bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of Sonic hedgehog in normal and abnormal craniofacial morphogenesis
Authors: Hu Diane , Helms Jill A. 
Published: April 2021

Abstract
There is growing evidence that implicates a role for Sonic hedgehog (SHH) in morphogenesis of the craniofacial complex. Mutations in human and murine SHH cause midline patterning defects that are manifested in the head as holoprosencephaly and cyclopia. In addition, teratogens such as jervine, which inhibit the response of tissues to SHH, also produce cyclopia. Thus, the loss of SHH signaling during early stages of neural plate patterning has a profound influence of craniofacial morphogenesis. However, the severity of these defects precludes analyses of SHH function during later stages of craniofacial development. We have used an embryonic chick system to study the role of SHH during these later stages of craniofacial development. Using a combination of surgical and molecular experiments, we show here that SHH is essential for morphogenesis of the frontonasal and maxillary processes (FNP and MXPs), which give rise to the mid-and upper face. Transient loss of SHH signaling in the embryonic face inhibits growth of the primordia and results in defects analogous to hypotelorism and cleft lip/palate, characteristics of the mild forms of holoprosencephaly. In contrast, excess SHH leads to a mediolateral widening of the FNP and a widening between the eyes, a condition known as hypertelorism. In severe cases, this widening is accompanied by facial duplications. Collectively, these experiments demonstrate that SHH has multiple and profound effects on the entire spectrum of craniofacial development, and perturbations in SHH signaling are likely to underlie a number of human craniofacial anomalies.
Engrailed defines the position of dorsal di-mesencephalic boundary by repressing diencephalic fate
Authors: Araki Isato , Nakamura Harukazu 
Published: April 2021

Abstract
Regionalization of a simple neural tube is a fundamental event during the development of central nervous system. To analyze in vivo the molecular mechanisms underlying the development of mesencephalon, we ectopically expressed Engrailed, which is expressed in developing mesencephalon, in the brain of chick embryos by in ovo electroporation. Misexpression of Engrailed caused a rostral shift of the di-mesencephalic boundary, and caused transformation of dorsal diencephalon into tectum, a derivative of dorsal mesencephalon. Ectopic Engrailed rapidly repressed Pax-6, a marker for diencephalon, which preceded the induction of mesencephalon-related genes such as Pax-2, Pax-5, Fgf8, Wnt-1 and EphrinA2. In contrast, a mutant Engrailed, En-2(F51→E), bearing mutation in EH1 domain, which has been shown to interact with a co-repressor, Groucho, did not show the phenotype induced by wild-type Engrailed. Furthermore, VP16-Engrailed chimeric protein, the dominant positive form of Engrailed, caused caudal shift of di-mesencephalic boundary and ectopic Pax-6 expression in mesencephalon. These data suggest that (1) Engrailed defines the position of dorsal di-mesencephalic boundary by directly repressing diencephalic fate, and (2) Engrailed positively regulates the expression of mesencephalon-related genes by repressing the expression of their negative regulator(s).
Cngsc, a homologue of goosecoid, participates in the patterning of the head, and is expressed in the organizer region of Hydra
Authors: Broun Mariya , Sokol Sergei , Bode Hans R. 
Published: April 2021

Abstract
We have isolated Cngsc, a hydra homologue of goosecoid gene. The homeodomain of Cngsc is identical to the vertebrate (65-72%) and Drosophila (70%) orthologues. When injected into the ventral side of an early Xenopus embryo, Cngsc induces a partial secondary axis. During head formation, Cngsc expression appears prior to, and directly above, the zone where the tentacles will emerge, but is not observed nearby when the single apical tentacle is formed. This observation indicates that the expression of the gene is not necessary for the formation of a tentacle per se. Rather, it may be involved in defining the border between the hypostome and the tentacle zone. When Cngsc+ tip of an early bud is grafted into the body column, it induces a secondary axis, while the adjacent Cngsc− region has much weaker inductive capacities. Thus, Cngsc is expressed in a tissue that acts as an organizer. Cngsc is also expressed in the sensory neurons of the tip of the hypostome and in the epithelial endodermal cells of the upper part of the body column. The plausible roles of Cngsc in organizer function, head formation and anterior neuron differentiation are similar to roles goosecoid plays in vertebrates and Drosophila. It suggests widespread evolutionary conservation of the function of the gene.
Identification of tissues and patterning events required for distinct steps in early migration of zebrafish primordial germ cells
Authors: Weidinger Gilbert , Wolke Uta , Köprunner Marion , Klinger Michael , Raz Erez 
Published: April 2021

Abstract
In many organisms, the primordial germ cells have to migrate from the position where they are specified towards the developing gonad where they generate gametes. Extensive studies of the migration of primordial germ cells in Drosophila, mouse, chick and Xenopus have identified somatic tissues important for this process and demonstrated a role for specific molecules in directing the cells towards their target. In zebrafish, a unique situation is found in that the primordial germ cells, as marked by expression of vasa mRNA, are specified in random positions relative to the future embryonic axis. Hence, the migrating cells have to navigate towards their destination from various starting positions that differ among individual embryos. Here, we present a detailed description of the migration of the primordial germ cells during the first 24 hours of wild-type zebrafish embryonic development. We define six distinct steps of migration bringing the primordial germ cells from their random positions before gastrulation to form two cell clusters on either side of the midline by the end of the first day of development. To obtain information on the origin of the positional cues provided to the germ cells by somatic tissues during their migration, we analyzed the migration pattern in mutants, including spadetail, swirl, chordino, floating head, cloche, knypek and no isthmus. In mutants with defects in axial structures, paraxial mesoderm or dorsoventral patterning, we find that certain steps of the migration process are specifically affected. We show that the paraxial mesoderm is important for providing proper anteroposterior information to the migrating primordial germ cells and that these cells can respond to changes in the global dorsoventral coordinates. In certain mutants, we observe accumulation of ectopic cells in different regions of the embryo. These ectopic cells can retain both morphological and molecular characteristics of primordial germ cells, suggesting that, in zebrafish at the early stages tested, the vasa-expressing cells are committed to the germ cell lineage.
SpSoxB1, a maternally encoded transcription factor asymmetrically distributed among early sea urchin blastomeres
Authors: Kenny Alan P. , Kozlowski David J. , Oleksyn David W. , Angerer Lynne M. , Angerer Robert C. 
Published: April 2021

Abstract
We have identified a Sox family transcription factor, SpSoxB1, that is asymmetrically distributed among blastomeres of the sea urchin embryo during cleavage, beginning at 4th cleavage. SpSoxB1 interacts with a cis element that is essential for transcription of SpAN, a gene that is activated cell autonomously and expressed asymmetrically along the animal-vegetal axis. In vitro translated SpSoxB1 forms a specific complex with this cis element whose mobility is identical to that formed by a protein in nuclear extracts. An anti-SpSoxB1 rabbit polyclonal antiserum specifically supershifts this DNA-protein complex and recognizes a single protein on immunoblots of nuclear proteins that comigrates with in vitro translated SpSoxB1. Developmental immunoblots of total proteins at selected early developmental stages, as well as EMSA of egg and 16-cell stage proteins, show that SpSoxB1 is present at low levels in unfertilized eggs and progressively accumulates during cleavage. SpSoxB1 maternal transcripts are uniformly distributed in the unfertilized egg and the protein accumulates to similar, high concentrations in all nuclei of 4- and 8-cell embryos. However, at fourth cleavage, the micromeres, which are partitioned by asymmetric division of the vegetal 4 blastomeres, have reduced nuclear levels of the protein, while high levels persist in their sister macromeres and in the mesomeres. During cleavage, the uniform maternal SpSoxB1 transcript distribution is replaced by a zygotic nonvegetal pattern that reinforces the asymmetric SpSoxB1 protein distribution and reflects the corresponding domain of SpAN mRNA accumulation at early blastula stage (∼150 cells). The vegetal region lacking nuclear SpSoxB1 gradually expands so that, after blastula stage, only cells in differentiating ectoderm accumulate this protein in their nuclei. The results reported here support a model in which SpSoxB1 is a major regulator of the initial phase of asymmetric transcription of SpAN in the nonvegetal domain by virtue of its distribution at 4th cleavage and is subsequently an important spatial determinant of expression in the early blastula. This factor is the earliest known spatially restricted regulator of transcription along the animal-vegetal axis of the sea urchin embryo.
Targeted deletion of the ATP binding domain of left-right dynein confirms its role in specifying development of left-right asymmetries
Authors: Supp Dorothy M. , Brueckner Martina , Kuehn Michael R. , Witte David P. , Lowe Linda A. , McGrath James , Corrales JoMichelle , Potter S. Steven 
Published: April 2021

Abstract
Vertebrates develop distinct asymmetries along the left-right axis, which are consistently aligned with the anteroposterior and dorsoventral axes. The mechanisms that direct this handed development of left-right asymmetries have been elusive, but recent studies of mutations that affect left-right development have shed light on the molecules involved. One molecule implicated in left-right specification is left-right dynein (LRD), a microtubule-based motor protein. In the LRD protein of the inversus viscerum (iv) mouse, there is a single amino acid difference at a conserved position, and the lrd gene is one of many genes deleted in the legless (lgl) mutation. Both iv and lgl mice display randomized left-right development. Here we extend the analysis of the lrd gene at the levels of sequence, expression and function. The complete coding sequence of the lrd gene confirms its classification as an axonemal, or ciliary, dynein. Expression of lrd in the node at embryonic day 7.5 is shown to be symmetric. At embryonic day 8.0, however, a striking asymmetric expression pattern is observed in all three germ layers of the developing headfold, suggesting roles in both the establishment and maintenance of left-right asymmetries.
At later times, expression of lrd is also observed in the developing floorplate, gut and limbs. These results suggest function for LRD protein in both cilitated and non-ciliated cells, despite its sequence classification as axonemal. In addition, a targeted mutation of lrd was generated that deletes the part of the protein required for ATP binding, and hence motor function. The resulting left-right phenotype, randomization of laterality, is identical to that of iv and lgl mutants. Gross defects in ciliary structure were not observed in lrd/lrd mutants. Strikingly, however, the monocilia on mutant embryonic node cells were immotile. These results prove the identity of the iv and lrd genes. Further, they argue that LRD motor function, and resulting nodal monocilia movement, are required for normal left-right development.
Movies available on-line:
http://www.biologists.com/Development/movies/dev3019.html
http://genome.chmcc.org/cilia/
Regulation of Ci-tropomyosin-like, a Brachyury target gene in the ascidian, Ciona intestinalis
Authors: Gregorio Anna Di , Levine Michael 
Published: April 2021

Abstract
Brachyury is a sequence-specific transcriptional activator that is essential for notochord differentiation in a variety of chordates. In vertebrates, Brachyury is expressed throughout the presumptive mesoderm, but becomes restricted to the notochord at later stages of development. In ascidians, such as Ciona intestinalis, Brachyury is expressed exclusively in the notochord and does not exhibit an early pan-mesodermal pattern. Subtractive hybridization screens were recently used to identify potential Ciona Brachyury (Ci-Bra) target genes (Takahashi, H., Hotta, K., Erives, A., Di Gregorio, A., Zeller, R. W., Levine, M. and Satoh, N. (1999). Genes Dev. 13, 1519-1523). Of the genes that were identified in this screen, one corresponds to a new member of the tropomyosin superfamily, Ciona tropomyosin (Ci-trop). Here we show that Ci-trop is specifically expressed in the developing notochord beginning at gastrulation, and expression persists in the notochord during tailbud and tadpole stages. A 3 kb region of the Ci-trop 5 ′-flanking sequence was characterized via electroporation of lacZ fusion genes into fertilized Ciona eggs. A minimal, 114 bp enhancer was identified that is sufficient to direct the expression of a heterologous promoter in the notochord. DNA binding assays indicate that this enhancer contains two sets of low-affinity Brachyury half-sites, which are bound in vitro by a GST/Ci-Bra fusion protein. Deletion of the distal sites inactivates the notochord-specific staining pattern mediated by an otherwise normal Ci-trop/lacZ transgene. These results suggest that Ci-trop is a direct target gene of Ci-Bra and that Brachyury plays an immediate role in the cellular morphogenesis of the notochord.
Abbreviations: bp, base pair(s); kb, kilobase(s), or 1000 base pairs; 5 ′-UTR, 5 ′ untranslated sequence; CNS, central nervous system; PCR, polymerase chain reaction; RACE, rapid amplification of cDNA ends; GST, glutathione S-transferase; GFP, green fluorescent protein.
Role for mRNA localization in translational activation but not spatial restriction of nanos RNA
Authors: Bergsten Sherri Evans , Gavis Elizabeth R. 
Published: April 2021

Abstract
Patterning of the anterior-posterior body axis during Drosophila development depends on the restriction of Nanos protein to the posterior of the early embryo. Synthesis of Nanos occurs only when maternally provided nanos RNA is localized to the posterior pole by a large, cis-acting signal in the nanos 3′ untranslated region (3′UTR); translation of unlocalized nanos RNA is repressed by a 90 nucleotide Translational Control Element (TCE), also in the 3′UTR. We now show quantitatively that the majority of nanos RNA in the embryo is not localized to the posterior pole but is distributed throughout the cytoplasm, indicating that translational repression is the primary mechanism for restricting production of Nanos protein to the posterior. Through an analysis of transgenes bearing multiple copies of nanos 3′UTR regulatory sequences, we provide evidence that localization of nanos RNA by components of the posteriorly localized germ plasm activates its translation by preventing interaction of nanos RNA with translational repressors. This mutually exclusive relationship between translational repression and RNA localization is mediated by a 180 nucleotide region of the nanos localization signal, containing the TCE. These studies suggest that the ability of RNA localization to direct wild-type body patterning also requires recognition of multiple, unique elements within the nanos localization signal by novel factors. Finally, we propose that differences in the efficiencies with which different RNAs are localized result from the use of temporally distinct localization pathways during oogenesis.
Formation of the vulva in Caenorhabditis elegans: a paradigm for organogenesis
Authors: Sharma-Kishore Ranjana , White John G. , Southgate Eileen , Podbilewicz Benjamin 
Published: April 2021

Abstract
The genes involved in the inductive interactions that specify cell fates in the vulva of Caenorhabditis elegans are known in some detail. However, little is known about the morphogenesis of this organ. Using a combination of cell biological and anatomical approaches, we have determined a complete morphogenetic pathway of cellular events that lead to the formation of the vulva. These events include reproducible cell divisions, migrations, remodeling of adherens junctions, cell fusions and muscle attachments. In the course of these events, an epithelial channel comprising a stack of 7 toroidal cells is formed that connects the internal epithelium of the uterus with the external body epithelium, forming the vulva. Vulval muscles attach to the epithelial channel and the whole structure everts during the final molt. The mature vulva has rotational, two-fold symmetry. Using laser microsurgery, we found that the two halves of the vulva develop autonomously.
Emergence of intraembryonic hematopoietic precursors in the pre-liver human embryo
Authors: Tavian Manuela , Hallais Marie-France , Péault Bruno 
Published: April 2021

Abstract
Hepatic hematopoiesis in the mouse embryo is preceded by two hematopoietic waves, one in the yolk sac, and the other in the paraaortic splanchnopleura, the presumptive aorta-gonad-mesonephros region that gives rise to prenatal and postnatal blood stem cells. An homologous intraembryonic site of stem cell emergence was previously identified at 5 weeks of human gestation, when hundreds of CD34++ Lin− high-proliferative potential hematopoietic cells border the aortic endothelium in the preumbilical region. In the present study, we have combined immunohistochemistry, semithin section histology, fluorescence-activated cell sorting and blood cell culture in an integrated study of incipient hematopoiesis in the human yolk sac, truncal arteries and embryonic liver from 21 to 58 days of development. The chronology of blood precursor cell emergence in these distinct tissues suggests a pivotal role in the settlement of liver hematopoiesis of endothelium-associated stem cell clusters, which emerge not only in the dorsal aorta but also in the vitelline artery. Anatomic features and in vitro functionality indicate that stem cells develop intrinsically to embryonic artery walls from a presumptive territory whose blood-forming potential exists from at least 24 days of gestation.
Origin and development of the zebrafish endoderm
Authors: Warga Rachel M. , Nüsslein-Volhard Christiane 
Published: April 2021

Abstract
The segregation of cells into germ layers is one of the earliest events in the establishment of cell fate in the embryo. In the zebrafish, endoderm and mesoderm are derived from cells that involute into an internal layer, the hypoblast, whereas ectoderm is derived from cells that remain in the outer layer, the epiblast. In this study, we examine the origin of the zebrafish endoderm and its separation from the mesoderm. By labeling individual cells located at the margin of the blastula, we demonstrate that all structures that are endodermal in origin are derived predominantly from the more dorsal and lateral cells of the blastoderm margin. Frequently marginal cells give rise to both endodermal and mesodermal derivatives, demonstrating that these two lineages have not yet separated. Cells located farther than 4 cell diameters from the margin give rise exclusively to mesoderm, and not to endoderm.
Following involution, we see a variety of cellular changes indicating the differentiation of the two germ layers. Endodermal cells gradually flatten and extend filopodial processes forming a noncontiguous inner layer of cells against the yolk. At this time, they also begin to express Forkhead-domain 2 protein. Mesodermal cells form a coherent layer of round cells separating the endoderm and ectoderm.
In cyclops-mutant embryos that have reduced mesodermal anlage, we demonstrate that by late gastrulation not only mesodermal but also endodermal cells are fewer in number. This suggests that a common pathway initially specifies germ layers together before a progressive sequence of determinative events segregate endoderm and mesoderm into morphologically distinct germ layers.
EGL-27 is similar to a metastasis-associated factor and controls cell polarity and cell migration in C. elegans
Authors: Herman Michael A. , Ch’ng QueeLim , Hettenbach Susan M. , Ratliff Thomas M. , Kenyon Cynthia , Herman Robert K. 
Published: April 2021

Abstract
Mutations in the C. elegans gene egl-27 cause defects in cell polarity and cell migration: the polarity of the asymmetric T cell division is disrupted and the descendants of the migratory QL neuroblast migrate incorrectly because they fail to express the Hox gene mab-5. Both of these processes are known to be controlled by Wnt pathways. Mosaic analysis indicates that egl-27 function is required in the T cell for proper cell polarity. We cloned egl-27 and discovered that a domain of the predicted EGL-27 protein has similarity to Mta1, a mammalian factor overexpressed in metastatic cells. Overlaps in the phenotypes of egl-27 and Wnt pathway mutants suggest that the EGL-27 protein interacts with Wnt signaling pathways in C. elegans.
Regulatory and functional interactions between the somatic sex regulatory gene transformer and the germline genes ovo and ovarian tumor
Authors: Hinson Shannon , Nagoshi Rod N. 
Published: April 2021

Abstract
In Drosophila, compatibility between the sexually differentiated state of the soma and the sex chromosome constitution of the germline is required for normal gametogenesis. In this study, we defined important aspects of the soma-germline interactions controlling early oogenesis. In particular, the sex-specific germline activity of the ovarian tumor promoter was found to be dependent upon somatic factors controlled by the somatic sex differentiation gene transformer. This regulation defines whether there is sufficient ovarian tumor expression in adult XX germ cells to support oogenesis. In addition, the ovarian tumor function required for female germline differentiation is dependent on the activity of another germline gene, ovo, whose regulation is transformer-independent. These and other data indicate that ovarian tumor plays a central role in coordinating regulatory inputs from the soma (as regulated by transformer) with those from the germline (involving ovo). We also demonstrate that transformer-dependent interactions influence whether XX germ cells require ovarian tumor or ovo functions to undergo early gametogenic differentiation. These results are incorporated into a model hypothesizing that the functions of ovarian tumor and ovo are dependent on an early sex determination decision in the XX germline that is at least partially controlled by somatic transformer activity.