bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ectopic expression of UBX and ABD-B proteins during Drosophila embryogenesis: competition, not a functional hierarchy, explains phenotypic suppression
Authors: Lamka Michele L. , Boulet Anne M. , Sakonju Shigeru 
Published: April 2021

ABSTRACT
The Abdominal-B (Abd-B) gene, a member of the bithorax complex (BX-C), specifies the identities of parasegments (PS) 10-14 in Drosophila. Abd-B codes for two structurally related homeodomain proteins, ABD-B m and ABD-B r, that are expressed in PS10-13 and PS14-15, respectively. Although ABD-B m and r proteins have distinct developmental functions, ectopic expression of either protein during embryogenesis induces the development of filzkörper and associated spiracular hairs, structures normally located in PS13, at ectopic sites in the larval thorax and abdomen. These results suggest that other parasegmental differences contribute to the phenotype specified by ABD-B r activity in PS14.
Both ABD-B m and r repress the expression of other homeotic genes, such as Ubx and abd-A, in PS10-14. However, the importance of these and other cross-regulatory interactions among homeotic genes has been questioned. Since ectopic UBX protein apparently failed to transform abdominal segments, González-Reyes et al. (González-Reyes, A., Urquía, N., Gehring, W. J., Struhl, G. and Morata, G. (1990). Nature 344, 78-80) proposed a functional hierarchy in which ABD-A and ABD-B activities override UBX activity. We tested this model by expressing UBX and ABD-B m proteins ectopically in wild-type and BX-C-deficient embryos. Ectopic ABD-B m does not prevent transformations induced by ectopic UBX. Instead, ectopic UBX and ABD-B m proteins compete for the specification of segmental identities in a dose-dependent fashion. Our results support a quantitative competition among the homeotic proteins rather than the existence of a strict functional hierarchy. Therefore, we suggest that cross-regulatory interactions are not irrelevant but are important for repressing the expression of competing homeotic proteins.
To explain the apparent failure of ectopic UBX to transform the abdominal segments, we expressed UBX at different times during embryonic development. Our results show that ectopic UBX affects abdominal cuticular identities if expressed during early stages of embryogenesis. In later embryonic stages, abdominal segments become resistant to transformation by ectopic UBX while thoracic segments remain susceptible. Head segments also show a similar stage-dependent susceptibility to transformation by ectopic UBX in early embryogenesis but become resistant in later stages. These results suggest that abdominal and head identities are determined earlier than are thoracic identities.
Molecular markers for identified neuroblasts and ganglion mother cells in the Drosophila central nervous system
Authors: Doe Chris Q. 
Published: April 2021

ABSTRACT
The first step in generating cellular diversity in the Drosophila central nervous system is the formation of a segmentally reiterated array of neural precursor cells, called neuroblasts. Subsequently, each neuroblast goes through an invariant cell lineage to generate neurons and/or glia. Using molecular lineage markers, I show that (1) each neuroblast forms at a stereotyped time and position; (2) the neuroblast pattern is indistinguishable between thoracic and abdominal segments; (3) the development of individual neuroblasts can be followed throughout early neurogenesis; (4) gene expression in a neuroblast can be reproducibly modulated during its cell lineage; (5) identified ganglion mother cells form at stereotyped times and positions; and (6) the cell lineage of four well-characterized neurons can be traced back to two identified neuroblasts. These results set the stage for investigating neuroblast specification and the mechanisms controlling neuroblast cell lineages.
Notochord grafts do not suppress formation of neural crest cells or commissural neurons
Authors: Artinger Kristin B. , Bronner-Fraser Marianne 
Published: April 2021

ABSTRACT
Grafting experiments previously have established that the notochord affects dorsoventral polarity of the neural tube by inducing the formation of ventral structures such as motor neurons and the floor plate. Here, we examine if the notochord inhibits formation of dorsal structures by grafting a notochord within or adjacent to the dorsal neural tube prior to or shortly after tube closure. In all cases, neural crest cells emigrated from the neural tube adjacent to the ectopic notochord. When analyzed at stages after ganglion formation, the dorsal root ganglia appeared reduced in size and shifted in position in embryos receiving grafts. Another dorsal cell type, commissural neurons, identified by CRABP and neurofilament immunoreactivity, differentiated in the vicinity of the ectopic notochord. Numerous neuronal cell bodies and axonal processes were observed within the induced, but not endogenous, floor plate 1 to 2 days after implantation but appeared to be cleared with time. These results suggest that dorsally implanted noto-chords cannot prevent the formation of neural crest cells or commissural neurons, but can alter the size and posi-tion of neural crest-derived dorsal root ganglia.
Cell motility driving mediolateral intercalation in explants of Xenopus laevis
Authors: Shih John , Keller Ray 
Published: April 2021

ABSTRACT
In Xenopus, convergence and extension are produced by active intercalation of the deep mesodermal cells between one another along the mediolateral axis (medi- olateral cell intercalation), to form a narrower, longer array. The cell motility driving this intercalation is poorly understood. A companion paper shows that the endodermal epithelium organizes the outermost meso- dermal cells immediately beneath it to undergo conver- gence and extension, and other evidence suggests that these deep cells are the most active participants in medi- olateral intercalation (Shih, J. and Keller, R. (1992) Development 116, 887-899). In this paper, we shave off the deeper layers of mesodermal cells, which allows us to observe the protrusive activity of the mesodermal cells next to the organizing epithelium with high reso- lution video microscopy. These mesodermal cells divide in the early gastrula and show rapid, randomly directed protrusive activity. At the early midgastrula stage, they begin to express a characteristic sequence of behaviors, called mediolateral intercalation behavior (MIB): (1) large, stable, filiform and lamelliform protrusions form in the lateral and medial directions, thus making the cells bipolar; (2) these protrusions are applied directly to adjacent cell surfaces and exert traction on them, without contact inhibition; (3) as a result, the cells elongate and align parallel to the mediolateral axis and perpendicular to the axis of extension; (4) the elongate, aligned cells intercalate between one another along the mediolateral axis, thus producing a longer, narrower array. Explants of essentially a single layer of deep mesodermal cells, made at stage 10.5, converge and extend by mediolateral intercalation. Thus by stage 10.5 (early midgastrula), expression of MIB among deep mesodermal cells is physiologically and mechanically independent of the organizing influence of the endoder- mal epithelium, described previously (Shih, J. and Keller, R. (1992) Development 116 887-899), and is the fundamental cell motility underlying mediolateral inter- calation and convergence and extension of the body axis.
Patterns of cell motility in the organizer and dorsal mesoderm of Xenopus laevis
Authors: Shih John , Keller Ray 
Published: April 2021

ABSTRACT
In a companion paper (Shih, J. and Keller, R. (1992) Development 116, 901-914), we described a sequence of cell behaviors, called mediolateral intercalation behavior (MIB), that produces mediolateral cell intercalation, the process that drives convergence and extension of the axial and paraxial mesoderm of Xenopus. In this paper, we describe the pattern of expression of MIB in the mesoderm during gastrulation, using video image pro- cessing and recording of cell behavior in ‘shaved’, open- faced explants of the marginal zone. At midgastrula stage (10.5), MIB begins at two dorsolateral sites in the prospective anterior mesoderm and progresses medially along two arcs that lengthen toward and meet at the midline to form a single arc of cells expressing MIB, called the vegetal alignment zone (VgAZ). The noto- chordal-somitic mesodermal boundary forms within the VgAZ at stage 11, and then progresses animally and lat- erally, along the prospective anterior-posterior axis, eventually bounding a trapezoidal area the shape of the fate-mapped notochord. Meanwhile, from its origin in the VgAZ, MIB spreads in the prospective posterior direction along the lateral boundaries of both the noto- chordal and somitic mesoderm. From there it spreads medially in both tissues. Subsequently, vacuolation of notochord cells, and segmentation and expression of a somite-specific marker repeat the progression of medi- olateral intercalation behavior. Thus cells in the posterior, medial regions of the notochordal and the somitic territories are the last to express mediolateral intercalation behavior and subsequent tissue differentiations. In explants that do not converge, these cells neither express mediolateral intercalation behavior nor differentiate. These facts suggest that progressions of MIB in the anterior-posterior and lateral-medial directions may be organized by signals emanating from the lateral somitic and notochordal boundaries. These signals may have limited range and may be dependent on convergence, driven by mediolateral cell intercalation, to bring cells within their range. In the embryo, the posterior progression of MIB results in arcs of convergence, anchored in the vegetal endoderm at each end, acting on the inside of the blastoporal lip to produce involution of the IMZ.
ming is expressed in neuroblast sublineages and regulates gene expression in the Drosophila central nervous system
Authors: Cui Xuan , Doe Chris Q. 
Published: April 2021

ABSTRACT
Cell diversity in the Drosophila central nervous system (CNS) is primarily generated by the invariant lineage of neural precursors called neuroblasts. We used an enhancer trap screen to identify the ming gene, which is transiently expressed in a subset of neuroblasts at reproducible points in their cell lineage (i.e. in neuro- blast ‘sublineages’), suggesting that neuroblast identity can be altered during its cell lineage. ming encodes a predicted zinc finger protein and loss of ming function results in precise alterations in CNS gene expression, defects in axonogenesis and embryonic lethality. We propose that ming controls cell fate within neuroblast cell lineages.
Increased levels of the Drosophila Abelson tyrosine kinase in nerves and muscles: subcellular localization and mutant phenotypes imply a role in cell-cell interactions
Authors: Bennett Randy L. , Hoffmann F. Michael 
Published: April 2021

ABSTRACT
Mutations in the Drosophila Abelson tyrosine kinase have pleiotropic effects late in development that lead to pupal lethality or adults with a reduced life span, reduced fecundity and rough eyes. We have examined the expression of the abl protein throughout embryonic and pupal development and analyzed mutant pheno- types in some of the tissues expressing abl. abl protein, present in all cells of the early embryo as the product of maternally contributed mRNA, transiently localizes to the region below the plasma membrane cleavage fur- rows as cellularization initiates. The function of this expression is not yet known. Zygotic expression of abl is first detected in the post-mitotic cells of the develop- ing muscles and nervous system midway through embryogenesis. In later larval and pupal stages, abl protein levels are also highest in differentiating muscle and neural tissue including the photoreceptor cells of the eye. abl protein is localized subcellularly to the axons of the central nervous system, the embryonic somatic muscle attachment sites and the apical cell junctions of the imaginal disk epithelium. Evidence for abl function was obtained by analysis of mutant phenotypes in the embryonic somatic muscles and the eye imaginal disk. The expression patterns and mutant phenotypes indi- cate a role for abl in establishing and maintaining cell- cell interactions.
The fat facets gene is required for Drosophila eye and embryo development
Authors: Fischer-Vize Janice A. , Rubin Gerald M. , Lehmann Ruth 
Published: April 2021

ABSTRACT
In a screen for mutations affecting Drosophila eye devel-opment, we have identified a gene called fat facets (faf) which is required for cell interactions that prevent par-ticular cells in the developing eye from becoming pho-toreceptors. Analysis of eyes mosaic for faf+ and faf cells shows that faf is required in cells near to, but out-side, normal developing photoreceptors and also outside of the ectopic photoreceptors in mutant facets. faf is also essential during oogenesis, and we show that a faf-lacZ hybrid protein is localized via the first 392 amino acids of faf to the posterior pole of oocytes. Posterior local-ization of faf-lacZ depends on oskar. oskar encodes a key organizer of the pole plasm, a specialized cytoplasm at the posterior pole of embryos. The pole plasm is required for germ cell formation and contains the deter-minant of posterior polarity, encoded by nanos. Although other pole plasm components are required for localization of nanos RNA or for nanos protein func-tion, faf is not. We have cloned the faf gene, and have shown that it encodes two similar large (∼300 103Mr) proteins that are unique with respect to other known proteins.
The patterning and functioning of protrusive activity during convergence and extension of the Xenopus organiser
Authors: Keller Ray , Shih John , Domingo Carmen 
Published: April 2021

ABSTRACT
We discuss the cellular basis and tissue interactions regulating convergence and extension of the vertebrate body axis in early embryogenesis of Xenopus. Convergence and extension occur in the dorsal mesoderm (prospective notochord and somite) and in the posterior nervous system (prospective hindbrain and spinal cord) by sequential cell intercalations. Several layers of cells intercalate to form a thinner, longer array (radial intercalation) and then cells intercalate in the mediolateral orientation to form a longer, narrower array (mediolateral intercalation). Fluorescence microscopy of labeled mesodermal cells in explants shows that protrusive activity is rapid and randomly directed until the midgastrula stage, when it slows and is restricted to the medial and lateral ends of the cells. This bipolar protrusive activity results in elongation, alignment and mediolateral intercalation of the cells. Mediolateral intercalation behavior (MIB) is expressed in an anterior-posterior and lateral-medial progression in the mesoderm. MIB is first expressed laterally in both somitic and notochordal mesoderm. From its lateral origins in each tissue, MIB progresses medially. If convergence does not bring the lateral boundaries of the tissues closer to the medial cells in the notochordal and somitic territories, these cells do not express MIB. Expression of tissue-specific markers follows and parallels the expression of MIB. These facts argue that MIB and some aspects of tissue differentiation are induced by signals emanating from the lateral boundaries of the tissue territories and that convergence must bring medial cells and boundaries closer together for these signals to be effective. Grafts of dorsal marginal zone epithelium to the ventral sides of other embryos, to ventral explants and to UV-ventralized embryos show that it has a role in organising convergence and extension, and dorsal tissue differentiation among deep mesodermal cells. Grafts of involuting marginal zone to animal cap tissue of the early gastrula shows that convergence and extension of the hindbrain-spinal cord are induced by planar signals from the involuting marginal zone.
trithorax regulates multiple homeotic genes in the bithorax and Antennapedia complexes and exerts different tissue-specific, parasegment-specific and promoter-specific effects on each
Authors: Breen T. R. , Harte P. J. 
Published: April 2021

ABSTRACT
The trithorax (trx) gene is required for normal development of the body plan in Drosophila embryos and adults. Mutations in trx cause homeotic transformations throughout the body. Genetic studies suggest that trx encodes a positive regulatory factor required throughout development for normal expression of multiple homeotic genes of the bithorax and Antennapedia complexes (BX-C and ANT-C). To determine how trx influences homeotic gene expression, we examined the expression of the BX-C genes Ultrabithorax, abdominal-A, Abdominal-B and the ANT-C genes Antennapedia, Sex combs reduced and Deformed in trx embryos. We show that trx does indeed exert its effects by positively regulating homeotic gene expression and that its effects on expression of individual homeotic genes are complex: each of the BX-C and ANT-C genes examined exhibits different tissue-specific, parasegment-specific and promoter-specific reductions in their expression. This implies that each of these genes have different requirements for trx in different spatial contexts in order to achieve normal expression levels, presumably depending on the promoters involved and the other regulatory factors bound at each of their multiple tissue- and parasegment-specific cis-regulatory sites in different regions of the embryo. These results also imply that those components of homeotic gene expression patterns for which trx is dispensable, require other factors, possibly those encoded by other trithorax-like genes.
Developmental origin of segmental identity in the leech mesoderm
Authors: Gleizer Lidia , Stent Gunther S. 
Published: April 2021

ABSTRACT
Segmentation in the leech embryo is established by a stereotyped cell lineage. Each of the 32 segments arises from homologous, bilaterally symmetrical complements of mesodermal and ectodermal blast cell clones. Although segments are homologous, they are regionally differentiated along the longitudinal body axis. Various segments display idiosyncratic ensembles of features, which constitute discrete segmental identities. The differentiation of segment-specific features, such as the mesoderm-derived nephridia, genital primordia and identified Small Cardioactive Peptide immunoreactive neurons, reflects a diversification of the developmental fates of homologous blast cell clones. We have investigated whether segment-specific differentiation of homologous mesodermal blast cell clones depends on cellintrinsic mechanisms (based on the cells’ lineage history) or on cell-extrinsic mechanisms (based on the cells’ interactions with their environment) in embryos of Theromyzon rude. For this purpose, we first mapped the segment-specific fates of individual mesodermal blast cell clones, and then induced mesodermal clones to take part in the formation of segments for which they are not normally destined. Two types of ectopic segmental position were produced: one in which a mesodermal blast cell clone was out of register with all other consegmental cells and one in which a mesodermal blast cell clone was out of register with its overlying ectoderm, but was in normal register with the mesoderm and ectoderm on the other side of the embryo. Mesodermal blast cell clones that developed in either type of ectopic segmental position gave rise to segment-specific features characteristic of their original segmental fates rather than their ectopic positions. Thus, the development of segmental identity in the leech mesoderm is attributable to a cell-intrinsic mechanism and, either before or soon after their birth, mesodermal blast cells are autonomously committed to segment-specific fates.
The Tribolium homeotic gene Abdominal is homologous to abdominal-A of the Drosophila bithorax complex
Authors: Stuart Jeffrey J. , Brown Susan J. , Beeman Richard W. , Denell Robin E. 
Published: April 2021

ABSTRACT
The Abdominal gene is a member of the single homeotic complex of the beetle, Tribolium castaneum. An integrated developmental genetic and molecular analysis shows that Abdominal is homologous to the abdominal- A gene of the bithorax complex of Drosophila. abdomi - nal-A mutant embryos display strong homeotic transformations of the anterior abdomen (parasegments 7-9) to PS6, whereas developmental commitments in the posterior abdomen depend primarily on Abdominal-B. In beetle embryos lacking Abdominal function, paraseg-ments throughout the abdomen are transformed to PS6. This observation demonstrates the general functional significance of parasegmental expression among insects and shows that the control of determinative decisions in the posterior abdomen by homeotic selector genes has undergone considerable evolutionary modification.
Capacity to form choroid plexus-like cells in vitro is restricted to specific regions of the mouse neural ectoderm
Authors: Thomas Tim , Dziadek Marie 
Published: April 2021

ABSTRACT
Neural ectoderm was dissected from 9.5-day and 8.5-day gestation mouse embryos and divided into fore-brain, midbrain, hindbrain and spinal cord regions. Forebrain and hindbrain material from 9.5-day neural ectoderm was further divided into presumptive choroid plexus regions and regions that would normally form nervous tissue in vivo. All tissues were plated onto a basement membrane substratum for culture in vitro. It was found that explants of neural ectoderm that would normally form choroid plexus in vivo, readily differentiated to form choroid plexus-like cells in culture. Cells from hindbrain segments and forebrain regions, which would normally form nervous tissue, also had the potential to differentiate into cells resembling the choroid plexus epithelium in culture, provided that the normal cell-cell interactions were disrupted. Cells from the midbrain neuromeres of 9.5-day embryos, which do not form a choroid plexus in vivo, did not form this lineage in vitro. However, cells cultured from the earlier headfold stage midbrain neural ectoderm could develop into choroid plexus epithelium. There was no evidence that neural ectoderm from the spinal cord had the developmental potential to form choroid plexus epithelial cells at either of these two developmental stages. These studies show that the restrictions in the potential of neural ectoderm stem cells to form different lineages proceeds according to morphological divisions that appear along the anterior-posterior axis during the early stages of brain development. These results suggest that the division of neural ectoderm into segments which contain discrete stem cell populations may be a general feature of the early phase of development of the central nervous system.
A mRNA localized to the vegetal cortex of Xenopus oocytes encodes a protein with a nanos-like zinc finger domain
Authors: Mosquera Luis , Forristall Caryl , Zhou Yi , King Mary Lou 
Published: April 2021

ABSTRACT
mRNAs concentrated in specific regions of the oocyte have been found to encode determinants that specify cell fate. We show that an intermediate filament fraction isolated from Xenopus stage VI oocytes specifically contains, in addition to Vg1 RNA, a new localized mRNA, Xcat-2. Like Vg1, Xcat-2 is found in the vegetal cortical region, is inherited by the vegetal blastomeres during development, and is degraded very early in development. Sequence analysis suggests that Xcat-2 encodes a protein that belongs to the CCHC RNA-binding family of zinc finger proteins. Interestingly, the closest known relative to Xcat-2 in this family is nanos, an RNA localized to the posterior pole of the Drosophila oocyte whose protein product suppresses the translation of the transcription factor hunchback. The localized and maternally restricted expression of Xcat-2 RNA suggests a role for its protein in setting up regional differences in gene expression that occur early in development.