bluuebunny/crossref_metadata_2025 huggingface dataset:
posterior end mark, a novel maternal gene encoding a localized factor in the ascidian embryo
Authors: Yoshida Shoko , Marikawa Yusuke , Satoh Noriyuki
Published: April 2021

Ascidian embryogenesis is regarded as a typical ‘mosaic’ type. Recent studies have provided convincing evidence that components of the posterior-vegetal cytoplasm of fertilized eggs are responsible for establishment of the anteroposterior axis of the embryo. We report here isolation and characterization of a novel maternal gene, posterior end mark (pem). After fertilization, the pem transcript is concentrated in the posterior-vegetal cytoplasm of the egg and later marks the posterior end of developing ascidian embryos. Despite its conspicuous localization pattern, the predicted PEM protein shows no significant homology to known proteins. Overexpression of this gene by microinjection of synthesized pem mRNA into fertilized eggs results in development of tadpole larvae with deficiency of the anteriormost adhesive organ, dorsal brain and sensory pigment-cells. Lineage tracing analysis revealed that the anterior epidermis and dorsal neuronal cells were translocated posteriorly into the tail region, suggesting that this gene plays a role in establishment of anterior and dorsal patterning of the embryo. The ascidian tadpole is regarded as a prototype of vertebrates, implying a similar function of pem in vertebrate embryogenesis.
Time-dependent responses to glp-1-mediated inductions in early C. elegans embryos
Authors: Shelton Christopher A. , Bowerman Bruce
Published: April 2021

In an embryo of the nematode Caenorhabditis elegans, two blastomeres at the 4-cell stage, ABa and ABp, are born with equivalent developmental potential. Subsequently, interactions with the P2 blastomere at the 4-cell stage and the MS blastomere at the 12-cell stage generate differences in developmental fate among descendants of ABa and ABp. We have reproduced these inductions in vitro using embryonic blastomeres isolated in cell-culture medium. We show that during these inductions only the responding AB descendants require the activity of the glp-1 gene, which is similar in sequence to Drosophila Notch, supporting models in which GLP-1 protein acts as a receptor for both the P2 and MS signals. We also show that P2 signaling requires the activity of the apx-1 gene, similar in sequence to Drosophila Delta, and that MS signaling requires the putative transcription factor SKN-1. We present evidence that the primary factor determining the different responses to these two signals is the age of the AB descendants, not the identity of the signaling cell or ligand. Therefore, we suggest that time-dependent changes in factors within AB descendants are responsible for their different responses to inductive signals that use a common receptor.
How is embryo size genetically regulated in rice?
Authors: Hong Soon K. , Kitano Hidemi , Satoh Hikaru , Nagato Yasuo
Published: April 2021

It is unclear how embryo size is genetically regulated in plants. Since cereals have a large persisting endosperm, it is expected that embryo size is affected by endosperm development. Nine single recessive mutations, four reduced embryo mutations representing three loci, REDUCED EMBRYO1, REDUCED EMBRYO2 and REDUCED EMBRYO3, four giant embryo mutations derived from a single locus GIANT EMBRYO, and one endospermless mutation endospermless1-2 were analyzed. Every reduced embryo mutation caused reduction of all the embryonic organs including apical meristems and the enlargement of the endosperm. The giant embryo mutants have a reduced endosperm and an enlarged scutellum. However, shoot and radicle sizes were not affected. All the reduced embryo and giant embryo mutations did not largely affect postembryonic development. Accordingly, the expression of genes analyzed are seed-specific. In reduced embryo and giant embryo mutations, abnormalities were detected in both embryo and endosperm as early as 2 days after pollination. endospermless1-1 resulted in an early loss of endosperm, yielding a giant embryo, suggesting that embryo growth was physically limited by the endosperm. A double mutant between giant embryo-2 and club-shaped embryo1-1, which has a normal endosperm and a minute undifferentiated embryo, resulted in a club-shaped embryo1-1 embryo and a reduced endosperm of giant embryo-2, indicating that GIANT EMBRYO regulates the endosperm development. Double mutants between giant embryo-2 and three reduced embryo mutants exhibited the reduced embryo phenotype in both embryo and endosperm, suggesting that reduced embryo mutations cause the enlarged endosperm. Further, a double mutant of reduced embryo3 and endospermless1-1 showed the enlarged embryo in endospermless seed. This confirms that reduced embryo3 does not regulate embryo size but enlarges endosperm size. Together with the results of the other double mutant analysis, REDUCED EMBRYO1, REDUCED EMBRYO2, REDUCED EMBRYO3 and GIANT EMBRYO are concluded to regulate endosperm development.
Persistence of rhombomeric organisation in the postsegmental hindbrain
Authors: Wingate Richard J. T. , Lumsden Andrew
Published: April 2021

Rhombomeres are morphological varicosities of the neural tube that are present between embryonic day (E) 1.5 and E5 and are characterised by compartment organisation, segmentally neuronal organisation and spatially restricted patterns of gene expression. After E5, the segmented origins of the hindbrain become indistinct, while the adult hindbrain has an longitudinal columnar nuclear organisation. In order to assess the impact of the early transverse pattern on later longitudinal organisation, we have used orthotopic quail grafts and in situ hybridisation to investigate the long-term fate of rhombomeres in the embryonic chick hindbrain.

The uniformity of mixing between quail and chick cells was first verified using short-term aggregation cultures. The dispersal of the progeny of individual rhombomeres (r) was then assessed by the unilateral, isochronic and orthotopic transplantation of either r2, r3, r4, r5 or r6 from quail to chick at embryonic day E2. In addition, orthotopic, partial rhombomere grafts, encompassing an inter-rhombomere boundary and adjacent rhombomere bodies were used to assess cell mixing within rhombomeres. Operated embryos were incubated to either E7 or E10 when chimaeric brains were removed. Quail cells were identified in whole mounts or serial sections using the quail-specific antibody QCPN. Subsequently, radial glia morphology was assessed either by immunohistochemistry or DiI labelling. A series of fixed hindbrains between E6 and E9 were probed for transcripts of Hoxa-2 and Hoxb-1.

Fate-mapping reveals that the progeny of individual rhombomeres form stripes of cells running dorsoventrally through the hindbrain. This pattern of dispersal precisely parallels the array of radial glia. Although the postmitotic progeny of adjacent rhombomeres spread to some extent into each others’ territory in intermediate and marginal zones, there is little or no mixing between rhombomeres in the ventricular zone, which thus remains compartmentalised long after the rhombomeric morphology disappears. Segmental gene expression within this layer is also maintained after E5. A more detailed analysis of mixing between proliferating cells, using partial rhombomere grafts, reveals that both mixing and growth are nonuniform within the ventricular layer, suggesting, in particular, that longitudinal expansion within this layer is restricted. Together, these observations suggest that rhombomeres do not disappear at E5, as has previously been supposed, rather they persist in the ventricular zone to at least E9, ensuring a continuity in the presumed segmental cues that specify neuroepithelial cells in the hindbrain.
Retinal dysplasia and degeneration in RARβ2/RARγ2 compound mutant mice
Authors: Grondona Jesús M. , Kastner Philippe , Gansmuller Anne , Décimo Didier , Chambon Pierre , Mark Manuel
Published: April 2021

The eye is the organ whose development is the most frequently altered in response to maternal vitamin A deficiency [VAD; Warkany, J. and Schraffenberger, S. (1946). Archs Ophthalmol. 35, 150-169]. With the exception of prenatal retinal dysplasia, all the ocular abnormalities of the fetal VAD syndrome are recapitulated in mouse mutants lacking either RARα and RARβ2, RARα and RARγ? RARγ and RARβ2, or RXRα [Lohnes, D., Mark, M., Mendelsohn, C., Dollé, P., Dierich, A., Gorry, P., Gansmuller, A. and Chambon, P. (1994) Development 120, 27232748; Mendelsohn, C., Lohnes, D. Décimo, D., Lufkin, T., LeMeur, M., Chambon, P. and Mark, M. (1994) Development 120, 2749-2771; Kastner, P., Grondona, J. Mark, M., Gansmuller, A., LeMeur, M., Décimo, D., Vonesch, J.L., Dollé, P. and Chambon, P. (1994) Cell 78, 987-1003], thus demonstrating that retinoic acid (RA) is the active vitamin A metabolite during prenatal eye morphogenesis. Whether retinoids are also involved in postnatal eye development could not be investigated, as VAD newborns are not viable and the above RAR double null mutants and RXRα null mutants died in utero or at birth.

We report here the generation of viable RARβ2/RARγ2 double null mutant mice, which exhibit several eye defects. The neural retina of newborn RARβ2γ2 mutants is thinner than normal due to a reduced rate of cell proliferation, and from day 4 shows multiple foci of disorganization of its layers. These RARβ2γ2 mutants represent the first genetically characterized model of retinal dysplasia and their phenotype demonstrates that RARs, and therefore RA, are required for retinal histogenesis. The RARβ2γ2 retinal pigment epithelium (RPE) cells display histological and/or ultrastructural alterations and/or fail to express cellular retinol binding protein I (CRBPI). Taken altogether, the early onset of the RPE histological defects and their striking colocalisation with areas of the neural retina displaying a faulty laminar organization, a reduced neuroblastic proliferation, and a lack of photoreceptor differentiation and/or increased apoptosis, make the RPE a likely target tissue of the RARβ2γ2 double null mutation. A degeneration of the adult neural retina, which may similarly be secondary to a defective RPE, is also observed in these mutants, thus demonstrating an essential role of RA in the survival of retinal cells. Moreover, all RARβ2γ2 mutants display defects in structures derived from the periocular mesenchyme including local agenesis of the choroid and of the sclera, small eyelids, and a persistence of the primary mesenchymal vitreous body. A majority of the RARβ2 single null mutants also exhibit this latter defect, thus demonstrating that the RARβ2 isoform plays a unique role in the formation of the definitive vitreous body.
PTP-NP, a new member of the receptor protein tyrosine phosphatase family, implicated in development of nervous system and pancreatic endocrine cells
Authors: Chiang Ming-Ko , Flanagan John G.
Published: April 2021

The regulation of protein tyrosine phosphorylation is an important mechanism for developmental control. We describe here a new member of the protein tyrosine phosphatase (PTP) family, called PTP-NP (for neural and pancreatic). The cDNA sequence indicates a receptor-type transmembrane molecule. At early organogenesis, in situ hybridization with a probe for the PTP-NP extracellular region detects expression confined to the region of the developing pancreas, an organ of medical importance, but poorly understood with regard to molecular mechanisms of developmental control. This localized expression appears early, even before morphological differentiation of the pancreas, and is found in presumptive precursors of the endocrine cells by the earliest times that they can be distinguished. In neural development, an alternate RNA with a different or missing extracellular region is expressed transiently at early stages of neurogenesis and the fulllength PTP-NP RNA appears later. To search for a ligand of PTP-NP, a fusion protein probe was made with the extracellular domain fused to an alkaline phosphatase tag. This probe bound strongly to pancreatic islets, providing evidence for a ligand-receptor interaction that could be involved in endocrine cell regulation. The results show PTP-NP is an especially early marker for pancreatic development and suggest it may be a receptor that could control the development of pancreatic endocrine cells.
Dpp receptors are autonomously required for cell proliferation in the entire developing Drosophila wing
Authors: Burke Richard , Basler Konrad
Published: April 2021

The mammalian growth factor TGFβ negatively regulates cell proliferation in various systems. Here we provide evidence that another TGFβ superfamily member, Drosophila Decapentaplegic (Dpp), stimulates cell proliferation. In the developing wing blade, somatic clones lacking the Dpp receptors Punt or Thick veins (Tkv), or lacking Schnurri, a transcription factor involved in Dpp signal interpretation, fail to grow when induced early in larval development. Furthermore the spatial requirement for these signaling components indicates that Dpp has to travel several cell diameters from its source in order to reach all cells that require its signal. The requirement for Tkv also depends on the distance of cells from the source of the Dpp signal. We propose that Dpp can act at a distance to positively control cell proliferation.
Developmentally regulated gene expression of thrombomodulin in postimplantation mouse embryos
Authors: Weiler-Guettler Hartmut , Aird William C. , Rayburn Helen , Husain Mansoor , Rosenberg Robert D.
Published: April 2021

Embryonic lethality of thrombomodulin-deficient mice has indicated an essential role for this regulator of blood coagulation in murine development. Here, the embryonic expression pattern of thrombomodulin was defined by surveying β-galactosidase activity in a mouse strain in which the reporter gene was placed under the regulatory control of the endogenous thrombomodulin promoter via homologous recombination in embryonic stem cells. The murine trophoblast was identified as a previously unrecognized anatomical site where TM expression is conserved between humans and mice and may exert a critical function during postimplantation development. Targeted reporter gene expression in mesodermal precursors of the endothelial cell lineage defined thrombomodulin as an early marker of vascular differentiation. Analysis of the thrombomodulin promoter in differentiating ES cells and in transgenic mice provided evidence for a disparate and cell type-specific gene regulatory control mechanism in the parietal yolk sac. The thrombomodulin promoter as defined in this study will allow the targeting of gene expression to the parietal yolk sac of transgenic mice and the initiation of investigations into the role of parietal endoderm in placental function.
The limb field mesoderm determines initial limb bud anteroposterior asymmetry and budding independent of sonic hedgehog or apical ectodermal gene expressions
Authors: Ros Maria A. , López-Martínez Alric , Simandl B. Kay , Rodriguez Concepción , Izpisúa Belmonte Juan Carlos , Dahn Randall , Fallon John F.
Published: April 2021

We have analyzed the pattern of expression of several genes implicated in limb initiation and outgrowth using limbless chicken embryos. We demonstrate that the expressions of the apical ridge associated genes, Fgf-8, Fgf-4, Bmp-2 and Bmp-4, are undetectable in limbless limb bud ectoderm; however, FGF2 protein is present in the limb bud ectoderm. Shh expression is undetectable in limbless limb bud mesoderm. Nevertheless, limbless limb bud mesoderm shows polarization manifested by the asymmetric expression of Hoxd-11, -12 and -13, Wnt-5a and Bmp-4 genes. The posterior limbless limb bud mesoderm, although not actually expressing Shh, is competent to express it if supplied with exogenous FGF or transplanted to a normal apical ridge environment, providing further evidence of mesodermal asymmetry. Exogenous FGF applied to limbless limb buds permits further growth and determination of recognizable skeletal elements, without the development of an apical ridge. However, the cells competent to express Shh do so at reduced levels; nevertheless, Bmp-2 is then rapidly expressed in the posterior limbless mesoderm. limbless limb buds appear as bi-dorsal structures, as the entire limb bud ectoderm expresses Wnt-7a, a marker for dorsal limb bud ectoderm; the ectoderm fails to express En-1, a marker of ventral ectoderm. As expected, C-Lmx1, which is downstream of Wnt-7a, is expressed in the entire limbless limb bud mesoderm. We conclude that anteroposterior polarity is established in the initial limb bud prior to Shh expression, apical ridge gene expression or dorsalventral asymmetry. We propose that the initial pattern of gene expressions in the emergent limb bud is established by axial influences on the limb field. These permit the bud to emerge with asymmetric gene expression before Shh and the apical ridge appear. We report that expression of Fgf8 by the limb ectoderm is not required for the initiation of the limb bud. The gene expressions in the pre-ridge limb bud mesoderm, as in the limb bud itself, are unstable without stimulation from the apical ridge and the polarizing region (Shh) after budding is initiated. We propose that the defect in limbless limb buds is the lack of a dorsalventral interface in the limb bud ectoderm where the apical ridge induction signal would be received and an apical ridge formed. These observations provide evidence for the hypothesis that the dorsal-ventral ectoderm interface is a precondition for apical ridge formation.
Late emigrating neural crest cells migrate specifically to the exit points of cranial branchiomotor nerves
Authors: Niederländer Christiane , Lumsden Andrew
Published: April 2021

Morphological segmentation of the avian hindbrain into rhombomeres is also reflected by the emergent organisation of branchiomotor nerves. In each case, the motor neurons of these nerves lie in two adjacent rhombomeres (e.g. of the Vth nerve in r2 and r3, VIIth in r4 and r5 etc.), and their outgrowing axons emerge into the periphery through defined exit points in rhombomeres r2, r4 and r6, respectively. Sensory axons of the cranial ganglia also enter the neuroepithelium at the same points. Motor axon outgrowth through experimentally rotated rhombomeres has suggested that a chemoattractive mechanism, involving the exit points, may form a component of their guidance. Yet so far, nothing is known about the establishment of the exit points or the identity of the cells that form them. In this study, we describe a group of late emigrating cranial neural crest cells which populate specifically the prospective exit points. Using chimaeras in which premigratory chick neural crest had been replaced orthotopically by quail cells, a population of neural crest was found to leave the cranial neural tube from about stage 10+ onwards and to migrate directly to the prospective exit points. These cells define the exit points by stage 12+, long before either motor or sensory axons have grown through them. The entire neural crest population of exit point cells expresses the recently described cell adhesion molecule c-cad7. Further, heterotopic grafting experiments show that midbrain and spinal cord crest, grafted at late stages in place of r4 crest, share the same migratory behaviour to the facial nerve exit points and express the same markers as cells contributed by the native r4 crest. It was not possible to generate new exit points in odd numbered rhombomeres simply by experimentally increasing their (normally insignificant) amount of crest production. Initiation of the exit point region probably lies, therefore, in the neuroepithelium.
An altered body plan is conferred on Arabidopsis plants carrying dominant alleles of two genes
Authors: Grbić Vojislava , Bleecker Anthony B.
Published: April 2021

In this paper, we describe a late-flowering ecotype of Arabidopsis, Sy-0, in which the axillary meristems maintain a prolonged vegetative phase, even though the primary shoot apical meristem has already converted to reproductive development. This novel heterochronic shift in the development of axillary meristems results in the formation of aerial rosettes of leaves at the nodes of the primary shoot axis. We present evidence that the aerial-rosette phenotype arises due to the interaction between dominant alleles of two genes: ART, aerial rosette gene (on chromosome 5) and EAR, enhancer of aerial rosette (on chromosome 4). EAR has been tentatively identified as a new allele of the FRI locus. The possible role of these two genes in the conversion of shoot apical meristems to reproductive development is discussed.
Requirement of neurotrophin-3 for the survival of proliferating trigeminal ganglion progenitor cells
Authors: ElShamy Wael M. , Ernfors Patrik
Published: April 2021

The aim of this study was to identify the physiological role of neurotrophin-3 (NT-3) in the development of trigeminal ganglion sensory neurons. For this purpose we have analysed mice carrying a deletion in the NT-3 gene (NT3−/− mice). In these mice, by embryonic day (E) 11, 25% of the trigeminal ganglion neurons were absent and one day later, approximately 50% were absent, after which no further significant changes were observed. Mice carrying one functional NT-3 gene (NT-3+/− mice) displayed a less severe deficit than that of NT-3−/− mice. Whereas programmed cell death occurred between E12 and E14 in the control mice, pronounced excessive cell death was apparent prior to this in the NT-3−/− mice. The excessive cell death led to a progressive decline in the number of proliferating cells without a significant change in the fraction of dividing cells and total number of neurons, indicating that the neuronal deficit of NT-3−/− mice was caused by cell death of trigeminal ganglion progenitors. Furthermore, the degenerating cells had incorporated BrdU, a nucleotide analogue which labels proliferating cells, and expressed nestin, a marker for progenitor cells. Only rarely were degenerating cells seen to express peripherin, present in postmitotic neurons. These data provide evidence that NT3 is a survival factor for trigeminal ganglion progenitor cells, and suggests that limiting amounts of NT-3 could influence progenitor cell numbers during gangliogenesis.
Stage-specific accumulation of the terminal differentiation factor LIN-29 during Caenorhabditis elegans development
Authors: Bettinger Jill C. , Lee Kimberly , Rougvie Ann E.
Published: April 2021

The Caenorhabditis elegans gene lin-29 is required for the terminal differentiation of the lateral hypodermal seam cells during the larval-to-adult molt. We find that lin-29 protein accumulates in the nuclei of these cells, consistent with its predicted role as a zinc finger transcription factor. The earliest detectable LIN-29 accumulation in seam cell nuclei is during the last larval stage (L4), following the final seam cell division, which occurs during the L3-to-L4 molt. LIN-29 accumulates in all hypodermal nuclei during the L4 stage. The time of LIN-29 appearance in the hypodermis is controlled by the heterochronic gene pathway: LIN-29 accumulates in the hypodermis abnormally early, during the third larval stage, in loss-of-function lin-14, lin-28 and lin-42 mutants, and fails to accumulate in hypodermis of lin-4 mutants. LIN-29 also accumulates stage-specifically in the nuclei of a variety of non-hypodermal cells during development. Its accumulation is dependent upon the upstream heterochronic genes in some, but not all, of these non-hypodermal cells.
A genetic screen for mutations affecting embryogenesis in zebrafish
Authors: Driever W. , Solnica-Krezel L. , Schier A. F. , Neuhauss S. C. F. , Malicki J. , Stemple D. L. , Stainier D. Y. R. , Zwartkruis F. , Abdelilah S. , Rangini Z. , Belak J. , Boggs C.
Published: April 2021

Systematic genome-wide mutagenesis screens for embryonic phenotypes have been instrumental in the understanding of invertebrate and plant development. Here, we report the results from the first application of such a large-scale genetic screening to vertebrate development.

Male zebrafish were mutagenized with N-ethyl N-nitrosourea to induce mutations in spermatogonial cells at an average specific locus rate of one in 651 mutagenized genomes. Mutations were transmitted to the F1 generation, and 2205 F2 families were raised. F3 embryos from sibling crosses within the F2 families were screened for develop-mental abnormalities. A total of 2337 mutagenized genomes were analyzed, and 2383 mutations resulting in abnormal embryonic and early larval phenotypes were identified. The phenotypes of 695 mutants indicated involvement of the identified loci in specific aspects of embryogenesis. These mutations were maintained for further characterization and were classified into categories according to their phenotypes. The analyses and genetic complementation of mutations from several categories are reported in separate manuscripts. Mutations affecting pig-mentation, motility, muscle and body shape have not been extensively analyzed and are listed here. A total of 331 mutations were tested for allelism within their respective categories. This defined 220 genetic loci with on average 1.5 alleles per locus. For about two-thirds of all loci only one allele was isolated. Therefore it is not possible to give a reliable estimate on the degree of saturation reached in our screen; however, the number of genes that can mutate to visible embryonic and early larval phenotypes in zebrafish is expected to be several-fold larger than the one for which we have observed mutant alleles during the screen. This screen demonstrates that mutations affecting a variety of developmental processes can be efficiently recovered from zebrafish.
A reference cross DNA panel for zebrafish (Danio rerio) anchored with simple sequence length polymorphisms
Authors: Knapik Ela W. , Goodman Alec , Atkinson O. Scott , Roberts Carole T. , Shiozawa Masahide , Sim Chäng U. , Weksler-Zangen Sarah , Trolliet Maria R. , Futrell Corey , Innes Brendan A. , Koike George , McLaughlin Michael G. , Pierre Luc , Simon Jason S. , Vilallonga Eduardo , Roy Millie , Chiang Pei-Wen , Fishman Mark C. , Driever Wolfgang , Jacob Howard J.
Published: April 2021

The ultimate informativeness of the zebrafish mutations described in this issue will rest in part on the ability to clone these genes. However, the genetic infrastructure required for the positional cloning in zebrafish is still in its infancy. Here we report a reference cross panel of DNA, consisting of 520 F2 progeny (1040 meioses) that has been anchored to a zebrafish genetic linkage map by 102 simple sequence length polymorphisms. This reference cross DNA provides: (1) a panel of DNA from the cross that was used to construct the genetic linkage map, upon which polymorphic gene(s) and genetic markers can be mapped; (2) a fine order mapping tool, with a maximum resolution of 0.1 cM; and (3) a foundation for the development of a physical map (an ordered array of clones each containing a known portion of the genome). This reference cross DNA will serve as a resource enabling investigators to relate genes or genetic markers directly to a single genetic linkage map and avoid the problem of integrating different maps with different genetic markers, as must be currently done when using randomly amplified polymorphic DNA markers, or as has occurred with human genetic linkage maps.
The role of selectins in Drosophila eye and bristle development
Authors: Leshko-Lindsay LeeAnn , Corces Victor G.
Published: April 2021

Mutations in the furrowed (fw) gene of Drosophila result in defects in the development of the eye and mechanosensory bristles. The eyes are reduced in size, have furrows or crevices in the retina, and show a disturbed patterning of ommatidia. In addition, the ommatidia have an altered morphology and often contain abnormal numbers of cells. The bristles show altered structure and polarity, and are occasionally duplicated or missing. These results suggest that the product of the fw gene is involved in cell determination events within sensory organs. The fw gene has been cloned and shown to encode a protein homologous to vertebrate selectins. Like selectins, Fw contains a lectinbinding domain, ten complement binding repeats, and a transmembrane domain. The Fw protein is expressed in the larval imaginal discs where it might mediate carbohydrateprotein interactions necessary for proper development of a subset of adult sensory organs.
The spalt gene links the A/P compartment boundary to a linear adult structure in the Drosophila wing
Authors: Sturtevant Mark A. , Biehs Brian , Marin Elizabeth , Bier Ethan
Published: April 2021

During Drosophila embryogenesis, each segment is subdivided into an anterior and a posterior compartment through the action of the engrailed gene. Compartmental boundaries bisect imaginal disc primordia which give rise to adult appendages. In early larval development, a short-range Hedgehog signal originating from the posterior compartment of the imaginal wing disc activates expression of genes including decapentaplegic (dpp) in a stripe running along the anterior-posterior compartment boundary. Secreted Dpp emanating from the A/P boundary of wing discs then acts as a secondary signal to organize the wing over large distances. The transcription factor encoded by spalt major (salm) gene, which is expressed in a broad wedge centered over the dpp stripe, is one target of Dpp signaling. In this manuscript, we show that the anterior edge of the salm expression domain abuts a narrow stripe of rhomboid (rho)-expressing cells corresponding to the L2 longitudinal vein primordium. hh mis-expression along the anterior wing margin induces a surrounding domain of salm expression, the anterior edge of which abuts a displaced rho L2 stripe. salm plays a key role in defining the position of the L2 vein since loss of salm function in mosaic patches induces the formation of ectopic L2 branches, which comprise salm− cells running along clone borders where salm− cells confront salm+ cells. These data suggest that salm determines the position of the L2 vein primordium by activating rho expression in neighboring cells through a locally non-autonomous mechanism. rho then functions to initiate and maintain vein differentiation. We discuss how these data provide the final link connecting the formation of a linear adult structure to the establishment of a boundary by the maternal Bicoid morphogen gradient in the blastoderm embryo.
Signaling through both type I DPP receptors is required for anterior-posterior patterning of the entire Drosophila wing
Authors: Singer Matthew A. , Penton Andrea , Twombly Vern , Hoffmann F. Michael , Gelbart William M.
Published: April 2021

The imaginal disk expression of the TGF-β superfamily member DPP in a narrow stripe of cells along the anterior-posterior compartment boundary is essential for proper growth and patterning of the Drosophila appendages. We examine DPP receptor function to understand how this localized DPP expression produces its global effects upon appendage development. Clones of saxophone (sax) or thick veins (tkv) mutant cells, defective in one of the two type I receptors for DPP, show shifts in cell fate along the anterior-posterior axis. In the adult wing, clones that are homozygous for a null allele of sax or a hypomorphic allele of tkv show shifts to more anterior fates when the clone is in the anterior compartment and to more posterior fates when the clone is in the posterior compartment. The effect of these clones upon the expression pattern of the down-stream gene spalt-major also correlates with these specific shifts in cell fate. The similar effects of sax null and tkv hypomorphic clones indicate that the primary difference in the function of these two receptors during wing patterning is that TKV transmits more of the DPP signal than does SAX. Our results are consistent with a model in which a gradient of DPP reaches all cells in the developing wing blade to direct anterior-posterior pattern.
Hedgehog acts by distinct gradient and signal relay mechanisms to organise cell type and cell polarity in the Drosophila abdomen
Authors: Struhl Gary , Barbash Daniel A. , Lawrence Peter A.
Published: April 2021

The epidermis of the adult Drosophila abdomen is formed by a chain of anterior (A) and posterior (P) compartments, each segment comprising one A and one P compartment. In the accompanying paper (Struhl et al., 1997), we provide evidence that Hedgehog protein (Hh), being secreted from P compartment cells, organises the pattern and polarity of A compartment cells. Here we test whether Hh acts directly or by a signal relay mechanism. We use mutations in Protein Kinase A(PKA) or smoothened (smo) to activate or to block Hh signal transduction in clones of A compartment cells. For cell type, a scalar property, both manipulations cause strictly autonomous transformations: the cells affected are exactly those and only those that are mutant. Hence, we infer that Hh acts directly on A compartment cells to specify the various types of cuticular structures that they differentiate. By contrast, these same manipulations cause non-autonomous effects on cell polarity, a vectorial property. Consequently, we surmise that Hh influences cell polarity indirectly, possibly by inducing other signalling factors. Finally, we present evidence that Hh does not polarise abdominal cells by utilising either Decapentaplegic (Dpp) or Wingless (Wg), the two morphogens through which Hh acts during limb development. We conclude that, in the abdomen, cell type and cell polarity reflect distinct outputs of Hh signalling and propose that these outputs are controlled by separable gradient and signal relay mechanisms.
The NIMA-related kinase 2, Nek2, is expressed in specific stages of the meiotic cell cycle and associates with meiotic chromosomes
Authors: Rhee Kunsoo , Wolgemuth Debra J.
Published: April 2021

The Aspergillus nimAgene encodes a Ser/Thr protein kinase which is required for mitosis, in addition to Cdc2, and which has been suggested to have a role in chromosomal condensation. In this study, we isolated a potential murine homologue of nimA, Nek2, which was shown to be expressed most abundantly in the testis of the adult tissues examined. Its expression in the testis was restricted to the germ cells, with highest levels detected in spermatocytes at pachytene and diplotene stages. Immunohistochemical analysis revealed that Nek2 localized to nuclei, exhibiting a nonuniform distribution within the nucleus. Nek2 appeared to be associated with meiotic chromosomes, an association that was better defined by immunolocalization to hypotonically dispersed meiotic chromosomes. This localization was more apparent in regions of dense chromatin, including the sex vesicle, and was also obvious at some of the chromosome ends. The presence of Nek2 protein was not unique to male germ cells, as it was found in meiotic pachytene stage oocytes as well. Furthermore, in an in vitro experimental setting in which meiotic chromosome condensation was induced with okadaic acid, a concomitant induction of Nek2 kinase activity was observed. The expression of Nek2 in meiotic prophase is consistent with the hypothesis that in vivo, Nek2 is involved in the G2/M phase transition of the cell cycle. Our results further provide evidence that in vivo, mouse Nek2 is involved in events of meiosis, including but not limited to chromosomal condensation.
A C. elegans E/Daughterless bHLH protein marks neuronal but not striated muscle development
Authors: Krause Michael , Park Morgan , Zhang Jian-Ming , Yuan Jeff , Harfe Brian , Xu Si-Qun , Greenwald Iva , Cole Michael , Paterson Bruce , Fire Andrew
Published: April 2021

The E proteins of mammals, and the related Daughterless (DA) protein of Drosophila, are ubiquitously expressed helix-loop-helix (HLH) transcription factors that play a role in many developmental processes. We report here the characterization of a related C. elegans protein, CeE/DA, which has a dynamic and restricted distribution during development. CeE/DA is present embryonically in neuronal precursors, some of which are marked by promoter activity of a newly described Achaete-scute-like gene hlh-3. In contrast, we have been unable to detect CeE/DA in CeMyoD-positive striated muscle cells. In vitro gel mobility shift analysis detects dimerization of CeE/DA with HLH-3 while efficient interaction of CeE/DA with CeMyoD is not seen. These studies suggest multiple roles for CeE/DA inC. elegans development and provide evidence that both common and alternative strategies have evolved for the use of related HLH proteins in controlling cell fates in different species.
The sidekick gene, a member of the immunoglobulin superfamily, is required for pattern formation in the Drosophila eye
Authors: Nguyen Duc N. T. , Liu Yang , Litsky Meredith L. , Reinke Rosemary
Published: April 2021

In the Drosophila eye imaginal disc the photoreceptor cells (R cells) differentiate according to a precise spatial and temporal order. The sidekick (sdk) gene is necessary to prevent extra R cells from differentiating during eye disc development. The extra cell appears between R3 and R4 early in R cell clusters and is most likely the result of the mystery cell inappropriately differentiating as an R cell. Mosaic analysis shows that sdk is required neither in the R cells nor in the extra cell, suggesting that sdk is necessary in the surrounding undifferentiated cells. The sdk gene codes for a protein that is a member of the immunoglobu-lin superfamily, having six immunoglobulin domains, thirteen fibronectin repeats and a transmembrane domain. The protein structure is consistent with its participation in cell-cell interaction during eye development.
Identification and localization of a sea urchin Notch homologue: insights into vegetal plate regionalization and Notch receptor regulation
Authors: Sherwood David R. , McClay David R.
Published: April 2021

The specifications of cell types and germ-layers that arise from the vegetal plate of the sea urchin embryo are thought to be regulated by cell-cell interactions, the molecular basis of which are unknown. The Notch intercellular signaling pathway mediates the specification of numerous cell fates in both invertebrate and vertebrate development. To gain insights into mechanisms underlying the diversification of vegetal plate cell types, we have identified and made antibodies to a sea urchin homolog of Notch (LvNotch). We show that in the early blastula embryo, LvNotch is absent from the vegetal pole and concentrated in basolateral membranes of cells in the animal half of the embryo. However, in the mesenchyme blastula embryo LvNotch shifts strikingly in subcellular localization into a ring of cells which surround the central vegetal plate. This ring of LvNotch delineates a boundary between the presumptive secondary mesoderm and presumptive endoderm, and has an asymmetric bias towards the dorsal side of the vegetal plate. Experimental perturbations and quantitative analysis of LvNotch expression demonstrate that the mesenchyme blastula vegetal plate contains both animal/vegetal and dorsoventral molecular organization even before this territory invaginates to form the archenteron. Furthermore, these experiments suggest roles for the Notch pathway in secondary mesoderm and endoderm lineage segregation, and in the establishment of dorsoventral polarity in the endoderm. Finally, the specific and differential subcellular expression of LvNotch in apical and basolateral membrane domains provides compelling evidence that changes in membrane domain localization of LvNotch are an important aspect of Notch receptor function.
Cell cycle progression, growth and patterning in imaginal discs despite inhibition of cell division after inactivation of Drosophila Cdc2 kinase
Authors: Weigmann Katrin , Cohen Stephen M. , Lehner Christian F.
Published: April 2021

During larval development, Drosophila imaginal discs increase in size about 1000-fold and cells are instructed to acquire distinct fates as a function of their position. The secreted signaling molecules Wingless and Decapentaplegic have been implicated as sources of positional information that globally control growth and patterning. Evidence has also been presented that local cell interactions play an important role in controlling cell proliferation in imaginal discs. As a first step to understanding how patterning cues influence growth we investigated the effects of blocking cell division at different times and in spatially controlled manner by inactivation of the mitotic kinase Cdc2 in developing imaginal discs. We find that cell growth continues after inactivation of Cdc2, with little effect on overall patterning. The mechanisms that regulate size of the disc therefore do not function by regulating cell division, but appear to act primarily by regulating size in terms of physical distance or tissue volume.
Patterning of the embryo along the anterior-posterior axis: the role of the caudal genes
Authors: Epstein Michal , Pillemer Graciela , Yelin Ronit , Yisraeli Joel K. , Fainsod Abraham
Published: April 2021

Patterning along the anterior-posterior axis takes place during gastrulation and early neurulation. Homeobox genes like Otx-2 and members of the Hox family have been implicated in this process. The caudal genes in Drosophila and C. elegans have been shown to determine posterior fates. In vertebrates, the caudal genes begin their expression during gastrulation and they take up a posterior position. By injecting sense and antisense RNA of the Xenopus caudal gene Xcad-2, we have studied a number of regulatory interactions among homeobox genes along the anterior-posterior axis. Initially, the Xcad-2 and Otx-2 genes are mutually repressed and, by late gastrulation, they mark the posterior- or anterior-most domains of the embryo, respectively. During late gastrulation and neurulation, Xcad-2 plays an additional regulatory function in relation to the Hox genes. Hox genes normally expressed anteriorly are repressed by Xcad-2 overexpression while those normally expressed posteriorly exhibit more anterior expression. The results show that the caudal genes are part of a posterior determining network which during early gastrulation functions in the subdivision of the embryo into anterior head and trunk domains. Later in gastrulation and neurulation these genes play a role in the patterning of the trunk region.
Floral determination and expression of floral regulatory genes in Arabidopsis
Authors: Hempel Frederick D. , Weigel Detlef , Mandel M. Alejandra , Ditta Gary , Zambryski Patricia C. , Feldman Lewis J. , Yanofsky Martin F.
Published: April 2021

The expression of the floral regulators LEAFY, APETALA1 and AGAMOUS-LIKE8 was examined during light treatments that induced flowering in Arabidopsis, and was compared to time points at which floral determination occurred. Extension of an 8-hour day by either continuous red- or far-red-enriched light induced LEAFY and AGAMOUS-LIKE8 expression within 4 hours. The 4 hours of additional light was sufficient for floral determination only in the far-red-enriched conditions, while 12-16 hours of additional light was required for floral determination in the red-enriched conditions. These results indicate that the induction of floral regulatory genes and induction of flower formation can be uncoupled under certain circumstances. Expression of LEAFY and AGAMOUS-LIKE8 in the shoot apex at the time of floral determination is also consistent with genetic data indicating that these genes are involved in the first steps of the transition from vegetative to reproductive development. In contrast to LEAFY and AGAMOUS-LIKE8, APETALA1 expression was first observed 16 hours after the start of photoinduction. Since this time point was always after floral determination, APETALA1 is an indicator of floral determination.
Maternal control of a zygotic patterning gene in Caenorhabditis elegans
Authors: Ahringer Julie
Published: April 2021

The transition from maternal to zygotic gene control is a key process in embryogenesis. Although many maternal effect genes have been studied in the C. elegans embryo, how their activities lead to the positional expression of zygotic patterning genes has not yet been established. Evidence is presented showing that expression of the zygotic patterning gene vab-7 does not depend on cell position or cell contacts, but rather on the production of a C blastomere. Furthermore, pal-1, a caudal homologue with maternal product necessary for the proper development of the C blastomere, is both necessary and sufficient for vab-7 expression. This provides a link between maternal gene activity and zygotic patterning gene expression in C. elegans. The results suggest that zygotic patterning genes might be generally controlled at the level of blastomere fate and not by position.
Control of dorsoventral pattern in the chick paraxial mesoderm
Authors: Dietrich Susanne , Schubert Frank R. , Lumsden Andrew
Published: April 2021

The most profound feature of the mature vertebrate somite is its organisation into dorsal dermomyotome, intermediate myotome and ventral sclerotome. We analysed the role of potential signalling structures in this dorsoventral pattern by ablating them or transplanting them to ectopic locations in chick embryos. Our data suggest that the somite represents a naïve tissue, entirely depending on external cues for its dorsoventral organisation. Dorsalisation by signals from dorsal neural tube and surface ectoderm stimulates the development of the dermomyotome. Likewise, signals from notochord and floor plate ventralise the somite, at high levels overriding any dorsal information and inducing the sclerotome. The dorsalising factors and lower levels of the ventralising factors act in concert to induce the myotome. Finally, the paraxial mesoderm intrinsically controls its competence to respond to the external inducers.