bluuebunny/crossref_metadata_2025 huggingface dataset:
Oligodendrocyte precursors originate at the ventral ventricular zone dorsal to the ventral midline region in the embryonic rat spinal cord
Authors: Noll Elizabeth , Miller Robert H.
Published: April 2021

The precursors for oligodendrocytes, the myelinating cells of the vertebrate CNS, appear to be initially restricted to ventral regions of the embryonic rat spinal cord. These cells subsequently populate dorsal spinal cord regions where they acquire the mature characteristics of oligodendrocytes. To determine the location and timing of proliferation of oligodendrocyte precursors in the ventral spinal cord, and to map their pathways of migration in vivo, an assay that identifies mitotic cells was used in conjunction with antibodies that distinguish astrocytes, oligodendrocytes and their precursors.

Between E16.5 and E18.5, two hours after a maternal injection of BrdU, the majority of proliferating cells were located in a discrete cluster at the ventral ventricular zone dorsal to the ventral midline region of the developing spinal cord. By contrast, 12 – 24 hours following a BrdU injection at E16.5, increasing numbers of labeled cells were seen in the dorsal and more lateral locations of the spinal cord. These observations suggest that BrdU-labeled ventral ventricular cells, or their progeny migrate dorsally and laterally during subsequent spinal cord development. To determine the nature of these proliferating cells, cultures of dorsal and ventral spinal cord from BrdU-labeled animals were doublelabeled with antibodies that identify oligodendrocytes or astrocytes and anti-BrdU. In dorsal spinal cord cultures derived from animals that had received a single injection of BrdU at E16.5, the majority of proliferating cells differentiated into astrocytes while, in ventrally derived cultures from the same animals, the majority of proliferating cells differentiated into oligodendrocytes. In dorsal cultures prepared from animals that received multiple injections of BrdU between E16.5 and E18.5, many more cells were labeled with BrdU and approximately half of these differentiated into oligodendrocytes. These observations suggest that during embryonic development proliferating oligodendrocyte precursors are initially located at the ventral ventricular zone dorsal to the ventral midline region of the spinal cord and during subsequent maturation these cells or their progeny migrated dorsally in the ventricular region of the spinal cord, and laterally to reside in the developing white matter.
Inactivation of an X-linked transgene in murine extraembryonic and adult tissues
Authors: Dandolo Luisa , Stewart Colin L. , Mattei Marie-Genevieve , Avner Philip R.
Published: April 2021

Transgenes located on the X chromosome have been used to study the mechanisms involved in X-chromosome inactivation. Analysis of the transgenic mouse strain M-TKneo1 carrying a neomycin resistance gene inserted in the X chromosome showed that, in adult somatic tissues, this transgene is subject to X-inactivation and to de novo methylation as other endogenous Xlinked genes.

During mouse embryogenesis, X-linked genes show a preferential paternal inactivation in extraembryonic tissues, whereas these genes are subject to random inactivation in embryonic tissues. It has been suggested that, in the mouse, the extraembryonic tissues carry a parental imprint at the time of inactivation.

The study of the neo transgene expression in extraembryonic endoderm has shown not only that neo is inactivated but also that, at the RNA level, paternal inactivation of the transgene seems essentially complete.

The differences between our results and previously obtained results with a mouse α-fetoprotein transgene, which was only inactivated in neonatal tissues but not in extraembryonic tissues, are discussed.
Mechanical evaluation of theories of neurulation using computer simulations
Authors: Clausi David A. , Brodland G. Wayne
Published: April 2021

Current theories about the forces that drive neurulation shape changes are evaluated using computer simulations. Custom, three-dimensional, finite element-based computer software is used. The software draws on current engineering concepts and makes it possible to construct a ‘virtual’ embryo with any user-specified mechanical properties. To test a specific hypothesis about the forces that drive neurulation, the whole virtual embryo or any selected part of it is ascribed with the force generators specified in the hypothesis. The shape changes that are produced by these forces are then observed and compared with experimental data.

The simulations demonstrate that, when uniform, isotropic circumferential microfilament bundle (CMB) constriction and cephalocaudal (axial) elongation act together on a circular virtual neural plate, it becomes keyhole shaped. When these forces act on a spherical (amphibian) embryo, dorsal surface flattening occurs. Simulations of transverse sections further show that CMB constriction, acting with or without axial elongation, can produce numerous salient transverse features of neurulation. These features include the sequential formation of distinct neural ridges, narrowing and thickening of the neural plate, skewing just medial to the ridges, ‘hinge’ formation and neural tube closure. No region-specific ‘programs’ or non-mechanical cell-cell communications are used. The increase in complexity results entirely from mechanical interactions. The transverse simulations show how changes to the driving forces would affect the patterns of shape change produced.

Hypotheses regarding force generation by microtubules, intercellular adhesions and forces extrinsic to the neural plate are also evaluated. The simulations show that these force-generating mechanisms do not, by themselves, produce shape changes that are consistent with normal development. The simulations support the concept of cooperation of forces and suggest that neurulation is robust because redundant force generating mechanisms exist.
Sex determination in the germ line of Drosophila melanogaster: activation of the gene Sex-lethal
Authors: Granadino Begoña , Santamaria Pedro , Sánchez Lucas
Published: April 2021

The germ line exhibits sexual dimorphism as do the somatic tissues. Cells with the 2X;2A chromosome constitution will follow the oogenic pathway and X;2A cells will develop into sperm. In both somatic and germ-line tissues, the sexual pathway chosen by the cells depends on the gene Sex-lethal (Sxl), whose function is continuously needed for female development. In the soma, the sex of the cells is autonomously determined by the X:A signal while, in the germ line, the sex is determined by cell autonomous (the X:A signal) and somatic inductive signals. Three X-linked genes have been identified, scute (sc), sisterless-a (sis-a) and runt (run), that determine the initial functional state of Sxl in the soma. Using pole cell transplantation, we have tested whether these genes are also needed to activate Sxl in the germ line. We found that germ cells simultaneously heterozygous for sc, sis-a, run and a deficiency for Sxl transplanted into wild-type female hosts develop into functional oocytes. We conclude that the genes sc, sis-a and run needed to activate Sxl in the soma seem not to be required to activate this gene in the germ line; therefore, the X:A signal would be made up by different genes in somatic and germ-line tissues. The Sxlf7M1/Sxlfc females do not have developed ovaries. We have shown that germ cells of this genotype transplanted into wild-type female hosts produce functional oocytes. We conclude that the somatic component of the gonads in Sxlf7M1/Sxlfc females is affected, and consequently germ cells do not develop. This result supports the existence of a somatic positive feminizing signal for germ-line development. The activation of Sxl in the germ line would be controlled by cell-autonomous genetic factors (the X:A signal) and a positive feminizing function from the female gonadal soma.
Age-dependent selection against hypoxanthine phosphoribosyl transferase-deficient cells in mouse haematopoiesis
Authors: Samuel K. , Clarke A. R. , Ansell J. D. , Hooper M. L.
Published: April 2021

The basis of a previously observed difference in the level of contribution of hypoxanthine phosphoribosyltrans-ferase-deficient cells between the haematopoietic and non-haematopoietic tissues of chimaeric and heterozy-gous mice has been clarified by studying two populations of female mice that differ only in that one is heterozy-gous for a null allele at the hprt locus and the other is wild type at this locus. Both populations are heterozy-gous for an electrophoretic variant allele at the X-linked Pgk-1 locus, so that X-chromosome inactivation generates cells expressing different isozymes of phos-phoglycerate kinase which can be assayed to monitor cell selection. The results show that hypoxanthine phospho-ribosyltransferase deficiency itself, rather than an effect of another X-linked gene, causes a reduced level of con-tribution to haematopoietic tissues. Further, the extent of the depletion increases significantly with age, and this effect is due to a progressive reduction in the level of con-tribution to haematopoietic tissues rather than to an increase in the level of contribution to non-haematopoi-etic tissues.
Lox10, a member of the NK-2 homeobox gene class, is expressed in a segmental pattern in the endoderm and in the cephalic nervous system of the leech Helobdella
Authors: Nardelli-Haefliger D. , Shankland M.
Published: April 2021

A novel leech homeobox gene, Lox10, is shown to encode a homeodomain sequence characteristic of a phyletically widespread NK-2 homeobox gene class. Lox10 expression was examined in leech embryos of various ages by in situ hybridization. In the unsegmented cephalic region, Lox10 RNA is expressed in a subset of the cells descended from the a' and b' micromeres, including a small cluster of cells, believed to be postmitotic neurons, within the supraesophageal ganglion of the central nervous system. Hybridization signal was not detected in either the mesoderm or ectoderm of the trunk segments, and the apparent restriction of Lox10 ectodermal expression to the nonsegmented cephalic domain resembles the restricted forebrain expression pattern of its mammalian homologues. Lox10 is also expressed within the endodermal tissues of the leech midgut, which arises by cellularization from a polynucleate syncytium. Endodermal expression is organized into a pattern of transverse stripes and spots which are aligned with the intersegmental septa, and which prefigure the pattern of gut wall constrictions observed at later stages of development. Lox10 is the first molecular marker of segmentally periodic endoderm differentiation reported for any animal species.
Influence of Drosophila ventral epidermal development by the CNS midline cells and spitz class genes
Authors: Kim Sang Hee , Crews Stephen T.
Published: April 2021

The ventral epidermis of Drosophila melanogaster is derived from longitudinal rows of ectodermal precursor cells that divide and expand to form the ventral embryonic surface. The spitz class genes are required for the proper formation of the larval ventral cuticle. Using a group of enhancer trap lines that stain subsets of epidermal cells, it is shown here that spitz class gene function is necessary for ventral epidermal development and gene expression. Analysis of single-minded mutant embryos implies that ventral epidermal cell fate is influenced by the CNS midline cells.
Inhibition of urokinase synthesis and cell surface binding alters the motile behavior of embryonic endocardial-derived mesenchymal cells in vitro
Authors: McGuire Paul G. , Alexander Susan M.
Published: April 2021

The expression of the serine protease urokinase is elevated during the epithelial-mesenchymal transformation of the endocardium in the developing avian heart. Elevated urokinase expression is associated with the migrating mesenchymal cells of the atrioventricular canal and bulbotruncus and not the myocardium. Treatment of isolated endocardial-derived mesenchymal cells with phosphatidyinositol-specific phospholipase C released urokinase and its receptor from the cell surface and caused significant alterations in cell morphology and motility. Likewise inhibition of urokinase synthesis by treatment of cells with antisense oligonucleotides also inhibited the migration and motility of the endocardialderived cells. These results suggest an important role for this enzyme in cell-matrix interactions and cell migration during development.
9-cis-retinoic acid, a potent inducer of digit pattern duplications in the chick wing bud
Authors: Thaller Christina , Hofmann Clementine , Eichele Gregor
Published: April 2021

The effects of retinoids are mediated by two types of receptors, the retinoic acid receptors (RARs) and the retinoid-X-receptors (RXRs). The physiological ligand of the RARs is all-trans-retinoic acid whereas RXRs have high affinity for 9-cis-retinoic acid, a naturally occurring retinoid isomer. RXRs are broadly expressed in embryonic and adult tissues, and they are capable of forming homodimers as well as heterodimers with RARs and other nuclear hormone receptors. The role of 9-cis-retinoic acid in regulating the activity of RXR homo-dimers and RXR-containing heterodimers is poorly understood in vivo. To begin to explore the function of 9-cis-retinoic acid in morphogenesis, we have examined the activity of this isomer in the chick wing. Using reverse transcriptase polymerase chain reaction analyses, we show that RXR is expressed in stage 20 wing buds. Similar to all-trans-retinoic acid, the 9-cis-isomer induces pattern duplications when locally applied to chick wing buds, but the 9-cis isomer is about 25 times more potent than the all-trans form. Furthermore, applied all-trans-retinoic acid is converted to the 9-cis isomer in the wing bud. The ratio of 9-cis to all-trans-retinoic acid established in the tissue is approximately 1:25. This quantitative agreement between the degree of conversion and the 25-fold higher efficacy of the 9-cis isomer, raises the possibility that, at least in part, the effects of all-trans-retinoic acid on the wing pattern result from a conversion to the 9-cis isomer. Therefore, it is possible that, in this system, the actual active species is 9-cis-retinoic acid and that the all-trans form serves as a precursor.
Modulated expression of a surface epitope on migrating germ cells of Manduca sexta embryos
Authors: Nardi James B.
Published: April 2021

In embryos of the moth Manduca sexta, the first cells that immunolabel with a monoclonal antibody to a surface epitope are the primordial germ cells. With this specific immunolabel, the migratory pathways of all primordial germ cells can be readily observed in whole mounts of embryos. The germ cells begin their migration by dispersing from an aggregate that lies on the midline of the embryonic germ band. Concurrently with segmentation of the embryo several hours later, germ cells segregate to several abdominal segments. With the advent of neurulation, germ cells again segregate, this time laterally within the segments. Shortly thereafter germ cells begin moving toward the lateral margins of abdominal segments. Simultaneously, two longitudinal strips of mesodermal cells along the lateral margins in each of four abdominal segments (3–6) begin expressing the surface epitope. The four initially noncontiguous strips on each side of the embryo fuse during the next several hours and form a single immunolabeled strip that stretches over four abdominal segments. Upon contacting these two lateral strips of mesodermal cells, germ cells begin moving bidirectionally along the anteroposterior embryonic axis toward the fifth abdominal segment where gonads will complete their morphogenesis. The immunolabel is asymmetrically distributed on the surfaces of germ cells during the early stages of migration and only during the later stages of migration after neurulation does the epitope adopt a more uniform distribution on the cells’ surfaces.
Genetic characterization of the multipotent dedifferentiated state of pigmented epithelial cells in vitro
Authors: Agata Kiyokazu , Kobayashi Hiroshi , Itoh Yoshiaki , Mochii Makoto , Sawada Kaichiro , Eguchi Goro
Published: April 2021

Retinal pigmented epithelial cells (PECs) of chicken embryos extensively and almost synchronously transdif-ferentiate into lens cells in medium containing phenylth-iourea and testicular hyaluronidase, passing through the bipotent dedifferentiated state. We have isolated genes that are expressed specifically by either pigment or lens cells and analyzed their expression in the transdifferentiation process. The expression of some proto-oncogenes was also studied. In the dedifferentiation process, expression of the c-myc gene was enhanced and the transcription of PEC-specific genes (MMP115, pP344) was completely repressed. However, transcription of lens-specific genes (α-, β γ- and -crystallin genes) remained silent in dedifferentiated pigment cells. Activation of lens- or PEC-specific genes occurred only in conditions permissive for lens or PEC differentiation, respectively. These results indicated that lens transdifferentiation from PECs proceeds through a multipotent (or at least bipotent) intermediate cell state in which the c-myc gene is activated, but neither PEC-nor lens-specific genes are expressed.
A repressor controls the timing and spatial localisation of stalk cell-specific gene expression in Dictyostelium
Authors: Harwood A. J. , Early A. , Williams J. G.
Published: April 2021

The ecmA and ecmB genes of Dictyostelium encode related extracellular matrix proteins and both are induced by DIF, the stalk cell-specific morphogen. The ecmA gene is expressed throughout the prestalk region of the migrating slug but only later, at culmination, do the prestalk cells express the ecmB gene. Expression of the ecmB gene is induced at the entrance to the stalk tube and we have identified two, apparently redundant, promoter elements that control this process. They act as repressors, preventing transcription in the tip of the migrating slug and the apical papilla of the culminant. They have a semi-palindromic consensus sequence TTGnCAA, where n is in one case 2 and in the other 4 bp. Either element alone is able to repress ecmB promoter activity in prestalk cells. Introduction of a single repressor element into the promoter of the ecmA gene changes its expression pattern to resemble that of the ecmB gene.

Mutant elements, where n is altered, cause repression during the slug stage but allow premature ecmB expression during culmination; suggesting that the effective strength of the inductive signal may increase during culmination. Inhibition of cAMP-dependent protein kinase (PKA) in prestalk cells blocks both stalk cell maturation and ecmB gene expression. We show that the block to gene expression correlates precisely with the presence of a functional repressor element and this is consistent with the notion that expression of the ecmB gene is controlled by a PKA-dependent release from transcriptional repression.
A central role for microtubules in the differentiation of Drosophila oocytes
Authors: Theurkauf William E. , Alberts Bruce M. , Jan Yuh Nung , Jongens Thomas A.
Published: April 2021

Drosophila oocytes develop within cysts containing 16 cells that are interconnected by cytoplasmic bridges. Although the cysts are syncytial, the 16 cells differentiate to form a single oocyte and 15 nurse cells, and several mRNAs that are synthesized in the nurse cells accumulate specifically in the oocyte. To gain insight into the mechanisms that generate the cytoplasmic asymmetry within these cysts, we have examined cytoskeletal organization during oocyte differentiation. Shortly after formation of the 16 cell cysts, a prominent microtubule organizing center (MTOC) is established within the syncytial cytoplasm, and at the time the oocyte is determined, a single microtubule cytoskeleton connects the oocyte with the remaining 15 cells of each cyst. Recessive mutations at the Bicaudal-D (Bic-D) and egalitarian (egl) loci, which block oocyte differentiation, disrupt formation and maintenance of this polarized microtubule cytoskeleton. Microtubule assembly-inhibitors phenocopy these mutations, and prevent oocyte-specific accumulation of oskar, cyclin B and 65F mRNAs. We propose that formation of the polarized microtubule cytoskeleton is required for oocyte differentiation, and that this structure mediates the asymmetric accumulation of mRNAs within the syncytial cysts.
Genomic organization and developmental pattern of expression of the engrailed gene from the brine shrimp Artemia
Authors: Manzanares Miguel , Marco Roberto , Garesse Rafael
Published: April 2021

We report the isolation and characterization of an engrailed gene in the crustacean Artemia franciscana. The Artemia gene spans a genomic region of 15 kilobases and the coding sequence is interrupted by two introns. It appears to be the only gene of the engrailed family present in the Artemia genome. The predicted engrailed-like protein is 349 amino acids long and contains several domains including the homeodomain, well conserved when compared to other proteins of the engrailed family. Based on sequence comparisons we have detected, in the Artemia engrailed protein, several features which are in common with the Drosophila and Bombyx engrailed proteins. It also has some features specific for invected proteins. Therefore, this gene appears to have diverged from an ancestral gene common to both the engrailed and invected insect genes. Whole-mount in situ hybridization experiments show that the expression of this gene in postembryonic development of Artemia is restricted to the posterior part of at least the thoracic and maxillar segments. The pattern is generated sequentially from a growth zone organized in columns of cells close to the caudal region of the larvae. Cell proliferation in the growth zone follows an interspersed pattern without evidence of early lineage restrictions. The engrailed expression is detected in the growth zone before any seg-mentation is visible and continues to be expressed in a posterior location in the segments that are morphologically defined. Initially expressed in isolated cells, it spreads into rows broadening to two-three cells as segments mature. The evidence presented here is compatible with the hypothesis that intercellular signaling mechanisms are in part responsible of the early activation of selector genes.
RNA regulatory element BLE1 directs the early steps of bicoid mRNA localization
Authors: Macdonald Paul M. , Kerr Karen , Smith Jeffrey L. , Leask Andrew
Published: April 2021

Deployment of the bicoid morphogen gradient in early Drosophila embryos requires the prelocalization of bicoid mRNA to the anterior pole of the egg. This anterior localization is mediated by a cis-acting localization signal contained within the 3 ′ untranslated region of the bicoid mRNA. Here we use a series of bicoid transgenes carrying small deletions in the 3 ′ untranslated region to survey for functional elements that constitute the localization signal. We identify and characterize one essential element, BLE1, which specifically directs the early steps of localization. In addition, we find that many deletions within the bicoid mRNA 3 ′ untranslated region impair but do not prevent localization. One such deletion specifically interferes with a later step in localization. Thus the bicoid mRNA localization signal appears to consist of multiple different elements, each responsible for different steps in the localization process.
Fertile females of the mole Talpa occidentalis are phenotypic intersexes with ovotestes
Authors: Jiménez Rafael , Burgos Miguel , Sánchez Antonio , Sinclair Andrew H. , Alarcón Francisco J. , Marín Juan J. , Ortega Esperanza , Díaz de la Guardia Rafael
Published: April 2021

We investigated the origin of XX sex reversal in the insectivorous mole Talpa occidentalis. Cytogenetic, histological and hormonal studies indicate that all XX individuals analyzed from two different populations are true hermaphrodites, with ovotestes. This suggests that XX sex reversal may be the norm in this species. The inter-sexes are functional fertile females and the trait is transmitted and maintained in the population. Intersexes lack the Y chromosome gene SRY (sex determining region Y gene), shown to be the testis determining gene. These results suggest that XX intersex moles may have arisen from a mutation of a gene located downstream from SRY/TDY in the testis determining pathway.
asense is a Drosophila neural precursor gene and is capable of initiating sense organ formation
Authors: Brand Michael , Jarman Andrew P. , Jan Lily Y. , Jan Yuh Nung
Published: April 2021

Neural precursor cells in Drosophila arise from the ectoderm in the embryo and from imaginal disc epithelia in the larva. In both cases, this process requires daugh - terless and the proneural genes achaete, scute and lethal-of-scute of the achaete-scute complex. These genes encode basic helix-loop-helix proteins, which are nuclear transcription factors, as does the asense gene of the achaete-scute complex. Our studies suggest that asense is a neural precursor gene, rather than a proneural gene. Unlike the proneural achaete-scute gene products, the asense RNA and protein are found in the neural precursor during its formation, but not in the proneural cluster of cells that gives rise to the neural precursor cell. Also, asense expression persists longer during neural precursor development than the proneural gene products; it is still expressed after the first division of the neural precursor. Moreover, asense is likely to be down-stream of the proneural genes, because (1) asense expression is affected in proneural and neurogenic mutant backgrounds, (2) ectopic expression of asense protein with an intact DNA-binding domain bypasses the requirement for achaete and scute in the formation of imaginal sense organs. We further note that asense ectopic expression is capable of initiating the sense organ fate in cells that do not normally require the action of asense. Our studies therefore serve as a cautionary note for the inference of normal gene function based on the gain-of-function phenotype after ectopic expression.
Preimplantation mouse embryos express a cell surface receptor for tissue-plasminogen activator
Authors: Carroll Pamela M. , Richards William G. , Darrow Andrew L. , Wells James M. , Strickland Sidney
Published: April 2021

The serine protease tissue-plasminogen activator (t-PA) has previously been shown to be intracellular in mouse secondary oocytes and extracellular in fertilized eggs. Here we demonstrate that extracellular t-PA activity is bound to the surface of the fertilized egg. The level of t-PA activity associated with preimplantation mouse embryos decreases in the 2-cell stage embryo, then increases in 4-cell and morula stage embryos. However, morulae grown in culture from fertilized eggs lack t-PA activity but are able to bind exogenously added mouse t-PA. Additionally, northern analysis indicates that preim-plantation embryos do not contain detectable levels of t-PA mRNA. Therefore, the enzyme activity associated with 4-cell and morula stage embryos in vivo is derived from t-PA present in the oviduct lumen that binds the embryo, and not from protein produced from translation of embryonic mRNA. The binding activity is species and protein specific in that neither mouse urokinase-type plasminogen activator (u-PA) nor human t-PA bind to cultured morulae. Furthermore, binding activity is dose-dependent and saturable, and does not require the active site of t-PA. These data indicate that a cell surface-specific t-PA-binding activity exists in the preimplantation mouse embryo and may localize function and concentrate the proteolytic activity of t-PA in early mouse development.
XASH-3, a novel Xenopus achaete-scute homolog, provides an early marker of planar neural induction and position along the mediolateral axis of the neural plate
Authors: Zimmerman Kathryn , Shih John , Bars Julie , Collazo Andres , Anderson David J.
Published: April 2021

We have isolated a novel Xenopus homolog of the Drosophila achaete-scute genes, called XASH-3. XASH-3 expression is neural specific and is detected as early as stage 11, making it one of the earliest markers of neural induction so far described. Moreover, XASH-3 expression within the neural plate is regionally restricted. Transverse bands of XASH-3 mRNA mark discrete positions along the anteroposterior axis, while longitudinal bands mark a discrete position along the mediolateral axis. This latter site of XASH-3 expression appears to demarcate the prospective sulcus limitans, a boundary zone that later separates the functionally distinct dorsal (alar) and ventral (basal) regions of the spinal cord. In sandwich explants lacking any underlying mesoderm, XASH-3 is expressed in longitudinal stripes located lateral to the midline. This provides the first indication that planar or midline-derived inductive signals are sufficient to establish at least some aspects of positional identity along the mediolateral axis of the neural plate. By contrast, the transverse stripes of XASH-3 expression are not detected, suggesting that this aspect of anteroposterior neural pattern is lost or delayed in the absence of vertically passed signals. The restricted mediolateral expression of XASH-3 suggests that mediolateral patterning of the neural plate is an early event, and that this regionalization can be achieved in the absence of inducing signals derived from underlying mesoderm.
The strawberry notch gene functions with Notch in common developmental pathways
Authors: Coyle-Thompson Catherine A. , Banerjee Utpal
Published: April 2021

Genetic and phenotypic analysis of strawberry notch suggests that its gene product is required during embryogenesis and oogenesis, and for the development of the eye, wing and leg. Several lines of evidence suggest that strawberry notch participates together with Notch in many common pathways. A number of strawberry notch mutant phenotypes are similar to those of Notch mutants and can be rescued by an extra copy of wild-type Notch. In addition, mutations in strawberry notch interact strongly with Notch mutants in a tissue-specific manner. Mutations in the strawberry notch and Notch loci also show very similar interactions with genes like Hairless, Delta, groucho, Serrate, and deltex that have all been proposed to participate in Notch related pathways. The genetic evidence presented here suggests that strawberry notch participates with members of the Notch pathway in facilitating developmentally relevant cell-cell communications.
Postimplantation expression patterns indicate a role for the mouse forkhead/HNF-3 α, β and γ genes in determination of the definitive endoderm, chordamesoderm and neuroectoderm
Authors: Monaghan A. Paula , Kaestner Klaus H. , Grau Evelyn , Schütz Günther
Published: April 2021

The HNF-3 α, β and γ genes constitute a family of transcription factors that are required for hepatocytespecific gene expression of a number of genes, e.g. transthyretin, α-1 antitrypsin and tyrosine aminotransferase. These genes share a highly conserved DNA-binding domain first found in the Drosophila gene, forkhead, which is required for the normal patterning of the developing gut and central nervous system in Drosophila. In adult mouse tissues, transcripts from HNF-3 αand β have been localised to the liver, intestine and lung, whereas HNF-3 γ is found in the liver, intestine and testis. In light of the early developmental significance of forkhead in Drosophila, we have compared the patterns of expression of HNF-3 α, β and γ mRNAs during murine embryogenesis. We find that these genes are sequentially activated during development in the definitive endoderm. HNF-3 β mRNA is expressed in the node at the anterior end of the primitive streak in all three germ layers and is the first gene of this family to be activated. Subsequently, HNF-3 α is transcribed in the primitive endoderm in the region of the invaginating foregut and HNF-3 γ appears upon hindgut differentiation. These genes have different anterior boundaries of mRNA expression in the developing endoderm and transcripts are found in all endoderm-derived structures that differentiate posterior to this boundary. Therefore, we propose that these genes define regionalisation within the definitive endoderm. Furthermore, differential mRNA expression of HNF-3 α and β is detected in cells of the ventral neural epithelium, chordamesoderm and notochord. In the neural epithelium, expression of HNF-3 αand β mRNA becomes localised to cells of the floor plate. We propose that, in addition to their characterised requirement for liver-specific gene expression, HNF-3 αand γ are required for mesoderm and neural axis formation. We also conclude that HNF-3 β is the true orthologue of the Drosophila forkhead gene.
Sympathetic neuroblasts undergo a developmental switch in trophic dependence
Authors: Birren Susan J. , Lo Liching , Anderson David J.
Published: April 2021

Sympathetic neurons require NGF for survival, but it is not known when these cells first become dependent on neurotrophic factors. We have examined in vitro mitotically active sympathetic neuroblasts immuno-isolated from different embryonic stages, and have correlated this functional data with the expression of neurotrophin receptor mRNAs in vivo. Cells from E14.5 ganglia are supported by neurotrophin-3 (NT-3) in a serum-free medium, but not by NGF; NT-3 acts as a bona fide survival factor for these cells and not simply as a mitogen. By birth, sympathetic neurons are well supported by NGF, whereas NT-3 supports survival only weakly and at very high doses. This change in neurotrophin-responsiveness is correlated with a reciprocal switch in the expression of trkC and trkA mRNAs by sympathetic neuroblasts in vivo. These data suggest that neurotrophic factors may control neuronal number at earlier stages of development than previously anticipated. They also suggest that the acquisition of NGF-dependence may occur, at least in part, through the loss of receptors for these interim survival factors.
The migrational patterns and developmental fates of glial precursors in the rat subventricular zone are temporally regulated
Authors: Levison Steven W. , Chuang Cathy , Abramson Bernetta J. , Goldman James E.
Published: April 2021

Postnatal gliogenesis in the rodent forebrain was studied by infecting subventricular zone cells of either neonates or juvenile rats with replication-deficient retroviruses that encode reporter enzymes, enabling the migration and fate of these germinal zone cells to be traced over the ensuing several weeks. Neither neonatal nor juvenile subventricular zone cells migrated substantially along the rostral-caudal axis. Neonatal subventricular zone cells migrated dorsally and laterally into hemispheric gray and white matter and became both astrocytes and oligodendrocytes. Juvenile subventricular zone cells migrated into more medial areas of the subcortical white matter and on occasion appeared in the white matter of the contralateral hemisphere, but rarely migrated into the neocortex. Juvenile subventricular zone cells almost exclusively differentiated into oligodendrocytes. Thus, the migratory patterns and the developmental fates of subventricular zone cells change during the first 2 weeks of life. When either neonatal or juvenile subventricular zone cells were labeled in vivo and then removed and cultured, some generated homogeneous clones that contained either astrocytes with a ‘type 1’ phenotype or oligodendrocytes, but some generated heterogeneous clones that contained both glial types. These results provide additional evidence for a common progenitor for astrocytes and oligodendrocytes and strongly suggest that temporally and spatially regulated environmental signals control the destiny of glial progenitors during postnatal development.
A Drosophila G1-specific cyclin E homolog exhibits different modes of expression during embryogenesis
Authors: Richardson Helena E. , O’Keefe Louise V. , Reed Steven I. , Saint Robert
Published: April 2021

We have isolated a Drosophila homolog of the human G1-specific cyclin E gene. Cyclin E proteins thus constitute an evolutionarily conserved subfamily of metazoan cyclins. The Drosophila cyclin E gene, DmcycE, encodes two proteins with a common C-terminal region and unique N-terminal regions. Unlike other Drosophila cyclins, DmcycE exhibits a dynamic pattern of expression during development. DmcycE is supplied maternally, but at the completion of the cleavage divisions and prior to mitosis 14, the maternal transcripts are rapidly degraded in all cells except the pole (germ) cells. Two modes of DmcycE expression are observed in the subsequent divisions. During cycles 14, 15 and 16 in non-neural cells, DmcycE mRNA levels show no cell-cycle-associated variation. DmcycE expression in these cells is therefore independent of the cell cycle phase. In contrast, expression in proliferating embryonic peripheral nervous system cells occurs during interphase as a brief pulse that initiates before and overlaps with S phase, demonstrating the presence of a G1 phase in these embryonic neural cell cycles. DmcycE appears not to be expressed in cells that undergo endoreplication cycles during polytenization. The structural homology to human cyclin E, the ability of DmcycE to rescue a G1 cyclin-deficient yeast strain, the presence of multiple PEST sequences characteristic of G1-specific cyclins and expression during G1 phase in proliferating peripheral nervous system cells all argue that Drosophila cyclin E is a G1 cyclin. Constitutive DmcycE expression in embryonic cycles lacking a G1 phase, in contrast to expression during the G1-S phase transition in cycles exhibiting a G1 phase, implicates DmcycE expression in the regulation of the G1 to S phase transition during Drosophila embryogenesis.
Pax-2 is required for mesenchyme-to-epithelium conversion during kidney development
Authors: Rothenpieler Uwe W. , Dressler Gregory R.
Published: April 2021

The conversion of mesenchyme to epithelium during the embryonic development of the mammalian kidney requires reciprocal inductive interactions between the ureter and the responding metanephric mesenchyme. The Pax-2 gene is activated in the mesenchyme in response to induction and is subsequently down-regulated in more differentiated cells derived from the mesenchyme. Pax-2 belongs to a family of genes, at least three of which encode morphogenetic regulatory transcription factors. In order to determine the role of Pax-2 during kidney development, we have generated a loss-of-function phenotype using antisense oligonucleotides in mouse kidney organ cultures. These oligonucleotides can specifically inhibit Pax-2 protein accumulation in kidney mesenchyme cells, where the intracellular concentrations are maximal. The kidney organ cultures were stained with uvomurulin and laminin antibodies as markers for epithelium formation. With significantly reduced Pax-2 protein levels, kidney mesenchyme cells fail to aggregate and do not undergo the sequential morphological changes characteristic of epithelial cell formation. The data demonstrate that Pax-2 function is required for the earliest phase of mesenchyme-to-epithelium conversion.
Spacing ensures autonomous expression of different stripe enhancers in the even-skipped promoter
Authors: Small Stephen , Arnosti David N. , Levine Michael
Published: April 2021

The even-skipped (eve) promoter contains a series of enhancers that control the expression of different seg-mentation stripes in the Drosophila embryo. The stripe 3 enhancer is located 1.7 kb upstream of the stripe 2 enhancer. Here we demonstrate that these enhancers must be physically separated by a minimum distance for proper stripe expression. When they are directly coupled in either orientation, the enhancers generate abnormal patterns of expression in the early embryo. For example, the levels of stripe 2 expression are augmented and there is a posterior expansion of the pattern when the stripe 3 enhancer is positioned immediately upstream of the stripe 2 enhancer. Despite this spacing requirement, the order of the enhancers within the eve promoter can be reversed without affecting the normal expression pattern. These results suggest that spacing maintains the autonomous activities of the stripe enhancers and that interactions between enhancers can generate novel patterns of gene expression.
Pattern formation in the limbs of Drosophila: bric à brac is expressed in both a gradient and a wave-like pattern and is required for specification and proper segmentation of the tarsus
Authors: Godt Dorothea , Couderc Jean-Louis , Cramton Sarah E. , Laski Frank A.
Published: April 2021

We have identified the gene bric à brac and show that it is required for pattern formation along the proximal-distal axis of the leg and antenna of Drosophila. In bric à brac mutant legs, the bristle pattern of the three central tarsal segments is transformed towards the pattern of the most proximal tarsal segment. In addition, bric à brac mutant legs and antennae have segmentation defects. bric à brac encodes a nuclear protein that shares a highly conserved domain with two transcription factors from Drosophila. bric à brac function is dosage dependent and is required in a graded manner for the specification of tarsal segments. The graded requirement for bric à brac correlates with its graded expression pattern, sug-gesting that the concentration of BRIC Á BRAC protein specifies segment identity in the tarsus.
X chromosome retains the memory of its parental origin in murine embryonic stem cells
Authors: Tada Takashi , Tada Masako , Takagi Nobuo
Published: April 2021

A cytogenetic and biochemical study of balloon-like cystic embryoid bodies, formed by newly established embryonic stem (ES) cell lines having a cytogenetically or genetically marked X chromosome, revealed that the paternally derived X chromosome was inactivated in the majority of cells in the yolk sac-like mural region consisting of the visceral endoderm and mesoderm. The nonrandomness was less evident in the more solid polar region containing the ectodermal vesicle, mesoderm and visceral endoderm. Since the same was true in embryoid bodies derived from ES cells at the 30th subculture generation, it was concluded that the imprinting responsible for the preferential inactivation of the paternal X chromosome that was limited to non-epiblast cells of the female mouse embryos, was stably maintained in undifferentiated ES cells. Differentiating epiblast cells should be able to erase or avoid responding to the imprint.
Adult phenotype in the mouse can be affected by epigenetic events in the early embryo
Authors: Reik Wolf , Römer Irmgard , Barton Sheila C. , Surani M. Azim , Howlett Sarah K. , Klose Joachim
Published: April 2021

Major epigenetic modifications apparently occur during early development in the mouse. The factors that induce such modifications are complex and may involve the various components of a zygote. We have started to explore whether changes in the nucleocytoplasmic composition brought about by micromanipulation can induce phenotypic effects through epigenetic modifications. Nucleocytoplasmic hybrids were therefore prepared by transplanting a female pronucleus into a recipient egg from a different genotype. As a result, the maternal genome was of a different genetic background as compared with the egg cytoplasm. Specifically, experimental zygotes had cytoplasm from the inbred strain C57BL/6, a maternal genome from DBA/2, and a paternal genome from C57BL/6 (termed BDB hybrids). The mirror-image combination, termed DBD, was also made. The reconstituted zygotes were transferred to recipients and allowed to develop to term. Mice born from manipulated zygotes showed transcriptional repression and DNA methylation of major urinary protein genes in their liver, as well as growth deficiency resulting in reduced adult body weight. No altered phenotype was observed in controls in which the maternal pronucleus was simply transplanted back into another zygote of the same genetic background. These results clearly demonstrate phenotypic as well as molecular effects on DNA methylation and expression of at least one gene. Phenotype was therefore no longer predicted by genotype as a result of epigenetic modifications in experimental embryos. What precisely triggers the phenotypic and epigenetic changes is unknown, but presumably, nucleocytoplasmic interactions in hybrid zygotes may be partly responsible.
Basic fibroblast growth factor promotes adhesive interactions of neuroepithelial cells from chick neural tube with extracellular matrix proteins in culture
Authors: Kinoshita Yoshito , Kinoshita Chizuru , Heuer Josef G. , Bothwell Mark
Published: April 2021

Fibroblast growth factors have been increasingly assigned mitogenic and trophic roles in embryonic and postnatal development of the nervous system. Little is known, however, of their functional roles in early embryonic neural development at the neural tube stage. We have examined the effect of basic fibroblast growth factor (bFGF) on the adhesive behavior in culture of dissociated brachio-thoracic neural tube cells from 26- to 30-somite stage chick embryos. Cells plated on collagen-coated substratum at a low density attach to the sub-stratum but show poor cell spreading. Addition of bFGF markedly promotes cell spreading, yielding an epithelial morphology. This effect becomes discernible 6-8 hours after cell plating with bFGF and is completed by 24 hours, with half-maximal and maximal effects attained at around 0.4 and 10 ng/ml, respectively. The number of cells remains largely constant up to 24 hours, and then cell survival and/or mitogenic effects of bFGF become apparent. The cell spreading effect is abolished by cyclo-heximide treatment, inhibited by the anti-β1-integrin antibody CSAT, and accompanied by about twofold increases in the expression of β1-integrin and vinculin, components of focal adhesion complexes. Cells cultured with bFGF for 24 hours exhibit enhanced cell attachment and cell spreading with little time lag following cell plating. In earlier embryonic stages, developmentally less mature cells depend much more on bFGF for their cell spreading and survival, while in later stages the cell spreading response to bFGF becomes undetectable as neural tube develops to spinal cord. The cell spreading effect of bFGF is realized on specific extracellular matrix proteins including laminin, fibronectin and collagen, but not on vitronectin, arg-gly-asp peptide (PepTite-2000), poly-L-ornithine or others. These results suggest that, in an early stage of neural tube development, bFGF is involved in the developmental regulation of adhesive interactions between neuroepithelial cells and the extra-cellular matrix, thereby controlling their proliferation, migration and differentiation.