published: April 2021

ABSTRACT
The enteric nervous system (ENS) of the moth, Mand - uca sexta, consists of two primary cellular domains and their associated nerves. The neurons of the anterior domain occupy two small peripheral ganglia (the frontal and hypocerebral ganglia), while a second population of neurons occupies a branching nerve plexus (the enteric plexus) that spans the foregut-midgut boundary. Previ-ously, we have shown these two regions arise by sepa-rate programs of neurogenesis: cells that form the ante-rior enteric ganglia are generated from three discrete proliferative zones that differentiate within the foregut epithelium. In contrast, the cells of the enteric plexus (the EP cells) emerge from a neurogenic placode within the posterior lip of the foregut. Both sets of neurons sub-sequently undergo an extended period of migration and reorganization to achieve their mature distributions. We now show that prior to the completion of neurogenesis, an additional class of precursor cells is generated from the three proliferative zones of the foregut. Coincident with the onset of neuronal migration, this precursor class enters a phase of enhanced mitotic activity, giving rise to a population of cells that continue to divide as the ENS matures. Using clonal analyses of individual precursors, we demonstrate that the progeny of these cells become distributed along the same pathways taken by the migratory neurons; subsequently, they contribute to an ensheathing layer around the branches of the enteric plexus and the enteric ganglia. We conclude that this additional precursor class, which shares a common developmental origin with the enteric neurons, gives rise to a distinct population of peripheral glial cells. More-over, the distribution of enteric glial cells is achieved by their migration and differentiation along the same path-ways that are formed during the preceding phases of neuronal migration.
Axis establishment and microtubule-mediated waves prior to first cleavage in Beroe ovata
Authors: Houliston Evelyn , Carré Danièle , Johnston Jennifer A. , Sardet Christian 
Published: April 2021

ABSTRACT
The single axis (oral-aboral) and two planes of symme-try of the ctenophore Beroe ovata become established with respect to the position of zygote nucleus formation and the orientation of first cleavage. Bisection of Beroe eggs at different times revealed that differences in egg organisation are established in relation to the pre-sumptive oral-aboral axis before first cleavage. Lateral fragments produced after but not before the time of first mitosis developed into larvae lacking comb-plates on one side. Time-lapse video demonstrated that waves of cytoplasmic reorganisation spread through the layer of peripheral cytoplasm (ectoplasm) of the egg during the 80 minute period between pronuclear fusion and first cleavage, along the future oral-aboral axis. These waves are manifest as the progressive displacement and dis-persal of plaques of accumulated organelles around supernumerary sperm nuclei, and a series of surface movements. Their timing and direction of propagation suggest they may be involved in establishing cytoplas-mic differences with respect to the embryonic axis.
Inhibitor experiments suggested that the observed cytoplasmic reorganisation involves microtubules. Noco-dazole and taxol, which prevent microtubule turnover, blocked plaque dispersal and reduced surface move-ments. The microfilament-disrupting drug cytochalasin B did not prevent plaque dispersal but induced abnor-mal surface contractions. We examined changes in microtubule organisation using immunofluorescence on eggs fixed at different times and in live eggs following injection of rhodamine-tubulin. Giant microtubule asters become associated with each male pronucleus after the end of meiosis. Following pronuclear fusion they disappear successively, those nearest the zygote nucleus shrinking first, to establish gradients of aster size within single eggs. Regional differences in micro-tubule behaviour around the time of mitosis were revealed by brief taxol treatment, which induced the for-mation of small microtubule asters in the region of the nucleus or spindle during both first and second cell cycles. The observed wave of change may thus reflect the local appearance and spreading of mitotic activity as the zygote nucleus approaches mitosis.
Specifying the path of the intersegmental nerve of the Drosophila embryo: a role for Delta and Notch
Authors: Giniger Edward , Jan Lily Yeh , Jan Yuh Nung 
Published: April 2021

ABSTRACT
The intersegmental nerve (ISN) of the Drosophila embryo follows a reproducible course near the anterior border of each segment. Based on the experiments reported here, we suggest that growth of the axons constituting the nerve is guided, in part, by the transmembrane proteins Delta and Notch. In particular, we suggest that expression of Delta protein on a branch of the trachea provides a path for the nerve through the lateral part of the embryo, and that the growing axons use the Notch protein on their surfaces to recognize this path. Consistent with this idea, we show that disruption of the trachea abolishes the ability of the ISN to extend through this part of the embryonic periphery. Finally, we argue that the same regulatory network that directs these peripheral axons also specifies the trajectory of part of the axonal scaffold of the central nervous system.
Antisense inhibition of AMEL translation demonstrates supramolecular controls for enamel HAP crystal growth during embryonic mouse molar development
Authors: Diekwisch Thomas , David Sasson , Bringas Pablo , Santos Valentino , Slavkin Harold C. 
Published: April 2021

ABSTRACT
During tooth development, enamel organ epithelial cells express a tissue-specific gene product (amelogenin) which presumably functions to control calcium hydroxyapatite crystal growth patterns during enamel biomineralization. The present studies were designed to test the hypothesis that amelogenin as a supramolecular aggregate regulates crystal growth during enamel biomineralization. Antisense oligodeoxynucleotide strategy was used in a simple organ culture system to inhibit amelogenin translation. Under these experimental conditions, antisense treatment prior to and during amelogenin expression resulted in inhibition of amelogenin translation products within immunoprecipitated [35S]methionine metabolically labeled proteins. To determine the efficiency of antisense treatment in this model system, digoxigenin-labeled oligodeoxynucleotides were observed to diffuse throughout the tooth explants including the target ameloblast cells within 24 hours. Ultrastructural analyses of amelogenin supramolecular assembly as electron-dense stippled materials in antisense treated cultures demonstrated dysmorphology of the extracelular enamel matrix with a significant reduction in crystal length and width. We conclude that secreted extracellular proteins form a supramolecular aggregate, which controls both the orientation and dimensions of enamel crystal formation during tooth development.
A singularity of PDGF alpha-receptor expression in the dorsoventral axis of the neural tube may define the origin of the oligodendrocyte lineage
Authors: Pringle Nigel P. , Richardson William D. 
Published: April 2021

ABSTRACT
During rat embryogenesis, PDGF alpha receptor (PDGF-R) mRNA is expressed in the ventral half of the spinal cord in two longitudinal columns, one each side of the central canal. Initially, these columns are only two cells wide but the cells subsequently appear to proliferate and disseminate throughout the spinal cord. Our previous studies of PDGF-R expression in the developing CNS suggested that PDGF-R may be a useful marker of the oligodendrocyte lineage in situ. The data presented here complement those studies and lead us to propose that the earliest oligodendrocyte precursors in the spinal cord originate in a very restricted region of the ventricular zone during a brief window of time around embryonic day 14 (E14). In the embryonic brain, migrating PDGF-R+ cells appear to originate in a localized germinal zone in the ventral diencephalon (beneath the foramen of Monro). Our data demonstrate that gene expression and cell fate can be regulated with exquisite spatial resolution along the dorsoventral axis of the mammalian neural tube.
Postnatal maturation of the dendritic fields of motoneuron pools supplying flexor and extensor muscles of the distal forelimb in the rat
Authors: Curfs M. H. J. M. , Gribnau A. A. M. , Dederen P. J. W. C. 
Published: April 2021

ABSTRACT
In the rat cervical spinal cord the corticospinal projection on motoneurons either direct or indirect (via interneurons) comes about postnatally making it accessible for experimental research. Therefore, the postnatal developmental changes of motoneurons and in particular their dendritic fields were examined. Motoneurons innervating the two antagonistic muscles in the distal forepaw, the m. flexor digitorum profundus and the m. extensor digitorum communis, were retrogradely labelled by intramuscular injections of cholera toxin subunit B conjugated with horseradish peroxidase in rats of various postnatal ages. Following a 48-72 hour survival period the motoneurons and their dendritic fields were studied in the seventh and eighth cervical spinal cord segments.
Both the number and the position of motoneurons were found to remain constant throughout postnatal development. Extensor motoneurons were positioned dorsolaterally in the ventral horn at the border of grey and white matter, flexor motoneurons were in general medial to extensor motoneurons. The results on the dendritic field demonstrate firstly, that during postnatal development the extension of the dendrites of both flexor and extensor motoneurons changes from spreading out in all directions at postnatal day 2 to spreading in only a few, specific directions from postnatal day 21 onwards, with the restriction that both motoneuron pools follow a different time scale to achieve this. Secondly, both pools have a temporal dendritic component extending into the white matter of the lateral funiculus. Thirdly, the dendritic extension pattern of flexor motoneurons differs from that of extensor motoneurons: the former has a permanent component in the medial part of lamina VI while the latter only has a transient component (from postnatal day 2 to 10) in the lateral part of lamina VI. The functional implications of the different dendritic extension patterns are discussed.
Complex regulation of early paired expression: initial activation by gap genes and pattern modulation by pair-rule genes
Authors: Gutjahr Thomas , Frei Erich , Noll Markus 
Published: April 2021

ABSTRACT
The paired gene is one of approximately 30 zygotic segmentation genes responsible for establishing the segmented body plan of Drosophila melanogaster. To gain insight into the mechanism by which the paired gene is expressed in a complex temporal and spatial pattern, we have examined paired protein expression in wild-type and mutant embryos. In wild-type embryos, paired protein is expressed in several phases. Initial expression in broad domains evolves into a pair-rule pattern of eight stripes during cellularization. Subsequently, a segmentpolarity-like pattern of fourteen stripes emerges. Later, at mid-embryogenesis, paired is expressed in specific regions of the head and in specific cells of the central nervous system. Analysis of the initial paired expression in the primary pair-rule mutants even-skipped, runt and hairy, and in all gap mutants suggests that the products of the gap genes hunchback, Krüppel, knirps and giant activate paired expression in stripes. With the exception of stripe 1, which is activated by even-skipped, and stripe 8, which depends upon runt, the primary pair-rule proteins are required for subsequent modulation rather than activation of the paired stripes. The factors activating paired expression in the pair-rule mode appear to interact with those activating it along the dorsoventral axis.
A role for wingless in the segmental gradient of Drosophila?
Authors: Sampedro Javier , Johnston Paul , Lawrence Peter A. 
Published: April 2021

ABSTRACT
The wild-type functions of the Wnt family of genes are still little understood (for review see Nusse and Varmus, Cell 69, 1073-1087, 1992). In Drosophila, the wingless (D- Wnt-1) protein is expressed in segmental stripes: its absence leads to a complete failure of segmentation, loss of engrailed expression and lack of pattern in the cuticle. A predominating hypothesis is that the spatial distribution of wingless is crucial to pattern; it might carry an instructive signal from cells that secrete the protein to cells nearby, or it might form a concentration gradient which acts as a morphogen.
We tested these hypotheses by expressing wingless ubiquitously in wingless embryos. The distribution of wingless protein in these embryos is uniform. Despite this, engrailed expression persists, is confined to the most anterior third of the parasegment, and delineates the parasegment border. The cuticle shows a segmentally reiterated pattern and, dorsally, the denticles are normally distributed and oriented. Because all these position-specific features cannot have been placed by a local source or a differential distribution of wingless protein, we conclude that, in the early embryo, the role of wing - less is neither to act as a local instructive signal, nor as a morphogen. We propose an alternative hypothesis that the wild-type function of the wingless protein is to maintain and ‘seal’ the parasegment borders; in its absence the borders fail to isolate abutting segmental gradients.
achaete-scute feminizing activities and Drosophila sex determination
Authors: Parkhurst Susan M. , Lipshitz Howard D. , Ish-Horowicz David 
Published: April 2021

ABSTRACT
Sex determination in Drosophila depends on X-linked ‘numerator’ genes activating early Sex-lethal (Sxl) transcription in females. One numerator gene, sisterless-b (sis-b), corresponds to the achaete-scute (AS-C) T4 basichelix-loop-helix (bHLH) gene. Two other closely related AS-C bHLH genes, T3 and T5, appear not to function as numerator elements. We analyzed endogenous AS-C expression and show that T4 is the major AS-C numerator gene because it is expressed earlier and more strongly than are T3 and T5. Only T4 expression is detectable during the early syncytial stages when Sxl state is being determined. Nevertheless, the effects of ectopic AS-C gene expression show that T3 and T5 proteins display weak but significant feminizing activities, enhancing male-lethality, and rescuing the femalelethality of sis mutations. Detailed examination of Sxl expression in rescued embryos suggests that female cells may be viable in the absence of detectable Sxl protein expression.
A new Drosophila homeobox gene, bsh, is expressed in a subset of brain cells during embryogenesis
Authors: Jones Bradley , McGinnis William 
Published: April 2021

ABSTRACT
Homeobox genes have been shown to control the determination of positional, tissue and cellular identity during the development of the fruitfly Drosophila melanogaster. Because genes involved in the determination of internal structures derived from neural, mesodermal and endodermal tissues may have been overlooked in conventional genetic screens, we undertook the identification of new homeobox genes expressed in these internal tissues. Here we describe the characterization of one of these new Drosophila homeobox genes, called brain-specific-homeobox (bsh). In embryos, bsh is expressed exclusively in the brain. bsh protein accumu-lates in approximately 30 cells in each brain hemisphere. One of these bsh expressing cells is closely associated with the terminus of the larval visual nerve (Bolwig’s nerve). While deletions of chromosomal interval containing the bsh gene show no dramatic changes in embryonic brain morphology, the expression pattern of the bsh gene suggests that it may play a highly specialized role in the determination and function of cell type in the Drosophila brain.
An activity gradient of decapentaplegic is necessary for the specification of dorsal pattern elements in the Drosophila embryo
Authors: Wharton Kristi A. , Ray Robert P. , Gelbart William M. 
Published: April 2021

ABSTRACT
decapentaplegic (dpp) is a zygotically expressed gene encoding a TGF-β-related ligand that is necessary for dorsal-ventral patterning in the Drosophila embryo. We show here that dpp is an integral part of a gradient that specifies many different cell fates via intercellular signalling. There is a graded requirement for dpp activity in the early embryo: high levels of dpp activity specify the amnioserosa, while progressively lower levels specify dorsal and lateral ectoderm. This potential for dpp to specify cell fate is highly dosage sensitive. In the wildtype embryo, increasing the gene dosage of dpp can shift cell fates along the dorsal-ventral axis. Furthermore, in mutant embryos, in which only a subset of the dorsalventral pattern elements are represented, increasing the gene dosage of dpp can specifically transform those pattern elements into more dorsal ones. We present evidence that the zygotic dpp gradient and the maternal dorsal gradient specify distinct, non-overlapping domains of the dorsal-ventral pattern.
Cortical development associated with conjugation of Paramecium
Authors: Romero M. Rosario , Torres Antonio 
Published: April 2021

ABSTRACT
The cortical cytoskeleton of Paramecium is character-ized by a complex, polarized and asymmetrical organi-zation. In order to analyse the cortical development of Paramecium tetraurelia during the sexual process of con-jugation, different antibodies have been used to follow the development of five cortical components: basal bodies, ciliary rootlets, outer lattice, epiplasm and cytospindle. This study demonstrates that the cortex of Paramecium undergoes an elaborate development process following conjugation. Some of the cortical structures that are not renewed at any other moment of the cell cycle, are resorbed after conjugation and replaced by other newly formed ones. The reorganiza-tion of the cortical components occurs according to dif-ferent morphogenetic waves that spread over the cell surface. The oral system and the preoral suture line act as morphogenetic epicentres.
Isoform-specific immunological detection of newt retinoic acid receptor δ1 in normal and regenerating limbs
Authors: Hill David S. , Ragsdale Clifton W. , Brockes Jeremy P. 
Published: April 2021

ABSTRACT
Retinoic acid (RA) exerts a variety of effects on the regenerating urodele limb including positional respecification of the blastema. The major RA receptor expressed in the newt limb and blastema is the 1 isoform and, in order to detect 1 in this context, we have made five affinity-purified antibodies against fusion proteins and peptides from non-overlapping regions of the molecule. These antibodies have been evaluated by reaction with transfected COS-7 cells, newt limb cells in culture and newt limb tissue sections. The most informative antibodies were RP6, directed against N-terminal region A sequence, and RP8, directed against C-terminal sequence. In western blots of blastemal extracts, 1 protein was detected as two major bands of immunoreactivity at positions consistent with the employment of two candidate methionine initiators identified by cDNA sequencing. Staining of adult limb sections with RP6 and RP8 showed reactivity in half of the nuclei in epidermal and mesenchymal tissues, a heterogeneity that was observed with adjacent nuclei in muscle fibres. In the regenerating limb, nuclei in the blastemal mesenchyme and wound epidermis were strongly reactive, although no axial variation in expression was detected.
A functionally specialized α-tubulin is required for oocyte meiosis and cleavage mitoses in Drosophila
Authors: Matthews Kathleen A. , Rees Dianne , Kaufman Thomas C. 
Published: April 2021

ABSTRACT
Three α-tubulin proteins contribute to microtubules during oogenesis and early embryogenesis in Drosophila melanogaster: αTUB84B, αTUB84D, and αTUB67C. αTUB67C is unique in two respects. It is a structurally divergent α-tubulin, sharing only 67% amino acid identity with the generic isotypes αTUB84B and αTUB84D, and its expression is exclusively maternal. The genetic analysis of the Tub67C gene described here demon strates that αTUB67C is required for nuclear division in the oocyte and early embryo. Both meiosis and cleavage-stage mitoses are severely affected by mutations that result in a substantial decrease in the ratio of αTUB67C/ αTUB84B+ αTUB84D. A large increase in this ratio, achieved by increasing the gene dosage of Tub67C, has little or no effect on meiosis, but severely disrupts mitotic spindle function. Thus, both classes of α-tubulin isotype present in the mature oocyte, αTUB67C and αTUB84B/84D, are essential for normal spindle function in early Drosophila development. These α-tubulins provide the first example of tubulin isotypes known to be coexpressed in wild-type animals whose encoded variation is required for the normal function of a microtubule array.