bluuebunny/crossref_metadata_2025 huggingface dataset:
Specification of the anterior hindbrain and establishment of a normal mid/hindbrain organizer is dependent on Gbx2 gene function
Authors: Wassarman Karen Montzka , Lewandoski Mark , Campbell Kenneth , Joyner Alexandra L. , Rubenstein John L. R. , Martinez Salvador , Martin Gail R.
Published: April 2021

Analysis of mouse embryos homozygous for a loss-of-function allele of Gbx2 demonstrates that this homeobox gene is required for normal development of the mid/hindbrain region. Gbx2 function appears to be necessary at the neural plate stage for the correct specification and normal proliferation or survival of anterior hindbrain precursors. It is also required to maintain normal patterns of expression at the mid/hindbrain boundary of Fgf8 and Wnt1, genes that encode signaling molecules thought to be key components of the mid/hindbrain (isthmic) organizer. In the absence of Gbx2 function, isthmic nuclei, the cerebellum, motor nerve V, and other derivatives of rhombomeres 1-3 fail to form. Additionally, the posterior midbrain in the mutant embryos appears to be extended caudally and displays abnormalities in anterior/posterior patterning. The failure of anterior hindbrain development is presumably due to the loss of Gbx2 function in the precursors of the anterior hindbrain. However, since Gbx2 expression is not detected in the midbrain it seems likely that the defects in midbrain anterior/posterior patterning result from an abnormal isthmic signaling center. These data provide genetic evidence for a link between patterning of the anterior hindbrain and the establishment of the mid/hindbrain organizer, and identify Gbx2 as a gene required for these processes to occur normally.
The prechordal region lacks neural inducing ability, but can confer anterior character to more posterior neuroepithelium
Authors: Foley Ann C. , Storey Kate G. , Stern Claudio D.
Published: April 2021

The avian equivalent of Spemann’s organizer, Hensen’s node, begins to lose its ability to induce a nervous system from area opaca epiblast cells at stage 4+, immediately after the full primitive streak stage. From this stage, the node is no longer able to induce regions of the nervous system anterior to the hindbrain. Stage 4+ is marked by the emergence from the node of a group of cells, the prechordal mesendoderm. Here we have investigated whether the prechordal region possesses the lost functions of the organizer, using quail-chick chimaeras to distinguish graft- and host-derived cells, together with several region-specific molecular markers. We find that the prechordal region does not have neural inducing ability, as it is unable to divert extraembryonic epiblast cells to a neural fate. However, it can confer more anterior character to prospective hindbrain cells of the host, making them acquire expression of the forebrain markers tailless and Otx-2. It can also rescue the expression of Krox-20 and Otx-2 from nervous system induced by an older (stage 5) node in extraembryonic epiblast. We show that these properties reflect a true change of fate of cells rather than recruitment from other regions. The competence of neuroectoderm to respond to anteriorizing signals declines by stages 7-9, but both posteriorizing signals and the ability of neuroectoderm to respond to them persist after this stage.
HSP70-2 is required for CDC2 kinase activity in meiosis I of mouse spermatocytes
Authors: Zhu Dahai , Dix David J. , Eddy E. M.
Published: April 2021

Cyclin B-dependent CDC2 kinase activity has a key role in triggering the G2/M-phase transition during the mitotic and meiotic cell cycles. The Hsp70-2 gene is expressed only in spermatogenic cells at a significant level. In Hsp70-2 gene knock-out (Hsp70-2−/−) mice, primary spermatocytes fail to complete meiosis I, suggesting a link between HSP70-2 heat-shock protein and CDC2 kinase activity during this phase of spermatogenesis. Members of the HSP70 protein family are molecular chaperones that mediate protein de novo folding, translocation and multimer assembly. This study used immunoprecipitation-coupled western blot and in vitro reconstitution experiments to show that HSP70-2 interacts with CDC2 in the mouse testis, appears to be a molecular chaperone for CDC2, and is required for CDC2/cyclin B1 complex formation. Previous studies reported that most CDC2 kinase activity in the mouse testis is present in pachytene spermatocytes. Although CDC2 kinase activity for histone H1 was present in the testis of wild-type mice, it was nearly absent from the testis of Hsp70-2−/− mice, probably due to defective CDC2/cyclin B1 complex formation. Furthermore, addition of HSP70-2 to freshly prepared extracts of testis from Hsp70-2−/− mice not only restored CDC2/cyclin B1 complex formation but also reconstituted CDC2 kinase activity in vitro. It appears that one cause of failure to complete meiosis I during spermatogenesis in Hsp70-2−/− mice is disruption of CDC2/cyclin B1 assembly in pachytene spermatocytes, thereby preventing development of the CDC2 kinase activity required to trigger G2/M-phase transition. These studies provide novel in vivo evidence for a link between an HSP70 molecular chaperone and CDC2 kinase activity essential for the meiotic cell cycle in spermatogenesis.
Xenopus msx1 mediates epidermal induction and neural inhibition by BMP4
Authors: Suzuki Atsushi , Ueno Naoto , Hemmati-Brivanlou Ali
Published: April 2021

Epidermal fate in Xenopus ectoderm has been shown to be induced by a secreted growth factor, Bone Morphogenetic Protein 4 (BMP4). However, the molecular mechanism mediating this response is poorly understood. Here, we show that the expression of the homeobox gene, msx1, is an immediate early response to BMP4 in Xenopus embryos. The timing of expression and embryonic distribution of msx1 parallel those described for BMP4. Moreover, over-expression of msx1 in early Xenopus embryos leads to their ventralization as described for BMP4. Consistent with mediating a BMP type of signaling, overexpression of msx1 is sufficient to induce epidermis in dissociated ectoderm cells, which would otherwise form neural tissue. Finally, msx1 can also rescue neuralization imposed by a dominant negative BMP receptor (tBR) in ectodermal explants. We propose that Xenopus msx1 acts as a mediator of BMP signaling in epidermal induction and inhibition of neural differentiation.
Mouse Dll3: a novel divergent Delta gene which may complement the function of other Delta homologues during early pattern formation in the mouse embryo
Authors: Dunwoodie Sally L. , Henrique Domingos , Harrison Stephen M. , Beddington Rosa S. P.
Published: April 2021

Mouse delta-like 3 (Dll3), a novel vertebrate homologue of the Drosophila gene Delta was isolated by a subtracted library screen. In Drosphila, the Delta/Notch signalling pathway functions in many situations in both embryonic and adult life where cell fate specification occurs. In addition, a patterning role has been described in the establishment of the dorsoventral compartment boundary in the wing imaginal disc. Dll3 is the most divergent Delta homologue identified to date. We confirm that Dll3 can inhibit primary neurogenesis when ectopically expressed in Xenopus, suggesting that it can activate the Notch receptor and therefore is a functional Delta homologue. An extensive expression study during gastrulation and early organogenesis in the mouse reveals a diverse and dynamic pattern of expression. The three major sites of expression implicate Dll3 in somitogenesis and neurogenesis and in the production of tissue from the primitive streak and tailbud. A careful comparison of Dll3 and Dll1 expression by double RNA in situ hybridisation demonstrates that these genes have distinct patterns of expression, but implies that together they operate in many of the same processes. We postulate that during somitogenesis Dll3 and Dll1 coordinate in establishing the intersomitic boundaries. We confirm that, during neurogenesis in the spinal cord, Dll1 and Dll3 are expressed by postmitotic cells and suggest that expression is sequential such that cells express Dll1 first followed by Dll3. We hypothesise that Dll1 is involved in the release of cells from the precursor population and that Dll3 is required later to divert neurons along a specific differentiation pathway.
Genetically engineered mice demonstrate that adenosine deaminase is essential for early postimplantation development
Authors: Blackburn Michael R. , Knudsen Thomas B. , Kellems Rodney E.
Published: April 2021

Adenosine deaminase (ADA) is an essential enzyme of purine metabolism that is enriched at the maternal-fetal interface of mice throughout postimplantation development. During early postimplantation stages Ada is highly expressed in both maternally derived decidual cells and zygotically derived trophoblast cells. For the current study we utilized genetically modified mice to delineate the relative contribution and importance of decidual and trophoblast ADA at the maternal-fetal interface. In females genetically engineered to lack decidual ADA a striking pattern of expression was revealed in giant trophoblast cells that surround the early postimplantation embryo. Embryos within gestation sites lacking both decidual and trophoblast ADA died during the early postimplantation period, whereas expression in trophoblast cells alone was sufficient for survival through this period. Severe disturbances in purine metabolism were observed in gestation sites lacking decidual ADA, including the accumulation of the potentially toxic ADA substrates adenosine and 2′-deoxyadenosine. These experiments provide genetic evidence that Ada expression at the maternal-fetal interface is essential for early postimplantation development in mice.
The role of the msh homeobox gene during Drosophila neurogenesis: implication for the dorsoventral specification of the neuroectoderm
Authors: Isshiki Takako , Takeichi Masatoshi , Nose Akinao
Published: April 2021

Development of the Drosophila central nervous system begins with the delamination of neural and glial precursors, called neuroblasts, from the neuroectoderm. An early and important step in the generation of neural diversity is the specification of individual neuroblasts according to their position. In this study, we describe the genetic analysis of the msh gene which is likely to play a role in this process. The msh/Msx genes are one of the most highly conserved families of homeobox genes. During vertebrate spinal cord development, Msx genes (Msx1-3) are regionally expressed in the dorsal portion of the developing neuroectoderm. Similarly in Drosophila, msh is expressed in two longitudinal bands that correspond to the dorsal half of the neuroectoderm, and subsequently in many dorsal neuroblasts and their progeny. We showed that Drosophila msh loss-of-function mutations led to cell fate alterations of neuroblasts formed in the dorsal aspect of the neuroectoderm, including a possible dorsal-to-ventral fate switch. Conversely, ectopic expression of msh in the entire neuroectoderm severely disrupted the proper development of the midline and ventral neuroblasts. The results provide the first in vivo evidence for the role of the msh/Msx genes in neural development, and support the notion that they may perform phylogenetically conserved functions in the dorsoventral patterning of the neuroectoderm.
klumpfuss, a Drosophila gene encoding a member of the EGR family of transcription factors, is involved in bristle and leg development
Authors: Klein Thomas , Campos-Ortega José A.
Published: April 2021

The klumpfuss (klu) transcription unit in Drosophila gives rise to two different transcripts of 4.5 and 4.9 kb, both of which encode a putative transcription factor with four zinc-finger motifs of the C2H2 class. Zinc-finger 2-4 are homologous to those of the proteins of the EGR transcription factor family. As in the case of the most divergent member of the family, the Wilms’ tumor suppressor gene (WT-1), klu contains an additional zinc finger, which is only distantly related. Loss of klumpfuss function is semilethal and causes a variety of defects in bristles and legs of adults, as well as in mouth hooks and brains of larvae. Analysis of the mutants indicates that klumpfuss is required for proper specification and differentiation of a variety of cells, including the sensory organ mother cells and those of the distal parts of tarsal segments.
Developmentally regulated activation of apoptosis early in Xenopus gastrulation results in cyclin A degradation during interphase of the cell cycle
Authors: Stack Jeffrey H. , Newport John W.
Published: April 2021

Previous work identified a developmental timer that controls the stability of cyclin A protein in interphase-arrested Xenopus embryos. It was shown that cyclins A1 and A2 abruptly become unstable in hydroxyurea-treated embryos at the time that untreated embryos are beginning gastrulation (early gastrulation transition; EGT). We have demonstrated here that cyclins A1 and A2 are degraded at the equivalent of the EGT by the ICE-like caspases that are responsible for programmed cell death or apoptosis. Analysis of embryos treated with hydroxyurea or cyclo-heximide showed widespread cellular apoptosis coincident with cyclin A cleavage. Our data further indicate that the apoptotic pathway is present in Xenopus embryos prior to the EGT; however, it is maintained in an inactive state in early cleaving embryos by maternally encoded inhibitors. Characterization of the timing of the activation of apoptosis implicates the initiation of zygotic transcription at the mid-blastula transition (MBT) in the suppression of apoptosis in normal embryos. The decreased biosynthetic capacity of embryos treated with hydroxyurea or cycloheximide most likely interferes with the ability to maintain sufficient levels of apoptotic inhibitors and results in widespread apoptosis. Our results suggest a scenario whereby the apoptotic pathway is suppressed in the early cleaving embryo by maternally contributed inhibitors. Degradation at the EGT of maternal RNAs encoding these inhibitors is compensated for by new zygotic transcription beginning at the MBT. This indicates that the interval between the MBT and the EGT represents a critical developmental period during which the regulation of embryonic cellular processes is transferred from maternal to zygotic control.
Role of GGF/neuregulin signaling in interactions between migrating neurons and radial glia in the developing cerebral cortex
Authors: Anton E. S. , Marchionni M. A. , Lee K-F. , Rakic P.
Published: April 2021

During neuronal migration to the developing cerebral cortex, neurons regulate radial glial cell function and radial glial cells, in turn, support neuronal cell migration and differentiation. To study how migrating neurons and radial glial cells influence each others’ function in the developing cerebral cortex, we examined the role of glial growth factor (a soluble form of neuregulin), in neuron-radial glial interactions. Here, we show that GGF is expressed by migrating cortical neurons and promotes their migration along radial glial fibers. Concurrently, GGF also promotes the maintenance and elongation of radial glial cells, which are essential for guiding neuronal migration to the cortex. In the absence of GGF signaling via erbB2 receptors, radial glial development is abnormal. Furthermore, GGF’s regulation of radial glial development is mediated in part by brain lipid-binding protein (BLBP), a neuronally induced, radial glial molecule, previously shown to be essential for the establishment and maintenance of radial glial fiber system. The ability of GGF to influence both neuronal migration and radial glial development in a mutually dependent manner suggests that it functions as a mediator of interactions between migrating neurons and radial glial cells in the developing cerebral cortex.
Cell migration in the developing chick diencephalon
Authors: Golden Jeffrey A. , Zitz Julie C. , McFadden Kathryn , Cepko Constance L.
Published: April 2021

We previously reported that retrovirally marked clones in the mature chick diencephalon were widely dispersed in the mediolateral, dorsoventral and rostrocaudal planes. The current study was undertaken to define the migration routes that led to the dispersion. Embryos were infected between stages 10 and 14 with a retroviral stock encoding alkaline phosphatase and a library of molecular tags. Embryos were harvested 2.5-5.5 days later and the brains were fixed and serially sectioned. Sibling relationships were determined following PCR amplification and sequencing of the molecular tag. On embryonic day 4, all clones were organized in radial columns spanning the neuroepithelium, which was composed primarily of a ventricular zone at this age. No tangential migration was seen in the ventricular zone. On embryonic day 5, most clones remained radial with many cells located in the ventricular zone; however, a few clones had cells migrating perpendicular to the radial column, in either a rostrocaudal or dorsoventral direction. The tangential migration began just beyond the basal limit of the ventricular zone. On embryonic days 6 and 7, many clones had cells migrating perpendicular to the radial column, which spanned from the ventricular to the pial surface. The migrating cells appeared to be aligned along axes that were perpendicular to the radial column. Using a combination of DiI tracing, immunohistochemistry and electron microscopy, we have determined that axonal tracts are present and are aligned with the migrating cells, suggesting that they support the non-radial cell migration. These data indicate that migration along pathways independent of radial glia occur outside of the ventricular zone in more than 50% of the clones in the chick diencephalon.
Targeted disruption of the mouse homologue of the Drosophila polyhomeotic gene leads to altered anteroposterior patterning and neural crest defects
Authors: Takihara Yoshihiro , Tomotsune Daihachiro , Shirai Manabu , Katoh-Fukui Yuko , Nishii Kiyomasa , Motaleb Md. Abdul , Nomura Midori , Tsuchiya Reiko , Fujita Yoshiaki , Shibata Yosaburo , Higashinakagawa Toru , Shimada Kazunori
Published: April 2021

The rae28 gene is a mouse homologue of the Drosophila polyhomeotic gene (Nomura, M., Takihara, Y. and Shimada, K. (1994) Differentiation 57, 39-50), which is a member of the Polycomb group (Pc-G) of genes (DeCamillis, M., Cheng, N., Pierre, D. and Brock, H.W. (1992) Genes Dev. 6, 223-232). The Pc-G genes are required for the correct expression of the Homeotic complex genes and segment specification during Drosophila embryogenesis and larval development. To study the role of the rae28 gene in mouse development, we generated rae28-deficient mice by gene targeting in embryonic stem cells. The rae28−/− homozygous mice exhibited perinatal lethality, posterior skeletal transformations and defects in neural crest-related tissues, including ocular abnormalities, cleft palate, parathyroid and thymic hypoplasia and cardiac anomalies.

The anterior boundaries of Hoxa-3, a-4, a-5, b-3, b-4 and d-4 expression were shifted rostrally in the paraxial mesoderm of the rae28−/− homozygous embryos, and those of Hoxb-3 and b-4 expression were also similarly altered in the rhombomeres and/or pharyngeal arches. These altered Hox codes were presumed to be correlated with the posterior skeletal transformations and neural crest defects observed in the rae28−/− homozygous mice. These results indicate that the rae28 gene is involved in the regulation of Hox gene expression and segment specification during paraxial mesoderm and neural crest development.
Role of Hoxa-2 in axon pathfinding and rostral hindbrain patterning
Authors: Gavalas Anthony , Davenne Marc , Lumsden Andrew , Chambon Pierre , Rijli Filippo M.
Published: April 2021

Segmentation plays an important role in neuronal diversification and organisation in the developing hindbrain. For instance, cranial nerve branchiomotor nuclei are organised segmentally within the basal plates of successive pairs of rhombomeres. To reach their targets, motor axons follow highly stereotyped pathways exiting the hindbrain only via specific exit points in the even-numbered rhombomeres. Hox genes are good candidates for controlling this pathfinding, since they are segmentally expressed and involved in rhom-bomeric patterning. Here we report that in Hoxa-2−/− embryos, the segmental identities of rhombomere (r) 2 and r3 are molecularly as well as anatomically altered. Cellular analysis by retrograde dye labelling reveals that r2 and r3 trigeminal motor axons turn caudally and exit the hindbrain from the r4 facial nerve exit point and not from their normal exit point in r2. Furthermore, dorsal r2-r3 patterning is affected, with loss of cochlear nuclei and enlargement of the lateral part of the cerebellum. These results point to a novel role for Hoxa-2 in the control of r2-r3 motor axon guidance, and also suggest that its absence may lead to homeotic changes in the alar plates of these rhombomeres.
The roles of hedgehog and engrailed in patterning adult abdominal segments of Drosophila
Authors: Kopp Artyom , Muskavitch Marc A. T. , Duncan Ian
Published: April 2021

We present evidence that hedgehog (hh) protein secreted by posterior compartment cells plays a key role in patterning the posterior portion of the anterior compartment in adult abdominal segments. Loss of function of hh in the hhts2 mutant causes the loss of posterior tergite characteristics in the anterior compartment, whereas ectopic expression driven by hs-hh or the gain-of-function allele hhMir causes transformation of anterior structures toward the posterior. FLP-out hh-expressing clones in the anterior compartment induce surrounding wild-type cells to produce posterior tergite structures, establishing that hh functions non-autonomously. The effects of pulses of ectopic expression driven by hs-hh indicate that bristle type and pigmentation are patterned by hh at widely different times in pupal development.

We also present evidence that the primary polarization of abdominal segments is symmetric. This symmetry is strikingly revealed by ectopic expression of engrailed (en). As expected, this transforms anterior compartment cells to posterior compartment identity. In addition, however, ectopic en expression causes an autonomous reversal of polarity in the anterior portion of the anterior compart-ment, but not the posterior portion. By determining the position of polarity reversal within en-expressing clones, we were able to define a cryptic line of symmetry that lies within the pigment band of the normal tergite. This line appears to be retained in hhts2 mutants raised at the restrictive temperature, suggesting it is not established by hh signaling. We argue that the primary role of hh in control-ling polarity is to cause anterior compartment cells to reverse their interpretation of an underlying symmetric polarization. Consistent with this, we find that strong ectopic expression of hh causes mirror-symmetric double posterior patterning, whereas hh loss of function can cause mirror-symmetric double anterior patterning.
The maternal par genes and the segregation of cell fate specification activities in early Caenorhabditis elegans embryos
Authors: Bowerman Bruce , Ingram Malene K. , Hunter Craig P.
Published: April 2021

After fertilization in C. elegans, activities encoded by the maternally expressed par genes appear to establish cellular and embryonic polarity. Loss-of-function mutations in the par genes disrupt anterior-posterior (a-p) asymmetries in early embryos and result in highly abnormal patterns of cell fate. Little is known about how the early asymmetry defects are related to the cell fate patterning defects in par mutant embryos, or about how the par gene products affect the localization and activities of developmental regulators known to specify the cell fate patterns made by individual blastomeres. Examples of such regulators of blastomere identity include the maternal proteins MEX-3 and GLP-1, expressed at high levels anteriorly, and SKN-1 and PAL-1, expressed at high levels posteriorly in early embryos. To better define par gene functions, we examined the expression patterns of MEX-3, PAL-1 and SKN-1, and we analyzed mex-3, pal-1, skn-1 and glp-1 activities in par mutant embryos. We have found that mutational inactivation of each par gene results in a unique phenotype, but in no case do we observe a complete loss of a-p asymmetry. We conclude that no one par gene is required for all a-p asymmetry and we suggest that, in some cases, the par genes act independently of each other to control cell fate patterning and polarity. Finally, we discuss the implications of our findings for understanding how the initial establishment of polarity in the zygote by the par gene products leads to the proper localization of more specifically acting regulators of blastomere identity.
Notch signalling mediates segmentation of the Drosophila leg
Authors: de Celis Jose F. , Tyler David M. , Celis Jesus de , Bray Sarah J.
Published: April 2021

The legs of Drosophila are divided into segments along the proximodistal axis by flexible structures called joints. The separation between segments is already visible in the imaginal disc as folds of the epithelium, and cells at segment boundaries have different morphology during pupal development. We find that Notch is locally activated in distal cells of each segment, as demonstrated by the restricted expression of the Enhancer of split mβ gene, and is required for the formation of normal joints. The genes fringe, Delta, Serrate and Suppressor of Hairless, also participate in Notch function during leg development, and their expression is localised within the leg segments with respect to segment boundaries. The failure to form joints when Notch signalling is compromised leads to shortened legs, suggesting that the correct specification of segment boundaries is critical for normal leg growth. The requirement for Notch during leg development resembles that seen during somite formation in vertebrates and at the dorsal ventral boundary of the wing, suggesting that the creation of boundaries of gene expression through Notch activation plays a conserved role in co-ordinating growth and patterning.
Repression of hedgehog signaling and BMP4 expression in growth plate cartilage by fibroblast growth factor receptor 3
Authors: Naski Michael C. , Colvin Jennifer S. , Coffin J. Douglas , Ornitz David M.
Published: April 2021

Fibroblast growth factor receptor 3 (FGFR3) is a key regulator of skeletal growth and activating mutations in Fgfr3 cause achondroplasia, the most common genetic form of dwarfism in humans. Little is known about the mechanism by which FGFR3 inhibits bone growth and how FGFR3 signaling interacts with other signaling pathways that regulate endochondral ossification. To understand these mechanisms, we targeted the expression of an activated FGFR3 to growth plate cartilage in mice using regulatory elements from the collagen II gene. As with humans carrying the achondroplasia mutation, the resulting transgenic mice are dwarfed, with axial, appendicular and craniofacial skeletal hypoplasia. We found that FGFR3 inhibited endochondral bone growth by markedly inhibiting chondrocyte proliferation and by slowing chondrocyte differentiation. Significantly, FGFR3 downregulated the Indian hedgehog (Ihh) signaling pathway and Bmp4 expression in both growth plate chondrocytes and in the perichondrium. Conversely, Bmp4 expression is upregulated in the perichondrium of Fgfr3−/− mice. These data support a model in which Fgfr3 is an upstream negative regulator of the hedgehog (Hh) signaling pathway. Additionally, Fgfr3 may coordinate the growth and differentiation of chondrocytes with the growth and differentiation of osteoprogenitor cells by simultaneously modulating Bmp4 and patched expression in both growth plate cartilage and in the perichondrium.
zfh-1 is required for germ cell migration and gonadal mesoderm development in Drosophila
Authors: Broihier Heather Tarczy , Moore Lisa A. , Doren Mark Van , Newman Stephanie , Lehmann Ruth
Published: April 2021

In Drosophila as well as many vertebrate systems, germ cells form extraembryonically and migrate into the embryo before navigating toward gonadal mesodermal cells. How the gonadal mesoderm attracts migratory germ cells is not understood in any system. We have taken a genetic approach to identify genes required for germ cell migration in Drosophila. Here we describe the role of zfh-1 in germ cell migration to the gonadal mesoderm. In zfh-1 mutant embryos, the initial association of germ cells and gonadal mesoderm is blocked. Loss of zfh-1 activity disrupts the development of two distinct mesodermal populations: the caudal visceral mesoderm and the gonadal mesoderm. We demonstrate that the caudal visceral mesoderm facilitates the migration of germ cells from the endoderm to the mesoderm. Zfh-1 is also expressed in the gonadal mesoderm throughout the development of this tissue. Ectopic expression of Zfh-1 is sufficient to induce additional gonadal mesodermal cells and to alter the temporal course of gene expression within these cells. Finally, through analysis of a tinman zfh-1 double mutant, we show that zfh-1 acts in conjunction with tinman, another homeodomain protein, in the specification of lateral mesodermal derivatives, including the gonadal mesoderm.
Nanos and Pumilio have critical roles in the development and function of Drosophila germline stem cells
Authors: Forbes Alexandria , Lehmann Ruth
Published: April 2021

The zinc-finger protein Nanos and the RNA-binding protein Pumilio act together to repress the translation of maternal hunchback RNA in the posterior of the Drosophila embryo, thereby allowing abdomen formation. nanos RNA is localized to the posterior pole during oogenesis and the posteriorly synthesized Nanos protein is sequestered into the germ cells as they form in the embryo. This maternally provided Nanos protein is present in germ cells throughout embryogenesis. Here we show that maternally deposited Nanos protein is essential for germ cell migration. Lack of zygotic activity of nanos and pumilio has a dramatic effect on germline development of homozygous females. Given the coordinate function of nanos and pumilio in embryonic patterning, we analyzed the role of these genes in oogenesis. We find that both genes act in the germline. Although the nanos and pumilio ovarian phenotypes have similarities and both genes ultimately affect germline stem cell development, the focus of these phenotypes appears to be different. While pumilio mutant ovaries fail to maintain stem cells and all germline cells differentiate into egg chambers, the focus of nanos function seems to lie in the differentiation of the stem cell progeny, the cystoblast. Consistent with the model that nanos and pumilio have different phenotypic foci during oogenesis, we detect high levels of Pumilio protein in the germline stem cells and high levels of Nanos in the dividing cystoblasts. We therefore suggest that, in contrast to embryonic patterning, Nanos and Pumilio may interact with different partners in the germline.
Requirements for the cytoplasmic domain of the αPS1, αPS2 and βPS integrin subunits during Drosophila development
Authors: Li Xitong , Graner Michael W. , Williams Erin L. , Roote Carol E. , Bunch Thomas A. , Zusman Susan
Published: April 2021

The integrins are a family of transmembrane heterodimeric proteins that mediate adhesive interactions and participate in signaling across the plasma membrane. In this study we examine the functional significance of the cytoplasmic domains of the αPS1, αPS2 and βPS subunits of the Drosophila Position Specific (PS) integrin family by analyzing the relationship between cytoplasmic domain structure and function in the context of a developing organism. By examining the ability of βPS molecules lacking the cytoplasmic domain to rescue embryonic abnormalities associated with PS integrin loss, we find that although many embryonic events require the βPS cytoplasmic domain, this portion of the molecule is not required for at least two processes requiring PS integrins: formation of midgut constrictions and maintaining germband integrity. Furthermore, our studies demonstrate that mutant proteins affecting four highly conserved amino acid residues in the cytoplasmic tail function with different efficiencies during embryonic development, suggesting that interaction of PS integrins with cytoplasmic ligands is developmentally modulated during embryogenesis.

We have also examined the ability of αPS1 and αPS2 to function without their cytoplasmic domains. By analyzing the ability of transgenes producing truncated αPS molecules to rescue abnormalities associated with integrin loss, we find that the cytoplasmic tail of αPS2 is essential for both embryonic and postembryonic processes, while this portion of αPS1 is not required for function in the wing and in the retina. Furthermore, temperature-shift experiments suggest roles for the αPS2 cytoplasmic domain in signaling events occurring in the developing wing.
A new role for Notch and Delta in cell fate decisions: patterning the feather array
Authors: Crowe Rebecca , Henrique Domingos , Ish-Horowicz David , Niswander Lee
Published: April 2021

Chick embryonic feather buds arise in a distinct spatial and temporal pattern. Although many genes are implicated in the growth and differentiation of the feather buds, little is known about how the discrete pattern of the feather array is formed and which gene products may be involved. Possible candidates include Notch and its ligands, Delta and Serrate, as they play a role in numerous cell fate decisions in many organisms. Here we show that Notch-1 and Notch-2 mRNAs are expressed in the skin in a localized pattern prior to feather bud initiation. In the early stages of feather bud development, Delta-1 and Notch-1 are localized to the forming buds while Notch-2 expression is excluded from the bud. Thus, Notch and Delta-1 are expressed at the correct time and place to be players in the formation of the feather pattern. Once the initial buds form, expression of Notch and its ligands is observed within each bud. Notch-1 and -2 and Serrate-1 and -2 are expressed throughout the growth and differentiation of the feathers whereas Delta-1 transcripts are downregulated.

We have also misexpressed chick Delta-1 using a replication competent retrovirus. This results in induction of Notch-1 and-2 and a loss of feather buds from the embryo in either large or small patches. In large regions of Delta-1 misexpression, feathers are lost throughout the infected area. In contrast, in small regions of misexpression, Delta-1 expressing cells differentiate into feather buds more quickly than normal and inhibit their neighbors from accepting a feather fate. We propose a dual role for Delta-1 in promoting feather bud development and in lateral inhibition. These results implicate the Notch/Delta receptor ligand pair in the formation of the feather array.
The PASTICCINO genes of Arabidopsis thaliana are involved in the control of cell division and differentiation
Authors: Faure Jean-Denis , Vittorioso Paola , Santoni Véronique , Fraisier Vincent , Prinsen Els , Barlier Isabelle , Onckelen Harry Van , Caboche Michel , Bellini Catherine
Published: April 2021

The control of cell division by growth regulators is critical to proper plant development. The isolation of single-gene mutants altered in the response to plant hormones should permit the identification of essential genes controlling the growth and development of plants. We have isolated mutants pasticcino belonging to 3 complementation groups (pas1, pas2, pas3) in the progeny of independent ethyl methane sulfonate and T-DNA mutagenized Arabidopsis thaliana plants. The screen was performed in the presence or absence of cytokinin. The mutants isolated were those that showed a significant hypertrophy of their apical parts when grown on cytokinin-containing medium. The pas mutants have altered embryo, leaf and root development. They display uncoordinated cell divisions which are enhanced by cytokinin. Physiological and biochemical analyses show that cytokinins are probably involved in pas phenotypes. The PAS genes have been mapped respectively to chromosomes 3, 5 and 1 and represent new plant genes involved in the control of cell division and plant development.
Mutations in the cadherin superfamily member gene dachsous cause a tissue polarity phenotype by altering frizzled signaling
Authors: Adler Paul N. , Charlton Jeannette , Liu Jingchun
Published: April 2021

The adult cuticular wing of Drosophila is covered by an array of distally pointing hairs that reveals the planar polarity of the wing. We report here that mutations in dachsous disrupt this regular pattern, and do so by affecting frizzled signaling. dachsous encodes a large membrane protein that contains many cadherin domains and dachsous mutations cause deformed body parts. We found that mutations in dachsous also result in a tissue polarity phenotype that at the cellular level is similar to frizzled, dishevelled and prickle, as many cells form a single hair of abnormal polarity. Although their cellular phenotype is similar to frizzled, dishevelled and prickle, dachsous mutant wings display a unique and distinctive abnormal hair polarity pattern including regions of reversed polarity. The development of this pattern requires the function of frizzled pathway genes suggesting that in a dachsous mutant the frizzled pathway is functioning - but in an abnormal way. Genetic experiments indicated that dachsous was not required for the intracellular transduction of the frizzled signal. However, we found that dachsous clones disrupted the polarity of neighboring wild-type cells suggesting the possibility that dachsous affected the intercellular signaling function of frizzled. Consistent with this hypothesis we found that frizzled clones in a dachsous mutant background displayed enhanced domineering non-autonomy, and that the anatomical direction of this domineering non-autonomy was altered in regions of dachsous wings that have abnormal hair polarity. The direction of this domineering nonautonomy was coincident with the direction of the abnormal hair polarity. We conclude that dachsous causes a tissue polarity phenotype because it alters the direction of frizzled signaling.
Systematic gain-of-function genetics in Drosophila
Authors: Rørth Pernille , Szabo Kornelia , Bailey Adina , Laverty Todd , Rehm Jay , Rubin Gerald M. , Weigmann Katrin , Milán Marco , Benes Vladimir , Ansorge Wilhelm , Cohen Stephen M.
Published: April 2021

A modular misexpression system was used to carry out systematic gain-of-function genetic screens in Drosophila. The system is based on inducible expression of genes tagged by insertion of a P-element vector carrying a GAL4-regulated promoter oriented to transcribe flanking genomic sequences. To identify genes involved in eye and wing development, the 2300 independent lines were screened for dominant phenotypes. Among many novel genes, the screen identified known genes, including hedgehog and decapentaplegic, implicated in these processes. A genetic interaction screen for suppressors of a cell migration defect in a hypomorphic slow border cells mutant identified known genes with likely roles in tyrosine kinase signaling and control of actin cytoskeleton, among many novel genes. These studies demonstrate the ability of the modular misexpression system to identify developmentally important genes and suggest that it will be generally useful for genetic interaction screens.
Apoptosis in late stage Drosophila nurse cells does not require genes within the H99 deficiency
Authors: Foley Kathleen , Cooley Lynn
Published: April 2021

We have determined that nurse cells are cleared from the Drosophila egg chamber by apoptosis. DNA fragmentation begins in nurse cells at stage 12, following the completion of cytoplasm transfer from the nurse cells to the oocyte. During stage 13, nurse cells increasingly contain highly fragmented DNA and disappear from the egg chamber concomitantly with the formation of apoptotic vesicles containing highly fragmented nuclear material. In dumpless mutant egg chambers that fail to complete cytoplasm transport from the nurse cells, DNA fragmentation is markedly delayed and begins during stage 13, when the majority of cytoplasm is lost from the nurse cells. These data suggest the presence of cytoplasmic factors in nurse cells that inhibit the initiation of DNA fragmentation. In addition, we have examined the ovarian expression patterns of regulatory genes implicated in Drosophila apoptosis. The positive regulators, reaper (rpr), head involution defective (hid) and grim, as well as the negative regulators, DIAP1 and DIAP2, are transcribed during oogenesis. However, germline clones homozygous for the deficiency Df(3)H99, which deletes rpr, hid and grim, undergo oogenesis in a manner morphologically indistinguishable from wild type, indicating that genes within this region are not necessary for apoptosis in nurse cells.
strabismus, a novel gene that regulates tissue polarity and cell fate decisions in Drosophila
Authors: Wolff Tanya , Rubin Gerald M.
Published: April 2021

Polarity in the Drosophila eye is manifested as a dorsoventral reflection of two chiral forms of the individual unit eyes, or ommatidia. These forms fall on opposite sides of a dorsoventral midline of mirror symmetry known as the equator. Polarity is established in the eye imaginal disc as cells adopt their fates and as the ommatidial precursors undergo coordinated rotation within the epithelium; the mechanisms that coordinate these early patterning events remain poorly understood. We have identified a novel gene, strabismus (stbm), which is required to establish polarity in the eye, legs and bristles of Drosophila. Many stbm ommatidia are reversed anteroposteriorly and/or dorsoventrally. In stbm eye discs, ommatidial rotation is delayed and some ommatidial precursors initiate rotation in the wrong direction. Mosaic analysis indicates that stbm is ommatidium autonomous and required in most, if not all, photoreceptors within an ommatidium to establish normal polarity. stbm also appears to play an instructive role during the establishment of the fates of photoreceptors R3 and R4. stbm encodes a novel protein with a potential PDZ domain-binding motif and two possible transmembrane domains. Sequence analysis of both vertebrate and invertebrate homologs indicates that stbm has been highly conserved throughout evolution.
Twist and Notch negatively regulate adult muscle differentiation in Drosophila
Authors: Anant Sumita , Roy Sudipto , VijayRaghavan K.
Published: April 2021

Twist is required in Drosophila embryogenesis for mesodermal specification and cell-fate choice. We have examined the role of Twist and Notch during adult indirect flight muscle development. Reduction in levels of Twist leads to abnormal myogenesis. Notch reduction causes a similar mutant phenotype and reduces Twist levels. Conversely, persistent expression, in myoblasts, of activated Notch causes continued twist expression and failure of differentiation as assayed by myosin expression. The gain-of-function phenotype of Notch is very similar to that seen upon persistent twist expression. These results point to a relationship between Notch function and twist regulation during indirect flight muscle development and show that decline in Twist levels is a requirement for the differentiation of these muscles, unlike the somatic muscles of the embryo.
Independent regulation of anterior/posterior and equatorial/polar polarity in the Drosophila eye; evidence for the involvement of Wnt signaling in the equatorial/polar axis
Authors: Wehrli Marcel , Tomlinson Andrew
Published: April 2021

The Drosophila retina is made from hundreds of asymmetric subunit ommatidia arranged in a crystalline-like array with each unit shaped and oriented in a precise way. One explanation for the precise cellular arrangements and orientations of the ommatidia is that they respond to two axes of polarized information present in the plane of the retinal epithelium. Earlier work showed that one of these axes lies in the anterior/posterior(A/P) direction and that the polarizing influence is closely associated with the sweep of the Hedgehog-dependent morphogenetic wave. Here we present evidence for a second and orthogonal axis of polarity, and show that it can be functionally separated from the A/P axis. Further, we show that the polarizing information acting in this equatorial/polar axis (Eq/Pl) is established in at least two steps – the activity of one signaling molecule functions to establish the graded activity of a second signal.
Medea is a Drosophila Smad4 homolog that is differentially required to potentiate DPP responses
Authors: Wisotzkey Robert G. , Mehra Arun , Sutherland David J. , Dobens Leonard L. , Liu Xiaoqing , Dohrmann Cord , Attisano Liliana , Raftery Laurel A.
Published: April 2021

Mothers against dpp (Mad) mediates Decapentaplegic (DPP) signaling throughout Drosophila development. Here we demonstrate that Medea encodes a MAD-related protein that functions in DPP signaling. MEDEA is most similar to mammalian Smad4 and forms heteromeric complexes with MAD. Like dpp, Medea is essential for embryonic dorsal/ventral patterning. However, Mad is essential in the germline for oogenesis whereas Medea is dispensable. In the wing primordium, loss of Medea most severely affects regions receiving low DPP signal. MEDEA is localized in the cytoplasm, is not regulated by phosphorylation, and requires physical association with MAD for nuclear translocation. Furthermore, inactivating MEDEA mutations prevent nuclear translocation either by preventing interaction with MAD or by trapping MAD/MEDEA complexes in the cytosol. Thus MAD-mediated nuclear translocation is essential for MEDEA function. Together these data show that, while MAD is essential for mediating all DPP signals, heteromeric MAD/MEDEA complexes function to modify or enhance DPP responses. We propose that this provides a general model for Smad4/MEDEA function in signaling by the TGF-β family.
Requirement for Xvent-1 and Xvent-2 gene function in dorsoventral patterning of Xenopus mesoderm
Authors: Onichtchouk Darya , Glinka Andrei , Niehrs Christof
Published: April 2021

Xvent-1 and Xvent-2 are members of a novel homeobox subfamily that have been implicated in dorsoventral patterning in Xenopus mesoderm and are thought to function in BMP signalling. Here we investigate the requirement for Xvent function by employing two dominant-negative strategies. Loss of Xvent function dorsalizes ventral mesoderm, induces secondary embryonic axes and directly neuralizes ectoderm. We further find that (1) Xvents act as transcriptional repressors, (2) Xvents function in an additive fashion and (3) a surprising number of genes are able to rescue dominant-negative Xvent phenotypes including Bmp-4, Smad-1 and wild-type Xvents and Xhox3, but not Xwnt-8. The results show that Xvent-1 and Xvent-2 are essential for ventral mesoderm formation and for preventing neural differentiation. A model is suggested to explain how Bmp-4 positional information is converted into distinct cellular responses.