bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and analysis of a gene that is essential for morphogenesis and prespore cell differentiation in Dictyostelium
Authors: Yasukawa Hiroo , Mohanty Sudhasri , Firtel Richard A.
Published: April 2021

We have identified a gene (PslA) that is expressed throughout Dictyostelium development and encodes a novel protein that is required for proper aggregation and subsequent cell-type differentiation and morphogenesis. pslA null (pslA−) cells produce large aggregation streams under conditions in which wild-type cells form discrete aggregates. Tips form along the stream, elongate to produce a finger, and eventually form a terminal structure that lacks a true sorus (spore head). More than half of the cells remain as a mass at the base of the developing fingers. The primary defect in the pslA− strain is the inability to induce prespore cell differentiation. Analyses of gene expression show a complete lack of prespore- specific gene expression and no mature spores are produced. In chimeras with wild-type cells, pslA− cells form the prestalk domain and normal, properly proportioned fruiting bodies can be produced. This indicates that pslA− cells are able to interact with wild- type cells and regulate patterning, even though pslA− cells are unable to express prespore cell-type-specific genes, do not participate in prespore cell differentiation and do not produce pslA− spores in the chimeras. While pslA− cells produce mature, vacuolated stalk cells during multicellular development, pslA− cells are unable to do so in vitro in response to exogenous DIF (a morphogen required for prestalk and stalk cell differentiation). These results indicate that pslA− cells exhibit a defect in the prestalk/stalk cell pathways under these experimental conditions. Our results suggest that PslA’s primary function is to regulate prespore cell determination very early in the prespore pathway via a cell-autonomous mechanism, possibly at the time of the initial prestalk/prespore cell-fate decision. Indirect immunofluorescence of myc-tagged PslA localizes the protein to the nucleus, suggesting that PslA may function to control the prespore pathway at the level of transcription.
Frizzled-8 is expressed in the Spemann organizer and plays a role in early morphogenesis
Authors: Deardorff Matthew A. , Tan Change , Conrad Leslee J. , Klein Peter S.
Published: April 2021

Wnts are secreted signaling molecules implicated in a large number of developmental processes. Frizzled proteins have been identified as likely receptors for Wnt ligands in vertebrates and invertebrates, but a functional role for vertebrate frizzleds has not yet been defined. To assess the endogenous role of frizzled proteins during vertebrate development, we have identified and characterized a Xenopus frizzled gene (xfz8). It is highly expressed in the deep cells of the Spemann organizer prior to dorsal lip formation and in the early involuting marginal zone. Ectopic expression of xfz8 in ventral cells leads to complete secondary axis formation and can synergize with Xwnt-8 while an inhibitory form of xfz8 (Nxfz8) blocks axis duplication by Xwnt-8, consistent with a role for xfz8 in Wnt signal transduction. Expression of Nxfz8 in dorsal cells has profound effects on morphogenesis during gastrulation and neurulation that result in dramatic shortening of the anterior-posterior axis. Our results suggest a role for xfz8 in morphogenesis during the gastrula stage of embryogenesis.
Isolation and developmental expression of the amphioxus Pax-6 gene (AmphiPax-6): insights into eye and photoreceptor evolution
Authors: Glardon Sacha , Holland Linda Z. , Gehring Walter J. , Holland Nicholas D.
Published: April 2021

Pax-6 genes have been identified from a broad range of invertebrate and vertebrate animals and shown to be always involved in early eye development. Therefore, it has been proposed that the various types of eyes evolved from a single eye prototype, by a Pax-6-dependent mechanism. Here we describe the characterization of a cephalochordate Pax-6 gene. The single amphioxus Pax-6 gene (AmphiPax-6) can produce several alternatively spliced transcripts, resulting in proteins with markedly different amino and carboxy termini. The amphioxus Pax-6 proteins are 92% identical to mammalian Pax-6 proteins in the paired domain and 100% identical in the homeodomain. Expression of AmphiPax-6 in the anterior epidermis of embryos may be related to development of an olfactory epithelium. Expression is also detectable in Hatschek’s left diverticulum as it forms the preoral ciliated pit, part of which gives rise to the homolog of the vertebrate anterior pituitary. A zone of expression in the anterior neural plate of early embryos is carried into the cerebral vesicle (a probable diencephalic homolog) during neurulation. This zone includes cells that will differentiate into the lamellar body, a presumed homolog of the vertebrate pineal eye. In neurulae, AmphiPax-6 is also expressed in ventral cells at the anterior tip of the nerve cord; these cells are precursors of the photoreceptive neurons of the frontal eye, the presumed homolog of the vertebrate paired eyes. However, AmphiPax-6 expression was not detected in two additional types of photoreceptors, the Joseph cells or the organs of Hesse, which are evidently relatively recent adaptations (ganglionic photoreceptors) and appear to be rare exceptions to the general rule that animal photoreceptors develop from a genetic program triggered by Pax-6.
faint sausage encodes a novel extracellular protein of the immunoglobulin superfamily required for cell migration and the establishment of normal axonal pathways in the Drosophila nervous system
Authors: Lekven Arne C. , Tepass Ulrich , Keshmeshian Mariana , Hartenstein Volker
Published: April 2021

We examined the structure of the nervous system in Drosophila embryos homozygous for a null mutation in the faint sausage (fas) gene. In the peripheral nervous system (PNS) of fas mutants, neurons fail to delaminate from the ectodermal epithelium; in the central nervous system (CNS), the positions of neuronal cell bodies and glial cells are abnormal and normal axonal pathways do not form. Sequence analysis of fas cDNAs revealed that the fas protein product has characteristics of an extracellular protein and that it is a novel member of the immunoglobulin (Ig) superfamily. In situ hybridization demonstrated that fas transcripts are expressed throughout the embryo but they are in relatively high concentrations in the lateral ectoderm, from which the peripheral nervous system delaminates and in the CNS. Antiserum directed against Fas protein was found to stain neurons but not glia in the CNS. We conclude that fas encodes a protein that, in the developing nervous system, is present on the surface of neurons and is essential for nerve cell migration and the establishment of axonal pathways.
Gli2 is required for induction of floor plate and adjacent cells, but not most ventral neurons in the mouse central nervous system
Authors: Matise Michael P. , Epstein Douglas J. , Park Heidi L. , Platt Kenneth A. , Joyner Alexandra L.
Published: April 2021

Induction of the floor plate at the ventral midline of the neural tube is one of the earliest events in the establishment of dorsoventral (d/v) polarity in the vertebrate central nervous system (CNS). The secreted molecule, Sonic hedgehog, has been shown to be both necessary and sufficient for this induction. In vertebrates, several downstream components of this signalling pathway have been identified, including members of the Gli transcription factor family. In this study, we have examined d/v patterning of the CNS in Gli2 mouse mutants. We have found that the floor plate throughout the midbrain, hindbrain and spinal cord does not form in Gli2 homozygotes. Despite this, motoneurons and ventral interneurons form in their normal d/v positions at 9.5 to 12.5 days postcoitum (dpc). However, cells that are generated in the region flanking the floor plate, including dopaminergic and serotonergic neurons, were greatly reduced in number or absent in Gli2 homozygous embryos. These results suggest that early signals derived from the notochord can be sufficient for establishing the basic d/v domains of cell differentiation in the ventral spinal cord and hindbrain. Interestingly, the notochord in Gli2 mutants does not regress ventrally after 10.5 dpc, as in normal embryos. Finally, the spinal cord of Gli1/Gli2 zinc-finger-deletion double homozygous mutants appeared similar to Gli2 homozygotes, indicating that neither gene is required downstream of Shh for the early development of ventral cell fates outside the ventral midline.
The Shh signalling pathway in tooth development: defects in Gli2 and Gli3 mutants
Authors: Hardcastle Zoë , Mo Rong , Hui Chi-chung , Sharpe Paul T.
Published: April 2021

The expression of genes involved in the Sonic Hedgehog signalling pathway, including Shh, Ptc, Smo, Gli1, Gli2 and Gli3, were found to be expressed in temporal and spatial patterns during early murine tooth development, suggestive of a role in early tooth germ initiation and subsequent epithelial-mesenchymal interactions. Of these Ptc, Smo, Gli1, Gli2 and Gli3 were expressed in epithelium and mesenchyme whereas Shh was only detected in epithelium. This suggests that Shh is involved in both lateral (epithelial-mesenchymal) and planar (epithelial-epithelial) signalling in early tooth development. Ectopic application of Shh protein to mandibular mesenchyme induced the expression of Ptc and Gli1. Addition of exogenous Shh protein directly into early tooth germs and adjacent to tooth germs, resulted in abnormal epithelial invagination, indicative of a role for Shh in epithelial cell proliferation.

In order to assess the possible role of this pathway, tooth development in Gli2 and Gli3 mutant embryos was investigated. Gli2 mutants were found to have abnormal development of maxillary incisors, probably resulting from a mild holoprosencephaly, whereas Gli3 mutants had no major tooth abnormalities. Gli2/Gli3 double homozygous mutants did not develop any normal teeth and did not survive beyond embryonic day 14.5; however, Gli2−/−; Gli3+/− did survive until birth and had small molars and mandibular incisors whereas maxillary incisor development was arrested as a rudimentary epithelial thickening.

These results show an essential role for Shh signalling in tooth development that involves functional redundancy of downstream Gli genes.
Differential regulation of T-box and homeobox transcription factors suggests roles in controlling chick limb-type identity
Authors: Logan Malcolm , Simon Hans-Georg , Tabin Cliff
Published: April 2021

The wing and the leg of the chick, although homologous structures, have characteristic patterns of skeletal elements, muscles, tendons, featherbuds and scales. Despite recent advances in understanding the common genetic pathways patterning the wing and leg, the molecular nature of the specification of limb-type identity has remained elusive.

Embryological experiments have indicated the existence of limb-specific territories in the flank. In the newt, deviation of nerves from the limb into the flank can induce ectopic limbs to form from this tissue. In the chick, Fibroblast growth factor (FGF)-soaked beads applied to the flank can induce ectopic formation of limbs from the surrounding tissue. In both cases, the type of limb that forms, either a wing/forelimb or leg/hindlimb, is dependent upon the location to which the limb-inducing signal is applied.

We have isolated and characterised three candidate genes for controlling limb identity in the chick. Two T-box transcription factors, cTbx4 and cTbx5, are expressed in a restricted manner in the leg bud and wing buds, respectively. cPtx1, a member of the Otx-related subclass of paired-type homeodomain proteins, is expressed exclusively in the leg bud. Using FGF to induce ectopic limb buds of wing, leg and intermediate identity, we show that early expression of cTbx5, cTbx4 and cPtx1 in the induced limb buds correlates with later wing- or leg-type identity of ectopic limbs. We observe a general correlation between the location of an ectopic outgrowth induced by FGF and the identity of the resulting limb but, significantly, we report that there is no definitive rostral-caudal level that divides the ectopic wing and leg territories.
Patterning of the follicle cell epithelium along the anterior-posterior axis during Drosophila oogenesis
Authors: González-Reyes Acaimo , Johnston Daniel St
Published: April 2021

Gurken signals from the oocyte to the adjacent follicle cells twice during Drosophila oogenesis; first to induce posterior fate, thereby polarising the anterior-posterior axis of the future embryo and then to induce dorsal fate and polarise the dorsal-ventral axis. Here we show that Gurken induces two different follicle cell fates because the follicle cells at the termini of the egg chamber differ in their competence to respond to Gurken from the main-body follicle cells in between. By removing the putative Gurken receptor, Egfr, in clones of cells, we show that Gurken signals directly to induce posterior fate in about 200 cells, defining a terminal competence domain that extends 10-11 cell diameters from the pole. Furthermore, small clones of Egfr mutant cells at the posterior interpret their position with respect to the pole and differentiate as the appropriate anterior cell type. Thus, the two terminal follicle cell populations contain a symmetric prepattern that is independent of Gurken signalling. These results suggest a three-step model for the anterior-posterior patterning of the follicular epithelium that subdivides this axis into at least five distinct cell types. Finally, we show that Notch plays a role in both the specification and patterning of the terminal follicle cells, providing a possible explanation for the defect in anterior-posterior axis formation caused by Notch and Delta mutants.
The rough sheath2 gene negatively regulates homeobox gene expression during maize leaf development
Authors: Schneeberger Richard , Tsiantis Miltos , Freeling Michael , Langdale Jane A.
Published: April 2021

Leaves of higher plants are produced in a sequential manner through the differentiation of cells that are derived from the shoot apical meristem. Current evidence suggests that this transition from meristematic to leaf cell fate requires the down-regulation of knotted1-like homeobox (knox) gene expression. If knox gene expression is not repressed, overall leaf shape and cellular differentiation within the leaf are perturbed. In order to identify genes that are required for the aquisition of leaf cell fates, we have genetically screened for recessive mutations that confer phenotypes similar to dominant mutations (e.g. Knotted1 and Rough sheath1) that result in the ectopic expression of class I knox genes. Independently derived mutations at the rough sheath2 (rs2) locus condition a range of pleiotropic leaf, node and internode phenotypes that are sensitive to genetic background and environment. Phenotypes include dwarfism, leaf twisting, disorganized differentiation of the blade-sheath boundary, aberrant vascular patterning and the generation of semi-bladeless leaves. knox genes are initially repressed in rs2 mutants as leaf founder cells are recruited in the meristem. However, this repression is often incomplete and is not maintained as the leaf progresses through developement. Expression studies indicate that three knox genes are ectopically or over-expressed in developing primordia and in mature leaves. We therefore propose that the rs2 gene product acts to repress knox gene expression (either directly or indirectly) and that rs2 gene action is essential for the elaboration of normal leaf morphology.
A subset of Notch functions during Drosophila eye development require Su(H) and the E(spl) gene complex
Authors: Ligoxygakis Petros , Yu Sung-Yun , Delidakis Christos , Baker Nicholas E.
Published: April 2021

The Notch signalling pathway is involved in many processes where cell fate is decided. Previous work showed that Notch is required at successive steps during R8 specification in the Drosophila eye. Initially, Notch enhances atonal expression and promotes atonal function. After atonal autoregulation has been established, Notch signalling represses atonal expression during lateral specification. In this paper we investigate which known components of the Notch pathway are involved in each signalling process. Using clonal analysis we show that a ligand of Notch, Delta, is required along with Notch for both proneural enhancement and lateral specification, while the downstream components Suppressor-of-Hairless and Enhancer-of-Split are involved only in lateral specification. Our data point to a distinct signal transduction pathway during proneural enhancement by Notch. Using misexpression experiments we also show that particular Enhancer-of-split bHLH genes can differ greatly in their contribution to lateral specification.
shaven and sparkling are mutations in separate enhancers of the Drosophila Pax2 homolog
Authors: Fu Weimin , Duan Hong , Frei Erich , Noll Markus
Published: April 2021

We have previously shown that the sparkling gene, which like mammalian Pax2 plays an important role in eye development, is encoded by the Drosophila homolog of Pax2. Here we demonstrate that D-Pax2 also encodes the shaven function, which is crucial during bristle development. Both sv and spa alleles, previously thought to represent different genes, are mutations in two widely separated enhancers of D-Pax2. The sv function of D-Pax2 acts in at least two distinct steps of mechanosensory bristle development: the specification of the alternative fate of shaft as opposed to socket cell, and later the differentiation of the shaft cell.
Interactions among Delta, Serrate and Fringe modulate Notch activity during Drosophila wing development
Authors: Klein T. , Arias A. Martinez
Published: April 2021

The Notch signalling pathway plays an important role during the development of the wing primordium, especially of the wing blade and margin. In these processes, the activity of Notch is controlled by the activity of the dorsal specific nuclear protein Apterous, which regulates the expression of the Notch ligand, Serrate, and the Fringe signalling molecule. The other Notch ligand, Delta, also plays a role in the development and patterning of the wing. It has been proposed that Fringe modulates the ability of Serrate and Delta to signal through Notch and thereby restricts Notch signalling to the dorsoventral boundary of the developing wing blade. Here we report the results of experiments aimed at establishing the relationships between Fringe, Serrate and Delta during wing development. We find that Serrate is not required for the initiation of wing development but rather for the expansion and early patterning of the wing primordium. We provide evidence that, at the onset of wing development, Delta is under the control of apterous and might be the Notch ligand in this process. In addition, we find that Fringe function requires Su(H). Our results suggest that Notch signalling during wing development relies on careful balances between positive and dominant negative interactions between Notch ligands, some of which are mediated by Fringe.
Cytoplasmic polyadenylation of Toll mRNA is required for dorsal-ventral patterning in Drosophila embryogenesis
Authors: Schisa Jennifer A. , Strickland Sidney
Published: April 2021

Toll encodes a receptor that is critical for dorsal-ventral patterning in the early Drosophila embryo. Previous data have suggested that the accumulation of Toll protein in the embryo temporally correlates with elongation of the poly (A) tail of the message. Here, we demonstrate that Toll mRNA is translationally activated by regulated cytoplasmic polyadenylation. We also identify a 192 nucleotide regulatory element in the Toll 3’ UTR that is necessary for robust translational activation of Toll mRNA and also regulates polyadenylation. UV crosslinking analyses suggest that two proteins bind specifically to the 192 nucleotide element. One or both of these proteins may be factors that are required for translational regulation or cytoplasmic polyadenylation. These studies demonstrate that regulated polyadenylation plays a critical role in the Drosophila dorsal-ventral patterning system.
A series of no isthmus (noi) alleles of the zebrafish pax2.1 gene reveals multiple signaling events in development of the midbrain-hindbrain boundary
Authors: Lun Klaus , Brand Michael
Published: April 2021

Generation of cell diversity in the vertebrate central nervous system starts during gastrulation stages in the ectodermal germ layer and involves specialized cell groups, such as the organizer located at the midbrain-hindbrain boundary (MHB). Mutations in the zebrafish no isthmus (noi) gene alter development of the MHB, and affect the pax2.1 gene (formerly pax(zf-b)). Analysis of the structure of pax2.1 reveals at least 12 normal splice variants. The noi alleles can be arranged, by molecular and phenotypic criteria, into a series of five alleles of differing strength, ranging from a null allele to weak alleles. In keeping with a role in development of the MHB organizer, gene expression is already affected in the MHB primordium of the gastrula neural ectoderm in noi mutants. eng3 activation is completely and eng2 activation is strongly dependent on noi function. In contrast, onset of wnt1, fgf8 and her5 expression occurs normally in the null mutants, but is eliminated later on. Our observations suggest that three signaling pathways, involving pax2.1, wnt1 and fgf8, are activated independently in early anterior-posterior patterning of this area. In addition, analysis of the allelic series unexpectedly suggests that noi activity is also required during dorsal-ventral patterning of the MHB in somitogenesis stages, and possibly in a later eng expression phase. We propose that noi/pax2.1 participates in sequential signaling processes as a key integrator of midbrain-hindbrain boundary development.
Intrinsic programs of patterned cell lineages in isolated vertebrate CNS ventricular zone cells
Authors: Qian Xueming , Goderie Susan K. , Shen Qin , Stern Jeffrey H. , Temple Sally
Published: April 2021

Using long-term, time-lapse video-microscopy, we investigated how single progenitor cells isolated from the early embryonic cerebral cortex produce neurons and glia over time. Clones of 10 cells or less were produced by short symmetric or asymmetric division patterns, commonly terminating in a ‘pair progenitor’ for two morphologically identical neurons. Larger trees were composites of these short sub-lineages: more prolific neuroblasts underwent repeated asymmetric divisions, each producing a minor neuroblast that typically made ≤10 progeny, and a sister cell capable of generating more progeny. Particular division patterns were seen repeatedly. In contrast, glioblasts underwent a prolonged series of symmetric divisions. These patterned lineage trees were generated from isolated cells growing on plastic, suggesting they are largely intrinsically programmed. Our data demonstrate for the first time that CNS progenitor cells have stereotyped division patterns, and suggest that as in invertebrates, these may play a role in neural development.
The role of p53 and cell death by apoptosis and necrosis in 4-hydroperoxycyclophosphamide-induced limb malformations
Authors: Moallem S. Adel , Hales Barbara F.
Published: April 2021

The exposure of embryonic murine limbs in vitro to an activated analog of cyclophosphamide, 4-hydroperoxycyclophosphamide (4OOH-CPA), induced limb malformations and apoptosis. The purpose of this study was to investigate the role of the tumor suppressor/cell cycle checkpoint gene, p53, and of cell cycle arrest in the response of the limbs to cyclophosphamide. Limbs, excised on day 12 of gestation from wild-type, heterozygous or homozygous p53-knockout transgenic murine embryos, were treated with vehicle (water) or 4OOH-CPA (0.3, 1.0 or 3.0 μg/ml) and cultured for 6 days. Exposure of wild-type (+/+) limbs to 4OOH-CPA resulted in limb malformations, and reduced limb areas and developmental scores. The homozygous (−/−) limbs were dramatically more sensitive to the effects of 4OOH-CPA, as assessed by limb morphology, area and score. Heterozygous limbs exposed to the drug were intermediate for each parameter. Apoptosis, as assessed by the formation of a DNA ladder, was increased in drug-exposed wild-type limbs, but not in the drug-exposed homozygous limbs. Light and electron microscopy examination of the limbs revealed that drug treatment of wild-type limbs induced the morphological changes typical of apoptosis, particularly in the interdigital regions. In contrast, there was no evidence of apoptosis in homozygous limbs exposed to 4-OOH-CPA; morphological characteristics of necrosis such as cell membrane breakdown, mitochondrial swelling and cellular disintegration were evident throughout these limbs. Heterozygous limbs had cells dying with the characteristics of both apoptosis and necrosis. Fragments of poly(ADP-ribose) polymerase characteristic of necrosis predominated in the drug-treated heterozygous and homozygous limbs. 4-OOH-CPA-treatment of limbs from wild-type embryos led to arrest of the cell cycle at the G1/S phase. No cell cycle arrest was observed after drug treatment of homozygous limbs, in which populations of cells in S and G2/M phases, as well as a population of sub G1 cells, were found. Thus, the presence of p53 and of p53-dependent apoptosis protect organogenesis-stage limbs from insult with a teratogen. The absence of p53 may decrease DNA repair capacity and contribute to the accumulation of DNA damage in limb cells and their daughter cells; the failure of apoptosis to eliminate cells with DNA damage may result in increased cell death by necrosis and major limb malformations.
The Drosophila EGF receptor controls the formation and specification of neuroblasts along the dorsal-ventral axis of the Drosophila embryo
Authors: Skeath James B.
Published: April 2021

The segmented portion of the Drosophila embryonic central nervous system develops from a bilaterally symmetrical, segmentally reiterated array of 30 unique neural stem cells, called neuroblasts. The first 15 neuroblasts form about 30-60 minutes after gastrulation in two sequential waves of neuroblast segregation and are arranged in three dorsoventral columns and four anteroposterior rows per hemisegment. Each neuroblast acquires a unique identity, based on gene expression and the unique and nearly invariant cell lineage it produces. Recent experiments indicate that the segmentation genes specify neuroblast identity along the AP axis. However, little is known as to the control of neuroblast identity along the DV axis. Here, I show that the Drosophila EGF receptor (encoded by the DER gene) promotes the formation, patterning and individual fate specification of early forming neuroblasts along the DV axis. Specifically, I use molecular markers that identify particular neuroectodermal domains, all neuroblasts or individual neuroblasts, to show that in DER mutant embryos (1) intermediate column neuroblasts do not form, (2) medial column neuroblasts often acquire identities inappropriate for their position, while (3) lateral neuroblasts develop normally. Furthermore, I show that active DER signaling occurs in the regions from which the medial and intermediate neuroblasts will later delaminate. In addition, I demonstrate that the concomitant loss of rhomboid and vein yield CNS phenotypes indistinguishable from DER mutant embryos, even though loss of either gene alone yields minor CNS phenotypes. These results demonstrate that DER plays a critical role during neuroblast formation, patterning and specification along the DV axis within the developing Drosophila embryonic CNS.
Paracrine PDGF-B/PDGF-Rβ signaling controls mesangial cell development in kidney glomeruli
Authors: Lindahl Per , Hellström Mats , Kalén Mattias , Karlsson Linda , Pekny Milos , Pekna Marcela , Soriano Philippe , Betsholtz Christer
Published: April 2021

Kidney glomerulus mesangial cells fail to develop in mice carrying targeted null mutations in the platelet-derived growth factor (PDGF)-B or PDGF-Rβ genes. We have examined the pattern of expression of these genes and smooth muscle markers during kidney development, to address the possible mechanisms underlying the mutant phenotypes. In wild-type embryos, PDGF-B was expressed in vascular endothelial cells, particularly in capillary endothelial cells in the developing glomeruli, whereas PDGF-Rβ was found in perivascular mesenchymal cells in the developing renal cortex. In the course of glomerular development, small groups of PDGF-Rβ and desmin-expressing cells collected in the ‘S’-shaped and early cup-shaped vesicles, and at later stages such cells were found in the glomerular mesangium. In PDGF-B or -Rβ null embryos, some PDGF-Rβ/desmin or desmin-positive cells, respectively, were seen in early cup-shaped vesicles, but fewer than in the wild type, and further development of the mesangium failed. In mouse chimeras composed of PDGF-Rβ +/+ and −/− cells, the Rβ−/− cells failed to populate the glomerular mesangium. Our results show that while the mesangial cell lineage is specified independently of PDGF-B/Rβ, these molecules provide critical permissive signals in mesangial cell development. We propose a model in which mesangial cells originate from PDGF-Rβ-positive progenitors surrounding the developing glomerular afferent and efferent arterioles, and are co-recruited in response to PDGF-B during angiogenic formation of the glomerular capillary tuft.
Patterned epidermal cell death in wild-type and segment polarity mutant Drosophila embryos
Authors: Pazdera Todd M. , Janardhan Prem , Minden Jonathan S.
Published: April 2021

Programmed cell death plays an essential role in the normal embryonic development of Drosophila melanogaster. One region of the embryo where cell death occurs, but has not been studied in detail, is the abdominal epidermis. Because cell death is a fleeting process, we have used time-lapse, fluorescence microscopy to map epidermal apoptosis throughout embryonic development. Cell death occurs in a stereotypically striped pattern near both sides of the segment border and to a lesser extent in the middle of the segment. This map of wild-type cell death was used to determine how cell death patterns change in response to genetic perturbations that affect epidermal patterning. Previous studies have suggested that segment polarity mutant phenotypes are partially the result of increased cell death. Mutations in wingless, armadillo, and gooseberry led to dramatic increases in apoptosis in the anterior of the segment while a naked mutation resulted in a dramatic increase in the death of engrailed cells in the posterior of the segment. These results show that segment polarity gene expression is necessary for the survival of specific rows of epidermal cells and may provide insight into the establishment of the wild-type epidermal cell death pattern.
Dermomyotomal origin of the ribs as revealed by extirpation and transplantation experiments in chick and quail embryos
Authors: Kato Noriko , Aoyama Hirohiko
Published: April 2021

To elucidate role of the dermomyotome in the formation of the axial skeleton, we performed extirpation and transplantation experiments on the dermomyotomes in chick and quail embryos. When the thoracic dermomyotomes of chick embryos were removed, the intercostal muscles and the distal ribs were deficient, while the proximal ribs were more or less normal. Quail tissues including the dermomyotome, the ectoderm and the medial edge of lateral plate, were transplanted to replace chick dermomyotomes. In these chimeras, the ribs, which would be deficient without the back-transplantation, were recovered. The cells of the recovered part of the ribs as well as the intercostal muscles were derived from the quail transplants. These findings suggest that the distal rib originated from the dermomyotomes and not the sclerotome as previously believed. To localize the origin of the distal rib further, we removed restricted regions of the dermomyotomes along the mediolateral and the rostrocaudal axis. The more lateral the part of the dermomyotomes that we removed, the more distal the part of the ribs affected. On the contrary, when the rostral and caudal edges of the dermomyotomes were removed, only the vertebral ribs showed extensive deficiencies while removal of the middle part between the edges caused less deficiency. The sternal ribs were not deficient in either case, but were extensively affected when the entire lateral edge of dermomyotomes was included in the region removed. We conclude that the lateral edges of the dermomyotomes are the primordia of the sternal ribs, and the rostral and/or caudal edges of the medial part of dermomyotomes are the primordia of the distal part and not of the proximal part of the vertebral ribs.
Regulation of BMP7 expression during kidney development
Authors: Godin Robert E. , Takaesu Norma T. , Robertson Elizabeth J. , Dudley Andrew T.
Published: April 2021

Members of the Bone Morphogenetic Protein (BMP) family exhibit overlapping and dynamic expression patterns throughout embryogenesis. However, little is known about the upstream regulators of these important signaling molecules. There is some evidence that BMP signaling may be autoregulative as demonstrated for BMP4 during tooth development. Analysis of BMP7 expression during kidney development, in conjunction with studies analyzing the effect of recombinant BMP7 on isolated kidney mesenchyme, suggest that a similar mechanism may operate for BMP7. We have generated a β-gal-expressing reporter allele at the BMP7 locus to closely monitor expression of BMP7 during embryonic kidney development. In contrast to other studies, our analysis of BMP7/lacZ homozygous mutant embryos, shows that BMP7 expression is not subject to autoregulation in any tissue. In addition, we have used this reporter allele to analyze the expression of BMP7 in response to several known survival factors (EGF, bFGF) and inducers of metanephric mesenchyme, including the ureteric bud, spinal cord and LiCl. These studies show that treatment of isolated mesenchyme with EGF or bFGF allows survival of the mesenchyme but neither factor is sufficient to maintain BMP7 expression in this population of cells. Rather, BMP7 expression in the mesenchyme is contingent on an inductive signal. Thus, the reporter allele provides a convenient marker for the induced mesenchyme. Interestingly LiCl has been shown to activate the Wnt signaling pathway, suggesting that BMP7 expression in the mesenchyme is regulated by a Wnt signal. Treatment of whole kidneys with sodium chlorate to disrupt proteoglycan synthesis results in the loss of BMP7 expression in the mesenchyme whereas expression in the epithelial components of the kidney are unaffected. Heterologous recombinations of ureteric bud with either limb or lung mesenchyme demonstrate that expression of BMP7 is maintained in this epithelial structure. Taken together, these data indicate that BMP7 expression in the epithelial components of the kidney is not dependent on cell-cell or cell-ECM interactions with the metanephric mesenchyme. By contrast, BMP7 expression in the metanephric mesenchyme is dependent on proteoglycans and possibly Wnt signaling.
Gene activation during early stages of lens induction in Xenopus
Authors: Zygar Carol A. , Cook T. Les , Grainger Robert M.
Published: April 2021

Several stages in the lens determination process have been defined, though it is not known which gene products control these events. At mid-gastrula stages in Xenopus, ectoderm is transiently competent to respond to lens-inducing signals. Between late gastrula and neural tube stages, the presumptive lens ectoderm acquires a lens-forming bias, becomes specified to form lens and begins differentiation. Several genes have been identified, either by expression pattern, mutant phenotype or involvement in crystallin gene regulation, that may play a role in lens bias and specification, and we focus on these roles here. Fate mapping shows that the transcriptional regulators Otx-2, Pax-6 and Sox-3 are expressed in the presumptive lens ectoderm prior to lens differentiation. Otx-2 appears first, followed by Pax-6, during the stages of lens bias (late neural plate stages); expression of Sox-3 follows neural tube closure and lens specification. We also demonstrate the expression of these genes in competent ectoderm transplanted to the lens-forming region. Expression of these genes is maintained or activated preferentially in ectoderm in response to the anterior head environment. Finally, we examined activation of these genes in response to early and late lens-inducing signals. Activation of Otx-2, Pax-6 and Sox-3 in competent ectoderm occurs in response to the early inducing tissue, the anterior neural plate. Since Sox-3 is activated following neural tube closure, we tested its dependence on the later inducing tissue, the optic vesicle, which contacts lens ectoderm at this stage. Sox-3 is not expressed in lens ectoderm, nor does a lens form, when the optic vesicle anlage is removed at late neural plate stages. Expression of these genes demarcates patterning events preceding differentiation and is tightly coupled to particular phases of lens induction.
Atypical protein kinase C cooperates with PAR-3 to establish embryonic polarity in Caenorhabditis elegans
Authors: Tabuse Yo , Izumi Yasushi , Piano Fabio , Kemphues Kenneth J. , Miwa Johji , Ohno Shigeo
Published: April 2021

Asymmetric cell divisions, critically important to specify cell types in the development of multicellular organisms, require polarized distribution of cytoplasmic components and the proper alignment of the mitotic apparatus. In Caenorhabditis elegans, the maternally expressed protein, PAR-3, is localized to one pole of asymmetrically dividing blastomeres and is required for these asymmetric divisions. In this paper, we report that an atypical protein kinase C (PKC-3) is essential for proper asymmetric cell divisions and co-localizes with PAR-3. Embryos depleted of PKC-3 by RNA interference die showing Par-like phenotypes including defects in early asymmetric divisions and mislocalized germline-specific granules (P granules). The defective phenotypes of PKC-3-depleted embryos are similar to those exhibited by mutants for par-3 and another par gene, par-6. Direct interaction of PKC-3 with PAR-3 is shown by in vitro binding analysis. This result is reinforced by the observation that PKC-3 and PAR-3 co-localize in vivo. Furthermore, PKC-3 and PAR-3 show mutual dependence on each other and on three of the other par genes for their localization. We conclude that PKC-3 plays an indispensable role in establishing embryonic polarity through interaction with PAR-3.
The Drosophila AP axis is polarised by the cadherin-mediated positioning of the oocyte
Authors: González-Reyes Acaimo , Johnston Daniel St
Published: April 2021

The anterior-posterior axis of Drosophila originates from two symmetry-breaking steps during early oogenesis. First, one of the two pro-oocytes within the cyst of 16 germline cells is selected to become the oocyte. This cell then comes to lie posterior to the other germline cells of the cyst, thereby defining the polarity of the axis. Here we show that the oocyte reaches the posterior of the cyst in two steps. (1) The cyst flattens as it enters region 2b of the germarium to place the two pro-oocytes in the centre of the cyst, where they contact the posterior follicle cells. (2) One cell is selected to become the oocyte and protrudes into the posterior follicle cell layer when the cyst rounds up on entering region 3. During this germ cell rearrangement, the components of the homophilic cadherin adhesion complex, DE-cadherin, Armadillo and α-catenin, accumulate along the border between the oocyte and the posterior follicle cells. Furthermore, the positioning of the oocyte requires cadherin-dependent adhesion between these two cell types, since the oocyte is frequently misplaced when DE-cadherin is removed from either the germline or the posterior follicle cells. We conclude that the oocyte reaches the posterior of the germline cyst because it adheres more strongly to the posterior follicle cells than its neighbours during the germ cell rearrangement that occurs as the cyst moves into region 3. The Drosophila anterior-posterior axis therefore becomes polarised by an unusual cadherin-mediated adhesion between a germ cell and mesodermal follicle cells.
ladybird determines cell fate decisions during diversification of Drosophila somatic muscles
Authors: Jagla Teresa , Bellard François , Lutz Yves , Dretzen Guy , Bellard Maria , Jagla Krzysztof
Published: April 2021

In the mesoderm of Drosophila embryos, a defined number of cells segregate as progenitors of individual body wall muscles. Progenitors and their progeny founder cells display lineage-specific expression of transcription factors but the mechanisms that regulate their unique identities are poorly understood. Here we show that the homeobox genes ladybird early and ladybird late are expressed in only one muscle progenitor and its progeny: the segmental border muscle founder cell and two precursors of adult muscles. The segregation of the ladybird-positive progenitor requires coordinate action of neurogenic genes and an interplay of inductive Hedgehog and Wingless signals from the overlying ectoderm. Unlike so far described progenitors but similar to the neuroblasts, the ladybird-positive progenitor undergoes morphologically asymmetric division. We demonstrate that the ectopic ladybird expression is sufficient to change the identity of a subset of progenitor/founder cells and to generate an altered pattern of muscle precursors. When ectopically expressed, ladybird transforms the identity of neighbouring, Krüppel-positive progenitors leading to the formation of giant segmental border muscles and supernumerary precursors of lateral adult muscles. In embryos lacking ladybird gene function, specification of two ladybird-expressing myoblast lineages is affected. The segmental border muscles do not form or have abnormal shapes and insertion sites while the number of lateral precursors of adult muscles is dramatically reduced. Altogether our results provide new insights into the genetic control of diversification of muscle precursors and indicate a further similarity between the myogenic and neurogenic pathways.
Disabled-1 acts downstream of Reelin in a signaling pathway that controls laminar organization in the mammalian brain
Authors: Rice Dennis S. , Sheldon Michael , D’Arcangelo Gabriella , Nakajima Kazunori , Goldowitz Dan , Curran Tom
Published: April 2021

Mutation of either reelin (Reln) or disabled-1 (Dab1) results in widespread abnormalities in laminar structures throughout the brain and ataxia in reeler and scrambler mice. Both exhibit the same neuroanatomical defects, including cerebellar hypoplasia with Purkinje cell ectopia and disruption of neuronal layers in the cerebral cortex and hippocampus. Despite these phenotypic similarities, Reln and Dab1 have distinct molecular properties. Reln is a large extracellular protein secreted by Cajal-Retzius cells in the forebrain and by granule neurons in the cerebellum. In contrast, Dab1 is a cytoplasmic protein which has properties of an adapter protein that functions in phosphorylation-dependent intracellular signal transduction. Here, we show that Dab1 participates in the same developmental process as Reln. In scrambler mice, neuronal precursors are unable to invade the preplate of the cerebral cortex and consequently, they do not align within the cortical plate. During development, cells expressing Dab1 are located next to those secreting Reln at critical stages of formation of the cerebral cortex, cerebellum and hippocampus, before the first abnormalities in cell position become apparent in either reeler or scrambler. In reeler, the major populations of displaced neurons contain elevated levels of Dab1 protein, although they express normal levels of Dab1 mRNA. This suggests that Dab1 accumulates in the absence of a Reln-evoked signal. Taken together, these results indicate that Dab1 functions downstream of Reln in a signaling pathway that controls cell positioning in the developing brain.
decapentaplegic and wingless are regulated by eyes absent and eyegone and interact to direct the pattern of retinal differentiation in the eye disc
Authors: Hazelett Dennis J. , Bourouis Marc , Walldorf Uwe , Treisman Jessica E.
Published: April 2021

Signaling by the secreted hedgehog, decapentaplegic and wingless proteins organizes the pattern of photoreceptor differentiation within the Drosophila eye imaginal disc; hedgehog and decapentaplegic are required for differentiation to initiate at the posterior margin and progress across the disc, while wingless prevents it from initiating at the lateral margins. Our analysis of these interactions has shown that initiation requires both the presence of decapentaplegic and the absence of wingless, which inhibits photoreceptor differentiation downstream of the reception of the decapentaplegic signal. However, wingless is unable to inhibit differentiation driven by activation of the epidermal growth factor receptor pathway. The effect of wingless is subject to regional variations in control, as the anterior margin of the disc is insensitive to wingless inhibition. The eyes absent and eyegone genes encode members of a group of nuclear proteins required to specify the fate of the eye imaginal disc. We show that both eyes absent and eyegone are required for normal activation of decapentaplegic expression at the posterior and lateral margins of the disc, and repression of wingless expression in presumptive retinal tissue. The requirement for eyegone can be alleviated by inhibition of the wingless signaling pathway, suggesting that eyegone promotes eye development primarily by repressing wingless. These results provide a link between the early specification and later differentiation of the eye disc.
Commissureless endocytosis is correlated with initiation of neuromuscular synaptogenesis
Authors: Wolf Brian , Seeger Mark A. , Chiba Akira
Published: April 2021

We show that the Commissureless (COMM) transmembrane protein is required at neuromuscular synaptogenesis. All muscles in the Drosophila embryo express COMM during the period of motoneuron-muscle interaction. It is endocytosed into muscles before synaptogenesis. In comm loss-of-function mutants, motoneuron growth cones fail to initiate synaptogenesis at target muscles. This stall phenotype is rescued by supplying wild-type COMM to the muscles. Cytoplasmically truncated COMM protein fails to internalize. Expressing this mutant protein in muscles phenocopies the synaptogenesis defects of comm mutants. Thus, synaptogenesis initiation is positively correlated with endocytosis of COMM in postsynaptic muscle cells. We propose that COMM is an essential part of the dynamic cell surface remodeling needed by postsynaptic cells in coordinating synaptogenesis initiation.
Function and specificity of LIM domains in Drosophila nervous system and wing development
Authors: O’Keefe David D. , Thor Stefan , Thomas John B.
Published: April 2021

LIM domains are found in a variety of proteins, including cytoplasmic and nuclear LIM-only proteins, LIM-homeodomain (LIM-HD) transcription factors and LIM-kinases. Although the ability of LIM domains to interact with other proteins has been clearly established in vitro and in cultured cells, their in vivo function is unknown. Here we use Drosophila to test the roles of the LIM domains of the LIM-HD family member Apterous (Ap) in wing and nervous system development. Using a rescuing assay of the ap mutant phenotype, we have found that the LIM domains are essential for Ap function. Furthermore, expression of LIM domains alone can act in a dominant-negative fashion to disrupt Ap function. The Ap LIM domains can be replaced by those of another family member to generate normal wing structure, but LIM domains are not interchangeable during axon pathfinding of the Ap neurons. This suggests that the Ap LIM domains mediate different protein interactions in different developmental processes, and that LIM domains can participate in conferring specificity of target gene selection.