bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential gene activation by ecdysone in Drosophila melanogaster: the hierarchical equivalence of early and early late genes
Authors: Huet François , Ruiz Claude , Richards Geoff
Published: April 2021

Ecdysteroids are key regulators of insect development. In Drosophila melanogaster the late larval response to ecdysone is characterised by a precise sequential activation of members of the superfamily of nuclear receptors (DHR3, DHR39, EcR, E75, E78, FTZ-F1, usp). Many of these genes are localised in the polytene chromosome puffs of the salivary gland previously classified as intermoult, early or early-late puff loci. Ashburner et al. (Ashburner, M., Chihara, C., Meltzer, P. and Richards, G. (1974) Cold Spring Harbour Symp. Quant. Biol. 38, 655-662) proposed a formal model describing interactions between ecdysone, its receptor and the early and late puffs during this ecdysone response. To integrate transcripts from the intermoult and early-late puffs into this model, we have used a micro RT-PCR assay to study their hormonal regulation using salivary gland culture protocols first used in the puffing analyses. We show that transcripts from certain early-late puffs are induced in parallel with the early transcripts and are thus hierarchically equivalent. In vivo the profile of the increase in hormone titre, the sensitivity of different promoters to hormone and the rate of transcript accumulation must contribute to the temporal differences in expression observed between these two classes.
The cAMP Response Element Binding protein is involved in hydra regeneration
Authors: Galliot Brigitte , Welschof Martin , Schuckert Oliver , Hoffmeister Sabine , Schaller H. Chica
Published: April 2021

Hydra provides an interesting developmental model system where pattern formation processes are easily accessible to experimentation during regeneration. Previous studies have shown that the neuropeptide head activator affects cellular growth and head-specific cellular differentiation during head regeneration and budding. In order to investigate the signal transduction pathway and the regulatory genes involved in these processes, we measured cAMP levels after head activator treatment and found that head activator leads to an increase in cAMP levels at concentrations where effects on nerve cell determination and differentiation are observed (10−11 to 10−9 M). Moreover, exposure of intact hydra to a permeable form of cAMP stimulates nerve-cell differentiation and thus mimicks the effect of endogenous head activator. Band-shift assays were performed to detect changes in hydra nuclear protein binding activity during regeneration or after head activator treatment. We found that the cAMP response element (CRE) promotes a specific and strong DNAbinding activity which is dramatically enhanced and modified during early regeneration or after HA treatment. We also identified a surprisingly highly conserved hydra gene encoding the cAMP Response Element Binding protein, which is involved in this CRE-binding activity. Initiation of regeneration upon wounding provokes an endogenous release of HA which leads to the final differentiation of determined nerve cells. We propose that the nerve-cell differentiation observed within the first 4-8 hours of regeneration relies on the agonist effect of head activator on the cAMP pathway, which would in turn modulate the CRE-binding activity of the hydra CREB protein and thus regulate the transcriptional activity of genes involved in regeneration processes.
LEUNIG regulates AGAMOUS expression in Arabidopsis flowers
Authors: Liu Zhongchi , Meyerowitz Elliot M.
Published: April 2021

LEUNIG was identified in a genetic screen designed to isolate second-site enhancer mutations of the floral homeotic mutant apetala2-1. leunig mutations not only enhance apetala2, but by themselves cause a similar but less-pronounced homeotic transformation than apetala2 mutations. leunig flowers have sepals that are transformed toward stamens and carpels, and petals that are either staminoid or absent. In situ hybridization experiments with leunig mutants revealed altered expression pattern of the floral homeotic genes APETALA1, APETALA3, PISTIL-LATA, and AGAMOUS. Double mutants of leunig and agamous exhibited a phenotype similar to agamous single mutants, indicating that agamous is epistatic to leunig. Our analysis suggests that a key role of LEUNIG is to negatively regulate AGAMOUS expression in the first two whorls of the Arabidopsis flower.
The C. elegans neuronally expressed homeobox gene ceh-10 is closely related to genes expressed in the vertebrate eye
Authors: Svendsen Pia C. , McGhee James D.
Published: April 2021

We describe the homeobox gene ceh-10 from the nematode Caenorhabditis elegans. The homeodomain of ceh-10 is closely related to the homeodomains of two genes recently cloned from the vertebrate retina, Chx10 from mice and Vsx-1 from goldfish. We show that the sequence conservation extends well beyond the homeodomain and includes a region (named the CVC domain) of roughly 60 amino acids immediately C-terminal to the homeodomain. As assayed in transgenic worms, the promoter region of ceh-10 directs expression of a lacZ reporter gene to a small number of neurons. We draw a parallel between the bipolar cells of the inner nuclear layer of the vertebrate retina, which express Chx10 and Vsx-1, and an interneuron in C. elegans called AIY, which expresses ceh-10. AIY receives synaptic input from a sensory cell, just as do bipolar cells of the vertebrate retina. In C. elegans, the sensory cell AFD is not known to be photosensitive but is known to be thermosensitive; moreover, a cell with similar position in the amphids of other nematodes has been suggested indeed to be photosensitive. Our results emphasize the highly conserved nature of sensory regulatory mechanisms and suggest one way in which photosensitive organelles might have originated in evolution.
Nonequivalent requirements for PS1 and PS2 integrin at cell attachments in Drosophila: genetic analysis of the αPS1 integrin subunit
Authors: Brower Danny L. , Bunch Thomas A. , Mukai Leona , Adamson Todd E. , Wehrli Marcel , Lam Suzanne , Friedlander Eric , Roote Carol E. , Zusman Susan
Published: April 2021

We report on the generation and phenotype of mutant alleles of multiple edematous wings (mew), the gene encoding the αPS1 subunit of the PS1 integrin of Drosophila. None of the six alleles examined makes detectable protein, and one allele results from a chromosome break near the middle of the translated sequence, so we are confident that we have described the null phenotype. In contrast to if (αPS2) and mys (βPS) mutants, most mutant mew embryos hatch, to die as larvae. Mutant mew embryos display abnormal gut morphogenesis but, unlike mys or if embryos, there is no evidence of defects in the somatic muscles. Thus, the complementary distributions of PS1 (αPS1βPS) and PS2 (αPS2βPS) integrin on tendon cells and muscle, respectively, do not reflect equivalent requirements at the myotendinous junction. Dorsal herniation, characteristic of the mys lethal phenotype, is not observed in mew or in mew if embryos. Clonal analysis experiments indicate that eye morphogenesis is disrupted in mew clones, but if clones in the eye are relatively normal in morphology. Adult wings display blisters around large dorsal but not ventral mew clones. In contrast to dorsal mys clones, small mew patches do not necessarily display morphogenetic abnormalities. Thus, another integrin in addition to PS1 appears to function on the dorsal wing surface.
Neural crest cell-cell adhesion controlled by sequential and subpopulationspecific expression of novel cadherins
Authors: Nakagawa Shinichi , Takeichi Masatoshi
Published: April 2021

We identified two cadherins, c-cad6B and c-cad7, expressed by neural crest cells at their premigratory and migratory stages, respectively, in chicken embryos. cDNA transfection experiments showed that both were homophilic adhesion molecules, endowing cells with specific adhesiveness. During development, c-cad6B appeared in the neural fold, localizing at the future neural crest area. This expression was maintained during neural tube closure, but disappeared after neural crest cells had left the neural tube, suggesting its role in neural fold fusion and/or in the formation and maintenance of the presumptive neural crest domain in the neural plate/tube. Crest cells emerging from the neural tube lost c-cad6B, and a subpopulation of them began to express c-cad7. This subpopulation-specific expression of c-cad7 persisted during their migration. The migrating c-cad7-positive cells clustered together, and eventually populated restricted regions including the dorsal and ventral roots but very little ganglia. The latter was populated with N-cadherin-positive crest cells. Migrating neural crest cells expressed αand βcatenin at cell-cell contacts, indicating that their cadherins are functioning. These results suggest that the migrating crest cells are grouped into subpopulations expressing different cadherins. The cadherin-mediated specific interaction between crest cells likely plays a role in intercellular signaling between homotypic cells as well as in sorting of heterotypic cells.
Cell fate control in the Drosophila retina by the orphan receptor seven-up: its role in the decisions mediated by the ras signaling pathway
Authors: Kramer Susanne , West Steven R. , Hiromi Yasushi
Published: April 2021

Drosophila seven-up is an orphan receptor of the steroid receptor family that is required to specify photoreceptor neuron subtypes in the developing compound eye. Expression of seven-up is confined to four of the eight photoreceptor precursors, R3/R4/R1/R6. We show that misexpression of seven-up in any of the other cell types within the developing ommatidium interferes with their differentiation. Each cell type responds differently to seven-up misexpression. For example, ectopic expression in the non-neuronal cone cells using the sevenless promoter/enhancer (sev-svp) causes the cone cells to take on a neuronal identity. Ectopic expression of seven-up in R2/R5 using the rough enhancer (ro-svp) causes these neurons to lose aspects of their photoreceptor subtype identity while remaining neuronal. Each cell type appears to have a different developmental time window that is sensitive to misexpressed seven-up. The temporal order of responsiveness of each cell type to misexpressed seven-up is similar but not identical to the order of neuronal differentiation. This suggests that there are processes of specification that are distinct from the specification to become a photoreceptor neuron. We have identified members of the ras signaling pathway as suppressors of the cone cell to R7 neuron transformation caused by sev-svp. Suppression of the sev-svp phenotype can be achieved by decreasing the gene-dosage of any of the members of the ras-pathway. This suggests that the function of seven-up in the cone cells requires ras signaling. However, a decrease in ras signaling results in enhancement of the phenotype caused by the rosvp transgene. We discuss the relationship between decisions controlled by seven-up and those controlled by ras signaling.
Ectoderm induces muscle-specific gene expression in Drosophila embryos
Authors: Baker Rob , Schubiger Gerold
Published: April 2021

We have inhibited normal cell-cell interactions between mesoderm and ectoderm in wild-type Drosophila embryos, and have assayed the consequences on muscle development. Although most cells in gastrulation-arrested embryos do not differentiate, they express latent germ layer-specific genes appropriate for their position. Mesoderm cells require proximity to ectoderm to express several muscle-specific genes. We show that ventral ectoderm induces mesoderm cells to express nautilus (a MyoD homologue) and to differentiate somatic myofibers, whereas dorsal ectoderm induces mesoderm cells to express visceral and cardiac muscle-specific genes. Our findings suggest that muscle determination in Drosophila is regulated by induction between germ layers during gastrulation.
The Drosophila E74 gene is required for the proper stageand tissue-specific transcription of ecdysone-regulated genes at the onset of metamorphosis
Authors: Fletcher Jennifer C. , Thummel Carl S.
Published: April 2021

The steroid hormone ecdysone directly induces a small set of early genes, visible as puffs in the larval salivary gland polytene chromosomes, as it signals the onset of Drosophila metamorphosis. The products of these genes appear to function as regulators that both repress their own expression and induce a large set of secondary-response late genes. We have identified recessive loss-of-function mutations in the early gene E74, a member of the ets protooncogene family that encodes two related DNA-binding proteins, E74A and E74B. These mutations cause defects in pupariation and pupation, and result in lethality during metamorphosis. Here we extend our phenotypic characterization of the E74A and E74B mutant alleles to the molecular level by examining their effects on the transcription of over 30 ecdysone-regulated genes. We show that the transcription of most ecdysone primary-response genes during late larval and prepupal development is unaffected by the E74 mutations. Rather, we find that E74 is necessary for the appropriate regulation of many ecdysone secondary-response genes. E74B is required for the maximal induction of glue genes in mid third instar larval salivary glands, while E74A is required in early prepupae for the proper timing and maximal induction of a subset of late genes. E74 activity is also necessary for the correct regulation of genes expressed predominantly in the fat body, epidermis or imaginal discs. These observations confirm that E74 plays a critical role in regulating transcription during the early stages of Drosophila metamorphosis. In addition, the widespread effects of the E74 mutations on transcription indicate that E74 functions in regulatory hierarchies not only in the larval salivary gland, but throughout the entire organism.
Linkage of cardiac left-right asymmetry and dorsal-anterior development in Xenopus
Authors: C. Danos Maria , Yost H. Joseph
Published: April 2021

The left-right body axis is defined relative to the dorsalventral and anterior-posterior body axes. Since left-right asymmetries are not randomly oriented with respect to dorsal-ventral and anterior-posterior spatial patterns, it is possible that a common mechanism determines all three axes in a coordinate manner. Two approaches were undertaken to determine whether alteration in dorsal-anterior development perturbs the left-right orientation of heart looping. Treatments known to decrease dorsal-anterior development in Xenopus laevis, UV irradiation during the first cell cycle or Xwnt-8 DNA injections into dorsal blastomeres, caused an increase in cardiac left-right reversals. The frequency of left-right reversal was correlated with the severity of dorsal-anterior perturbation and with the extent of anterior notochord regression. Injection of Xwnt-8 DNA into dorsal midline cells resulted in decreased dorsalanterior development and a correlated increase in cardiac left-right reversals. In contrast, injection of Xwnt-8 DNA into cardiac progenitor blastomeres did not result in leftright reversals, and dorsal-anterior development and notochord formation were normal. Disrupting development of dorsal-anterior cells, including cells that give rise to the Organizer region and the notochord, results in the randomization of cardiac left-right asymmetry. These results suggest dorsal-anterior development and the regulation of left-right orientation are linked.
Developmental biology of the pancreas
Authors: Slack J. M. W.
Published: April 2021

The pancreas is an organ containing two distinct populations of cells, the exocrine cells that secrete enzymes into the digestive tract, and the endocrine cells that secrete hormones into the bloodstream. It arises from the endoderm as a dorsal and a ventral bud which fuse together to form the single organ. Mammals, birds, reptiles and amphibians have a pancreas with similar histology and mode of development, while in some fish, the islet cells are segregated as Brockmann bodies. Invertebrates do not have a pancreas, but comparable endocrine cells may be found in the gut or the brain.

The early pancreatic bud shows uniform expression of the homeobox gene IPF-1 (also known as IDX-1, STF-1 or PDX), which when mutated to inactivity leads to total absence of the organ. The occurrence of heterotopic pancreas in the embryo, and also the metaplasias that can be displayed by a regenerating pancreas in the adult, both suggest that only a few gene products distinguish the pancreatic cell state from that of the surrounding tissues of duodenum, gall bladder and liver.

In the developing pancreatic buds, the endocrine cells start to differentiate before the exocrine cells, and coexpression of different hormones by the same cell is often observed at early stages. Although pancreatic endocrine cells produce many gene products also characteristic of neurons, evidence from in vitro cultures and from quail-chick grafts shows that they are of endogenous and not of neural crest origin. Observational studies suggest strongly that both endocrine and exocrine cells arise from the same endodermal rudiment.

Development of the pancreas in embryonic life requires a trophic stimulus from the associated mesenchyme. In postnatal life, all cell types in the pancreas continue to grow. Destruction of acinar tissue by duct ligation or ethionine treatment is followed by rapid regeneration. Surgical removal of parts of the pancreas is followed by moderate but incomplete regeneration of both acini and islets. Poisoning with alloxan or streptozotocin can lead to permanent depletion of β cells. Although the cell kinetics of the pancreas are not understood, it seems likely that there is a continuous slow turnover of cells, fed from a stem cells population in the ducts, and that the controls on the production rate of each cell type are local rather than systemic.
Mouse chick chimera: a new model to study the in ovo developmental potentialities of mammalian somites
Authors: Fontaine-Perus J. , Jarno V. , Ray C. Fournier le , Li Z. , Paulin D.
Published: April 2021

Chimeras were prepared by transplanting somites from 9-day post-coïtum mouse embryos or somitic dermomyotomes from 10-day post-coïtum mouse embryos into 2-day-old chick embryos at different axial levels. Mouse somitic cells then differentiated in ovo in dermis, cartilage and skeletal muscle as they normally do in the course of development and were able to migrate into chick host limb. To trace the behavior of somitic myogenic stem cells more closely, somites arising from mice bearing a transgene of the desmin gene linked to a reporter gene coding for Escherichia coli β-galactosidase (lacZ) were grafted in ovo. Interestingly, the transgene was rapidly expressed in myotomal muscles derived from implants. In the limb muscle mass, positive cells were found several days after implantation. Activation of desminnls lacZ also occurred in in vitro cultures of somite-derived cells. Our experimental method facilitates investigation of the mechanisms of mammalian development, allowing the normal fate of implanted mouse cells to be studied and providing suitable conditions for identification of descendants of genetically modified cells.
Early development and dispersal of oligodendrocyte precursors in the embryonic chick spinal cord
Authors: Ono Katsuhiko , Bansal Rashmi , Payne Jennifer , Rutishauser Urs , Miller Robert H.
Published: April 2021

Oligodendrocytes, the myelinating cells of the vertebrate CNS, originally develop from cells of the neuroepithelium. Recent studies suggest that spinal cord oligodendrocyte precursors are initially localized in the region of the ventral ventricular zone and subsequently disperse throughout the spinal cord. The characteristics of these early oligodendrocyte precursors and their subsequent migration has been difficult to assay directly in the rodent spinal cord due to a lack of appropriate reagents. In the developing chick spinal cord, we show that oligodendrocyte precursors can be specifically identified by labeling with O4 monoclonal antibody. In contrast to rodent oligodendrocyte precursors, which express O4 immunoreactivity only during the later stages of maturation, in the chick O4 immunoreactivity appears very early and its expression is retained through cellular maturation. In embryos older than stage 35, O4+ cells represent the most immature, self-renewing, cells of the chick spinal cord oligodendrocyte lineage. In the intact chick spinal cord, the earliest O4+ cells are located at the ventral ventricular zone where they actually contribute to the ventricular lining of the central canal. The subsequent migration of O4+ cells into the dorsal region of the spinal cord temporally correlates with the capacity of isolated dorsal spinal cord to generate oligodendrocytes in vitro. Biochemical analysis suggests O4 labels a POA-like antigen on the surface of chick spinal cord oligodendrocyte precursors. These studies provide direct evidence for the ventral ventricular origin of spinal cord oligodendrocytes, and suggest that this focal source of oligodendrocytes is a general characteristic of vertebrate development.
Specification, migration and assembly of the somatic cells of the Drosophila gonad
Authors: Boyle Monica , DiNardo Stephen
Published: April 2021

The adult ovaries and testes contain several specialized somatic cell types that support the differentiation of germ cells into mature gametes. Each of these cell types arise from mesodermal cells that constitute the embryonic gonad. To explore the mechanisms governing the development and differentiation of these cells, we focus on the formation of the gonad during Drosophila development. Using markers for the precursors of the somatic cells of the gonad, we identify discrete steps in the development of the gonad. Our results suggest the existence of different populations of gonadal precursors at early stages in gonadogenesis that represent precursors of cell types found within the adult gonad. The functions of the homeotic genes abdominal A and Abdominal B are required for the development of gonadal precursors, however, here we provide evidence that each plays a distinct role. abd A activity alone specifies anterior gonadal precursor fates, whereas abd A and Abd B act together to specify a posterior subpopulation of gonadal precursors. Once specified, gonadal precursors born within posterior parasegments must move to the site of gonad formation. Here, we show that the proper regional identities, as established by homeotic gene function, are required for the arrest of migration at the correct position. Finally, our analysis of late stages of gonadogenesis suggests that abd A is required in a population of cells within parasegments 10 and 11 that partially ensheath the coalescing gonad. Mutations in iab-4 abolish expression of abd A within these cells, and as a result block the coalescence of the gonad.
Defective haematopoiesis and vasculogenesis in transforming growth factor-β1 knock out mice
Authors: Dickson Marion C. , Martin Julie S. , Cousins Frances M. , Kulkarni Ashok B. , Karlsson Stefan , Akhurst Rosemary J.
Published: April 2021

Transforming growth factor β1 (TGFβ1) is shown here to be required for yolk sac haematopoiesis and endothelial differentiation. Mice with a targeted mutation in the TGFβ1 gene were examined to determine the cause of prenatal lethality, which occurs in 50% of homozygous TGFβ1 null (TGFβ1−/−) conceptions. 50% of TGFβ1−/− and 25% of TGFβ1+/− conceptuses were found to die at around 10.5 dpc. The primary defects were restricted to extraembryonic tissues, namely the yolk sac vasculature and haematopoietic system. The embryos per se showed developmental retardation, oedema and necrosis, which were probably secondary to the extraembryonic lesions. The defect in vasculogenesis appeared to affect endothelial differentiation, rather than the initial appearance and outgrowth of endothelial cells. Initial differentiation of yolk sac mesoderm to endothelial cells occurred, but defective differentiation resulted in inadequate capillary tube formation, and weak vessels with reduced cellular adhesiveness. Defective haematopoiesis resulted in a reduced erythroid cell number within the yolk sac. Defective yolk sac vasculogenesis and haematopoiesis were present either together, or in isolation of each other. The phenotypes are consistent with the observation of abundant TGFβ1 gene expression in both endothelial and haematopoietic precursors. The data indicate that the primary effect of loss of TGFβ1 function in vivo is not increased haematopoietic or endothelial cell proliferation, which might have been expected by deletion of a negative growth regulator, but defective haematopoiesis and endothelial differentiation.
Dorsal-ventral patterning and differentiation of noggin-induced neural tissue in the absence of mesoderm
Authors: Knecht Anne K. , Good Peter J. , Dawid Igor B. , Harland Richard M.
Published: April 2021

In Xenopus development, dorsal mesoderm is thought to play a key role in both induction and patterning of the nervous system. Previously, we identified a secreted factor, noggin, which is expressed in dorsal mesoderm and which can mimic that tissue’ s neural-inducing activity, without inducing mesoderm. Here the neural tissue induced in ectodermal explants by noggin is further characterized using four neural-specific genes: two putative RNA-binding proteins, nrp-1 and etr-1; the synaptobrevin sybII; and the lipocalin cpl-1. First we determine the expression domain of each gene during embryogenesis. Then we analyze expression of these genes in noggin-treated explants. All markers, including the differentiated marker sybII, are expressed in noggin-induced neural tissue. Furthermore, cpl-1, a marker of dorsal brain, and etr-1, a marker absent in much of the dorsal forebrain, are expressed in non-over-lapping territories within these explants. We conclude that the despite the absence of mesoderm, noggin-induced neural tissue shows considerable differentiation and organization, which may represent dorsal-ventral patterning of the forebrain.
Mutations in a novel gene, myoblast city, provide evidence in support of the founder cell hypothesis for Drosophila muscle development
Authors: Rushton Emma , Drysdale Rachel , Abmayr Susan M. , Michelson Alan M. , Bate Michael
Published: April 2021

We have used mutations in the newly identified gene myoblast city to investigate the founder cell hypothesis of muscle development in Drosophila melanogaster. In embryos mutant for myoblast city the fusion of myoblasts into multinucleate muscles is virtually abolished. Nevertheless, a subset of the myoblasts develop specific muscle-like characteristics, including gene expression appropriate to particular muscles, migration to the appropriate part of the segment, correct position and orientation, and contact by motor neurons. We suggest that this subset of myoblasts represents the proposed muscle founder cells and we draw an analogy between these founder cells and the muscle pioneers described for grasshopper muscle development.
Two CDC25 homologues are differentially expressed during mouse development
Authors: Wickramasinghe Dineli , Becker Sandy , Ernst Mary K. , Resnick James L. , Centanni John M. , Tessarollo Lino , Grabel Laura B. , Donovan Peter J.
Published: April 2021

The cdc25 gene product is a tyrosine phosphatase that acts as an initiator of M-phase in eukaryotic cell cycles by activating p34cdc2. Here we describe the cloning and characterization of the developmental expression pattern of two mouse cdc25 homologs. Sequence comparison of the mouse genes with human CDC25 genes reveal that they are most likely the mouse homologs of human CDC25A and CDC25B respectively. Mouse cdc25a, which has not been described previously, shares 84% sequence identity with human CDC25A and has a highly conserved phosphatase domain characteristic of all cdc25 genes. A glutathione-S-transferase-cdc25a fusion protein can hydrolyze para-nitrophenylphosphate confirming that cdc25a is a phosphatase. In adult mice, cdc25a transcripts are expressed at high levels in the testis and at lower levels in the ovary, particularly in germ cells; a pattern similar to that of twn, a Drosophila homolog of cdc25. Lower levels of transcript are also observed in kidney, liver, heart and muscle, a transcription pattern that partially overlaps, but is distinct from that of cdc25b. Similarly, in the postimplantation embryo cdc25a transcripts are expressed in a pattern that differs from that of cdc25b. cdc25a expression is observed in most developing embryonic organs while cdc25b expression is more restricted. An extended analysis of cdc25a and cdc25b expression in preimplantation embryos has also been carried out. These studies reveal that cdc25b transcripts are expressed in the one-cell embryo, decline at the two-cell stage and are re-expressed at the four-cell stage, following the switch from maternal to zygotic transcription which mirrors the expression of string, another Drosophila homolog of cdc25. In comparison, cdc25a is not expressed in the preimplantation embryo until the late blastocyst stage of development, correlating with the establishment of a more typical G1 phase in the embryonic cell cycles. Both cdc25a and cdc25b transcripts are expressed at high levels in the inner cell mass and the trophectoderm, which proliferate rapidly prior to implantation. These data suggest the cdc25 genes may have distinct roles in regulating the pattern of cell division during mouse embryogenesis and gametogenesis.
Stem cell defects in parthenogenetic peri-implantation embryos
Authors: Newman-Smith Erin D. , Werb Zena
Published: April 2021

Mouse embryos containing only maternal chromosomes (parthenotes) develop abnormally in vivo, usually failing at the peri-implantation stage. We have analyzed the development of parthenote embryos by using an inner cell mass (ICM) outgrowth assay that mimics peri-implantation development. ICMs from normal embryos maintained undifferentiated stem cells positive for stage-specific embryonic antigen-1 and Rex-1 while differentiating into a variety of cell types, including visceral endoderm-like cells and parietal endoderm cells. In contrast, ICMs from parthenotes failed to maintain undifferentiated stem cells and differentiated almost exclusively into parietal endoderm. This suggests that parthenote ICMs have a defect that leads to differentiation, rather than maintenance, of the stem cells, and a defect that leads to a parietal endoderm fate for the stem cells. To test the hypothesis that the ICM population is not maintained owing to a lack of proliferation of the stem cells, we investigated whether mitogenic agents were able to maintain the ICM population in parthenotes. When parthenote blastocysts were supplied with the insulin-like growth factor-1 receptor (Igf-1r) and insulin-like growth factor-2 (Igf-2), two genes not detectable in parthenote blastocysts by in situ hybridization, the ICM population was maintained. Similarly, culture of parthenote blastocysts in medium conditioned by embryonic fibroblasts and supplemented with the maternal factor leukemia inhibitory factor maintained the ICM population. However, once this growth factor-rich medium was removed, the parthenote ICM cells still differentiated predominantly into parietal endoderm. These data suggest that the parthenote ICM cells have both a proliferation defect and a cell fate defect owing to misregulation of genes critical to growth and differentiation, and that these defects are responsible, in part, for the abnormal development of peri-implantation parthenote embryos.
Dorsalization of the neural tube by the non-neural ectoderm
Authors: Dickinson Mary E. , Selleck Mark A. J. , McMahon Andrew P. , Bronner-Fraser Marianne
Published: April 2021

The patterning of cell types along the dorsoventral axis of the spinal cord requires a complex set of inductive signals. While the chordamesoderm is a well-known source of ventralizing signals, relatively little is known about the cues that induce dorsal cell types, including neural crest. Here, we demonstrate that juxtaposition of the non-neural and neural ectoderm is sufficient to induce the expression of dorsal markers, Wnt-1, Wnt-3a and Slug, as well as the formation of neural crest cells. In addition, the competence of neural plate to express Wnt-1 and Wnt-3a appears to be stage dependent, occurring only when neural tissue is taken from stage 8-10 embryos but not from stage 4 embryos, regardless of the age of the non-neural ectoderm. In contrast to the induction of Wnt gene expression, neural crest cell formation and Slug expression can be induced when either stage 4 or stage 8-10 neural plates are placed in contact with the non-neural ectoderm. These data suggest that the non-neural ectoderm provides a signal (or signals) that specifies dorsal cell types within the neural tube, and that the response is dependent on the competence of the neural tissue.
Astroglial control of oligodendrocyte survival mediated by PDGF and Leukemia Inhibitory Factor-like protein
Authors: Gard A. L. , Burrell M. R. , Pfeiffer S. E. , Rudge J. S. , Williams W. C.
Published: April 2021

Programmed death and the identification of growth factors delaying this process in the oligodendrocyte lineage suggest that other cell types provide oligodendrogliotrophins. To determine their source, primary cultures of oligodendroblasts immunopurified from postnatal rat cerebrum were used to screen other cultured neural and non-neural cell types for the release of survival factors into a defined insulin-containing medium. In non-conditioned medium, oligodendroblasts died 1-2 days after undergoing terminal differentiation into oligodendrocytes, as defined by the onset of expression of galactocerebroside. In medium conditioned by astrocytes, unlike the other tested cell types, differentiated oligodendrocytes survived for weeks in a mature myelinogenic state. Survival was partially reduced by immunoabsorption of the medium with antibodies to platelet-derived growth factor and abolished by immunoabsorption with antibodies to leukemia inhibitory factor. By the same criterion, survival activity was not attributed to other astrocytic products, ciliary neurotrophic factor and basic fibroblast growth factor. Membrane ultrafiltration analysis indicated the activity corresponded to heat-labile protein smaller (Mr = 10-30×103) than native rat leukemia inhibitory factor (Mr = 43×103). The astrocytic stimulus was >4-fold more efficacious than other known oligodendrogliotrophic cytokines, including ciliary neurotrophic factor, neurotrophin-3 and leukemia inhibitory factor itself, tested singly or in combination, and promoted survival additively with these agents. These findings suggest that astrocytes function as paracrine regulators of oligodendroblast and oligodendrocyte survival and that their effect is mediated initially by platelet-derived growth factor and thereafter by a powerful cytokine related to leukemia inhibitory factor.
The Breathless FGF receptor homolog, a downstream target of Drosophila C/EBP in the developmental control of cell migration
Authors: Murphy Anne Marie , Lee Tzumin , Andrews Cynthia M. , Shilo Ben-Zion , Montell Denise J.
Published: April 2021

To investigate the molecular mechanisms responsible for the temporal and spatial control of cell movements during development, we have been studying the migration of a small group of follicle cells, called the border cells, in the Drosophila ovary. Timely initiation of border cell migration requires the product of the slow border cells (slbo) locus, which encodes the Drosophila homolog of the transcription factor C/EBP. Here we report evidence that one target of C/EBP in the control of border cell migration is the FGF receptor homolog encoded by the breathless (btl) locus. btl expression in the ovary was border cell-specific, beginning just prior to the migration, and this expression was reduced in slbo mutants. btl mutations dominantly enhanced the border cell migration defects found in weak slbo alleles. Furthermore, C/EBP-independent btl expression was able to rescue the migration defects of hypomorphic slbo alleles. Purified Drosophila C/EBP bound eight sites in the btl 5′ flanking region by DNAse I footprinting. Taken together these results suggest that btl is a key, direct target for C/EBP in the regulation of border cell migration.
wingless and patched are negative regulators of the morphogenetic furrow and can affect tissue polarity in the developing Drosophila compound eye
Authors: Ma Chaoyong , Moses Kevin
Published: April 2021

In the developing Drosophila compound eye, a wave of pattern formation and cell-type determination sweeps across the presumptive eye epithelium. This ‘morpho-genetic furrow’ coordinates the epithelial cells’ division cycle, shape and gene expression to produce evenly spaced neural cell clusters that will eventually form the adult ommatidia. As these clusters develop, they rotate inwards to face the eye’s equator and establish tissue polarity. We have found that wingless is strongly expressed in the dorsal margin of the presumptive eye field, ahead of the morpho-genetic furrow. We have shown that inactivation of Wingless results in the induction of an ectopic furrow that proceeds ventrally from the dorsal margin. This ectopic furrow is normal in most respects, however the clusters formed by it fail to rotate, and we propose a two-vector model to account for normal rotation and tissue polarity in the retina. A second consequence of this inactivation of Wingless is that the dorsal head is largely deleted. We have also found that patched loss-of-function mosaic clones induce circular ectopic morphogenetic furrows (consistent with the observations of other workers with the hedgehog, and PKA genes). We use such patched induced furrows to test the two-vector model for cluster rotation and tissue polarity.
Patterns of free calcium in multicellular stages of Dictyostelium expressing jellyfish apoaequorin
Authors: Cubitt Andrew B. , Firtel Richard A. , Fischer Gabriele , Jaffe Lionel F. , Miller Andrew L.
Published: April 2021

To examine the patterns of high free cytosolic calcium or [Ca2+]i during Dictyostelium’s development, we expressed apoaequorin in D. discoideum, reconstituted aequorin and observed the resultant patterns of calcium-dependent luminescence. Specific, high calcium zones are seen throughout normal multicellular development and are roughly coincident with those regions that later differentiate into stalk or stalk-like cells. A slug, for example, shows a primary high calcium zone within its front quarter and a secondary one around its tail; while a mound shows such a zone around the periphery of its base. Combined with previous evidence, our findings support the hypothesis that high [Ca2+]i feeds back to favor the stalk pathway.

We also discovered several high calcium zones within the mound’s base that do not coincide with any known prepatterns in D. discoideum. These include two, relatively persistent, antipodal strips along the mound’s periphery.

These various persistent zones of high calcium are largely made up of frequent, 10 to 30 second long, semi-periodic calcium spikes. Each of these spikes generates a correspondingly short-lived, 200 to 500 μm long, high calcium band which extends along the nearby surface. Similar, but relatively large and infrequent, spikes generate cross bands which extend across migrating slugs and just behind their advancing tips as well as across the peripheries of rotating mounds and midway between their antipodal strips. Moreover, calcium has a doubling time of about a second as various spikes rise. This last observation suggests that the calcium bands seen in Dictyostelium may be generated by so-called fast calcium waves.
Initiation of cardiac differentiation occurs in the absence of anterior endoderm
Authors: Gannon Maureen , Bader David
Published: April 2021

Anterior endoderm has been proposed to be a specific inducer of cardiac differentiation in vertebrates (reviewed in Jacobson and Sater, Development 104, 341-359, 1988). The ability of cardiogenic mesoderm to differentiate in a minimal culture system was examined using cardiac-specific gene expression as an assay. Anterior lateral plate mesoderm was explanted from chick embryos with and without associated endoderm at developmental stages from just after gastrulation (stage 4; Hamburger and Hamilton, J. Morph. 88, 49-67, 1951) to just prior to contraction (stage 9). At all stages examined, cardiogenic mesoderm expressed a profile of cardiac-specific mRNAs after two days in minimal medium independent of the presence of endoderm. Our studies indicate that endoderm is necessary for the generation of stable sarcomeric protein expression, organized myofibrils and beating tissue from stage 4-6. Subsequent to this stage, an interaction with anterior endoderm is no longer required. Examination of cardia bifida embryos from which anterior endoderm had been unilaterally removed also showed a stage-dependent effect of endoderm on beating, while cardiac gene expression and heart morphogenesis were unaffected. These results demonstrate that anterior endoderm does not induce or maintain cardiac gene expression, nor is it required for terminal differentiation. Endoderm does appear to be necessary for a short period of time between initiation of cardiac gene expression and the onset of contraction.
Distribution of Sonic hedgehog peptides in the developing chick and mouse embryo
Authors: Martí Elisa , Takada Ritsuko , Bumcrot David A. , Sasaki Hiroshi , McMahon Andrew P.
Published: April 2021

Sonic hedgehog (Shh) encodes a signal that is implicated in both short-and long-range interactions that pattern the vertebrate central nervous system (CNS), somite and limb. Studies in vitro indicate that Shh protein undergoes an internal cleavage to generate two secreted peptides. We have investigated the distribution of Shh peptides with respect to these patterning events using peptide-specific antibodies. Immunostaining of chick and mouse embryos indicates that Shh peptides are expressed in the notochord, floor plate and posterior mesenchyme of the limb at the appropriate times for their postulated patterning functions. The amino peptide that is implicated in intercellular signaling is secreted but remains tightly associated with expressing cells. The distribution of peptides in the ventral CNS is polarized with the highest levels of protein accumulating towards the luminal surface. Interestingly, Shh expression extends beyond the floor plate, into ventrolateral regions from which some motor neuron precursors are emerging. In the limb bud, peptides are restricted to a small region of posterior-distal mesenchyme in close association with the apical ectodermal ridge; a region that extends 50-75 μm along the anterior-posterior axis. Temporal expression of Shh peptides is consistent with induction of sclerotome in somites and floor plate and motor neurons in the CNS, as well as the regulation of anterior-posterior polarity in the limb. However, we can find no direct evidence for long-range diffusion of the 19×103Mr peptide which is thought to mediate both short-and long-range cell interactions. Thus, either long-range signaling is mediated indirectly by the activation of other signals, or alternatively the low levels of diffusing peptide are undetectable using available techniques.
Innervation is essential for the development and differentiation of a sex-specific adult muscle in Drosophila melanogaster
Authors: Currie Douglas A. , Bate Michael
Published: April 2021

The adult abdominal muscles in Drosophila are generated de novo during metamorphosis and form a simple and characteristic pattern. Throughout adult abdominal development there is a close association between nerves and myoblasts. However, the role of innervation in adult myogenesis is unclear. In males there is an additional muscle, which is unique to abdominal segment 5 (A5). This male specific muscle forms from the same pool of myoblasts as other dorsal muscles in A5 but develops several distinctive characteristics. Previous work indicates the genotype of the innervation of this male specific muscle may play a crucial role in its proper development, although the part played by innervation in the development of other muscles is unknown. Here we test directly the function of innervation in adult myogenesis in general and for the development and differentiation of the male specific muscle in particular. After denervation at the onset of metamorphosis, muscle growth is impaired although the overall muscle pattern continues to develop. Uniquely, the male specific muscle fails to form. Our results indicate that there is an essential role for innervation during the period of metamorphosis for the formation of a full complement of abdominal muscles and for muscle growth. Furthermore, innervation is absolutely required for the formation of the male specific muscle and the development of its special characteristics.
Cranial paraxial mesoderm and neural crest cells of the mouse embryo: co-distribution in the craniofacial mesenchyme but distinct segregation in branchial arches
Authors: Trainor Paul A. , Tam Patrick P. L.
Published: April 2021

The spatial distribution of the cranial paraxial mesoderm and the neural crest cells during craniofacial morphogenesis of the mouse embryo was studied by micromanipulative cell grafting and cell labelling. Results of this study show that the paraxial mesoderm and neural crest cells arising at the same segmental position share common destinations. Mesodermal cells from somitomeres I, III, IV and VI were distributed to the same craniofacial tissues as neural crest cells of the forebrain, the caudal midbrain, and the rostral, middle and caudal hindbrains found respectively next to these mesodermal segments. This finding suggests that a basic meristic pattern is established globally in the neural plate ectoderm and paraxial mesoderm during early mouse development. Cells from these two sources mixed extensively in the peri-ocular, facial, periotic and cervical mesenchyme. However, within the branchial arches a distinct segregation of these two cell populations was discovered. Neural crest cells colonised the periphery of the branchial arches and enveloped the somitomere-derived core tissues on the rostral, lateral and caudal sides of the arch. Such segregation of cell populations in the first three branchial arches is apparent at least until the 10.5-day hindlimb bud stage and could be important for the patterning of the skeletal and myogenic derivatives of the arches.