bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of cell polarity, radial intercalation and epiboly inXenopus: novel roles for integrin and fibronectin
Authors: Marsden Mungo , DeSimone Douglas W.
Published: April 2021

Fibronectin (FN) is reported to be important for early morphogenetic movements in a variety of vertebrate embryos, but the cellular basis for this requirement is unclear. We have used confocal and digital time-lapse microscopy to analyze cell behaviors in Xenopus gastrulae injected with monoclonal antibodies directed against the central cell-binding domain of fibronectin. Among the defects observed is a disruption of fibronectin matrix assembly, resulting in a failure of radial intercalation movements, which are required for blastocoel roof thinning and epiboly. We identified two phases of FN-dependent cellular rearrangements in the blastocoel roof. The first involves maintenance of early roof thinning in the animal cap, and the second is required for the initiation of radial intercalation movements in the marginal zone. A novel explant system was used to establish that radial intercalation in the blastocoel roof requires integrin-dependent contact of deep cells with fibronectin. Deep cell adhesion to fibronectin is sufficient to initiate intercalation behavior in cell layers some distance from the substrate. Expression of a dominant-negative β1 integrin construct in embryos results in localized depletion of the fibronectin matrix and thickening of the blastocoel roof. Lack of fibronectin fibrils in vivo is correlated with blastocoel roof thickening and a loss of deep cell polarity. The integrin-dependent binding of deep cells to fibronectin is sufficient to drive membrane localization of Dishevelled-GFP, suggesting that a convergence of integrin and Wnt signaling pathways acts to regulate radial intercalation in Xenopus embryos.
Steroidogenic factor 1 (SF1) is essential for pituitary gonadotrope function
Authors: Zhao Liping , Bakke Marit , Krimkevich Yelena , Cushman Lisa J. , Parlow A. F. , Camper Sally A. , Parker Keith L.
Published: April 2021

Knockout mice lacking the orphan nuclear receptor steroidogenic factor 1 (SF1) exhibit a complex endocrine phenotype that includes adrenal and gonadal agenesis, impaired expression of pituitary gonadotropins, and absence of the ventromedial hypothalamic nucleus (VMH). These multiple defects complicate efforts to delineate primary versus secondary effects of SF1 deficiency in different tissues, such that its direct role in gonadotropes remains uncertain. To define this role, we have expressed Cre recombinase driven by the promoter region of the common α subunit of glycoprotein hormones (αGSU), thereby inactivating a loxP-modified SF1 locus in the anterior pituitary gland. Although pituitary-specific SF1 knockout mice were fully viable, they were sterile and failed to develop normal secondary sexual characteristics.

Their adrenal glands and VMH appeared normal histologically, but their testes and ovaries were severely hypoplastic. αGSU-Cre, loxP mice had normal levels of most pituitary hormones, but had markedly decreased expression of LH and FSH. Treatment with exogenous gonadotropins stimulated gonadal steroidogenesis, inducing germ cell maturation in males and follicular and uterine maturation in females – establishing that the gonads can respond to gonadotropins. The pituitary-specific SF1 knockout mice are a novel genetic model of hypogonadotropic hypogonadism that establishes essential role(s) of SF1 in pituitary gonadotropes.
Hindgut visceral mesoderm requires an ectodermal template for normal development inDrosophila
Authors: Martin Beatriz San , Bate Michael
Published: April 2021

During Drosophila embryogenesis, the development of the midgut endoderm depends on interactions with the overlying visceral mesoderm. Here we show that the development of the hindgut also depends on cellular interactions, in this case between the inner ectoderm and outer visceral mesoderm. In this section of the gut, the ectoderm is essential for the proper specification and differentiation of the mesoderm, whereas the mesoderm is not required for the normal development of the ectoderm. Wingless and the fibroblast growth factor receptor Heartless act over sequential but interdependent phases of hindgut visceral mesoderm development. Wingless is required to establish the primordium and to enhance Heartless expression. Later, Heartless is required to promote the proper differentiation of the hindgut visceral mesoderm itself.
The EGF receptor and N signalling pathways act antagonistically in Drosophila mesothorax bristle patterning
Authors: Culí Joaquim , Martín-Blanco Enrique , Modolell Juan
Published: April 2021

An early step in the development of the large mesothoracic bristles (macrochaetae) of Drosophila is the expression of the proneural genes of the achaete-scute complex (AS-C) in small groups of cells (proneural clusters) of the wing imaginal disc. This is followed by a much increased accumulation of AS-C proneural proteins in the cell that will give rise to the sensory organ, the SMC (sensory organ mother cell). This accumulation is driven by cis-regulatory sequences, SMC-specific enhancers, that permit self- stimulation of the achaete, scute and asense proneural genes. Negative interactions among the cells of the cluster, triggered by the proneural proteins and mediated by the Notch receptor (lateral inhibition), block this accumulation in most cluster cells, thereby limiting the number of SMCs. Here we show that the proneural proteins trigger, in addition, positive interactions among cells of the cluster that are mediated by the Epidermal growth factor receptor (EGFR) and the Ras/Raf pathway. These interactions, which we denominate ‘lateral co-operation’, are essential for macrochaetae SMC emergence. Activation of the EGFR/Ras pathway appears to promote proneural gene self-stimulation mediated by the SMC-specific enhancers. Excess EGFR signalling can overrule lateral inhibition and allow adjacent cells to become SMCs and sensory organs. Thus, the EGFR and Notch pathways act antagonistically in notum macrochaetae determination.
RET signaling is essential for migration, axonal growth and axon guidance of developing sympathetic neurons
Authors: Enomoto Hideki , Crawford Peter A. , Gorodinsky Alexander , Heuckeroth Robert O. , Johnson Eugene M. , Milbrandt Jeffrey
Published: April 2021

Sympathetic axons use blood vessels as an intermediate path to reach their final target tissues. The initial contact between differentiating sympathetic neurons and blood vessels occurs following the primary sympathetic chain formation, where precursors of sympathetic neurons migrate and project axons along or toward blood vessels. We demonstrate that, in Ret-deficient mice, neuronal precursors throughout the entire sympathetic nervous system fail to migrate and project axons properly. These primary deficits lead to mis-routing of sympathetic nerve trunks and accelerated cell death of sympathetic neurons later in development. Artemin is expressed in blood vessels during periods of early sympathetic differentiation, and can promote and attract axonal growth of the sympathetic ganglion in vitro. This analysis identifies RET and artemin as central regulators of early sympathetic innervation.
Tramtrack controls glial number and identity in theDrosophilaembryonic CNS
Authors: Badenhorst Paul
Published: April 2021

Neurons and glia are often derived from common multipotent stem cells. In Drosophila, neural identity appears to be the default fate of these precursors. Stem cells that generate either neurons or glia transiently express neural stem cell-specific markers. Further development as glia requires the activation of glial-specific regulators. However, this must be accompanied by simultaneous repression of the alternate neural fate. I show that the Drosophila transcriptional repressor Tramtrack is a key repressor of neuronal fates. It is expressed at high levels in all mature glia of the embryonic central nervous system. Analysis of the temporal profile of Tramtrack expression in glia shows that it follows that of existing glial markers. When expressed ectopically before neural stem cell formation, Tramtrack represses the neural stem cell-specific genes asense and deadpan. Surprisingly, Tramtrack protein levels oscillate in a cell cycle-dependent manner in proliferating glia, with expression dropping before replication, but re-initiating after S phase. Overexpression of Tramtrack blocks glial development by inhibiting S-phase and repressing expression of the S-phase cyclin, cyclin E. Conversely, in tramtrack mutant embryos, glia are disrupted and undergo additional rounds of replication. I propose that Tramtrack ensures stable mature glial identity by both repressing neuroblast-specific genes and controlling glial cell proliferation.
A morphogen gradient of Wnt/β-catenin signalling regulates anteroposterior neural patterning inXenopus
Authors: Kiecker Clemens , Niehrs Christof
Published: April 2021

Anteroposterior (AP) patterning of the vertebrate neural plate is initiated during gastrulation and is regulated by Spemann’s organizer and its derivatives. The prevailing model for AP patterning predicts a caudally increasing gradient of a ‘transformer’ which posteriorizes anteriorly specified neural cells. However, the molecular identity of the transforming gradient has remained elusive. We show that in Xenopus embryos (1) dose-dependent Wnt signalling is both necessary and sufficient for AP patterning of the neuraxis, (2) Wnt/β-catenin signalling occurs in a direct and long-range fashion within the ectoderm, and (3) that there is an endogenous AP gradient of Wnt/β-catenin signalling in the presumptive neural plate of the Xenopus gastrula. Our results indicate that an activity gradient of Wnt/β-catenin signalling acts as transforming morphogen to pattern the Xenopus central nervous system.
Characterization ofDrosophila hibris, a gene related to human nephrin
Authors: Dworak Heather A. , Charles Michael A. , Pellerano Lidia B. , Sink Helen
Published: April 2021

Hibris encodes a protein that is a newly identified member of the immunoglobulin superfamily and has homology to vertebrate Nephrins and Drosophila Sticks-and-Stones. The Hibris protein has eight Ig-like domains, a fibronectin domain and a 160 amino acid cytoplasmic tail. The hibris transcript is expressed in a broad range of tissues and across life stages. In the embryo, hibris transcript is present in the mesectoderm, then in a group of cells at the developing CNS midline and in a subset of glia. In the periphery, hibris is expressed by fusion competent myoblasts and the epidermal muscle attachment site cells. Deletion analyses show that loss of hibris does not visibly affect embryonic CNS or somatic muscle development. However overexpressing hibris in the somatic mesoderm disrupts myoblast fusion. Furthermore, when overexpressed in the epidermis, Hibris causes comprehensive derangement of muscle insertion locations. A similar myoblast fusion defect is observed when the Drosophila homologs of DM-GRASP/BEN/SC1 (irregular chiasm-roughest and dumbfounded) are deleted together. Our S2 cell aggregation assays have revealed a heterotypic interaction between Hibris and Dumbfounded, but not between Hibris and Irregular Chiasm-Roughest. We propose that Hibris is an extracellular partner for Dumbfounded and potentially mediates the response of myoblasts to this attractant.
Groucho mediates a Ci-independent mechanism ofhedgehogrepression in the anterior wing pouch
Authors: Apidianakis Yiorgos , Grbavec Diane , Stifani Stefano , Delidakis Christos
Published: April 2021

Groucho (Gro) is the founding member of a family of transcriptional co-repressors that are recruited by a number of different transcription factors. Drosophila has a single gro gene, whose loss of function affects processes ranging from sex determination to embryonic patterning and neuroblast specification. We have characterized a function of Gro in imaginal development, namely the repression of hedgehog (hh) in anterior wing pouch cells. hh encodes a secreted morphogen with potent patterning activities. In Drosophila thoracic appendages (legs, wings, halteres), hh is expressed in posterior compartments and induces the anteroposterior (AP) pattern organizer in the cells across the AP boundary. hh is repressed in anterior compartments at least partly via Ci[rep], a form of the multifunctional transcription factor Cubitus interruptus (Ci). We show that cells in the wing primordium close to the AP boundary need gro activity to maintain repression of hh transcription, whereas in more anterior cells gro is dispensable. This repressive function of Gro does not appear to be mediated by Ci[rep]. Analysis of mutant gro transgenes has revealed that the Q and WD40 domains are both necessary for hh repression. Yet, deletion of the WD40 repeats does not always abolish Gro activity. Our findings provide new insights both into the mechanisms of AP patterning of the wing and into the function of Gro.
EphA4/ephrin-A5 interactions in muscle precursor cell migration in the avian forelimb
Authors: Swartz Mary E. , Eberhart Johann , Pasquale Elena B. , Krull Catherine E.
Published: April 2021

Limb muscles derive from muscle precursor cells that lie initially in the lateral portion of the somitic dermomyotome and subsequently migrate to their target limb regions, where muscle-specific gene transcription is initiated. Although several molecules that control the generation and delamination of muscle precursor cells have been identified, little is known about the mechanisms that guide muscle precursor cell migration in the limb. We have examined the distribution of members of the Eph family during muscle precursor cell development. The EphA4 receptor tyrosine kinase and its ligand, ephrin-A5, are expressed by muscle precursor cells and forelimb mesoderm in unique spatiotemporal patterns during the period when muscle precursors delaminate from the dermomyotome and migrate into the limb. To test the function of EphA4/ephrin-A5 interactions in muscle precursor migration, we used targeted in ovo electroporation to express ephrin-A5 ectopically specifically in the presumptive limb mesoderm. In the presence of ectopic ephrin-A5, Pax7-positive muscle precursor cells are significantly reduced in number in the proximal limb, compared with controls, and congregate abnormally near the lateral dermomyotome. In stripe assays, isolated muscle precursor cells avoid substrate-bound ephrin-A5 and this avoidance is abolished by addition of soluble ephrin-A5. These data suggest that ephrin-A5 normally restricts migrating, EphA4-positive muscle precursor cells to their appropriate territories in the forelimb, disallowing entry into abnormal embryonic regions.
Dpp and Hh signaling in theDrosophilaembryonic eye field
Authors: Chang Ting , Mazotta Julie , Dumstrei Karin , Dumitrescu Andra , Hartenstein Volker
Published: April 2021

We have analyzed the function of the Decapentaplegic (Dpp) and Hedgehog (Hh) signaling pathways in partitioning the dorsal head neurectoderm of the Drosophila embryo. This region, referred to as the anterior brain/eye anlage, gives rise to both the visual system and the protocerebrum. The anlage splits up into three main domains: the head midline ectoderm, protocerebral neurectoderm and visual primordium. Similar to their vertebrate counterparts, Hh and Dpp play an important role in the partitioning of the anterior brain/eye anlage. Dpp is secreted in the dorsal midline of the head. Lowering Dpp levels (in dpp heterozygotes or hypomorphic alleles) results in a ‘cyclops’ phenotype, where mid-dorsal head epidermis is transformed into dorsolateral structures, i.e. eye/optic lobe tissue, which causes a continuous visual primordium across the dorsal midline. Absence of Dpp results in the transformation of both dorsomedial and dorsolateral structures into brain neuroblasts. Regulatory genes that are required for eye/optic lobe fate, including sine oculis (so) and eyes absent (eya), are turned on in their respective domains by Dpp. The gene zerknuellt (zen), which is expressed in response to peak levels of Dpp in the dorsal midline, secondarily represses so and eya in the dorsomedial domain. Hh and its receptor/inhibitor, Patched (Ptc), are expressed in a transverse stripe along the posterior boundary of the eye field. As reported previously, Hh triggers the expression of determinants for larval eye (atonal) and adult eye (eyeless) in those cells of the eye field that are close to the Hh source. Eya and So, which are induced by Dpp, are epistatic to the Hh signal. Loss of Ptc, as well as overexpression of Hh, results in the ectopic induction of larval eye tissue in the dorsal midline (cyclopia). We discuss the similarities between vertebrate systems and Drosophila with regard to the fate map of the anterior brain/eye anlage, and its partitioning by Dpp and Hh signaling.
Notch-Delta signaling induces a transition from mitotic cell cycle to endocycle inDrosophilafollicle cells
Authors: Deng Wu-Min , Althauser Cassandra , Ruohola-Baker Hannele
Published: April 2021

In many developmental processes, polyploid cells are generated by a variation of the normal cell cycle called the endocycle in which cells increase their genomic content without dividing. How the transition from the normal mitotic cycle to endocycle is regulated is poorly understood. We show that the transition from mitotic cycle to endocycle in the Drosophila follicle cell epithelium is regulated by the Notch pathway. Loss of Notch function in follicle cells or its ligand Delta function in the underlying germline disrupts the normal transition of the follicle cells from mitotic cycle to endocycle, mitotic cycling continues, leading to overproliferation of these cells. The regulation is at the transcriptional level, as Su(H), a downstream transcription factor in the pathway, is also required cell autonomously in follicle cells for proper transitioning to the endocycle. One target of Notch and Su(H) is likely to be the G2/M cell cycle regulator String, a phosphatase that activates Cdc2 by dephosphorylation. String is normally repressed in the follicle cells just before the endocycle transition, but is expressed when Notch is inactivated. Analysis of the activity of String enhancer elements in follicle cells reveals the presence of an element that promotes expression of String until just before the onset of polyploidy in wild-type follicle cells but well beyond this stage in Notch mutant follicle cells. This suggests that it may be the target of the endocycle promoting activity of the Notch pathway. A second element that is insensitive to Notch regulation promotes String expression earlier in follicle cell development, which explains why Notch, while active at both stages, represses String only at the mitotic cycle-endocycle transition.
Dual function of polysialic acid during zebrafish central nervous system development
Authors: Marx Monika , Rutishauser Urs , Bastmeyer Martin
Published: April 2021

Polysialic acid (PSA), a carbohydrate epitope attached to the neural cell adhesion molecule, serves as a modulator of axonal interactions during vertebrate nervous system development. We have used PSA-specific antibodies and whole-mount immunocytochemistry to describe the spatiotemporal expression pattern of PSA during zebrafish central nervous system development. PSA is transiently expressed on all cell bodies and, except for the posterior commissure, it is not found on axons. Floorplate cells in the spinal cord and hindbrain strongly express PSA throughout development. Enzymatic removal of PSA leads to a defasciculated growth pattern of the posterior commissure and also affects distinct subsets of commissural axons in the hindbrain, which fail to cross the midline. Whereas the disordered growth pattern of hindbrain commissures produced by PSA-removal could be mimicked by injections of soluble PSA, the growth of axons in the posterior commissure was unaffected by such treatment. These results suggest that there are distinct mechanisms for PSA action during axon growth and pathfinding in the developing zebrafish CNS.
Genetic manipulation of hedgehog signaling in the endochondral skeleton reveals a direct role in the regulation of chondrocyte proliferation
Authors: Long Fanxin , Zhang Xiaoyan M. , Karp Seth , Yang Yingzi , McMahon Andrew P.
Published: April 2021

Indian hedgehog (Ihh), one of the three mammalian hedgehog (Hh) proteins, coordinates proliferation and differentiation of chondrocytes during endochondral bone development. Smoothened (Smo) is a transmembrane protein that transduces all Hh signals. In order to discern the direct versus indirect roles of Ihh in cartilage development, we have used the Cre-loxP approach to remove Smo activity specifically in chondrocytes. Animals generated by this means develop shorter long bones when compared to wild-type littermates. In contrast to Ihh mutants (Ihhn/Ihhn), chondrocyte differentiation proceeds normally. However, like Ihhn/Ihhn mice, proliferation of chondrocytes is reduced by about 50%, supporting a direct role for Ihh in the regulation of chondrocyte proliferation. Moreover, by overexpressing either Ihh or a constitutively active Smo allele (Smo*) specifically in the cartilage using the bigenic UAS-Gal4 system, we demonstrate that activation of the Ihh signaling pathway is sufficient to promote chondrocyte proliferation. Finally, expression of cyclin D1 is markedly downregulated when either Ihh or Smo activity is removed from chondrocytes, indicating that Ihh regulates chondrocyte proliferation at least in part by modulating the transcription of cyclin D1. Taken together, the present study establishes Ihh as a key mitogen in the endochondral skeleton.
The transcription factor neurogenin 2 restricts cell migration from the cortex to the striatum
Authors: Chapouton Prisca , Schuurmans Carol , Guillemot François , Götz Magdalena
Published: April 2021

The dorsal and ventral domains of the telencephalon are delineated by a unique boundary structure that restricts the migration of dorsal and ventral cells to a different extent. While many cells invade the dorsal cortex from the ventral ganglionic eminence (GE), hardly any cortical cells cross the boundary into the GE. Several molecules have been implicated in the regulation of ventral to dorsal cell migration, but so far nothing is known about the molecular mechanisms restricting cortical cell migration in vivo. Here we show that in the absence of the transcription factor neurogenin 2, cells from the cortex migrate into the GE in vitro and in vivo as detected in transgenic mice containing a lacZ gene in the neurogenin 2 locus. In contrast, the migration of cells from the GE is not affected. Molecular and cellular analysis of the cortico-striatal boundary revealed that neurogenin 2 regulates the fasciculation of the cortico-striatal boundary which may explain the non cell-autonomous nature of the migration defect as detected by in vitro transplantation. Taken together, these results show that distinct cues located in the cortico-striatal boundary restrict cells in the dorsal and ventral telencephalon.
The Hox gene Abdominal-B antagonizes appendage development in the genital disc of Drosophila
Authors: Estrada Beatriz , Sánchez-Herrero Ernesto
Published: April 2021

In Drosophila, the Hox gene Abdominal-B is required to specify the posterior abdomen and the genitalia. Homologues of Abdominal-B in other species are also needed to determine the posterior part of the body. We have studied the function of Abdominal-B in the formation of Drosophila genitalia, and show here that absence of Abdominal-B in the genital disc of Drosophila transforms male and female genitalia into leg or, less frequently, into antenna. These transformations are accompanied by the ectopic expression of genes such as Distal-less or dachshund, which are normally required in these appendages. The extent of wild-type and ectopic Distal-less expression depends on the antagonistic activities of the Abdominal-B gene, as a repressor, and of the decapentaplegic and wingless genes as activators. Absence of Abdominal-B also changes the expression of Homothorax, a Hox gene co-factor. Our results suggest that Abdominal-B forms genitalia by modifying an underlying positional information and repressing appendage development. We propose that the genital primordia should be subdivided into two regions, one of them competent to be transformed into an appendage in the absence of Abdominal-B.
Distinct cortical migrations from the medial and lateral ganglionic eminences
Authors: Anderson Stewart A. , Marín Oscar , Horn Carrie , Jennings Kelly , Rubenstein John L. R.
Published: April 2021

Recent evidence suggests that projection neurons and interneurons of the cerebral cortex are generally derived from distinct proliferative zones. Cortical projection neurons originate from the cortical ventricular zone (VZ), and then migrate radially into the cortical mantle, whereas most cortical interneurons originate from the basal telencephalon and migrate tangentially into the developing cortex. Previous studies using methods that label both proliferative and postmitotic cells have found that cortical interneurons migrate from two major subdivisions of the developing basal telencephalon: the medial and lateral ganglionic eminences (MGE and LGE). Since these studies labeled cells by methods that do not distinguish between the proliferating cells and those that may have originated elsewhere, we have studied the contribution of the MGE and LGE to cortical interneurons using fate mapping and genetic methods. Transplantation of BrdU-labeled MGE or LGE neuroepithelium into the basal telencephalon of unlabeled telencephalic slices enabled us to follow the fate of neurons derived from each of these primordia. We have determined that early in neurogenesis GABA-expressing cells from the MGE tangentially migrate into the cerebral cortex, primarily via the intermediate zone, whereas cells from the LGE do not. Later in neurogenesis, LGE-derived cells also migrate into the cortex, although this migration occurs primarily through the subventricular zone. Some of these LGE-derived cells invade the cortical plate and express GABA, while others remain within the cortical proliferative zone and appear to become mitotically active late in gestation. In addition, by comparing the phenotypes of mouse mutants with differential effects on MGE and LGE migration, we provide evidence that the MGE and LGE may give rise to different subtypes of cortical interneurons.
SpKrl: a direct target of β-catenin regulation required for endoderm differentiation in sea urchin embryos
Authors: Howard Eric W. , Newman Laurel A. , Oleksyn David W. , Angerer Robert C. , Angerer Lynne M.
Published: April 2021

Localization of nuclear β-catenin initiates specification of vegetal fates in sea urchin embryos. We have identified SpKrl, a gene that is activated upon nuclear entry of β-catenin. SpKrl is upregulated when nuclear β-catenin activity is increased with LiCl and downregulated in embryos injected with molecules that inhibit β-catenin nuclear function. LiCl-mediated SpKrl activation is independent of protein synthesis, indicating that SpKrl is a direct target of β-catenin and TCF. Embryos in which SpKrl translation is inhibited with morpholino antisense oligonucleotides lack endoderm. Conversely, SpKrl mRNA injection rescues some vegetal structures in β-catenin-deficient embryos. SpKrl negatively regulates expression of the animalizing transcription factor, SpSoxB1. We propose that SpKrl functions in patterning the vegetal domain by suppressing animal regulatory activities.
Enhancement of foot formation in Hydra by a novel epitheliopeptide, Hym-323
Authors: Harafuji Naoe , Takahashi Toshio , Hatta Masayuki , Tezuka Hideo , Morishita Fumihiro , Matsushima Osamu , Fujisawa Toshitaka
Published: April 2021

During the course of a systematic screening of peptide signaling molecules in Hydra magnipapillata, a novel peptide, Hym-323, which enhances foot regeneration was identified. The peptide is 16 amino acids long, and is encoded in the precursor protein as a single copy. Northern blot analysis, in situ hybridization analysis and immunohistochemistry showed that it was expressed in both ectodermal and endodermal epithelial cells throughout the body, except for the basal disk and the head region. The peptide enhanced foot regeneration by acting on epithelial cells. Lateral transplantation experiments indicated that the foot activation potential was increased in the peptide-treated tissue. These results suggest that Hym-323 is a peptide involved in a foot-patterning process in Hydra.
Role of cadherins in maintaining the compartment boundary between the cortex and striatum during development
Authors: Inoue Takayoshi , Tanaka Taro , Takeichi Masatoshi , Chisaka Osamu , Nakamura Shun , Osumi Noriko
Published: April 2021

In ventricular cells of the mouse telencephalon, differential expression of cadherin cell adhesion molecules defines neighbouring regions; R-cadherin delineates the future cerebral cortex, while cadherin-6 delineates the lateral ganglionic eminence. By using cell labelling analyses in the whole embryo culture system, we demonstrated that the interface between R-cadherin and cadherin-6 expression is a boundary for cell lineage restriction at embryonic day 10.5. Interestingly, when a group of cells with exogenous cadherin-6 were generated to straddle the cortico-straital boundary by electroporation at embryonic day 11.0, ectopic cadherin-6-expressing cortical cells were sorted into the striatal compartment, and the reverse was the trend for ectopic R-cadherin-expressing striatal cells. Although cadherin-6 gene knockout mice engineered in this study showed no obvious phenotype in telencephalic compartmentalisation, the preferential sorting of ectopic cadherin-6-expressing cells was abolished in this mutant background. Thus, the differential expression pattern of cadherins in the embryonic telencephalon is responsible for maintaining the cortico-striatal compartment boundary.
Lilliputian: an AF4/FMR2-related protein that controls cell identity and cell growth
Authors: Wittwer Franz , Straten Alexandra van der , Keleman Krystyna , Dickson Barry J. , Hafen Ernst
Published: April 2021

Members of the AF4/FMR2 family of nuclear proteins are involved in human diseases such as acute lymphoblastic leukemia and mental retardation. Here we report the identification and characterization of the Drosophila lilliputian (lilli) gene, which encodes a nuclear protein related to mammalian AF4 and FMR2. Mutations in lilli suppress excessive neuronal differentiation in response to a constitutively active form of Raf in the eye. In the wild type, Lilli has a partially redundant function in the Ras/MAPK pathway in differentiation but it is essential for normal growth. Loss of Lilli function causes an autonomous reduction in cell size and partially suppresses the increased growth associated with loss of PTEN function. These results suggest that Lilli acts in parallel with the Ras/MAPK and the PI3K/PKB pathways in the control of cell identity and cellular growth.
Differential expression and functional analysis of Pitx2 isoforms in regulation of heart looping in the chick
Authors: Yu Xueyan , Amand Tara R. St , Wang Shusheng , Li Guangyu , Zhang Yanding , Hu YuePing , Nguyen Lan , Qiu MengSheng , Chen YiPing
Published: April 2021

Pitx2, a bicoid-related homeobox gene, plays a crucial role in the left-right axis determination and dextral looping of the vertebrate developing heart. We have examined the differential expression and function of two Pitx2 isoforms (Pitx2a and Pitx2c) that differ in the region 5′ to the homeodomain, in early chick embryogenesis. Northern blot and RT-PCR analyses indicated the existence of Pitx2a and Pitx2c but not Pitx2b in the developing chick embryos. In situ hybridization demonstrated a restricted expression of Pitx2c in the left lateral plate mesoderm (LPM), left half of heart tube and head mesoderm, but its absence in the extra- embryonic tissues where vasculogenesis occurs. RT-PCR experiments revealed that Pitx2a is absent in the left LPM, but is present in the head and extra-embryonic mesoderm. However, ectopic expression of either Pitx2c or Pitx2a via retroviral infection to the right LMP equally randomized heart looping direction. Mapping of the transcriptional activation function to the C terminus that is identical in both isoforms explained the similar results obtained by the gain-of-function approach. In contrast, elimination of Pitx2c expression from the left LMP by antisense oligonucleotide resulted in a randomization of heart looping, while treatment of embryos with antisense oligonucleotide specific to Pitx2a failed to generate similar effect. We further constructed RCAS retroviral vectors expressing dominant negative Pitx2 isoforms in which the C-terminal transcriptional activation domain was replaced by the repressor domain of the Drosophila Engrailed protein (Enr). Ectopic expression of Pitx2c-Enr, but not Pitx2a-Enr, to the left LPM randomized the heart looping. The results thus demonstrate that Pitx2c plays a crucial role in the left-right axis determination and rightward heart looping during chick embryogenesis.
Tissue-restricted expression of thrombomodulin in the placenta rescues thrombomodulin-deficient mice from early lethality and reveals a secondary developmental block
Authors: Isermann Berend , Hendrickson Sara B. , Hutley Kristi , Wing Mark , Weiler Hartmut
Published: April 2021

The endothelial cell surface receptor thrombomodulin (TM) inhibits blood coagulation by forming a complex with thrombin, which then converts protein C into the natural anticoagulant, activated protein C. In mice, a loss of TM function causes embryonic lethality at day 8.5 p.c. (post coitum) before establishment of a functional cardiovascular system. At this developmental stage, TM is expressed in the developing vasculature of the embryo proper, as well as in non-endothelial cells of the early placenta, giant trophoblast and parietal endoderm. Here, we show that reconstitution of TM expression in extraembryonic tissue by aggregation of tetraploid wild-type embryos with TM-null embryonic stem cells rescues TM-null embryos from early lethality. TM-null tetraploid embryos develop normally during midgestation, but encounter a secondary developmental block between days 12.5 and 16.5 p.c. Embryos lacking TM develop lethal consumptive coagulopathy during this period, and no live embryos are retrieved at term. Morphogenesis of embryonic blood vessels and other organs appears normal before E15. These findings demonstrate a dual role of TM in development, and that a loss of TM function disrupts mouse embryogenesis at two different stages. These two functions of TM are exerted in two distinct tissues: expression of TM in non-endothelial extraembryonic tissues is required for proper function of the early placenta, while the absence of TM from embryonic blood vessel endothelium causes lethal consumptive coagulopathy.
Polycomb group proteins and heritable silencing of Drosophila Hox genes
Authors: Beuchle Dirk , Struhl Gary , Müller Jürg
Published: April 2021

Early in Drosophila embryogenesis, transcriptional repressors encoded by Gap genes prevent the expression of particular combinations of Hox genes in each segment. During subsequent development, those Hox genes that were initially repressed in each segment remain off in all the descendent cells, even though the Gap repressors are no longer present. This phenomenon of heritable silencing depends on proteins of the Polycomb Group (PcG) and on cis-acting Polycomb response elements (PREs) in the Hox gene loci. We have removed individual PcG proteins from proliferating cells and then resupplied these proteins after a few or several cell generations. We show that most PcG proteins are required throughout development: when these proteins are removed, Hox genes become derepressed. However, we find that resupply of at least some PcG proteins can cause re-repression of Hox genes, provided that it occurs within a few cell generations of the loss of repression. These results suggest a functional distinction between transcriptional repression and heritable silencing: in at least some contexts, Hox genes can retain the capacity to be heritably silenced, despite being transcribed and replicated. We propose that silenced Hox genes bear a heritable, molecular mark that targets them for transcriptional repression. Some PcG proteins may be required to define and propagate this mark; others may function to repress the transcription of Hox genes that bear the mark.
Embryonic retinoic acid synthesis is essential for heart morphogenesis in the mouse
Authors: Niederreither Karen , Vermot Julien , Messaddeq Nadia , Schuhbaur Brigitte , Chambon Pierre , Dollé Pascal
Published: April 2021

Retinoic acid (RA), the active derivative of vitamin A, has been implicated in various steps of cardiovascular development, but its contribution to early heart morphogenesis has not been clearly established in a mammalian system. To block endogenous RA synthesis, we have disrupted the gene encoding RALDH2, the first retinaldehyde dehydrogenase whose expression has been detected during early mouse post-implantation development. We describe here the heart abnormalities of the RA-deficient Raldh2 mutants that die in utero at gestational day 10.5. The embryonic heart tube forms properly, but fails to undergo rightward looping and, instead, forms a medial distended cavity. Expression of early heart determination factors is not altered in mutants, and the defect in heart looping does not appear to involve the Nodal/Lefty/Pitx2 pathway. Histological and molecular analysis reveal distinct anteroposterior components in the mutant heart tube, although posterior chamber (atria and sinus venosus) development is severely impaired. Instead of forming trabeculae, the developing ventricular myocardium consists of a thick layer of loosely attached cells. Ultrastructural analysis shows that most of the ventricular wall consists of prematurely differentiated cardiomyocytes, whereas undifferentiated cells remain clustered rostrally. We conclude that embryonic RA synthesis is required for realization of heart looping, development of posterior chambers and proper differentiation of ventricular cardiomyocytes. Nevertheless, the precise location of this synthesis may not be crucial, as these defects can mostly be rescued by systemic (maternal) RA administration. However, cardiac neural crest cells cannot be properly rescued in Raldh2− /− embryos, leading to outflow tract septation defects.
Inducible nuclear translocation of a STAT protein in Dictyostelium prespore cells: implications for morphogenesis and cell-type regulation
Authors: Dormann Dirk , Abe Tomoaki , Weijer Cornelis J. , Williams Jeffrey
Published: April 2021

Dd-STATa, the Dictyostelium STAT (signal transducer and activator of transcription) protein, is selectively localised in the nuclei of a small subset of prestalk cells located in the slug tip. Injection of cAMP into the extracellular spaces in the rear of the slug induces rapid nuclear translocation of a Dd-GFP:STATa fusion protein in prespore cells surrounding the site of injection. This suggests that cAMP signals that emanate from the tip direct the localised nuclear accumulation of Dd-STATa. It also shows that prespore cells are competent to respond to cAMP, by Dd- STATa activation, and it implies that cAMP signalling is in some way limiting in the rear of the slug. Co-injection of a specific inhibitor of the cAR1 serpentine cAMP receptor almost completely prevents the cAMP-induced nuclear translocation, showing that most or all of the cAMP signal is transduced by cAR1. Dd-GFP:STATa also rapidly translocates into the nuclei of cells adjoining the front and back cut edges when a slug is bisected. Less severe mechanical disturbances, such as pricking the rear of a slug with an unfilled micropipette, also cause a more limited nuclear translocation of Dd-GFP:STATa. We propose that these signalling events form part of a repair mechanism that is activated when the migrating slug suffers mechanical damage.

Movies available on-line: http://www.personal.dundee.ac.uk/∼cjweijer/STATa_GFP.htm and http://www.biologists.com/Development/movies/dev3344.html
An instructive function for Notch in promoting gliogenesis in the zebrafish retina
Authors: Scheer Nico , Groth Anne , Hans Stefan , A. Campos-Ortega José
Published: April 2021

The Gal4-UAS technique has been used to misexpress a constitutively active Notch receptor variant (notch1a-intra) in the developing zebrafish retina. This is the first study to use this technique to misexpress genes and assess their function in neural development of the zebrafish. Expression of activated Notch1a either ubiquitously, driven by a heat- shock70 promoter, or in a spatially regulated manner, controlled by the deltaD promoter, causes a block in neuronal differentiation that affects all cell types. Developing cells take on either a glial fate or remain undifferentiated. A large number of cells eventually undergo apoptosis. These phenotypic effects of activated Notch1a are expressed cell autonomously. Cells within central regions of the retina adopt a glial fate if they express activated Notch1a in a time window that extends from 27 to 48 hours postfertilization. This period corresponds mainly to the time of origin of ganglion cells in the normal retina. Activation of notch1a at later stages results in defects in cell type specification that remain restricted to the ciliary marginal zone, whereas neuronal types are specified normally within the central region. These observations indicate that glial differentiation is initiated by Notch1a-intra expressing cells, which become postmitotic in the same time window. Our results strongly suggest that Notch1a instructs a certain cell population to enter gliogenesis, and keeps the remaining cells in an undifferentiated state. Some or all of these cells will eventually succumb to apoptosis.
Regulation of imprinted X-chromosome inactivation in mice by Tsix
Authors: Sado Takashi , Wang Zhenjuan , Sasaki Hiroyuki , Li En
Published: April 2021

In mammals, X-chromosome inactivation is imprinted in the extra-embryonic lineages with paternal X chromosome being preferentially inactivated. In this study, we investigate the role of Tsix, the antisense transcript from the Xist locus, in regulation of Xist expression and X- inactivation. We show that Tsix is transcribed from two putative promoters and its transcripts are processed. Expression of Tsix is first detected in blastocysts and is imprinted with only the maternal allele transcribed. The imprinted expression of Tsix persists in the extra- embryonic tissues after implantation, but is erased in embryonic tissues. To investigate the function of Tsix in X- inactivation, we disrupted Tsix by insertion of an IRESβgeo cassette in the second exon, which blocked transcripts from both promoters. While disruption of the paternal Tsix allele has no adverse effects on embryonic development, inheritance of a disrupted maternal allele results in ectopic Xist expression and early embryonic lethality, owing to inactivation of both X chromosomes in females and single X chromosome in males. Further, early developmental defects of female embryos with maternal transmission of Tsix mutation can be rescued by paternal inheritance of the Xist deletion. These results provide genetic evidence that Tsix plays a crucial role in maintaining Xist silencing in cis and in regulation of imprinted X-inactivation in the extra- embryonic tissues.
Analysis of RNA associated with P granules in germ cells of C. elegans adults
Authors: A. Schisa Jennifer , N. Pitt Jason , R.Priess James
Published: April 2021

P granules are cytoplasmic structures of unknown function that are associated with germ nuclei in the C. elegans gonad, and are localized exclusively to germ cells, or germ cell precursors, throughout the life cycle. All the known protein components of P granules contain putative RNA- binding motifs, suggesting that RNA is involved in either the structure or function of the granules. However, no specific mRNAs have been identified within P granules in the gonad. We show here that P granules normally contain a low level of RNA, and describe conditions that increase this level. We present evidence that several, diverse mRNAs, including pos-1, mex-1, par-3, skn-1, nos-2 and gld- 1 mRNA, are present at least transiently within P granules.

In contrast, actin and tubulin mRNA and rRNA are either not present in P granules, or are present at relatively low levels. We show that pgl-1 and the glh (Vasa-related) gene family, which encode protein components of P granules, do not appear essential for RNA to concentrate in P granules; these proteins may instead function in events that are a prerequisite for RNAs to be transported efficiently from the nuclear surface.
Meis3 synergizes with Pbx4 and Hoxb1b in promoting hindbrain fates in the zebrafish
Authors: Vlachakis Nikolaos , Choe Seong-Kyu , Sagerström Charles
Published: April 2021

Many Hox proteins are thought to require Pbx and Meis co-factors to specify cell identity during embryogenesis. Here we demonstrate that Meis3 synergizes with Pbx4 and Hoxb1b in promoting hindbrain fates in the zebrafish. We find that Hoxb1b and Pbx4 act together to induce ectopic hoxb1a expression in rhombomere 2 of the hindbrain. In contrast, Hoxb1b and Pbx4 acting together with Meis3 induce hoxb1a, hoxb2, krox20 and valentino expression rostrally and cause extensive transformation of forebrain and midbrain fates to hindbrain fates, including differentiation of excess rhombomere 4-specific Mauthner neurons. This synergistic effect requires that Hoxb1b and Meis3 have intact Pbx-interaction domains, suggesting that their in vivo activity is dependent on binding to Pbx4. In the case of Meis3, binding to Pbx4 is also required for nuclear access. Our results are consistent with Hoxb1b and Meis3 interacting with Pbx4 to form complexes that regulate hindbrain development during zebrafish embryogenesis.
The role of presenilin 1 during somite segmentation
Authors: Koizumi Ken-ichi , Nakajima Mitsunari , Yuasa Shigeki , Saga Yumiko , Sakai Tsuyoshi , Kuriyama Takayuki , Shirasawa Takuji , Koseki Haruhiko
Published: April 2021

The Notch signalling pathway plays essential roles during the specification of the rostral and caudal somite halves and subsequent segmentation of the paraxial mesoderm. We have re-investigated the role of presenilin 1 (Ps1; encoded by Psen1) during segmentation using newly generated alleles of the Psen1 mutation. In Psen1-deficient mice, proteolytic activation of Notch1 was significantly affected and the expression of several genes involved in the Notch signalling pathway was altered, including Delta-like3, Hes5, lunatic fringe (Lfng) and Mesp2. Thus, Ps1-dependent activation of the Notch pathway is essential for caudal half somite development. We observed defects in Notch signalling in both the caudal and rostral region of the presomitic mesoderm. In the caudal presomitic mesoderm, Ps1 was involved in maintaining the amplitude of cyclic activation of the Notch pathway, as represented by significant reduction of Lfng expression in Psen1-deficient mice. In the rostral presomitic mesoderm, rapid downregulation of the Mesp2 expression in the presumptive caudal half somite depends on Ps1 and is a prerequisite for caudal somite half specification. Chimaera analysis between Psen1-deficient and wild-type cells revealed that condensation of the wild-type cells in the caudal half somite was concordant with the formation of segment boundaries, while mutant and wild-type cells intermingled in the presomitic mesoderm. This implies that periodic activation of the Notch pathway in the presomitic mesoderm is still latent to segregate the presumptive rostral and caudal somite. A transient episode of Mesp2 expression might be needed for Notch activation by Ps1 to confer rostral or caudal properties. In summary, we propose that Ps1 is involved in the functional manifestation of the segmentation clock in the presomitic mesoderm.