bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential expression of acidic cytokeratins 18 and 19 during sexual differentiation of the rat gonad
Authors: Fridmacher Valérie , Locquet Odette , Magre Solange
Published: April 2021

The expression of cytokeratins (CKs) 8, 18 and 19 was analyzed in male and female rat gonads from the undifferentiated stage (12.5 days of gestation) until two weeks after birth by indirect immunofluorescence, using specific monoclonal antibodies anti-CK 8 (LE41), anti-CK 19 (LP2K) and anti-CK 18 (LE65 and RGE53). In the undifferentiated blastema, the somatic cells were stained for CK 8 and CK 19, whereas no detectable immunoreactivity for CK 18 was obtained. The same staining CK pattern was observed in ovaries, in the somatic cells of ovigerous cords and in primary follicles. The staining was progressively decreasing in growing follicles after one week after birth. At the onset of testicular differentiation, when the first Sertoli cells differentiate in the gonad of 13.5-day old male fetuses, positive staining for CK 18 became evident, in addition to CK 8 and CK 19 expression. In the following days,CK 8, CK 18 and CK 19 were detected in Sertoli cells in the differentiating seminiferous cords, but progressively the reactivity for CK 19 decreased and was no longer observed after 18.5-19.5 days of gestation. In all cases, CKs were found to be coexpressed with vimentin, and germ cells were negative for both vimentin and CKs. The results reported here show first, that CKs are expressed before sexual differentiation in gonadal blastema in which no epithelial organization is observed, and second, that there is a CK 18/CK 19 shift in expression during morphogenesis of the testis which is not observed in the differentiating ovary. Future studies will have to determine whether these differences in CK expression are due to epitope-masking phenomena or to the regulation of CK synthesis.
β-integrin is a maternal protein that is inserted into all newly formed plasma membranes during early Xenopus embryogenesis
Authors: Gawantka V. , Ellinger-Ziegelbauer H. , Hausen P.
Published: April 2021

A monoclonal antibody (mAb 8C8) that recognizes the Xenopus β1-integrin chain was used to study the appearance, synthesis and distribution of this integrin subunit during the early development of Xenopus. Both the precursor and the mature form of β1-integrin are provided maternally. They do not increase significantly in amount until early gastrula when the level of both forms begins to rise gradually.

Synthesis of β1-integrin from maternal mRNA is observed throughout the pregastrula phase, though it seems to add only little to the total β1-integrin of the embryo. Until late blastula only small amounts of precursor are processed into the mature form.

Starting with the formation of the first cleavage membrane, mature β1-integrin is inserted into the newly formed plasma membranes of all cells. The membrane domains forming the outer surface of the embryo remain devoid of the antigen. The data suggest an as yet unknown function of β1-integrin during the cleavage phase.
The neural tube/notochord complex is necessary for vertebral but not limb and body wall striated muscle differentiation
Authors: M.Rong P. , Teillet M.-A. , Ziller C. , Douarin N.M. Le
Published: April 2021

The aim of this work was to investigate the role played by the axial organs, neural tube and notochord, on the differentiation of muscle cells from the somites in the avian embryo. Two of us have previously shown that neuralectomy and notochordectomy is followed by necrosis of the somites and consecutive absence of vertebrae and of most muscle cells derived from the myotomes while the limbs develop normally with muscles. Here we have focused our attention on muscle cell differentiation by using the 13F4 mAb that recognizes a cytoplasmic antigen specific of all types of muscle cells. We show that differentiation of muscle cells of myotomes can occur in the absence of notochord and neural tube provided that the somites from which they are derived have been in contact with the axial organs for a defined period of time, about 10 hours for the first somites formed at the cervical level, a duration that progressively reduces caudalward (i. e. for thoracic and lumbar somites). Either one or the other of the two axial organs, the neural tube or the noto-chord can prevent somitic cell death and fulfill the requirements for myotomal muscle cell differentiation. Separation of the neural tube/notochord complex from the somites by a surgical slit on one side of the embryo gave the same results as extirpation of these organs and provided a perfect control on the non-operated side. A striking finding was that limb and body wall muscles, although derived from the somites, differentiated in the absence of the axial organs. However, limb muscles that develop after excision of the neural tube started to degenerate from E10 onward due to lack of innervation. In vitro explantation of somites from different axial levels confirmed and defined precisely the chronology of muscle cell commitment in the myotomes as revealed by the in vivo experiments.
Overexpression of Dd PK2 protein kinase causes rapid development and affects the intracellular cAMP pathway of Dictyostelium discoideum
Authors: Anjard Christophe , Pinaud Stephane , Kay Robert R. , D. Reymond Christophe
Published: April 2021

The Dd PK2 gene codes for a putative protein of 648 amino acids with a C-terminal half sharing high homology with protein kinase A catalytic subunits from other organisms. In order to find out more about the physiological role of the Dd PK2 kinase, its gene, and a version having a frame shift mutation in the middle of the catalytic region, were overexpressed in developing Dictyostelium cells. Both the intact gene (K-) and the frame shift mutant (Kdel-) caused rapid development with spores formed in 16-18 hours compared to the 24 hours required by their parent. This result was confirmed by the pattern of expression of some developmentally regulated genes. Other rapid developing strains (rde) are activated in the cAMP second messenger system. Both K- and Kdel-containing strains have lower cAMP levels than the parental strain during late development, thus resembling rdeC mutants. K-cells (but not Kdel-cells) produced bizarre fruiting bodies with many prostrate forms. The parallel with rde mutants was confirmed by demonstrating that K-cells are able to form spores in submerged monolayer culture. Furthermore, K-cells have about four times more protein kinase A (cAPK) activity than wild-type cells. These results indicate that the N-terminal domain of Dd PK2 is sufficient to influence cAMP levels and to provoke rapid development, whereas kinase activity seems to be required for the sporogenous phenotype. The association between elevated cAPK and Dd PK2 overexpression phenotype further indicates a role for cAPK in the formation of spores.
orthodenticle activity is required for the development of medial structures in the larval and adult epidermis of Drosophila
Authors: Wieschaus Eric , Perrimon Norbert , Finkelstein Robert
Published: April 2021

Lethal alleles of orthodenticle (=otd) cause abnormalities in the embryonic head that reflect an early role in anterior pattern formation. In addition, otd activity is required for the development of the larval and adult epidermis. Clonal analysis of both viable and lethal alleles shows that the adult requirement for otd is restricted to medial regions of certain discs. When otd activity is reduced or removed, some medial precursor cells produce bristles and cuticle characteristic of more lateral structures. Similar medial defects are observed in the larval epidermis of embryos homozygous for lethal otd alleles. Antibodies to otd recognize a nuclear protein found at high levels in the medial region of the eye antennal discs, the leg discs, the genital discs and along the ventral midline of the ventral epidermis of the embryo. These results suggest that the otd gene product is required to specify medial cell fates in both the larval and adult epidermis.
Platelet derived growth factor (PDGF) stimulates development of bovine embryos during the fourth cell cycle
Authors: Larson R. C. , Ignotz G. G. , Currie W. B.
Published: April 2021

In vitro produced, 2-cell bovine embryos were cultured in serum-free medium supplemented with various combinations of growth factors to test the hypothesis that these polypeptide factors are able to signal preimplantation development. The developmental arrest that occurs during the 8-cell stage with typical culture methods might be relieved by a growth factor-dependent mechanism that would stimulate expression of the embryonic genome, thereby mimicking events that occur in vivo in the oviduct during the fourth cell cycle (8-to 16-cell stage). Subsequently, other growth factors might promote compaction and blastulation, processes which normally occur in the uterus.

The effects of growth factors on early embryos were evaluated using phase contrast microscopy to monitor progression to the 8-cell stage, completion and duration of the fourth cell cycle, and blastocyst formation.

Platelet derived growth factor (PDGF) promoted development beyond the 16-cell stage in 39.1% of the 2-cell embryos examined in all experiments. The duration of the fourth cell cycle among these embryos was approximately 26 hours. During development after the 16-cell stage, PDGF reduced the proportion of embryos bastulating from 12.7% to 5.8%; in contrast, transforming growth factor (TGF ), acting during the same developmental time period, increased the proportion of embryos blastulating from 8.6% to 40.6%.

These results, using serum-free medium, indicated that PDGF signalled completion of the fourth cell cycle. TGF and perhaps basic fibroblast growth factor (bFGF), promoted blastulation of 16-cell embryos during subsequent culture.
Nuclear rotation and lineage specification in Pelvetia embryos
Authors: Allen Victoria W. , Kropf Darryl L.
Published: April 2021

The first division of Pelvetia zygotes is an unequal division which produces two cells with distinct developmental fates. The smaller rhizoid cell gives rise to the holdfast of the mature plant, and the larger thallus cell is the progenitor of the stipe and fronds. We have investigated the role of the cytoskeleton in determining the orientation of this invariant division. Prior to mitosis, microtubuleorganizing centers (MtOCs) associated with the nuclear envelope undergo a precise realignment from transverse to axial with respect to the rhizoid/thallus axis. This is accomplished by a 90° rotation of the entire nuclear/MtOC complex. After rotation, each MtOC serves as a spindle pole during mitosis, and subsequently cytokinesis bisects the spindle. Both nocodazole and cytochalasin D cause incorrect alignment of MtOCs, indicating that both microtubules and microfilaments are required for nuclear/MtOC rotation. These inhibitors also result in aberrant orientation of the first division plane. Microtubules visualized by confocal microscopy connect the rotating nucleus to the apical cortex and may provide the force for rotation.
Platelet-derived growth factor-A and its receptor are expressed in separate, but adjacent cell layers of the mouse embryo
Authors: Orr-Urtreger Avi , Lonai Peter
Published: April 2021

The localized developmental expression of murine platelet-derived growth factor A (PDGF-A) was compared to that of itsreceptor (Pdgfra). Our in situ hybridization study included germ layers of primitive streak embryos, early axial structures (dermatome, myotome, sclerotome, floor plate), the skin and some of its derivatives (hair and mammary gland), the developing fore-limb, the branchial arches and various sense organs (otic vesicle, olfactory epithelium and the eye). We report that PDGF-A and Pdgfra are expressed in separate, but adjacent cell layers in these structures and that in most, the ligand is expressed in the epithelium, whereas the receptor in the mesenchyme. This localization corresponds to classical experimental evidence for develop-mental interactions across cell layers. We suggest that the spatio-temporal regulation of PDGF-A and Pdgfra, and other related systems, represents one model for the spatial regulation of receptor-ligand interactions.
The developmental switch in embryonic ρ-globin expression is correlated with erythroid lineage-specific differences in transcription factor levels
Authors: Minie Mark E. , Kimura Takeshi , Felsenfeld Gary
Published: April 2021

During chicken embryogenesis, the ρ--globin gene is expressed only in the early developmental stages. We have examined the mechanisms that are responsible for this behavior. The transcription of the ρ--globin gene is strongly correlated with the presence during development of primitive erythroid lineage cells, consistent with the idea that the expression of the ρ--globin gene is restricted to that lineage. The “switching off” of ρ--globin during development thus reflects the change from primitive to definitive cell lineages which occurs during erythropoiesis in chicken. We use transient expression assays in primary erythroid and other cells to show that the information for lineage- and tissue-specific expression of the ρ--globin gene is contained in a 456 bp region upstream of the gene’s translational start site. DNA-binding studies, coupled with analysis of the effect on expression of deletions and binding site mutations, were used to identify important control elements within this 456 bp region. We find that binding sites for the ubiquitous transcription factor Sp1, and the specific hematopoietic factor GATA-1, are crucial for expression of the gene in primitive erythroid cells. Quantitative analysis shows that nuclei of the primitive erythroid lineage contain 10-fold more of these factors than do the nuclei of definitive cells. We show that in principle these differences in factor concentration are sufficient to explain the lineage-specific behavior that we observe in our assays. We suggest that this may be an important part of the mechanism for lineage-restricted ρ--globin expression during chicken erythroid development. Similar mechanisms may be involved in regulation of other (but not all) members of the globin family.
The involvement of the Notch locus in Drosophila oogenesis
Authors: Xu Tian , A. Caron Laurent , G. Fehon Richard , Artavanis-Tsakonas Spyros
Published: April 2021

The Notch gene in Drosophila encodes a transmembrane protein with homology to EGF that, in a variety of tissues, appears to mediate cell interactions necessary for cell fate choices. Here we demonstrate that oogenesis and spermatogenesis depend on Notch. We examine the phenotypes of the temperature-sensitive Notch allele, Nts1, and, using a monoclonal antibody, determine the cellular and subcellular distribution of Notch protein during oogenesis. We show that Nts1 is associated with a missense mutation in the extracellular, EGF homologous region of Notch and that at non-permissive temperatures oogenesis is blocked and the subcellular distribution of the protein is altered. In wild-type ovaries, Notch protein is found on the apical surface of somatically derived follicle cells, while in the germline-derived cells the protein is not polarized. These findings are discussed in view of the hypothesis that Notch acts as a multifunctional receptor to mediate developmentally important cell interactions.
Relationship between Wnt-1 and En-2 expression domains during early development of normal and ectopic met-mesencephalon
Authors: Bally-Cuif Laure , Alvarado-Mallart Rosa-Magda , Darnell Diana K. , Wassef Marion
Published: April 2021

Grafting a met-mesencephalic portion of neural tube from a 9.5-day mouse embryo into the prosencephalon of a 2-day chick embryo results in the induction of chick En-2 (ChickEn) expression in cells in contact with the graft (Martinez et al., 1991). In this paper we investigate the possibility of Wnt-1 being one of the factors involved in En-2 induction. Since Wnt-1 and En-2 expression patterns have been described as diverging during development of the met-mesencephalic region, we first compared Wnt-1 and En-2 expression in this domain by in situ hybridization in mouse embryos after embryonic day 8.5. A ring of Wnt-1-expressing cells is detected encircling the neural tube in the met-mesencephalic region at least until day 12.5. This ring consistently overlapped with the En-2 expression domain, and corresponds to the position of this latter gene’s maximal expression. We subsequently studied ChickEn ectopic induction in chick embryos grafted with various portions of met-mesencephalon. When the graft originated from the level of the Wnt-1-positive ring, ChickEn induction was observed in 71% of embryos, and in these cases correlated with Wnt-1 expression in the grafted tissue. In contrast, this percentage dropped significantly when the graft was taken from more rostral or caudal parts of the mesencephalic vesicle. Taken together, these results are compatible with a prolonged role of Wnt-1 in the specification and/or development of the met-mesencephalic region, and show that Wnt-1 could be directly or indirectly involved in the regulation of En-2 expression around the Wnt-1-positive ring during this time. We also provide data on the position of the Wnt-1-positive ring relative to anatomical boundaries in the neural tube, which suggest a more general role for the Wnt-1 protein as a positional signal involved in organizing the met-mesencephalic domain.
Synergistic principles of development: overlapping patterning systems in Xenopus mesoderm induction
Authors: Kimelman David , Christian Jan L. , Moon Randall T.
Published: April 2021

The first inductive event in Xenopus development establishes the mesoderm at the equator of the developing embryo. As part of this process, the dorsal-ventral and anterior-posterior axes of the embryo are initially established. A number of signalling molecules which may play a role in mesodermal induction and patterning have been identified in the last several years, including members of the FGF, TGFand Wnt gene families. A variety of experiments, using either purified factors or injection of RNA encoding these factors, have added to the wealth of classical embryogical experimental data collected over the last century.

We have synthesized some recent results with the classical data to provide a framework for examining the process of mesoderm induction, and to formulate putative roles for some of the different factors. We incorporate these ideas into a working model of mesoderm induction that provides a basis for future experimental directions. Finally, we suggest that mesoderm induction may not be a discrete set of well separated events, but instead may be a process involving partially overlapping signals that produce the same pattern.
Cleavage and gastrulation in the shrimp Sicyonia ingentis: invagination is accompanied by oriented cell division
Authors: Hertzler Philip L. , Clark Wallis H.
Published: April 2021

Embryos of the penaeoidean shrimp Sicyonia ingentis were examined at intervals during cleavage and gastrulation using antibodies to β-tubulin and DNA and laser scanning confocal microscopy. Cleavage occurred in a regular pattern within four domains corresponding to the 4-cell-stage blastomeres and resulted in two interlocking bands of cells, each with similar spindle orientations, around a central blastocoel. Right-left asymmetry was evident at the 32-cell-stage, and mirror-image embryos occurred in a 50:50 ratio. Gastrulation was initiated by invagination into the blastocoel at the 62-cellstage of two mesendoderm cells, which arrested at the 32-cell-stage. Further invagination and expansion of the archenteron during gastrulation was accompanied by rapid and oriented cell division. The archenteron was composed of presumptive naupliar mesoderm and the blastopore was located at the site of the future anus of the nauplius larva. In order to trace cell lineages and determine axial relationships, single 2and 4-cell-stage blastomeres were microinjected with rhodamine-dextran. The results showed that the mesendoderm cells which initiated gastrulation were derived from the vegetal 2-cell-stage blastomere, which could be distinguished by its slightly larger size and the location of the polar bodies. The mesendoderm cells descended from a single vegetal blastomere of the 4-cell-stage. This investigation provides the first evidence for oriented cell division during gastrulation in a simple invertebrate system. Oriented cell division has previously been discounted as a potential morphogenetic force, and may be a common mechanism of invagination in embryos that begin gastrulation with a relatively small number of cells.
Drosophila PS2 integrin mediates RGD-dependent cell-matrix interactions
Authors: Bunch Thomas A. , Brower Danny L.
Published: April 2021

Integrins are a family of transmembrane glycoproteins that mediate cell-matrix and cell-cell interactions. We have transfected cultured Drosophila cells with genes that express the Drosophila PS2 integrin. We demonstrate that this integrin is expressed on the surface of the cells and can mediate cell spreading on an undefined component of fetal calf serum or on the purified vertebrate matrix molecules vitronectin and fibronectin. Additionally, PS2 integrin can cause cell spreading on RGD peptide. The spreading on matrix components or RGD peptide can be inhibited by soluble RGD peptide and is dependent on divalent cations.
goosecoid and the organizer
Authors: De Robertis Eddy M. , Blum Martin , Niehrs Christof , Steinbeisser Herbert
Published: April 2021

The molecular nature of Spemann’s organizer phenomenon has long attracted the attention of embryologists. goosecoid is a homeobox gene with a DNA-binding specificity similar to that of Drosophila bicoid. Xenopus goosecoid is expressed on the dorsal side of the embryo before the dorsal lip is formed. Cells expressing goosecoid are fated to become pharyngeal endoderm, head mesoderm and notochord. Transplantation of goosecoid mRNA to the ventral side of Xenopus embryos by microinjection mimics the properties of Spemann’s organizer, leading to the formation of twinned body axes, goosecoid is activated by dorsal inducers and not affected by ventral inducers. In the mouse, goosecoid is expressed in the anterior tip of the primitive streak. The availability of two early markers, goosecoid and Brachyury, opens the way for the comparative analysis of the vertebrate gastrula. The results suggest that the goosecoid homeodomain protein is an integral component of the biochemical pathway leading to Spemann’s organizer phenomenon.
Cell movements and cell fate during zebrafish gastrulation
Authors: Ho Robert K.
Published: April 2021

The early lineages of the zebrafish are indeterminate and a single cell labeled before the late blastula period will contribute progeny to a variety of tissues. Therefore, early cell lineages in the zebrafish do not establish future cell fates and early blastomeres must necessarily remain pluripotent. Eventually, after a period of random cell mixing, individual cells do become tissue restricted according to their later position within the blastoderm. The elucidation of a fate map for the zebrafish gastrula (Kimmel et al., 1990), has made it possible to study the processes by which cellular identity is conferred and maintained in the zebrafish. In this chapter, I describe single cell transplantation experiments designed to test for the irreversible restriction or ‘commitment’ of embryonic blastomeres in the zebrafish embryo. These experiments support the hypothesis that cell fate in the vertebrate embryo is determined by cell position. Work on the spadetail mutation will also be reviewed; this mutation causes a subset of mesodermal precursors to mismigrate during gastrulation thereby leading to a change in their eventual cell identity.
Interaction between splotch (Sp) and curly tail (ct) mouse mutants in the embryonic development of neural tube defects
Authors: Estibeiro J. Peter , Brook Frances A. , Copp Andrew J.
Published: April 2021

The mouse mutations splotch (Sp) and curly tail (ct) both produce spinal neural tube defects with closely similar morphology, but achieve this by different embryonic mechanisms. To determine whether the mutants may interact during development, we constructed mice carrying both mutations. Double heterozygotes exhibited tail defects in 10% of cases, although the single het-erozygotes do not express this phenotype. Backcrosses of double heterozygotes to ct/ct produced offspring with an elevated incidence of neural tube defects, both spina bifida and tail defects, compared with a control backcross in which Sp was not involved. Use of the deletion allele Sp2H permitted embryos carrying a splotch mutation to be recognised by polymerase chain reaction assay. This experiment showed that only embryos carrying Sp2H develop spina bifida in the backcross with ct/ct, suggesting that the genotype Sp2H/+, ct/ct is usually lethal around the time of birth as a result of severe disturbance of neurulation. The interaction between Sp and ct was investigated further by examining embryos in the backcross for developmental markers of the Sp/Sp and ct/ct genotypes. Sp/Sp embryos characteristically lack neural crest derivatives, such as dorsal root ganglia, and die on day 13 of gestation. Double mutant embryos from the backcross did not exhibit either of these characteristics suggesting that homozygosity for ct does not cause Sp/+ embryos to develop as if they were of genotype Sp/Sp. The angle of ventral curvature of the posterior neuropore region is enhanced in affected ct/ct embryos whereas it was found to be reduced in Sp/Sp embryos compared with their normal littermates. Double mutant embryos from the backcross had an angle of curvature that resembled the ct/ct pattern but was less exaggerated. We conclude that the non-allelic mutations Sp and ct interact to promote the development of neural tube defects in a manner that does not involve exacerbation of the specific developmental effects of either gene. The presence of enhanced curvature of the caudal region, which is responsible for neurulation disturbance in ct/ct embryos, summates with the reduced neurulation potential of the neuroepithelium in the Sp/+ genotype leading to the development of severe spina bifida. This study demonstrates that the finding of a significant interaction between genes in double mutant mice cannot be assumed to indicate that the genes operate in the same genetic pathway.
Induction of terminal differentiation of Dictyostelium by cAMP-dependent protein kinase and opposing effects of intracellular and extracellular cAMP on stalk cell differentiation
Authors: Hopper Neil A. , Anjard Christophe , Reymond Christophe D. , Williams Jeffrey G.
Published: April 2021

Expression of the catalytic (C) subunit of the cAMP-dependent protein kinase (PKA) of Dictyostelium under the control of heterologous, cell-type-specific promoters causes ectopic terminal differentiation. When expressed under the control of a prespore-specific promoter, development is accelerated, to yield highly aberrant fruiting bodies that contain a basal mass of spore cells surrounding a central stalk-like structure. When expressed under the control of a prestalk-specific promoter, development arrests much earlier, at the tight mound stage. Prestalk cells move to the apices of these mounds, apparently normally, but no tip is formed. Most of the prestalk cells remain arrested in their development but there are a few isolated stalk cells scattered within such mounds.

We show that extracellular cAMP represses stalk cell specific gene expression in cells where the kinase is con stitutively active, suggesting that inhibition of stalk cell differentiation by cAMP in normal cells (Berks and Kay, 1988) occurs because of an effect of extracellular cAMP on an intracellular signalling pathway independent of PKA. We propose a scheme whereby two separate events, a rise in intracellular cAMP levels and a fall in extracellular cAMP concentration, are required to induce stalk cell differentiation.
FGF-4 maintains polarizing activity of posterior limb bud cells in vivo and in vitro
Authors: Vogel Astrid , Tickle Cheryll
Published: April 2021

The polarizing region is a major signalling tissue involved in patterning the tissues of the vertebrate limb. The polarizing region is located at the posterior margin of the limb bud and can be recognized by its ability to induce additional digits when grafted to the anterior margin of a chick limb bud. The signal from the polarizing region operates at the tip of the bud in the progress zone, a zone of undifferentiated mesenchymal cells, maintained by interactions with the apical ectodermal ridge. A number of observations have pointed to a link between the apical ectodermal ridge and signalling by the polarizing region. To test this possibility, we removed the posterior apical ectodermal ridge of chick wing buds and assayed posterior mesenchyme for polarizing activity. When the apical ectodermal ridge is removed, there is a marked decrease in polarizing activity of posterior cells. The posterior apical ectodermal ridge is known to express FGF-4 and we show that the decrease in polarizing activity of posterior cells of wing buds that normally follows ridge removal can be prevented by implanting a FGF-4-soaked bead. Furthermore, we show that both ectoderm and FGF-4 maintain polarizing activity of limb bud cells in culture.
Heterotopic transplantation of presumptive placodal ectoderm changes the fate of sensory neuron precursors
Authors: Vogel Kristine S. , Davies Alun M.
Published: April 2021

The placode-derived cranial sensory neurons of the vestibular and nodose ganglia in avian embryos exhibit differences in neurite growth rate and the duration of neurotrophin-independent survival in vitro that arise prior to gangliogenesis and target contact (Davies, A. M. (1989) Nature 337, 553-555; Vogel, K. S. and Davies, A. M. (1991) Neuron 7, 819-830). To ascertain the state of commitment of presumptive placodal ectoderm to dif-ferentiate into neurons of the vestibular or nodose type, we performed heterotopic transplantation of labelled presumptive placodal ectoderm at E1.5 in the chicken embryo. We then assayed transplant-derived neurons for hindbrain innervation patterns, neurite growth and survival at E3.5. We show that presumptive placodal ectoderm is not determined to give rise to neurons of the vestibular or nodose phenotype at E1.5. Explantation of presumptive placodal ectoderm at E1.5 showed that this ectoderm is also not specified to differentiate into neurons at this stage. In addition, we demonstrate that non-neurogenic ectoderm from the trunk can give rise to nodose-type neurons when transplanted heterotopically to the nodose region.
Experimental analysis of the control of expression of the homeobox-gene Msx-1 in the developing limb and face
Authors: Brown J. M. , Wedden S. E. , Millburn G. H. , Robson L. G. , Hill R. E. , Davidson D. R. , Tickle C.
Published: April 2021

Mouse mesenchyme was grafted into chick embryos to investigate the control of mesenchymal expression of Msx-1 in the developing limb and face. In situ hybridization, using species-specific probes, allows a comparison between Msx-1 expression in the graft and the host tissue. The results show that Msx-1 expression in both limb-to-limb and face-to-face grafts corresponds closely with the level of Msx-1 expression in the surrounding chick mesenchyme. Cells in grafts that end up within the host domain of Msx-1 express the gene irrespective of whether they were from normally expressing, or non-expressing, regions. Therefore Msx-1 expression in both the developing limb and the developing face appears to be position-dependent. Mesenchyme from each of the three major facial primordia behaved in the same way when grafted to the chick maxillary primordium. Reciprocal grafts between face and limb gave a different result: Msx-1 expression was activated when facial mesenchyme was grafted to the limb but not when limb mesenchyme was grafted to the face. This suggests either that there are quantitative or qualitative differences in two local signalling systems or that additional factors determine the responsiveness of the mesenchyme cells.
A GATA family transcription factor is expressed along the embryonic dorsoventral axis in Drosophila melanogaster
Authors: Winick Jeffrey , Abel Ted , Leonard Mark W. , M. Michelson Alan , Chardon-Loriaux Isabelle , Holmgren Robert A. , Maniatis Tom , Engel James Douglas
Published: April 2021

The GATA transcription factors are a family of C4 zinc finger-motif DNA-binding proteins that play defined roles in hematopoiesis as well as presumptive roles in other tissues where they are expressed (e.g., testis, neuronal and placental trophoblast cells) during vertebrate development. To investigate the possibility that GATA proteins may also be involved in Drosophila development, we have isolated and characterized a gene (dGATAa) encoding a factor that is quite similar to mammalian GATA factors. The dGATAa protein sequence contains the two zinc finger DNA-binding domain of the GATA class but bears no additional sequence similarity to any of the vertebrate GATA factors. Analysis of dGATAa gene transcription during Drosophila development revealed that its mRNA is expressed at high levels during early embryogenesis, with transcripts first appearing in the dorsal portion of the embryo just after cellularization. As development progresses, dGATAa mRNA is present at high levels in the dorsal epidermis, suggesting that dGATAa may be involved in determining dorsal cell fate. The pattern of expression in a variety of dorsoventral polarity mutants indicates that dGATAa lies downstream of the zygotic patterning genes decapentaplegic and zerknüllt.
Embryonic mesodermal defects in α5 integrin-deficient mice
Authors: Yang Joy T. , Rayburn Helen , Hynes Richard O.
Published: April 2021

A loss of function mutation of the murineα5 integrin gene generated by gene targeting in embryonic stem cells is a recessive embryonic lethal. The mutant embryos start to show observable defects by day 9 of gestation and die around day 10-11. Theα5-null embryos have pronounced defects in posterior trunk and yolk sac mesodermal structures, suggesting a role forα5 β1 integrin in mesoderm formation, movement or function. However, the embryos progress significantly further than embryos null for fibronectin, for whichα5 β1 integrin is a receptor, suggesting the involvement of other fibronectin receptors. In vitro studies on cells derived from theα5-null embryos confirm that theα5 β1 integrin is not expressed on mutant cells and show that the mutant cells are able to assemble fibronectin matrix, form focal contacts, and migrate on fibronectin despite the complete absence of theα5 β1 fibronectin receptor integrin. All these functions have previously been thought to involve or requireα5 β1. The results presented show that these cellular functions involving fibronectin can proceed using other receptors.
A role for the mesoderm in endodermal migration and morphogenesis in Drosophila
Authors: Reuter Rolf , Grunewald Barbara , Leptin Maria
Published: April 2021

The endodermal midgut arises from two primordia, the anterior midgut (AMG) primordium and the posterior midgut (PMG) primordium, which are separated by almost the entire length of the Drosophila embryo. To form the midgut, these two parts have to extend towards each other and to fuse laterally on both sides of the yolk. Shortly before and during that movement, AMG and PMG are arranged as mesenchymal cell masses, but later the midgut cells form an epithelium. We show that these two aspects of midgut development, migration of AMG and PMG and transition to an epithelium, depend on the mesoderm. The extension of the midgut primordia is achieved by cell migration along the visceral mesoderm which forms a continuous layer of cells within the germ band. In mutant embryos lacking the entire mesoderm or failing to differentiate the visceral mesoderm, AMG and PMG are formed but do not migrate properly. In addition, they fail to form an epithelium and instead either remain as compact cell masses anterior and posterior to the yolk (in twist and snail mutant embryos) or only occasionally wrap around the yolk before embryogenesis is completed (in tinmandeficient embryos). We conclude that the visceral mesoderm serves as a substratum for the migrating endodermal cells and that the contact between visceral mesoderm and endoderm is required for the latter to become an epithelium.
Cwnt-8C: a novel Wnt gene with a potential role in primitive streak formation and hindbrain organization
Authors: Hume Clifford R. , Dodd Jane
Published: April 2021

To begin to examine the possibility that Wnt proteins act as cell signalling molecules during chick embryogenesis, PCR was used to identify Wnt genes expressed in Hensen’s node. We have identified a novel member of the Wnt gene family, Cwnt-8C, which is expressed prior to gastrulation in the posterior marginal zone, the primitive streak and Hensen’s node. Injection of Cwnt-8C mRNA into Xenopus embryos caused axis duplication and dorsalization of mesodermal tissues. During neurulation, Cwnt-8C is expressed transiently in a restricted domain of the prospective hindbrain neurectoderm that will give rise to rhombomere 4. This domain is defined prior to the formation of rhombomere boundaries and also precedes the up-regulation and restriction of expression of Hox B1 in the same region. Thus, Cwnt-8C is potentially involved in the regulation of axis formation and hindbrain patterning.
Developmental regulation of integrin expression at the time of implantation in the mouse embryo
Authors: Sutherland A. E. , Calarco P. G. , Damsky C. H.
Published: April 2021

The trophectoderm layer of the mouse blastocyst differentiates at the late blastocyst stage to form the invasive trophoblast that mediates implantation of the embryo into the uterine wall. The first sign that trophoblast cells have developed an invasion-specific cell behavior appears about 10-15 hours after the embryo hatches from the zona pellucida, when the quiescent, nonadherent trophectoderm cells initiate protrusive activity and become adhesive to extracellular matrix. Our previous findings that trophoblast outgrowth on extracellular-matrix-coated substrata involves the integrin family of adhesion receptors (Sutherland, A. E., Calarco, P. G. and Damsky, C. H., 1988, J. Cell Biol. 106, 13311348), suggested that the onset of trophoblast adhesive and migratory behavior at the time of implantation may be due to changes in expression or distribution of integrin receptors. We have thus examined the mRNA and protein expression of individual integrin subunits during preand periimplantation development (E0E7.5). A basic repertoire of integrins, including receptors for fibronectin ( 5 1), laminin ( 6B 1) and vitronectin ( v 3), was expressed continuously throughout this period, whereas the expression of five other integrin subunits was developmentally regulated. The mRNA for three of these ( 2, 6A and 7) was first detected in the late blastocyst, coincident with endoderm differentiation and development of attachment competence. The mRNA for another ( 1) was not detected until after trophoblast outgrowth had begun, suggesting that its expression may be induced by contact with matrix. At E7.5, three of the temporally regulated integrins (α1, α6A, α7), all of which can form receptors for laminin, were detected only in the ectoplacental cone (differentiating trophoblast), and may thus play specific roles in trophoblast adhesion and/or differentiation.

Because laminin expression is upregulated in decidualized uterine stroma in response to the implanting embryo, we examined trophoblast-laminin interactions, using laminin fragments and integrin antibodies to determine which integrin receptors were involved. Trophoblast cells attached and spread on both the E8 and P1 fragments of laminin; however, the P1 binding site was cryptic in intact laminin. Interaction with P1 was RGDand αvβ3-dependent, whereas outgrowth on E8 was RGD-independent and not inhibited by antibodies to the laminin receptor α6β1, suggesting that α7β1 is the major trophoblast integrin E8 receptor. In contrast, migration of parietal endoderm cells on laminin was blocked by antibodies to α6, demonstrating that these two contemporaneous migratory cell populations have different modes of interaction with laminin. We conclude that developmental regulation of integrin expression appears to have functional significance for trophoblast invasion of the laminin-rich uterine stroma.
Structure of the zebrafish snail1 gene and its expression in wild-type, spadetail and no tail mutant embryos
Authors: Thisse C. , Thisse B. , Schilling T. F. , Postlethwait J. H.
Published: April 2021

Mesoderm formation is critical for the establishment of the animal body plan and in Drosophila requires the snail gene. This report concerns the cloning and expression pattern of the structurally similar gene snail1 from zebrafish. In situ hybridization shows that the quantity of snail1 RNA increases at the margin of the blastoderm in cells that involute during gastrulation. As gastrulation begins, snail1 RNA disappears from the dorsal axial mesoderm and becomes restricted to the paraxial mesoderm and the tail bud. snail1 RNA increases in cells that define the posterior border of each somite and then disappears when somitic cells differentiate. Later in development, expression appears in cephalic neural crest derivatives. Many snail1-expressing cells were missing from mutant spadetail embryos and the quantity of snail1 RNA was greatly reduced in mutant no tail embryos. The work presented here suggests that snail1 is involved in morphogenetic events during gastrulation, somitogenesis and development of the cephalic neural crest, and that no tail may act as a positive regulator of snail1.
The ventral and posterior expression of the zebrafish homeobox gene eve1 is perturbed in dorsalized and mutant embryos
Authors: Joly Jean-Stéphane , Joly Claire , Schulte-Merker Stefan , Boulekbache Habib , Condamine Hubert
Published: April 2021

We have identified and characterized zebrafish eve1, a novel member of the Drosophila even-skipped (eve) gene family. eve1 RNAs are expressed initially in late blastulae with a peak during the gastrula stage, at which time expression is confined to ventral and lateral cells of the marginal zone of the zebrafish embryo. Later, eve1 transcripts are located in the most posterior part of the extending tail tip. We show that LiCl, known to dorsalize Xenopus embryos, has the same effect in zebrafish, resulting in embryos with exaggerated dorsoanterior structures. In LiCl-treated embryos, eve1 transcripts are completely absent. eve1 is therefore a marker of ventral and posterior cells.

In the light of its ventroposterior expression domain, the localization of eve1 transcripts was analysed in spadetail (spt) and no tail (ntl), two mutants with abnormal caudal development. In sptb140 homozygous mutants, there is an accumulation of cells in the tail region, resulting from inadequate migratory behaviour of precursors to the trunk somites. These cells, in their abnormal environment, express eve1, emphasizing the correlation between ventroposterior position and eve1 expression. In homozygous mutant embryos for the gene ntl (the homologue of mouse Brachyury, originally called Zf-T), posterior structures are missing (M. E. Halpern, C. B. Kimmel, R. K. Ho and C. Walker, 1993; Cell In press). While mutant and wild-type embryos do not differ in their eve1 transcript distribution during gastrulation, eve1 expression is absent in the caudal region of mutant ntl embryos during early somitogenesis, indicating a requirement for ntl in the maintenance of eve1 expression during tail extension.

Our findings suggest that eve1 expression is correlated with a ventral and posterior cell fate, and provide first insights into its regulation.
Autosomal P[ovo
D1
] dominant female-sterile insertions in Drosophila and their use in generating germ-line chimeras
Authors: Chou Tze-Bin , Noll Elizabeth , Perrimon Norbert
Published: April 2021

The ‘dominant female-sterile’ technique used to generate germ-line mosaics in Drosophila is a powerful tool to determine the tissue specificity (germ line versus somatic) of recessive female-sterile mutations as well as to analyze the maternal effect of recessive zygotic lethal mutations. This technique requires the availability of germ-line-dependent, dominant female-sterile (DFS) mutations that block egg laying but do not affect viability. To date only one X-linked mutation, ovoD1 has been isolated that completely fulfills these criteria. Thus the ‘DFS technique’ has been largely limited to the Xchromosome. To extend this technique to the autosomes, we have cloned the ovoD1 mutation into a P-element vector and recovered fully expressed P[ovoD1] insertions on each autosomal arm. We describe the generation of these P[ovoD1] strains as well as demonstrate their use in generating germ-line chimeras. Specifically, we show that the Gap1 gene, which encodes a Drosophila homologue of mammalian GTPase-activating protein, is required in somatic follicle cells for embryonic dorsoventral polarity determination.
A model system for cell adhesion and signal transduction in Drosophila
Authors: Peifer Mark , Orsulic Sandra , Pai Li-Mei , Loureiro Joseph
Published: April 2021

Cells must cooperate and communicate to form a multicellular animal. Information about the molecules required for these processes have come from a variety of sources; the convergence between the studies of particular molecules by vertebrate cell biologists and the genes identified by scientists investigating development in Drosophila has been especially fruitful. We are interested in the connection between cadherin proteins that regulate cell-cell adhesion and the wingless/wnt-1 cell-cell signaling molecules controlling pattern formation during development. The Drosophila segment polarity gene armadillo, homolog of the vertebrate adherens junction protein |3-catenin, is required for both cell adhesion and wg signaling. We review what is known about wingless signaling in Drosophila, and discuss the role of cell-cell junctions in both cell adhesion and cell communication. We then describe the results of our preliminary structure-function analysis of Armadillo protein in both cell adhesion and wingless signaling. Finally, we discuss evidence supporting a direct role for Armadillo and adherens junction in transduction of wingless signal.
Cell fate specification in the developing Drosophila retina
Authors: Cagan Ross
Published: April 2021

The developing Drosophila retina provides an excellent experimental system in which to address questions of cell fate choice and patterning. By focusing first on a detailed morphological description of eye development and more recently on the genes required for its development, the first steps have been taken toward understanding how these two aspects combine to direct cell fate in the retinal neuroepithelium. In addition, developing cell types emerge within the ommatidium in stereotyped patterns; these patterns may provide further chics regarding the mechanisms involved in cell fate choice. Previous reviews have focused on the detailed morphological description of, and molecules involved with, retinal development. This review focuses on current progress in understanding the role of several genes that play critical roles in retinal development, with special emphasis on how they define symmetric groups of cells within each ommatidium. In addition, the role of local cell interactions in directing cell fate is assessed.