bluuebunny/crossref_metadata_2025 huggingface dataset:
Tenascin M
r 220000 isoform expression correlates with corneal cell migration
Authors: Kaplony Angelika , Zimmermann Dieter R. , Fischer René W. , Imhof Beata. , Odermatt Bernhard F. , Winterhalter Kaspar H. , Vaughan Lloyd
Published: April 2021

The three isoforms of chicken tenascin, an extracellular matrix glycoprotein, are generated by alternatively spliced fibronectin type III domains. The resulting proteins migrate as bands of MT 220000 (ten220), Mr 200000 (ten200) and Mr 190000 (tenl90) on SDS-PAGE. We describe here two monoclonal antibodies, one specific for ten220 (mAb T17) and another that recognizes all isoforms (mAb T16). These were used to examine the differential expression of isoforms during development.

Most impressive is the close correlation between ten220 expression and cell migration in the embryonic cornea. Initially (stage 18), tenl90/200 can be detected within the corneal epithelium and along the basement membranes of the lens and sclera. Ten220 appears within the primary stroma immediately prior to the invasion by neural-crest-derived cells. This expression is maintained during the subsequent migration of fibro blasts from the conjunctiva into the primary stroma. With the completion of migration and the marked increase in matrix synthesis by corneal fibroblasts, ten220 disappears. Tenl90/200 remains in the region adjoining the endothelium, the Bowman’s membrane and the adjacent stroma. The cell-migration-associated isoform is isolated from extracts of embryonic tissues as a homohexamer. Low molecular weight forms appeared absent but a new tenascin band of Mr 210 000 could be detected in brain extracts which may be a new isoform. We conclude that the synthesis of tenascin isoforms is under tight developmental control and speculate that a function of the additional domains is to facilitate cell migration.
Gradient fields and homeobox genes
Authors: Robertis Eddy M. De , Morita Elaine A. , Cho Ken W. Y.
Published: April 2021

We review here old experiments that defined the existence of morphogenetic gradient fields in vertebrate embryos. The rather abstract idea of cell fields of organforming potential has become less popular among modern developmental and molecular biologists. Results obtained with antibodies directed against homeodomain proteins suggest that gradient fields may indeed be visualized at the level of individual regulatory molecules in vertebrate embryos.
Cell-fate determination in the developing Drosophila eye: role of the rough gene
Authors: Heberlein Ulrike , Mlodzik Marek , Rubin Gerald M.
Published: April 2021

The homeobox-gene rough is required in photoreceptor cells R2 and R5 for normal ommatidial assembly in the developing Drosophila eye. We have used several cell-type-specific markers and double mutant combinations to analyze cell-fate determination in rough. We show that the cells that would normally become R2 and/or R5 express a marker, a lacZ insertion in the seven-up (svp) gene, which is indicative of the Rl/3/4/6 cell fate. In addition, the analysis of mitotically induced svp,ro double mutant clones in the eye indicates that in rough all outer photoreceptors are under the genetic control of the svp gene. These results show that, in the absence of rough function, R2 and R5 fail to be correctly determined and appear to be transformed into cells of the R3/4/1/6 subtype. This transformation and the subsequent developmental defects do not preclude the recruitment of R7 cells. However, the presence of ommatidia containing more than one R7 and/or R8 cell in rough implies a complex network of cellular interactions underlying cell-fate determination in the Drosophila retina
Specification of neurepithelium and surface epithelium in avian transplantation chimeras
Authors: Schoenwolf Gary C. , Alvarez Ignacio S.
Published: April 2021

Previous studies of the avian blastoderm have revealed that extensive displacements occur within the epiblast during gastrulation and neurulation. The present study had two main purposes: (1) to map the origin and movement of prospective surface epithelial cells, and (2) to ask whether neurepithelial and surface epithelial cell fates are determined prior to cell movement, or whether they arise later as a result of the ultimate position attained by cells through their movement. Our results show that the rostral and lateral intraembryonic and extraembryonic surface epithelium originates as far laterally as at the area pellucida-area opaca interface of the early epiblast. Intraembryonic surface epithelial cells rearrange relative to one another, extending medially to contribute to the formation of the neural folds, whereas extraembryonic surface epithelial cells maintain their lateral positions, spreading uniformly as the epiblast expands. Our results further show that surface epithelial and neurepithelial cell fates are labile at the onset of neurulation, suggesting that cell fate is specified following cell movement.
Polyclonal origin of pancreatic islets in aggregation mouse chimaeras
Authors: Deltour L. , Leduque P. , Paldi A. , Ripoche M. A. , Dubois P. , Jami J.
Published: April 2021

In the present study, we have examined the origin and growth pattern of the β cells in pancreatic islets, to determine whether a single progenitor cell gave rise to all the precursors of the islets, or if each of a few progenitor cells is the founder of a different islet, or if each islet is a mixture of cells originating from a pool of progenitor cells. Aggregation mouse chimaeras where the pancreatic β cells derived from each embryo can be identified in the islets on histological sections were analyzed. In two chimaeras, all the islets contained cells from both the aggregated embryo. This clearly demonstrates that each islet resulted from several independent cells. In addition, the β cells derived from either embryo component were in very small clusters in the islets, suggesting that in situ cell division did not account significantly for islet growth.
Migrating neural crest cells in the trunk of the avian embryo are multipotent
Authors: Fraser Scott E. , Bronner-Fraser Marianne
Published: April 2021

Trunk neural crest cells migrate extensively and give rise to diverse cell types, including cells of the sensory and autonomic nervous systems. Previously, we demonstrated that many premigratory trunk neural crest cells give rise to descendants with distinct phenotypes in multiple neural crest derivatives. The results are consistent with the idea that neural crest cells are multipotent prior to their emigration from the neural tube and become restricted in phenotype after leaving the neural tube either during their migration or at their sites of localization. Here, we test the developmental potential of migrating trunk neural crest cells by microinjecting a vital dye, lysinated rhodamine dextran (LRD), into individual cells as they migrate through the somite. By two days after injection, the LRD-labelled clones contained from 2 to 67 cells, which were distributed unilaterally in all embryos. Most clones were confined to a single segment, though a few contributed to sympathetic ganglia over two segments. A majority of the clones gave rise to cells in multiple neural crest derivatives. Individual migrating neural crest cells gave rise to both sensory and sympathetic neurons (neurofilament-positive), as well as cells with the morphological characteristics of Schwann cells, and other non-neuronal cells (both neurofilament-negative). Even those clones contributing to only one neural crest derivative often contained both neurofilament-positive and neurofilament-negative cells. Our data demonstrate that migrating trunk neural crest cells can be multipotent, giving rise to cells in multiple neural crest derivatives, and contributing to both neuronal and non-neuronal elements within a given derivative. Thus, restriction of neural crest cell fate must occur relatively late in migration or at the final sites of neural crest cell localization.
Quantitative analysis of protein synthesis in mouse embryos. I. Extensive reprogramming at the one- and two-cell stages
Authors: Latham Keith E. , Garrels James I. , Chang Cecile , Solter Davor
Published: April 2021

A quantitative, high-resolution, two-dimensional gel protein database has been constructed for the mouse embryo. This database has been used to obtain a detailed accounting of the amount and relative timing of changes in protein synthesis that occur during the 1-, 2-, and 4-cell stages along with a description of the most prevalent developmentally regulated patterns of synthesis. We find that during these early stages of development the pattern of proteins synthesized changes to a much greater extent than previously appreciated. During the 1- and 2-cell stages, the majority (60 % and 85 %, respectively) of the analyzed proteins exhibit twofold or greater changes in their rates of synthesis. The periods of greatest change are the late 1-cell and mid 2-cell stages, during which an extensive remodelling of protein synthetic pattern occurs that is largely complete by 15 h following the first cleavage. Once this reprogramming is complete, very little change is observed during the late 2-cell and 4-cell stages. Cluster analysis of individual protein synthesis patterns reveals a limited number of coordinately regulated protein sets that are responsible for most of the changes observed during the and 2-cell stages. During the 2-cell stage, one third of the proteins increase by an average of fivefold, another third decrease by an average of sevenfold, and 10% undergo transient changes in rates of synthesis. These patterns reflect the switch from zygotic to maternal mRNA utilization following transcriptional activation. Significantly, a set of proteins exhibiting relatively constant rates of synthesis is not observed during the 2-cell stage, indicating that the rate of synthesis of almost every detectable protein changes significantly during this period. Overall, our data indicate that the transition from maternal to embryonic control of development results in an abrupt and extensive reprogramming of the early embryo with respect to the pattern of proteins synthesized.
Segmentation gene expression in the housefly Musca domestica
Authors: Sommer Ralf , Tautz Diethard
Published: April 2021

Drosophila and Musca both belong to the group of higher dipteran flies and show morphologically a very similar early development. However, these two species are evolutionary separated by at least 100 million years. This presents the opportunity for a comparative analysis of segmentation gene expression across a large evolutionary distance in a very similar embryonic background. We have analysed in detail the early expression of the maternal gene bicoid, the gap genes hunchback, Krüppel, knirps and tailless, the pair-rule gene hairy, the segmentpolarity gene engrailed and the homoeotic gene Ultrabithorax. We show that the primary expression domains of these genes are conserved, while some secondary expression aspects have diverged. Most notable is the finding of hunchback expression in 11 –13 stripes shortly before gastrulation, as well as a delayed expression of terminal domains of various genes. We conclude that the early developmental gene hierarchy, as it has been defined in Drosophila, is evolutionary conserved in Musca domestica.
Drosophila PS integrins recognize vertebrate vitronectin and function as cell-substratum adhesion receptors in vitro
Authors: Hirano Shinji , Ui Kumiko , Miyake Tadashi , Uemura Tadashi , Takeichi Masatoshi
Published: April 2021

Using the Drosophila cell line MLDmBG-1, a monoclonal antibody aBG-1 that can inhibit not only cell clumping but also cell spreading was generated. This antibody immunoprecipitates a complex of molecules consisting of a major 120×103Mr and other components. To characterize the 120×103Mr component, we purified it, generated antibodies to it, and cloned its cDNA. Sequencing of this cDNA suggests that the 120×103Mr molecule is identical to PSβ, a β chain of Drosophila integrins. The other components immunoprecipitated included two a chains of Drosophila integrins, PSlα and PS2α, as revealed using specific antibodies to these molecules. These suggest that aBG-1 recognizes the PSβ associated with PSlα or PS2α. However, immunostaining of embryos and larvae with aBG-1 showed that the staining pattern is similar to that for PS2α but not for PSβ, suggesting that the antibody preferentially recognizes the PSβ associated with particular a chains in situ. We then attempted to characterize the ligands for these integrin complexes, using culture dishes coated with various vertebrate matrix proteins. These cells spread very well on dishes coated with vitronectin and, to a lesser extent, on those with fibronectin. This spreading was partially inhibited by aBG-1, but not by other control antibodies or RGD peptides. The cell attachment to these substrata was not affected by the antibody. The cells also can attach to dishes coated with laminin but without spreading, and this attachment was not inhibited by aBG-1. Furthermore, they do not attach to dishes coated with collagen type I, type IV, and fibrinogen. These results indicate that Drosophila PS integrins can recognize vertebrate vitronectin, and also fibronectin with a weaker affinity, at sites other than RGD sequences, and thus can function in cell-substratum adhesion.
Regeneration of the root pole in surgically transected carrot embryos occurs by position-dependent, proximodistal replacement of missing tissues
Authors: Schiavone F. M. , Racusen R. H.
Published: April 2021

Torpedo-stage carrot embryos were surgically transected at various locations along the shoot-root axis and explants of the cotyledon-bearing shoot pole were sectioned and examined in order to provide a more detailed description of root pole regeneration. When excisions occurred at the sites of the future hypocotyl, the future radicle or the future root apical meristem, the regenerating axial tissues exhibited patterns of cellular organization that were nearly identical to those seen in unsevered controls. To accomplish this restoration, new cells, of the type normally found at each cutting site, were produced behind a regeneration dome that formed over the original surgical site. The regeneration dome was displaced by division and expansion-driven extension of the longitudinal axis, and cells in the renewed region quickly acquired individual anatomical traits and collective tissue morphologies that corresponded to those of cells in the analogous locations in intact embryos. Although no clear mechanism is implied, the results of these experiments suggest that interactions between cells near the surgical margin permit them to retain their-sense of location within the original structure, and apprise them of the removal of their basipetally positioned neighbors. With varying-length remnants of the shoot serving as the only vestige of the original size and shape of the embryo, cells close to the site of excision were apparently reconfigured to commence ordered divisions that ultimately reconstituted the embryonic axis.
Response to fibronectin of mouse primordial germ cells before, during and after migration
Authors: Ffrench-Constant Charles , Hollingsworth Andrew , Heasman Janet , Wylie Christopher C.
Published: April 2021

The adhesive extracellular matrix glycoprotein fibronectin is thought to play a central role in cell migration during embryogenesis. In order to define this role, we have examined the response to fibronectin in cell culture of mouse primordial germ cells (PGCs) before, during and after their migration from the hindgut into their target tissue, the genital ridges. Using an explant culture system, we show that PGCs will emigrate from tissue fragments containing hindgut, and that fibronectin stimulates this migration. Adhesion assays show that the start of PGC migration is associated with a fall in adhesion to fibronectin. Double-labelling studies using in situ hybridization and histochemistry demonstrate that migrating PGCs do not contain detectable fibronectin mRNA, suggesting that they do not synthesize and secrete the fibronectin within their migratory substratum. Taken together, these findings are consistent with an important role for fibronectin in stimulating PGC migration. In addition, however, they suggest that the interaction between PGCs and fibronectin may be important in timing the start of migration, with the fall in adhesion allowing the PGCs to commence their migration towards the genital ridges.
Altered expression of the chicken homeobox-containing genes GHox-7 and GHox-8 in the limb buds of limbless mutant chick embryos
Authors: Coelho Caroline N. D. , Krabbenhoft Karen M. , Upholt William B. , Fallon John F. , Kosher Robert A.
Published: April 2021

It has been suggested that the reciprocal expression of the chicken homeobox-containing genes GHox-8 and GHox-7 by the apical ectodermal ridge and subjacent limb mesoderm might be involved in regulating the proximodistal outgrowth of the developing chick limb bud. In the present study the expression of GHox-7 and GHox-8 has been examined by in situ and dot blot hybridization in the developing limb buds of limbless mutant chick embryos. The limb buds of homozygous mutant limbless embryos form at the proper time in development (stage 17/18), but never develop an apical ectodermal ridge, fail to undergo normal elongation, and eventually degenerate. At stage 18, which is shortly following the formation of the limb bud, the expression of GHox-7 is considerably reduced (about 3-fold lower) in the mesoderm of limbless mutant limb buds compared to normal limb bud mesoderm. By stages 20 and 21, as the limb buds of limbless embryos cease outgrowth, GHox-7 expression in limbless mesoderm declines to very low levels, whereas GHox-7 expression increases in the mesoderm of normal limb buds which are undergoing outgrowth. In contrast to GHox-7, expression of GHox-8 in limbless mesoderm at stage 18 is quantitatively similar to its expression in normal limb bud mesoderm, and in limbless and normal mesoderm GHox-8 expression is highly localized in the anterior mesoderm of the limb bud. In normal limb buds, GHox-8 is also expressed in high amounts by the apical ectodermal ridge. However, expression of GHox-8 is severely impaired in the ectoderm of limbless mutant limb buds, which lack an apical ectodermal ridge. The severely impaired expression of GHox-7 in the mesoderm of limbless limb buds suggests that the normal expression of GHox-7 by limb mesoderm during limb bud outgrowth may be regulated by the apical ectodermal ridge, and further suggests the possibility that expression of GHox-7 by subridge mesenchymal cells may be required for normal limb outgrowth to occur. Furthermore, the severely impaired expression of GHox-8 by limbless ectoderm suggests GHox-8 may indeed be involved in ridge function. These observations also raise the interesting possibility that normal GHox-8 expression by the apical ectodermal ridge may be required for normal expression of GHox-7 by the subridge mesenchymal cells.
Genetic and cytological control of the asymmetric divisions that pattern the Volvox embryo
Authors: Kirk David L. , Kaufman Melissa R. , Keeling Richard M. , Stamer Kandace A.
Published: April 2021

The highly regular pattern in which approximately 2000 small somatic cells and 16 large reproductive cells (or ‘gonidia’) are arranged in a typical asexual adult of Volvox carteri can be traced back to a stereotyped program of embryonic cleavage divisions. After five symmetrical divisions have produced 32 cells of equal size, the anterior 16 cells cleave asymmetrically, to produce one small somatic cell initial and one larger gonidial initial each. The gonidial initials then cease dividing before the somatic cell initials do. The significance of the visibly asymmetric divisions is underscored by genetic and experimental evidence that differences in size - rather than differences in cytoplasmic quality - are causally important in activating the programs that cause small cells to become mortal somatic cells and large cells to differentiate as reproductive cells. A number of loci, including at least five mul (‘multiple gonidia’) loci, appear to be responsible for determining where and when asymmetric divisions will occur, since mutations at these loci result in modified temporal and/or spatial patterns of asymmetric division in one or more portions of the life cycle. But the capacity to divide asymmetrically at all appears to require a function encoded by the gls (gonidialess) locus, since gls mutants fail to execute any asymmetric divisions. Second-site suppressors of gls that have been identified may encode other functions required for asymmetric division. Cytological and immunocytochemical studies of dividing embryos are being undertaken in an attempt to elucidate the mechanisms by which cell-division planes are established - and shifted - under the influence of such pattern-specifying genes. Studies to date clearly indicate a central role for the basal body apparatus, and particularly its microtubular rootlets, in establishing the orientation of both the mitotic spindle and the cleavage furrow; but it remains to be determined how behavior of the division apparatus becomes modified during asymmetric division.
Polyphosphoinositlde metabolism during the fertilization wave in sea urchin eggs
Authors: Ciapa Brigitte , Borg Béatrice , Whitaker Michael
Published: April 2021

A transient increase in intracellular free calcium is believed to be the signal responsible for the stimulation of the egg metabolism at fertilization and the resumption of the cell cycle. We have studied how the polyphospho-inositides (PP1) turn over at fertilization in sea urchin eggs, in order to determine the relationship between the metabolism of these lipids and the calcium signal. We compare the patterns of PPI turnover that occur during the first minute following fertilization in eggs in which PPI are labelled to steady state with [3H]inositol or [3H]arachidonate with that in which PPI are labelled for a shorter period with [3H]inositol. When eggs are labelled to apparent isotopic equilibrium with either [3H]inositol or [3H]arachidonate, no early increase in [3H]PtdlnsP2occurs while Ptdins decreases slightly. On the contrary, when not labelled to isotopic equilibrium, all [3H]PPI increase during the first 15 seconds following fertilization. We find that, within seconds, fertilization triggers a 600-fold increase in the turnover of PPI, producing an amount of lnsP3 apparently sufficient to trigger calcium release. We suggest that phosphoinositi dase C and PtdlnsP kinase, responsible respectively for the hydrolysis and synthesis of PtdlnsP2, are both stimulated to a comparable degree in the first 30 seconds following fertilization and that net changes in the amount of PtdlnsP2at fertilization are very sensitive to the relative levels of activation of the two enzymes. Activating the eggs with the calcium ionophore A23187 showed that both these enzymes are sensitive to calcium, suggesting that calcium-dependent lnsP3 production might play a role in the initiation and/or the propagation of the fertilization calcium wave. A comparison of the rates of PPI turnover in fertilized and A23187-activated eggs confirms that the fertilizing sperm stimulates an early and possibly calcium-dependent increase in PtdlnsP kinase activity.
engrailedexpression in the anterior lineage compartment of the developing wing blade ofDrosophila
Authors: Blair Seth S.
Published: April 2021

The developing wing of Drosophila melanogaster was examined at larval and pupal stages of development to determine whether the anterior-posterior lineage boundary, as identified by lineage restrictions, was congruent with the boundaries defined by the expression of posterior-specific (engrailed, inverted), and anterior-specific (cubitus interruptus-D) genes. The lineage boundary was identified by marking mitotic recombinant clones, using an enhancer trap line with ubiquitous β-gal expression in imaginai tissues; clones of +/+ cells were identified by their lack of β-gal expression. Domains of gene expression were localized using antibodies and gene specific lacZ constructs. Surprisingly, it was found that engrailed expression extended a small distance into the anterior lineage compartment of the wing blade, as identified with anti-en/tnv mAh, anti-en polyclonal antiserum, or an en-promoter-lacZ insert, ryxho25. This anterior expression was not present in early third instar discs, but appeared during subsequent larval and pupal development. In contrast, the expression of cubitus interruptus-D, as identified using the ci-Dplac insert, appeared to be limited to the anterior lineage compartment. Thus, en expression is not limited to cells from the posterior lineage compartment, and en and ci-D activities can overlap in a region just anterior to the lineage compartment boundary in the developing wing. The lineage boundary could also be identified by a line of aligned cells in the prospective wing blade region of wandering third instar discs. A decapeniaplegic-lacZ construct was expressed in a stripe several cells anterior to the lineage boundary, and did not define or overlap into the posterior lineage compartment.
bicoid and the terminal system activate tailless expression in the early Drosophila embryo
Authors: Pignoni F. , Steingrímsson E. , Lengyel J.A.
Published: April 2021

In the early Drosophila embryo, the maternal terminal genes are required for formation of the acron at the anterior and the telson at the posterior. We show here that the terminal system, a signal transduction pathway active at the poles of the embryo, is required to activate transcription of the key zygotic gene tailless (tll) in two symmetrical domains. Consistent with the characterization of the tll protein as a putative transcription factor (a member of the steroid receptor superfamily) that represses segmentation genes and activates terminal-specific genes, we observe a correlation between the presence of the posterior cap of tll expression and differentiation of a telson.

While the maternal patterning systems of the Drosophila embryo function for the most part independently, the maternal anterior system, in which the bicoid (bcd) protein functions as a graded morphogen, is required together with the terminal system to establish the acron. This dual requirement is evident at the molecular level in the control of tll expression. We find that bcd and the terminal system are required together to activate the anterior-dorsal stripe of tll expression that is correlated with formation of the acron. In the absence of bcd, the anterior cap of tll expression established by the terminal system persists and an ectopic telson forms at the anterior, while in the absence of terminal system activity only an abnormal anterior stripe forms. This is the first describcd example of how, by jointly controlling expression of the same gene, two systems of positional information function together to set unique positional values.
Identification and characterization of a novel, evolutionarily conserved gene disrupted by the murine Hβ58 embryonic lethal transgene insertion
Authors: Lee James J. , Radice Glenn , Perkins Christopher P. , Costantini Frank
Published: April 2021

The Hβ58 transgenic mouse line carries a recessive insertional mutation that results in developmental abnormalities beginning at day 7.5 p.c. and embryonic arrest at about day 9.5. In this paper, we describe the characterization of a novel gene encoded at the Hβ58locus, whose disruption appears to be responsible for the mutant phenotype. The wild-type Hβ58 gene encodes a single 2.7 kb mRNA during embryonic and fetal development, and in many adult somatic tissues. In the mutant locus, this transcription unit is split by the transgene insertion, and one of its coding exons is deleted. Consistent with the physical disruption of the gene, the level of the Hβ58 mRNA in heterozygous mutant mouse tissues was half the normal level, indicating that the mutant allele fails to encode a stable mRNA. In situ hybridization studies revealed that expression of the wild-type Hβ58 gene begins in the oocyte, and continues throughout pre- and post-implantation embryogenesis, despite the fact that homozygous mutant embryos develop successfully through the egg cylinder stage (day 6.5 p.c.). In the early post-implantation embryo, expression of the normal Hβ58 gene is relatively low in the embryonic ectoderm, the tissue displaying the earliest phenotypic effects of the mutation, and highest in the visceral endoderm. We therefore propose that the effects of the mutation on the embryonic ectoderm may be exerted indirectly, via the visceral endoderm. Sequence analysis of Hβ58 cDNA clones revealed no homology between the 38 ×103MrHβ58 protein and other known proteins. However, the Hβ58 gene displayed extremely strong conservation between mammals and birds (>96% amino acid identity), although it appeared less conserved in amphibians and invertebrates.
A genetic model for light-regulated seedling development in Arabidopsis
Authors: Chory Joanne
Published: April 2021

The genetic interactions among mutations that define eight distinct loci involved in light-regulated development in Arabidopsis thaliana are described. The mutations in these eight genes define two distinct phenotypic classes with opposite characteristics. Recessive mutations in either one of two genes, DET1 or DET2, result in dark-grown plants that develop as light-grown wild-type seedlings. Mutants in the second class exhibit a reduced response to light Recessive mutations in any one of five genes, HY1, HY2, HY3, HY5, or HY6 cause reduced responses to red-light Four of these genes, HY1,2,3, and 6, affect the activity of one or all of the red-light photoreceptors, the phytochromes. The HY4 gene product is involved in blue-light perception or action. The experiments described here examine how these eight genes interact to control a particular event, the switch from developmental arrest in the dark (etiolation) to growth in the light (deetiolation). The phenotypes of doubly mutant strains suggest a hierarchical regulatory network among these genes in the control of the switch from etiolated to de-etiolated growth strategies.
Secretory and inductive properties of Drosophila wingless protein in Xenopus oocytes and embryos
Authors: Chakrabarti Arthur , Matthews Glenn , Colman Alan , Dale Leslie
Published: April 2021

Like its vertebrate homologues, Xenopus wnt-8 and murine wnt-1, we find that Drosophila wingless (wg) protein causes axis duplication when overexpressed in embryos of Xenopus laevis after mRNA injection. In many cases, the secondary axes contain eyes and cement glands, which reflect the induction of the most dorsoanterior mesodermal type, prechordal mesoderm. We show that the extent of axis duplication is dependent on the embryonic site of expression, with ventral expression leading to a more posterior point of axis bifurcation. The observed duplications are due to de novo generation of new axes as shown by rescue of UV-irradiated embryos. The true dorsal mesoderm-inducing properties of wg protein are indicated by its ability to generate extensive duplications after mRNA injection into D-tier cells of 32-cell embryos. As revealed by lineage mapping, the majority of these D cell progeny populate the endoderm; injections into animal blastomeres at this stage are far less effective in inducing secondary axes. However, when expressed in isolated animal cap expiants, wg protein induces only ventral mesoderm, unless basic fibroblast growth factor is added, whereupon induction of muscle and occasionally notochord is seen. We conclude that in intact embryos, wg acts in concert with other factors to cause axis duplication.

Immunolocalisation studies in embryos indicate that wg protein remains localised to the blastomeres synthesizing it and has a patchy, often perinuclear distribution within these cells, although some gets to the surface. In oocytes, the pool of wg protein is entirely intracellular and relatively unstable. When the polyanion suramin is added, most of the intracellular material is recovered in the external medium.
Analysis of glia cell differentiation in the developing chick peripheral nervous system: sensory and sympathetic satellite cells express different cell surface antigens
Authors: Rüdel Christiana , Rohrer Hermann
Published: April 2021

To identify and analyse precursor cells of neuronal and glial cell lineages during the early development of the chick peripheral nervous system, monoclonal antibodies were raised against a population of undifferentiated cells of E6 dorsal root ganglia (DRG).

Non-neuronal cells of E6 DRG express surface antigens that are recognized by four monoclonal antibodies, G1, G2, GLI 1 and GLI 2. The proportion of non-neuronal cells in DRG that express the GLI 1 antigen is very high during ganglion formation (80% at E4) and decreases during later development (15% at E14). GLI 2 antigen is expressed only on a minority of the cells at E6 and increases with development. The G1 and G2 antigens are expressed on about 60-80% of the cells between E6 and E14. All cells that express the established glia marker O4 are also positive for the new antigens. In addition, it was demonstrated that GLI 1positive cells from early DRG, which are devoid of O4 antigen, could be induced in vitro to express the O4 antigen. Thus, the antigen-positive cells are considered as glial cells or glial precursor cells.

Surprisingly, the antigen expression by satellite cells of peripheral ganglia is dependent on the type of ganglion: antigens G1, G2 and GLI 1 were not detectable on glial cells of lumbosacral sympathetic ganglia and GLI 2 was expressed only by a small subpopulation. These results demonstrate an early immunological difference between satellite cells of sensory DRG and sympathetic ganglia. As the antigens could however be induced in vitro also in sympathetic ganglion cells, it is suggested that the specific antigen expression is due to specific environmental cues acting on precursor cells in different types of ganglia rather than to intrinsic differences between sensory and sympathetic glial precursor cells.
Cultured dermal papilla cells induce follicle formation and hair growth by transdifferentiation of an adult epidermis
Authors: Reynolds Amanda J. , Jahoda Colin A. B.
Published: April 2021

Adult rat pelage follicle dermal papilla cells induced follicle neogenesis and external hair growth when associated with adult footpad skin epidermis. They thus demonstrated a capacity to completely change the structural arrangement and gene expression of adult epidermis - an ability previously undocumented for cultured adult cells. Isolation chambers ensured that de novo follicle formation must have occurred by eliminating the possibility of cellular contributions, and/or inductive influences, from local skin follicles. These findings argue against previous suggestions of vibrissa follicle specificity, and imply that the potential for hair follicle induction may be common to all adult papilla cells.
The expression of neuropeptide Y immunoreactivity in the avian sympathoadrenal system conforms with two models of coexpression development for neurons and chromaffin cells
Authors: García-Arrarás José E. , Lugo-Chinchilla Ana M. , Chévere-Colón Iván
Published: April 2021

We have studied the expression and development of neuropeptide Y-like immunoreactivity (NPY-LI) in the sympathoadrenal system of the chicken using single and double immunocytochemical techniques and radioimmunoassay. NPY-LI is expressed by neurons of the paravertebral sympathetic ganglia and by chromaffin cells of the adrenal gland in embryonic and adult chickens. The peptide is coexpressed with catecholamin-ergic properties in neurons. In chromaffin cells, it is also expressed with immunoreactivity to somatostatin and serotonin.

We have used the expression of NPY-LI to analyze how cells that coexpress two or more neuroactive substances arrive at their final phenotype. Our results suggest that the ontogeny of coexpression in neurons of the avian paravertebral sympathetic ganglia occurs in a sequential pattern, where the expression of the peptide follows the initial expression of the “classical neurotransmitter”. In contrast, in chromaffin cells, expression of the peptides occurs concomitantly with expression of catecholamin-ergic properties or soon after. Initially, coexpression of several neuroactive substances occurs, but this is followed by further specialization where the expression of one peptide prevails over the other. We believe that the two models of coexpression shown by our results can be used to describe the ontogeny of coexpression in other cells of the nervous system.
Synaptic basal lamina contains a signal for synapse-specific transcription
Authors: Jo Sangmee Ahn , Burden Steven J.
Published: April 2021

Nuclei in the synaptic region of multinucleated skeletal myofibers are transcriptionally distinct, since acetylcholine receptor genes are transcribed at a high rate by these nuclei, but not by nuclei elsewhere in the myofiber. Although this spatially restricted transcription pattern is presumably imposed by the motor nerve, the continuous presence of the nerve is not required, since synapsespecific transcription persists after denervation. These results suggest either that a transcriptional signal persists at synaptic sites after nerve terminals have degenerated, or that a transcriptional pattern in the myofiber, once established, is stable in the absence of a nerve-derived signal. To distinguish between these possibilities, we denervated muscle and damaged the myofibers and specialized cells located near synaptic sites, and then studied transcription of an acetylcholine receptor gene in myofibers that regenerated in their original basal lamina sheaths, but remained denervated. We show that synapse-specific transcription is re-induced in these regenerated myofibers, and we conclude that a signal for synapse-specific transcription is stably maintained in the synaptic basal lamina.
Cell fate in the shoot apical meristem of Arabidopsis thaliana
Authors: Furner Ian J. , Pumfrey Joanne E.
Published: April 2021

Seeds of Arabidopsis thaliana, heterozygous for the alb1 mutation were treated with X-rays to generate sectors of albino tissue in the mature plants. Sectors were observed in tissues derived from L2 and L3 layers of the shoot meristem. Altogether 324 sectors were obtained affecting 512 leaves or the inflorescence. The majority of sectors affected only one or other of the first leaf pair. In later leaves, sectors were less frequent, and often affected more than one leaf. Sectors seen in the flowers almost invariably included some of the cauline leaves. Sectors in any region of the plant were of variable length and width. The axillary meristems of Arabidopsis were found to be clonally related to two or more cells near the centre of the subtending leaf. Overall the data are compatible with the idea that there are few, if any, restrictions on cell fate within the cell layers of the dry seed meristem. As in other higher plants, developmental fate could only be predicted in a general and probabilistic way. Such a pattern might be generated if the acquisition of cell fate occurred continuously as the plant grows, in a position-dependent, lineage-independent fashion. A general model of the meristem has been produced to accommodate the observations concerning the great majority of the sectors.
Transgenic mouse eggs with functional hamster sperm receptors in their zona pellucida
Authors: Kinloch Ross A. , Mortillo Steven , Wassarman Paul M.
Published: April 2021

Sperm receptors are located in the mammalian egg extracellular coat, or zona pellucida. Mouse and hamster sperm receptor glycoproteins, mZP3 (83 × 103Mr) and hZP3 (56 × 103Mr), respectively, have very similar polypeptides (44×103Mr; 81% identical) that are glycosylated to different extents. Purified mZP3 and hZP3 can bind to mouse sperm, prevent them from binding to eggs and induce them to undergo exocytosis, the acrosome reaction, in vitro. A DNA construct that placed the hZP3 gene under the control of mZP3 gene 5 -flanking sequence was used in this report to produce two mouse lines that harbored the foreign sperm receptor transgene. In both lines, the transgene was expressed only by growing oocytes, at a level comparable to that of the endogenous mZP3 gene, and the developmental pattern of transgene expression resembled that of the mZP3 gene. In addition to mZP3, transgenic mouse oocytes synthesized and secreted a glycoprotein indistinguishable from hZP3, and incorporated both glycoproteins into a mosaic zona pellucida. Importantly, hZP3 purified from such zonae pellucidae exhibited both sperm receptor and acrosome reaction-inducing activities in vitro and, following fertilization of transgenic mouse eggs, was inactivated. These results demonstrate that a biologically active foreign sperm receptor can be synthesized and secreted by transgenic mouse oocytes, assembled into a mosaic zona pellucida, and inactivated following fertilization as part of the secondary block to polyspermy.
Differential distribution patterns of CRABP I and CRABP II transcripts during mouse embryogenesis
Authors: Ruberte Esther , Friederich Valérie , Morriss-Kay Gillian , Chambon Pierre
Published: April 2021

We have compared the transcript distribution of cellular retinoic acid binding protein (CRABP) I and II genes in mouse embryos at various stages of development. Both CRABP transcripts are present in embryonic structures from the earliest stages studied and exhibit specific patterns of distribution, suggesting that the two retinoic acid (RA) binding proteins perform different functions during mouse embryogenesis. The CRABP I transcript distribution correlates well with structures known to be targets of excess retinoid-induced terato-genesis (e.g. neural crest cells and hindbrain), suggesting that cells expressing CRABP I are those that cannot tolerate high levels of RA for their normal developmental function. The embryonic structures expressing CRABP II transcripts include those structures that have been shown to be adversely affected by excess of retinoids, such as limbs and hindbrain, but CRABP II transcripts are also found in structures not known to be specifically vulnerable to raised RA levels. The CRABP II gene is coexpressed with retinoic acid receptor (RAR)- and cellular retinol binding protein (CRBP) I genes in a number of tissues such as the gut endoderm, hypophysis and interdigital mesenchyme, all of which are devoid of CRABP I transcripts. Interestingly, the expression of the three genes, RAR-, CRABP II and CRBP I, is induced by retinoic acid, which suggests a link between the synthesis of RA from retinol and the control of expression of subsets of RA-responsive genes. The transcript distribution of CRABP I and II is discussed in relation to the teratogenic effects of RA, and compared to the RA-sensitive pattern of expression of other important developmental genes.
Down-regulation of the POU transcription factor SCIP is an early event in oligodendrocyte differentiation in vitro
Authors: Collarini Ellen J. , Kuhn Rainer , Marshall Caroline J. , Monuki Edwin S. , Lemke Greg , Richardson William D.
Published: April 2021

The POU-domain transcription factor SCIP (also known as Tst-1) has been implicated in the development of Schwann cells, the myelinating cells of the peripheral nervous system (PNS). We have investigated the possibility that SCIP also might play a role in the development of oligodendrocytes, the myelinating cells of the central nervous system (CNS). We purified oligodendrocyte precursors (O–2A progenitors) by immunoselection and cultured them in the presence of plateletderived growth factor (PDGF) and basic fibroblast growth factor (bFGF), which together keep O–2A progenitors proliferating and prevent oligodendrocyte differentiation. Under these culture conditions, O–2A progenitors expressed high levels of SCIP mRNA and protein, and did not express myelin-specific genes. When oligodendrocyte differentiation was initiated by withdrawing the growth factors, SCIP mRNA was rapidly down-regulated, followed by a decline in SCIP protein and the sequential activation of myelin-specific genes. Rapid down-regulation of SCIP mRNA required continued protein synthesis. In O–2A progenitors that were cultured in the presence of PDGF alone, SCIP expression declined to an intermediate level, and low levels of the myelin gene products were induced. Thus, the level of SCIP expression in O–2A progenitors is inversely related to the level of myelin gene expression, suggesting that SCIP may be involved in the developmental switch from proliferation to differentiation in the oligodendrocyte lineage. When O–2A progenitors are cultured in the presence of 10% fetal calf serum, they differentiate into type-2 astrocytes rather than oligodendrocytes. SCIP mRNA was also down-regulated in type-2 astrocytes, which do not express myelin genes, so down-regulation of SCIP seems to be more closely linked to the cessation of cell proliferation per se than the expression of a particular differentiated phenotype.
Pintallavis, a gene expressed in the organizer and midline cells of frog embryos: involvement in the development of the neural axis
Authors: Altaba A. Ruiz i , Jessell T. M.
Published: April 2021

We have identified a novel frog gene, Pintallavis (the Catalan for lipstick), that is related to the fly fork head and rat HNF-3 genes. Pintallavis is expressed in the organizer region of gastrula embryos as a direct zygotic response to dorsal mesodermal induction. Subsequently, Pintallavis is expressed in axial midline cells of all three germ layers. In axial mesoderm expression is graded with highest levels posteriorly. Midline neural plate cells that give rise to the floor plate transiently express Pin tallavis, apparently in response to induction by the notochord. Overexpression of Pintallavis perturbs the development of the neural axis, suppressing the differentiation of anterior and dorsal neural cell types but causing an expansion of the posterior neural tube. Our results suggest that Pintallavis functions in the induction and patterning of the neural axis.
Mechanisms of early Drosophila mesoderm formation
Authors: Leptin Maria , Casal José , Grunewald Barbara , Reuter Rolf
Published: April 2021

Several morphogenetic processes occur simultaneously during Drosophila gastrulation, including ventral furrow invagination to form the mesoderm, anterior and posterior midgut invagination to create the endoderm, and germ band extension. Mutations changing the behaviour of different parts of the embryo can be used to test the roles of different cell populations in gastrulation. Posterior midgut morphogenesis and germ band extension are partly independent, and neither depends on mesoderm formation, nor mesoderm formation on them. The invagination of the ventral furrow is caused by forces from within the prospective mesoderm (i. e. the invaginating cells) without any necessary contribution from other parts of the embryo. The events that lead to the cell shape changes mediating ventral furrow formation require the transcription of zygotic genes under the control of twist and snail. Such genes can be isolated by molecular and genetic screens.