bluuebunny/crossref_metadata_2025 huggingface dataset:
The roles of cell migration and myofiber intercalation in patterning formation of the postmitotic myotome
Authors: Kahane Nitza , Cinnamon Yuval , Kalcheim Chaya
Published: April 2021

We have previously found that the postmitotic myotome is formed by two successive waves of myoblasts. A first wave of pioneer cells is generated from the dorsomedial region of epithelial somites. A second wave originates from all four edges of the dermomyotome but cells enter the myotome only from the rostral and caudal lips. We provide new evidence for the existence of these distinctive waves. We show for the first time that when the somite dissociates, pioneer myotomal progenitors migrate as mesenchymal cells from the medial side towards the rostral edge of the segment. Subsequently, they generate myofibers that elongate caudally. Pioneer myofiber differentiation then progresses in a medial-to-lateral direction with fibers reaching the lateralmost region of each segment. At later stages, pioneers participate in the formation of multinucleated fibers during secondary myogenesis by fusing with younger cells. We also demonstrate that subsequent to primary myotome formation by pioneers, growth occurs by uniform cell addition along the dorsoventral myotome. At this stage, the contributing cells arise from multiple sources as the myotome keeps growing even in the absence of the dorsomedial lip. Moreover, as opposed to suggestions that myotome growth is driven primarily and directly by the medial and lateral edges, we demonstrate that there is no direct fiber generation from the dorsomedial lip. Instead, we find that added fibers elongate from the extreme edges. Altogether, the integration between both myogenic waves results in an even pattern of dorsoventral growth of the myotome which is accounted for by progressive cell intercalation of second wave cells between preexisting pioneer fibers.
Specific ablation of the nidogen-binding site in the laminin γ1 chain interferes with kidney and lung development
Authors: Willem Michael , Miosge Nicolai , Halfter Willi , Smyth Neil , Jannetti Iris , Burghart Elke , Timpl Rupert , Mayer Ulrike
Published: April 2021

Basement membrane assembly is of crucial importance in the development and function of tissues and during embryogenesis. Nidogen 1 was thought to be central in the assembly processes, connecting the networks formed by collagen type IV and laminins, however, targeted inactivation of nidogen 1 resulted in no obvious phenotype. We have now selectively deleted the sequence coding for the 56 amino acid nidogen-binding site, γ1III4, within the Lamc1 gene by gene targeting. Here, we show that mice homozygous for the deletion die immediately after birth, showing renal agenesis and impaired lung development. These developmental defects were attributed to locally restricted ruptures in the basement membrane of the elongating Wolffian duct and of alveolar sacculi. These data demonstrate that an interaction between two basement membrane proteins is required for early kidney morphogenesis in vivo.
Characterization of a dominant negativeC. elegansTwist mutant protein with implications for human Saethre-Chotzen syndrome
Authors: Corsi Ann K. , Brodigan Thomas M. , Jorgensen Erik M. , Krause Michael
Published: April 2021

Twist is a transcription factor that is required for mesodermal cell fates in all animals studied to date. Mutations of this locus in humans have been identified as the cause of the craniofacial disorder Saethre-Chotzen syndrome. The Caenorhabditis elegans Twist homolog is required for the development of a subset of the mesoderm. A semidominant allele of the gene that codes for CeTwist, hlh-8, has defects that occur earlier in the mesodermal lineage than a previously studied null allele of the gene. The semidominant allele has a charge change (E29K) in the basic DNA-binding domain of CeTwist. Surprisingly, the mutant protein retains DNA-binding activity as both a homodimer and a heterodimer with its partner E/Daughterless (CeE/DA). However, the mutant protein blocks the activation of the promoter of a target gene. Therefore, the mutant CeTwist may cause cellular defects as a dominant negative protein by binding to target promoters as a homo- or heterodimer and then blocking transcription. Similar phenotypes as those caused by the E29K mutation were observed when amino acid substitutions in the DNA-binding domain that are associated with the human Saethre-Chotzen syndrome were engineered into the C. elegans protein. These data suggest that Saethre-Chotzen syndrome may be caused, in some cases, by dominant negative proteins, rather than by haploinsufficiency of the locus.
Fate map of the chicken neural plate at stage 4
Authors: Fernández-Garre Pedro , Rodríguez-Gallardo Lucia , Gallego-Díaz Victoria , Alvarez Ignacio S. , Puelles Luis
Published: April 2021

A detailed fate map was obtained for the early chick neural plate (stages 3d/4). Numerous overlapping plug grafts were performed upon New-cultured chick embryos, using fixable carboxyfluorescein diacetate succinimidyl ester to label donor chick tissue. The specimens were harvested 24 hours after grafting and reached in most cases stages 9-11 (early neural tube). The label was detected immunocytochemically in wholemounts, and cross-sections were later obtained. The positions of the graft-derived cells were classified first into sets of purely neural, purely non-neural and mixed grafts. Comparisons between these sets established the neural plate boundary at stages 3d/4. Further analysis categorized graft contributions to anteroposterior and dorsoventral subdivisions of the early neural tube, including data on the floor plate and the eye field. The rostral boundary of the neural plate was contained within the earliest expression domain of the Ganf gene, and the overall shape of the neural plate was contrasted and discussed with regard to the expression patterns of the genes Plato, Sox2, Otx2 and Dlx5 (and others reported in the literature) at stages 3d/4.
Cytosolic phospholipase A2α is crucial for ‘on-time’ embryo implantation that directs subsequent development
Authors: Song Haengseok , Lim Hyunjung , Paria Bibhash C. , Matsumoto Hiromichi , Swift Lany L. , Morrow Jason , Bonventre Joseph V. , Dey Sudhansu K.
Published: April 2021

Cytosolic phospholipase A2α (cPLA2α) is a major provider of arachidonic acid (AA) for the cyclooxygenase (COX) system for the biosynthesis of prostaglandins (PGs). Female mice with the null mutation for Pla2g4a (cPLA2α) produce small litters and often exhibit pregnancy failures, although the cause(s) of these defects remains elusive. We show that the initiation of implantation is temporarily deferred in Pla2g4a–/– mice, shifting the normal ‘window’ of implantation and leading to retarded feto-placental development without apparent defects in decidual growth. Furthermore, cPLA2α deficiency results in aberrant uterine spacing of embryos. The deferred implantation and deranged gestational development in Pla2g4a–/– mice were significantly improved by exogenous PG administration. The results provide evidence that cPLA2α-derived AA is important for PG synthesis required for on-time implantation. This study in Pla2g4a–/– mice, together with the results of differential blastocyst transfers in wild-type mice provides the first evidence for a novel concept that a short delay in the initial attachment reaction creates a ripple effect propagating developmental anomalies during the subsequent course of pregnancy.
Generation of different fates from multipotent muscle stem cells
Authors: Wada Michiko R. , Inagawa-Ogashiwa Masayo , Shimizu Shirabe , Yasumoto Shigeru , Hashimoto Naohiro
Published: April 2021

Although neuronal and mesenchymal stem cells exhibit multipotentiality, this property has not previously been demonstrated for muscle stem cells. We now show that muscle satellite cells of adult mice are able to differentiate into osteoblasts, adipocytes and myotubes. Undifferentiated muscle progenitor cells derived from a single satellite cell co-expressed multiple determination genes including those for MyoD and Runx2, which are specific for myogenic and osteogenic differentiation, respectively. Determination genes not relevant to the induced differentiation pathway were specifically downregulated in these cells. Similar multipotent progenitor cells were isolated from adult human muscle. Based on these observations, we propose a ‘stock options’ model for the generation of different fates from multipotent stem cells.
Disruption ofacvrl1increases endothelial cell number in zebrafish cranial vessels
Authors: Roman Beth L. , Pham Van N. , Lawson Nathan D. , Kulik Magdalena , Childs Sarah , Lekven Arne C. , Garrity Deborah M. , Moon Randall T. , Fishman Mark C. , Lechleider Robert J. , Weinstein Brant M.
Published: April 2021

The zebrafish mutant violet beauregarde (vbg) can be identified at two days post-fertilization by an abnormal circulation pattern in which most blood cells flow through a limited number of dilated cranial vessels and fail to perfuse the trunk and tail. This phenotype cannot be explained by caudal vessel abnormalities or by a defect in cranial vessel patterning, but instead stems from an increase in endothelial cell number in specific cranial vessels. We show that vbg encodes activin receptor-like kinase 1 (Acvrl1; also known as Alk1), a TGFβ type I receptor that is expressed predominantly in the endothelium of the vessels that become dilated in vbg mutants. Thus, vbg provides a model for the human autosomal dominant disorder, hereditary hemorrhagic telangiectasia type 2, in which disruption of ACVRL1 causes vessel malformations that may result in hemorrhage or stroke.

Movies available on-line
DrosophilaRhoA regulates the cytoskeleton and cell-cell adhesion in the developing epidermis
Authors: Bloor James W. , Kiehart Daniel P.
Published: April 2021

The small GTPase Rho is a molecular switch that is best known for its role in regulating the actomyosin cytoskeleton. We have investigated its role in the developing Drosophila embryonic epidermis during the process of dorsal closure. By expressing the dominant negative DRhoAN19 construct in stripes of epidermal cells, we confirm that Rho function is required for dorsal closure and demonstrate that it is necessary to maintain the integrity of the ventral epidermis. We show that defects in actin organization, nonmuscle myosin II localization, the regulation of gene transcription, DE-cadherin-based cell-cell adhesion and cell polarity underlie the effects of DRhoAN19 expression. Furthermore, we demonstrate that these changes in cell physiology have a differential effect on the epidermis that is dependent upon position in the dorsoventral axis. In the ventral epidermis, cells either lose their adhesiveness and fall out of the epidermis or undergo apoptosis. At the leading edge, cells show altered adhesive properties such that they form ectopic contacts with other DRhoAN19-expressing cells.

Movies available on-line
Pericardin, aDrosophilatype IV collagen-like protein is involved in the morphogenesis and maintenance of the heart epithelium during dorsal ectoderm closure
Authors: Chartier Aymeric , Zaffran Stéphane , Astier Martine , Sémériva Michel , Gratecos Danielle
Published: April 2021

The steps that lead to the formation of a single primitive heart tube are highly conserved in vertebrate and invertebrate embryos. Concerted migration of the two lateral cardiogenic regions of the mesoderm and endoderm (or ectoderm in invertebrates) is required for their fusion at the midline of the embryo. Morphogenetic signals are involved in this process and the extracellular matrix has been proposed to serve as a link between the two layers of cells.

Pericardin (Prc), a novel Drosophila extracellular matrix protein is a good candidate to participate in heart tube formation. The protein has the hallmarks of a type IV collagen α-chain and is mainly expressed in the pericardial cells at the onset of dorsal closure. As dorsal closure progresses, Pericardin expression becomes concentrated at the basal surface of the cardioblasts and around the pericardial cells, in close proximity to the dorsal ectoderm. Pericardin is absent from the lumen of the dorsal vessel.Genetic evidence suggests that Prc promotes the proper migration and alignment of heart cells. Df(3)vin6 embryos, as well as embryos in which prc has been silenced via RNAi, exhibit similar and significant defects in the formation of the heart epithelium. In these embryos, the heart epithelium appears disorganized during its migration to the dorsal midline. By the end of embryonic development, cardial and pericardial cells are misaligned such that small clusters of both cell types appear in the heart; these clusters of cells are associated with holes in the walls of the heart. A prc transgene can partially rescue each of these phenotypes, suggesting that prc regulates these events. Our results support, for the first time, the function of a collagen-like protein in the coordinated migration of dorsal ectoderm and heart cells.
Wingless blocks bristle formation and morphogenetic furrow progression in the eye through repression of Daughterless
Authors: Cadigan Kenneth M. , Jou Austin D. , Nusse Roel
Published: April 2021

In the developing eye, wingless activity represses proneural gene expression (and thus interommatidial bristle formation) and positions the morphogenetic furrow by blocking its initiation in the dorsal and ventral regions of the presumptive eye. We provide evidence that wingless mediates both effects, at least in part, through repression of the basic helix-loop-helix protein Daughterless. daughterless is required for high proneural gene expression and furrow progression. Ectopic expression of wingless blocks Daughterless expression in the proneural clusters. This repression, and that of furrow progression, can be mimicked by an activated form of armadillo and blocked by a dominant negative form of pangolin/TCF. Placing daughterless under the control of a heterologous promoter blocks the ability of ectopic wingless to inhibit bristle formation and furrow progression. hedgehog and decapentapleigic could not rescue the wingless furrow progression block, indicating that wingless acts downstream of these genes. In contrast, Atonal and Scute, which are thought to heterodimerize with Daughterless to promote furrow progression and bristle formation, respectively, can block ectopic wingless action. These results are summarized in a model where daughterless is a major, but probably not the only, target of wingless action in the eye.
TheIIIcalternative ofFgfr2is a positive regulator of bone formation
Authors: Eswarakumar Vereragavan P. , Monsonego-Ornan Efrat , Pines Mark , Antonopoulou Ileana , Morriss-Kay Gillian M. , Lonai Peter
Published: April 2021

Fibroblast growth factor receptor type 2 (FGFR2) plays major roles in development. Like FGFR1 and FGFR3, it exists as two splice variants, IIIb and IIIc. We have investigated in the mouse the function of FGFR2IIIc, the mesenchymal splice variant of FGFR2. Fgfr2IIIc is expressed in early mesenchymal condensates and in the periosteal collar around the cartilage models; later it is expressed in sites of both endochondral and intramembranous ossification. A translational stop codon inserted into exon 9 disrupted the synthesis of Fgfr2IIIc without influencing the localized transcription of Fgfr2IIIb, the epithelial Fgfr2 variant. The recessive phenotype of Fgfr2IIIc–/– mice was characterized initially by delayed onset of ossification, with continuing deficiency of ossification in the sphenoid region of the skull base. During subsequent stages of skeletogenesis, the balance between proliferation and differentiation was shifted towards differentiation, leading to premature loss of growth, synostosis in certain sutures of the skull base and in the coronal suture of the skull vault, with dwarfism in the long bones and axial skeleton. The retarded ossification was correlated with decrease in the localized transcription of the osteoblast markers secreted phosphoprotein 1 (Spp1) and Runx2/Cbfa1. A decrease in the domain of transcription of the chondrocyte markers Ihh and PTHrP (Pthlh) corresponded with a decrease in their transcripts in the proliferative and hypertrophic chondrocyte zones. These results suggest that Fgfr2IIIc is a positive regulator of ossification affecting mainly the osteoblast, but also the chondrocyte, lineages. This role contrasts with the negative role of Fgfr3, although recent reports implicate FGF18, a ligand for FGFR3IIIc and FGFR2IIIc, as a co-ordinator of osteogenesis via these two receptors.
Segmental relationship between somites and vertebral column in zebrafish
Authors: Morin-Kensicki Elizabeth M. , Melancon Ellie , Eisen Judith S.
Published: April 2021

The segmental heritage of all vertebrates is evident in the character of the vertebral column. And yet, the extent to which direct translation of pattern from the somitic mesoderm and de novo cell and tissue interactions pattern the vertebral column remains a fundamental, unresolved issue. The elements of vertebral column pattern under debate include both segmental pattern and anteroposterior regional specificity. Understanding how vertebral segmentation and anteroposterior positional identity are patterned requires understanding vertebral column cellular and developmental biology. In this study, we characterized alignment of somites and vertebrae, distribution of individual sclerotome progeny along the anteroposterior axis and development of the axial skeleton in zebrafish. Our clonal analysis of zebrafish sclerotome shows that anterior and posterior somite domains are not lineage-restricted compartments with respect to distribution along the anteroposterior axis but support a ‘leaky’ resegmentation in development from somite to vertebral column. Alignment of somites with vertebrae suggests that the first two somites do not contribute to the vertebral column. Characterization of vertebral column development allowed examination of the relationship between vertebral formula and expression patterns of zebrafish Hox genes. Our results support co-localization of the anterior expression boundaries of zebrafish hoxc6 homologs with a cervical/thoracic transition and also suggest Hox-independent patterning of regionally specific posterior vertebrae.
Gli2, but notGli1, is required for initial Shh signaling and ectopic activation of the Shh pathway
Authors: Bai C. Brian , Auerbach Wojtek , Lee Joon S. , Stephen Daniel , Joyner Alexandra L.
Published: April 2021

The Shh signaling pathway is required in many mammalian tissues for embryonic patterning, cell proliferation and differentiation. In addition, inappropriate activation of the pathway has been implicated in many human tumors. Based on transfection assays and gain-of-function studies in frog and mouse, the transcription factor Gli1 has been proposed to be a major mediator of Shh signaling. To address whether this is the case in mouse, we generated a Gli1 null allele expressing lacZ. Strikingly, Gli1 is not required for mouse development or viability. Of relevance, we show that all transcription of Gli1 in the nervous system and limbs is dependent on Shh and, consequently, Gli1 protein is normally not present to transduce initial Shh signaling. To determine whether Gli1 contributes to the defects seen when the Shh pathway is inappropriately activated and Gli1 transcription is induced, Gli1;Ptc double mutants were generated. We show that Gli1 is not required for the ectopic activation of the Shh signaling pathway or to the early embryonic lethal phenotype in Ptc null mutants. Of significance, we found instead that Gli2 is required for mediating some of the inappropriate Shh signaling in Ptc mutants. Our studies demonstrate that, in mammals, Gli1 is not required for Shh signaling and that Gli2 mediates inappropriate activation of the pathway due to loss of the negative regulator Ptc.
On the organisation of the regulatory region of the zebrafishdeltaDgene
Authors: Hans Stefan , Campos-Ortega José A.
Published: April 2021

deltaD is one of the four zebrafish Delta homologues presently known. Experimental evidence indicates that deltaD participates in a number of important processes during embryogenesis, including early neurogenesis and somitogenesis, whereby the protein it encodes acts as a ligand for members of the Notch receptor family. In accordance with its functional role, deltaD is transcribed in several domains of mesodermal and ectodermal origin during embryogenesis. We have analysed the organisation of the regulatory region of the deltaD gene using fusions to the reporter gene gfp and germline transgenesis. Cis-regulatory sequences are dispersed over a stretch of 12.5 kb of genomic DNA, and are organised in a similar manner to those in the regulatory region of the Delta-like 1 gene of mouse. Germline transformation using a minigene comprising 10.5 kb of this genomic DNA attached to the 3′ end of a full-length cDNA clone rescues the phenotype of embryos homozygous for the amorphic deltaD mutation after eightAR33. Several genomic regions that drive transcription in mesodermal and neuroectodermal domains have been identified. Transcription in all the neural expression domains, with one exception, is controlled by two relatively small genomic regions, which are regulated by the proneural proteins neurogenin 1 and zash1a/b acting as transcriptional activators that bind to so-called E-boxes. Transcriptional control of deltaD by proneural proteins therefore represents a molecular target for the regulatory feedback loop mediated by the Notch pathway in lateral inhibition.
A sonic hedgehog-dependent signaling relay regulates growth of diencephalic and mesencephalic primordia in the early mouse embryo
Authors: Ishibashi Makoto , McMahon Andrew P.
Published: April 2021

Sonic hedgehog (Shh) is a key signal in the specification of ventral cell identities along the length of the developing vertebrate neural tube. In the presumptive hindbrain and spinal cord, dorsal development is largely Shh independent. By contrast, we show that Shh is required for cyclin D1 expression and the subsequent growth of both ventral and dorsal regions of the diencephalon and midbrain in early somite-stage mouse embryos. We propose that a Shh-dependent signaling relay regulates proliferation and survival of dorsal cell populations in the diencephalon and midbrain. We present evidence that Fgf15 shows Shh-dependent expression in the diencephalon and may participate in this interaction, at least in part, by regulating the ability of dorsal neural precursors to respond to dorsally secreted Wnt mitogens.
Mutant alleles ofArabidopsis RADIALLY SWOLLEN 4and7reduce growth anisotropy without altering the transverse orientation of cortical microtubules or cellulose microfibrils
Authors: Wiedemeier Allison M. D. , Judy-March Jan E. , Hocart Charles H. , Wasteneys Geoffrey O. , Williamson Richard E. , Baskin Tobias I.
Published: April 2021

The anisotropic growth of plant cells depends on cell walls having anisotropic mechanical properties, which are hypothesized to arise from aligned cellulose microfibrils. To test this hypothesis and to identify genes involved in controlling plant shape, we isolated mutants in Arabidopsis thaliana in which the degree of anisotropic expansion of the root is reduced. We report here the characterization of mutants at two new loci, RADIALLY SWOLLEN 4 (RSW4) and RSW7. The radial swelling phenotype is temperature sensitive, being moderate (rsw7) or negligible (rsw4) at the permissive temperature, 19°C, and pronounced at the restrictive temperature, 30°C. After transfer to 30°C, the primary root’s elongation rate decreases and diameter increases, with all tissues swelling radially. Swelling is accompanied by ectopic cell production but swelling is not reduced when the extra cell production is eliminated chemically. A double mutant was generated, whose roots swell constitutively and more than either parent. Based on analytical determination of acid-insoluble glucose, the amount of cellulose was normal in rsw4 and slightly elevated in rsw7. The orientation of cortical microtubules was examined with immunofluorescence in whole mounts and in semi-thin plastic sections, and the orientation of microfibrils was examined with field-emission scanning electron microscopy and quantitative polarized-light microscopy. In the swollen regions of both mutants, cortical microtubules and cellulose microfibrils are neither depleted nor disoriented. Thus, oriented microtubules and microfibrils themselves are insufficient to limit radial expansion; to build a wall with high mechanical anisotropy, additional factors are required, supplied in part by RSW4 and RSW7.
Control of growth and patterning of theDrosophilawing imaginal disc by EGFR-mediated signaling
Authors: Zecca Myriam , Struhl Gary
Published: April 2021

The subdivision of the Drosophila wing imaginal disc into dorsoventral (DV) compartments and limb-body wall (wing-notum) primordia depends on Epidermal Growth Factor Receptor (EGFR) signaling, which heritably activates apterous (ap) in D compartment cells and maintains Iroquois Complex (Iro-C) gene expression in prospective notum cells. We examine the source, identity and mode of action of the EGFR ligand(s) that specify these subdivisions. Of the three known ligands for the Drosophila EGFR, only Vein (Vn), but not Spitz or Gurken, is required for wing disc development. We show that Vn activity is required specifically in the dorsoproximal region of the wing disc for ap and Iro-C gene expression. However, ectopic expression of Vn in other locations does not reorganize ap or Iro-C gene expression. Hence, Vn appears to play a permissive rather than an instructive role in organizing the DV and wing-notum segregations, implying the existance of other localized factors that control where Vn-EGFR signaling is effective. After ap is heritably activated, the level of EGFR activity declines in D compartment cells as they proliferate and move ventrally, away from the source of the instructive ligand. We present evidence that this reduction is necessary for D and V compartment cells to interact along the compartment boundary to induce signals, like Wingless (Wg), which organize the subsequent growth and differentiation of the wing primordium.
An adjunct mammary epithelial cell population in parous females: its role in functional adaptation and tissue renewal
Authors: Wagner Kay-Uwe , Boulanger Corinne A. , Henry MaLinda D. , Sgagias Magdalene , Hennighausen Lothar , Smith Gilbert H.
Published: April 2021

Mammary gland biologists have long assumed that differentiated secretory epithelial cells undergo programmed cell death at the end of lactation and that the alveolar compartment is reconstituted from undifferentiated precursor cells in subsequent pregnancies. It is generally agreed that the remodeled gland in a parous animal resembles that of a mature virgin at the morphological level. However, several physiological differences have been noted in comparing the responses of mammary epithelia from nulliparous versus parous females to hormonal stimulation and carcinogenic agents. We present genetic evidence that an involuted mammary gland is fundamentally different from a virgin gland, despite its close morphological resemblance. This difference results from the formation of a new mammary epithelial cell population that originates from differentiating cells during pregnancy. In contrast to the majority of fully committed alveolar cells, this epithelial population does not undergo cell death during involution or remodeling after lactation. We show that these cells can function as alveolar progenitors in subsequent pregnancies and that they can play an important role in functional adaptation in genetically engineered mice, which exhibit a reversion of a lactation-deficient phenotype in multiparous animals. In transplantation studies, this parity-induced epithelial population shows the capacity for self-renewal and contributes significantly to the reconstitution of the resulting mammary outgrowth (i.e. ductal morphogenesis and lobulogenesis). We propose that this parity-induced population contributes importantly to the biological differences between the mammary glands of parous and nulliparous females.
The developmental expression of vasoactive intestinal peptide (VIP) in cholinergic sympathetic neurons depends on cytokines signaling through LIFRβ-containing receptors
Authors: Duong Chi Vinh , Geissen Markus , Rohrer Hermann
Published: April 2021

Sympathetic ganglia are composed of noradrenergic and cholinergic neurons. Cholinergic sympathetic neurons are characterized by the expression of choline acetyl transferase (ChAT), vesicular acetylcholine transporter (VAChT) and the vasoactive intestinal peptide (VIP). To investigate the role of cytokine growth factor family members in the development of cholinergic sympathetic neurons, we interfered in vivo with the function of the subclass of cytokine receptors that contains LIFRβ as essential receptor subunit. Expression of LIFRβ antisense RNA interfered with LIFRβ expression and strongly reduced the developmental induction of VIP expression. By contrast, ganglion size and the number of ChAT-positive cells were not reduced. These results demonstrate a physiological role of cytokines acting through LIFRβ-containing receptors in the control of VIP expression in sympathetic neurons.
A mitogen gradient of dorsal midline Wnts organizes growth in the CNS
Authors: Megason Sean G. , McMahon Andrew P.
Published: April 2021

Cell cycle progression and exit must be precisely patterned during development to generate tissues of the correct size, shape and symmetry. Here we present evidence that dorsal-ventral growth of the developing spinal cord is regulated by a Wnt mitogen gradient. Wnt signaling through the β-catenin/TCF pathway positively regulates cell cycle progression and negatively regulates cell cycle exit of spinal neural precursors in part through transcriptional regulation of cyclin D1 and cyclin D2. Wnts expressed at the dorsal midline of the spinal cord, Wnt1 and Wnt3a, have mitogenic activity while more broadly expressed Wnts do not. We present several lines of evidence suggesting that dorsal midline Wnts form a dorsal to ventral concentration gradient. A growth gradient that correlates with the predicted gradient of mitogenic Wnts emerges as the neural tube grows with the proliferation rate highest dorsally and the differentiation rate highest ventrally. These data are rationalized in a ‘mitogen gradient model’ that explains how proliferation and differentiation can be patterned across a growing field of cells. Computer modeling demonstrates this model is a robust and self-regulating mechanism for patterning cell cycle regulation in a growing tissue.

Supplemental data available on-line
Hes6 regulates myogenic differentiation
Authors: Cossins Judy , Vernon Ann E. , Zhang Yun , Philpott Anna , Jones Philip H.
Published: April 2021

Hes6 is a basic helix-loop-helix transcription factor homologous to Drosophila Enhancer of Split (EoS) proteins. It is known to promote neural differentiation and to bind to Hes1, a related protein that is part of the Notch signalling pathway, affecting Hes1-regulated transcription. We show that Hes6 is expressed in the murine embryonic myotome and is induced on C2C12 myoblast differentiation in vitro. Hes6 binds DNA containing the Enhancer of Split E box (ESE) motif, the preferred binding site of Drosophila EoS proteins, and represses transcription of an ESE box reporter. When overexpressed in C2C12 cells, Hes6 impairs normal differentiation, causing a decrease in the induction of the cyclin-dependent kinase inhibitor, p21Cip1, and an increase in the number of cells that can be recruited back into the cell cycle after differentiation in culture. In Xenopus embryos, Hes6 is co-expressed with MyoD in early myogenic development. Microinjection of Hes6 RNA in vivo in Xenopus embryos results in an expansion of the myotome, but suppression of terminal muscle differentiation and disruption of somite formation at the tailbud stage. Analysis of Hes6 mutants indicates that the DNA-binding activity of Hes6 is not essential for its myogenic phenotype, but that protein-protein interactions are. Thus, we demonstrate a novel role for Hes6 in multiple stages of muscle formation.
Control of photoreceptor cell morphology, planar polarity and epithelial integrity duringDrosophilaeye development
Authors: Pickup Amanda T. , Lamka Michele L. , Sun Qi , Yip Man Lun R. , Lipshitz Howard D.
Published: April 2021

We report that the hindsight (hnt) gene, which encodes a nuclear zinc-finger protein, regulates cell morphology, cell fate specification, planar cell polarity and epithelial integrity during Drosophila retinal development. In the third instar larval eye imaginal disc, HNT protein expression begins in the morphogenetic furrow and is refined to cells in the developing photoreceptor cell clusters just before their determination as neurons. In hnt mutant larval eye tissue, furrow markers persist abnormally posterior to the furrow, there is a delay in specification of preclusters as cells exit the furrow, there are morphological defects in the preclusters and recruitment of cells into specific R cell fates often does not occur. Additionally, genetically mosaic ommatidia with one or more hnt mutant outer photoreceptor cells, have planar polarity defects that include achirality, reversed chirality and misrotation. Mutants in the JNK pathway act as dominant suppressors of the hnt planar polarity phenotype, suggesting that HNT functions to downregulate JUN kinase (JNK) signaling during the establishment of ommatidial planar polarity. HNT expression continues in the photoreceptor cells of the pupal retina. When an ommatidium contains four or more hnt mutant photoreceptor cells, both genetically mutant and genetically wild-type photoreceptor cells fall out of the retinal epithelium, indicating a role for HNT in maintenance of epithelial integrity. In the late pupal stages, HNT regulates the morphogenesis of rhabdomeres within individual photoreceptor cells and the separation of the rhabdomeres of adjacent photoreceptor cells. Apical F-actin is depleted in hnt mutant photoreceptor cells before the observed defects in cellular morphogenesis and epithelial integrity. The analyses presented here, together with our previous studies in the embryonic amnioserosa and tracheal system, show that HNT has a general role in regulation of the F-actin-based cytoskeleton, JNK signaling, cell morphology and epithelial integrity during development.
Some effects of de-afferentation on the developing amphibian nervous system
Authors: Hughes Arthur
Published: April 2021

An adult anuran can still walk or swim if the nerves supplying one or even two limbs are de-afferentated (Gray, 1950). However, in a developing amphibian, a limb at motile stages becomes paralysed when deprived of its sensory input. A sequence of degenerative changes then follow in the cord and in peripheral nerves.
The maturation of cortisone-treated embryonic duodenumin vitro. I. The villus
Authors: Hayes Raymond L.
Published: April 2021

Mitotic expansion of the mucosa coupled with contraction of intrinsic longitudinal and circular muscle fibers produces previllous ridges on the luminal surface of the embryonic chick duodenum by the thirteenth day of incubation. Subsequently, remodelling by periodic indentation of the mucosal surface yields primitive villi which expand and elongate to form the tall, finger-like projections characterizing the absorptive surface of the mature duodenum (Hilton, 1902; Pap, 1933; Coulombre & Coulombre, 1958).
La régression du mésonéphros chez l’embryon de poulet
Authors: Salzgeber Berthe , Weber Rudolf
Published: April 2021

The regression of the mesonephros in the chick embryo: a study of acid phosphatase and cathepsin activity analysed biochemically, histochemically, and by electron microscopy

Cathepsin and acid phosphatase activity and total nitrogen were determined in homogenates of mesonephros during growth (at 14 days) and regression (at 21 days). The loss of total nitrogen in this period is as much as 62%. Specific cathepsin activity, expressed as μg casein destroyed per hour per μg total nitrogen, does not change much. The increase of 19·4% observed was not significant. Specific acid phosphatase activity, expressed as 10−3μM phosphate liberated per hour per μg of total nitrogen, increases appreciably during regression. The increase between the 14th and 21st day of incubation is by 114·4%. The absolute levels of cathepsin and acid phosphatase activity are reduced during mesonephric regression by 57·6 % and 24·7 % respectively. Fractionation showed that these enzymes were solubilized during mesonephric regression. The soluble component increased by 28·4% in the case of cathepsin and by 44% in the case of acid phosphatase. Histochemical preparations for acid phosphatase and for non-specific esterases showed that these enzymes were most abundant in the apical part of the cells of the proximal tubules (secretory region with brush border). During regression, the intensity of the acid phosphatase reaction increased and large granules appear in the cells of the tubules, while the connective tissue shows cells with inclusions which could be macrophages. Electron microscopy revealed important changes in the cells of the secretory tubules during regression. On the one hand mitochondria degenerate while on the other hand cytoplasmic inclusions appear, among which are dense membranous bodies reacting positively for acid phosphatase. Mesonephric regression is compared with that of other larval and embryonic organs and its mechanism is discussed.
DNA synthesis and cell proliferation during the formation of deciduomata in mice
Authors: Zhinkin L. N. , Samoshkina N. A.
Published: April 2021

After ovulation and fertilization of the ovum, several typical changes occur in the uterus of pregnant mammals that are related to the implantation of the blastocyst. The formation of a deciduoma, in which endometrial cells are transformed to decidual ones, is one of these changes (Shelesnyak, 1957, 1960). Apart from an interplay of hormones the formation of a deciduoma is determined by local effects. Loeb (1907) was the first to show this by traumatizing the uterine wall. Since then the role played by hormones, histamine and other agents in the production of deciduomata has been intensively studied (Rigler & Rosenkranz, 1955; Rosenkranz & Rigler, 1958; Shelesnyak, 1959a, b, c; and many others.)
ATP level and respiration of embryos
Authors: Zotin A. I. , Faustov V. S. , Radzinskaja L. I. , Ozernyuk N. D.
Published: April 2021

A considerable increase in the rate of oxygen consumption is known to occur during the development of embryos (cf. Needham, 1931; Tuft, 1953; Brachet, 1960; Gustafson, 1965). However, the mechanism of the increase in respiration during embryonic development is still unclear. A certain correlation seems to exist between DNA synthesis and the respiration of embryos (Comita & Whiteleley, 1953; Brachet, 1960). According to Commoner (1964), this correlation is determined by a change in the level of free nucleotides in cells when the rate of DNA synthesis changes. Free nucleotides control cell metabolism, oxidative processes in particular. The ADP+P/ATP ratio is known to control the rate and direction of electron transfer in the respiratory chain (Chance & Hagihara, 1961 ; Klingenberg & Schollmeyer, 1961). The ADP/ATP system is suggested to control the rate of oxidative metabolism in fertilization (Monroy, 1965 a, b;Zotin, Milman & Faustov, 1967).
The tyrosinases of Fundulus heteroclitus at different stages of embryonic development
Authors: Spitz Leslie M. , Burnett Jean B.
Published: April 2021

The study described here was undertaken in an effort to determine whether multiple forms of tyrosinase (EC 1.10.3.1) are present in Fundulus heteroclitus during embryonic development. If they are present, do they appear simultaneously in the course of development and do they continue to be produced and maintained without change during the part of the life cycle when tyrosinase should normally be active? Multiple forms of tyrosinase have been found in Neurospora crassa (Sussman, 1961; Fox & Burnett, 1962; Fling, Horowitz & Heinemann, 1963), mushroom (Smith & Kruger, 1962; Bouchilloux, McMahill & Mason, 1963; Jolley & Mason, 1965), potato (Patil & Zucker, 1965), Drosophila melanogaster (Lewis & Lewis, 1963; Mitchell & Weber, 1965), the eggs of Rana pipiens (Turney, 1964), goldfish (Kim & Tchen, 1962; Kim, Tchen & Chavin, 1962), hamster melanoma (Pomerantz, 1963, 1966) and mouse melanoma (Shimao, 1962; Burnett, Seiler & Brown, 1967). By using a variety of physical and chemical techniques to isolate the tyrosinases present in various organisms and organs, the investigators cited above have been able to establish numerous specific characteristics of the enzymes. Their published data suggest that in both plants and animals there may be variation in the chemical and physical characteristics of individual, enzymically active tyrosinase molecules. Experiments have not yet revealed, however, the metabolic or functional significance of the various forms of an enzyme within a single system. Since the presence of multiple forms of tyrosinase within a single system seems to be universal, it was anticipated from the outset that multiple forms of tyrosinase would be found in the embryos of Fundulus heteroclitus.
Rôle de la compétition osseuse dans la forme des os du toit cranien des Urodèles
Authors: Corsin Par Jacqueline
Published: April 2021

Dès 1932, Troitsky chez les Mammifères, puis, en 1934 Tatarko chez les Téléostéens, ont cherché à étudier les problèmes de compétition osseuse.
Observations sur la différenciation in vitro descellules myéloïdes d’embryons de poulet
Authors: Salvatorelli Germano , Callegarini Carlo , Gulinati Anna Maria , Gardenghi Giuseppe
Published: April 2021

Observations on the differentiation in vitro of erythropoietic cellsof the chick embryo

Erythrocytes differentiated fromexplantsof bone marrow cultured in association with embryonic chick liver by the technique of Wolff & Haffen show certain morphological and biochemical differences from those found in peripheral blood or normal bone marrow. The mean values of cell size and N/P ratio of the erythrocytes from explants are different from those of controls of corresponding age. The globin and haem content of erythrocytes fromexplantsis less than that of controls. The presence of small quantities of RNA in the cytoplasm of expiant erythrocytes is probably related to a retarded maturation process. Haemoglobin synthesised in vitro shows the same electrophoretic behaviour as that of in vivo controls.
Studies on the DNA of Xenopus laevis oocytes
Authors: Hanocq-Quertier J. , Baltus E. , Ficq A. , Brachet J.
Published: April 2021

The existence of substantial amounts of deoxyribonucleic acid (DNA) in the cytoplasm of amphibian eggs is no longer a matter of discussion (review, Brachet, 1957). However, their intracellular distribution, role and origin remain controversial.
Etude autoradiographique du muscle strié en régénération in vivo
Authors: Reznik M.
Published: April 2021

La régénération du muscle strié squelettique est assurée par des éléments plurinucléés qui se différencient ultérieurement en fibres plus ou moins normales. Ces structures plurinucléées peuvent affecter différentes formes. Le plus souvent, ce sont des éléments allongés contenant de nombreux noyaux disposés en file au centre d’un sarcoplasme basophile. On leur a donné des noms divers: myotubes, ‘Muskelschlâuche’, rubans musculaires. D’autres fois, des renflements massués plurinucléés se développent à l’extrémité de fibres indemnes ou de myotubes: ce sont les ‘bourgeons musculaires’. On donne le nom de ‘sarco-blastes ‘à l’ensemble des structures plurinucléées qui constituent un stade intermédiaire dans la régénération des fibres striées adultes.
The evolution of cell lineage in nematodes
Authors: Sommer Ralf J. , Carta Lynn K. , Sternberg Paul W.
Published: April 2021

The invariant development of free-living nematodes combined with the extensive knowledge of Caenorhabditis elegans developmental biology provides an experimental system for an analysis of the evolution of developmental mechanisms. We have collected a number of new nematode species from soil samples. Most are easily cultured and their development can be analyzed at the level of individual cells using techniques standard to Caenorhabditis. So far, we have focused on differences in the development of the vulva among species of the families Rhabditidae and Panagrolaimidae. Preceding vulval development, twelve Pn cells migrate into the ventral cord and divide to produce posterior daughters [Pn.p cells] whose fates vary in a position specific manner [from Pl.p anterior to P12.p posterior]. In C. elegans hermaphrodites, P(3-8).p are tripotent and form an equivalence group. These cells can express either of two vulval fates (1° or 2°) in response to a signal from the anchor cell of the somatic gonad, or a non-vulval fate (3°), resulting in a 3°-3°-2°-Io-2°-3° pattern of cell fates. Evolutionary differences in vulval development include the number of cells in the vulval equivalence group, the number of 1° cells, the number of progeny generated by each vulval precursor cell, and the position of VPCs before morphogenesis. Examples of three Rhabditidae genera have a posterior vulva in the position of P9-P11 ectoblasts. In Cruznema tripartitum, P(5-7).p form the vulva as in Caenorhabditis, but they migrate posteriorly before dividing. Induction occurs after the gonad grows posteriorly to the position of P(5-7).p cells. In two other species, Mesorhabditis sp. PS 1179 and Teratorhabditis palmarum, we have found changes in induction and competence with respect to their presumably more C. elegans-\Wse ancestor. In Mesorhabditis, P(5-7).p form the vulva after migrating to a posterior position. However, the gonad is not required to specify the pattern of cell fates 3°-20-l°-2°-3°. Moreover, the Pn.p cells are not equivalent in their potentials to form the vulva. A regulatory constraint in this family thus forces the same set of precursors to generate the vulva, rather than more appropriately positioned Pn.p cells.
Determination in the Cranial Neural Crest of the Axolotl
Authors: Newth D. R.
Published: April 2021

The neural folds of the Axolotl neurula transplanted homoplastically from the branchial region to the trunk give rise to cartilage in only a small proportion of cases, even where the grafts are allowed to live for very considerable periods. It is concluded that the determination of the skeletogenous component of the neural crest of the young neurula has proceeded some way, but that its cells are not yet rigidly bound to their presumptive fate.
The Effect of Environmental Factors on the Differentiation of the Allantoic Endoderm in Organ Culture
Authors: Fell Honor B.
Published: April 2021

When the allantoic sac of the 4-day embryonic chick was grown as an organ culture in vitro, the endoderm showed great variation in its histological structure. The intact sac formed a closed vesicle lined by columnar epithelium containing many mucus-secreting goblet cells. When everted and grown in a stiff clot, the endoderm formed a tall columnar epithelium with few or no goblet cells. In a soft clot the everted sac became cystic and distended; the endoderm then resembled that of the normal chorio-allantoic membrane. In places the everted endoderm formed papillomatous, secreting outgrowths in both stiff and soft medium. It is suggested that these histological variations represent ‘modulations’ of the endoderm (Weiss).