bluuebunny/crossref_metadata_2025_split huggingface dataset:
A highly conserved centrosomal kinase, AIR-1, is required for accurate cell cycle progression and segregation of developmental factors in Caenorhabditis elegans embryos
Authors: Schumacher Jill M. , Ashcroft Neville , Donovan Peter J. , Golden Andy 
Published: April 2021

ABSTRACT
S. cerevisiae Ipl1, Drosophila Aurora, and the mammalian centrosomal protein IAK-1 define a new subfamily of serine/threonine kinases that regulate chromosome segregation and mitotic spindle dynamics. Mutations in ipl1 and aurora result in the generation of severely aneuploid cells and, in the case of aurora, monopolar spindles arising from a failure in centrosome separation. Here we show that a related, essential protein from C. elegans, AIR-1 (Aurora/Ipl1 related), is localized to mitotic centrosomes. Disruption of AIR-1 protein expression in C. elegans embryos results in severe aneuploidy and embryonic lethality. Unlike aurora mutants, this aneuploidy does not arise from a failure in centrosome separation. Bipolar spindles are formed in the absence of AIR-1, but they appear to be disorganized and are nucleated by abnormal-looking centrosomes. In addition to its requirement during mitosis, AIR-1 may regulate microtubule-based developmental processes as well. Our data suggests AIR-1 plays a role in P-granule segregation and the association of the germline factor PIE-1 with centrosomes.
Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first pause, restart, then stop: correlations with cell cycle kinase activity
Authors: McDougall Alex , Levasseur Mark 
Published: April 2021

ABSTRACT
We have investigated the relationship between the sperm-triggered Ca2+ oscillations and the activities of two cell cycle kinases (MPF activity and MAP kinase activity) at fertilisation of Ascidiella aspersa oocytes. Maturation Promoting Factor (MPF) activity is elevated in the metaphase I (MI)-arrested unfertilised oocyte (as measured by phosphorylation of exogenous histone H1) and falls 5 minutes after fertilisation to remain at low levels for 5 minutes. The first polar body (pb1) is extruded when the MPF activity is low. The MPF activity is elevated again 15 minutes after fertilisation and finally becomes inactivated 25 minutes after fertilisation when the pb2 is extruded. MAP kinase activity increases from an initially elevated level to reach maximal activity 10 minutes after fertilisation and subsequently falls to reach low levels 25 minutes after fertilisation. Sperm trigger a series of Ca2+ oscillations that pause for 5 minutes while only the MPF activity is low and are present when both MPF and MAP kinase activity are elevated.
We next attempted to determine whether the second phase of calcium oscillations is required to reactivate the MPF activity that precedes extrusion of the second polar body. To do this, we triggered a monotonic Ca2+ signal. This leads to the inactivation of MPF followed by MPF reactivation. The MPF activity then remains elevated for an extended period of time. During this period, the chromatin remains condensed and a metaphase II (MII) spindle forms. Fertilisation of these MII oocytes triggers extrusion of pb2 in 7 minutes. Interestingly, the second phase of Ca2+ oscillations is completely absent when MII oocytes are fertilised. Thus, in both MI and MII oocytes, the sperm-triggered Ca2+ oscillations follow the MPF activity.
Finally we discuss our finding that the Ca2+ release system remains sensitive during the metaphase-like state (including the period when the Ca2+ oscillations pause).
A GATA-dependent nkx-2.5 regulatory element activates early cardiac gene expression in transgenic mice
Authors: Searcy Robin D. , Vincent Eric B. , Liberatore Christine M. , Yutzey Katherine E. 
Published: April 2021

ABSTRACT
nkx-2.5 is one of the first genes expressed in the developing heart of early stage vertebrate embryos. Cardiac expression of nkx-2.5 is maintained throughout development and nkx-2.5 also is expressed in the developing pharyngeal arches, spleen, thyroid and tongue. Genomic sequences flanking the mouse nkx-2.5 gene were analyzed for early developmental regulatory activity in transgenic mice. Approximately 3 kb of 5′ flanking sequence is sufficient to activate gene expression in the cardiac crescent as early as E7.25 and in limited regions of the developing heart at later stages. Expression also was detected in the developing spleen anlage at least 24 hours before the earliest reported spleen marker and in the pharyngeal pouches and their derivatives including the thyroid. The observed expression pattern from the −3 kb construct represents a subset of the endogenous nkx-2.5 expression pattern which is evidence for compartment-specific nkx-2.5 regulatory modules. A 505 bp regulatory element was identified that contains multiple GATA, NKE, bHLH, HMG and HOX consensus binding sites. This element is sufficient for gene activation in the cardiac crescent and in the heart outflow tract, pharynx and spleen when linked directly to lacZ or when positioned adjacent to the hsp68 promoter. Mutation of paired GATA sites within this element eliminates gene activation in the heart, pharynx and spleen primordia of transgenic embryos. The dependence of this nkx-2.5 regulatory element on GATA sites for gene activity is evidence for a GATA-dependent regulatory mechanism controlling nkx-2.5 gene expression. The presence of consensus binding sites for other developmentally important regulatory factors within the 505 bp distal element suggests that combinatorial interactions between multiple regulatory factors are responsible for the initial activation of nkx-2.5 in the cardiac, thyroid and spleen primordia.
Stage-specific expression of the Kit receptor and its ligand (KL) during male gametogenesis in the mouse: a Kit-KL interaction critical for meiosis
Authors: Vincent Stéphane , Segretain Dominique , Nishikawa Satomi , Nishikawa Shin-Ichi , Sage Julien , Cuzin François , Rassoulzadegan Minoo 
Published: April 2021

ABSTRACT
The Kit receptor and its ligand KL, which together constitute an essential effector at various stages of embryonic development, are both present during adult gametogenesis. In the testis, KL is expressed in Sertoli cells, and Kit in germ cells, starting at the premeiotic stages. A series of observations indicated previously a role in spermatogonia survival, without excluding a possible function at later stages. We identified a complex pattern of expression of the two components in the adult murine testis, suggestive of a role in the meiotic progression of spermatocytes. At stages VII-VIII of the cycle of the seminiferous epithelium, the time when spermatocytes enter meiosis, the membrane-associated form of KL extends on the Sertoli cell from the peripheral to the adluminal compartment of the tubule. We also found that the receptor is present on the surface of germ cells up to the pachytene stage. The availability of differentiated Sertoli cell lines, which express the KL protein and support part of the maturation of germ cells in coculture, allowed us to ask whether, in the in vitro reconstructed system, transit of spermatocytes through meiosis requires the Kit-KL interaction. Addition of a blocking monoclonal antibody against the Kit receptor (ACK2) inhibited extensively the appearance of haploid cells and the expression of a haploid-phase-specific gene (Prm1). Recognition of the supporting Sertoli cell by germ cells was not affected, indicating a requirement for the activity of the receptor for either entering or completing meiosis. Involvement of the membrane-associated form of the ligand was suggested by the observation that addition of the soluble form of KL was equally inhibitory.
Hematopoietic induction and respecification of A-P identity by visceral endoderm signaling in the mouse embryo
Authors: Belaoussoff Maria , Farrington Sarah M. , Baron Margaret H. 
Published: April 2021

ABSTRACT
The anteroposterior axis of the developing embryo becomes morphologically apparent at the onset of gastrulation with the formation of the primitive streak. This structure, where the first mesodermal cells arise, marks the posterior aspect of the embryo. To examine the potential role of non-mesodermal signals in specifying posterior (hematopoietic and endothelial) cell fates in the mouse embryo, we have devised a transgenic explant culture system. We show that interactions between primitive endoderm and adjacent embryonic ectoderm or nascent mesoderm are required early in gastrulation for initiation of hematopoiesis and vasculogenesis. Surprisingly, primitive endoderm signals can respecify anterior (prospective neural) ectoderm to a posterior mesodermal fate, resulting in formation of blood and activation of endothelial markers. Reprogramming of anterior ectoderm does not require cell contact and is effected by stage-dependent, short-range, diffusible signal(s). Therefore, primitive endoderm signaling is a critical early determinant of hematopoietic and vascular development and plays a decisive role in anterior-posterior patterning during mouse embryogenesis.
Nod factor internalization and microtubular cytoskeleton changes occur concomitantly during nodule differentiation in alfalfa
Authors: Timmers Antonius C. J. , Auriac Marie-Christine , de Billy Françoise , Truchet Georges 
Published: April 2021

ABSTRACT
Reorganization of the plant cytoskeleton is thought to play an important role during nodule ontogeny. In situ immunolocalisation of tubulin reveals that important cytoskeletal changes, implying a transient disorganization followed by a newly patterned reorganization, occur in indeterminate and determinate nodules. In alfalfa nodules, cytoskeletal changes closely parallel the symbiotic differentiation features related to cell infection, bacterial release, endopolyploidization, cell enlargement, cell spatial organization and organelle ultrastructure and positioning. Moreover, the fact that microtubule disorganization can be correlated with Nod factor internalization in central infected cells suggests that Nod factors are possibly involved in the control of cytoskeletal changes which direct the differentiation of bacteria-containing cells.
Early posterior neural tissue is induced by FGF in the chick embryo
Authors: Storey Kate G. , Goriely Anne , Sargent Catherine M. , Brown Jennifer M. , Burns Helen D. , Abud Helen M. , Heath John K. 
Published: April 2021

ABSTRACT
Signals that induce neural cell fate in amniote embryos emanate from a unique cell population found at the anterior end of the primitive streak. Cells in this region express a number of fibroblast growth factors (FGFs), a group of secreted proteins implicated in the induction and patterning of neural tissue in the amphibian embryo. Here we exploit the large size and accessibility of the early chick embryo to analyse the function of FGF signalling specifically during neural induction. Our results demonstrate that extraembryonic epiblast cells previously shown to be responsive to endogenous neural-inducing signals express early posterior neural genes in response to local, physiological levels of FGF signal. This neural tissue does not express anterior neural markers or undergo neuronal differentiation and forms in the absence of axial mesoderm. Prospective mesodermal tissue is, however, induced and we present evidence for both the direct and indirect action of FGFs on prospective posterior neural tissue. These findings suggest that FGF signalling underlies a specific aspect of neural induction, the initiation of the programme that leads to the generation of the posterior central nervous system.
Retinal axon guidance by region-specific cues in diencephalon
Authors: Tuttle Rebecca , Braisted Janet E. , Richards Linda J. , O’Leary Dennis D. M. 
Published: April 2021

ABSTRACT
Retinal axons show region-specific patterning along the dorsal-ventral axis of diencephalon: retinal axons grow in a compact bundle over hypothalamus, dramatically splay out over thalamus, and circumvent epithalamus as they continue toward the dorsal midbrain. In vitro, retinal axons are repulsed by substrate-bound and soluble activities in hypothalamus and epithalamus, but invade thalamus. The repulsion is mimicked by a soluble floor plate activity. Tenascin and neurocan, extracellular matrix molecules that inhibit retinal axon growth in vitro, are enriched in hypothalamus and epithalamus. Within thalamus, a stimulatory activity is specifically upregulated in target nuclei at the time that retinal axons invade them. These findings suggest that region-specific, axon repulsive and stimulatory activities control retinal axon patterning in the embryonic diencephalon.
Dual genetic pathways of endothelin-mediated intercellular signaling revealed by targeted disruption of endothelin converting enzyme-1 gene
Authors: Yanagisawa Hiromi , Yanagisawa Masashi , Kapur Raj P. , Richardson James A. , Williams S. Clay , Clouthier David E. , Wit Damiane de , Emoto Noriaki , Hammer Robert E. 
Published: April 2021

ABSTRACT
Recent gene targeting studies have revealed unexpected roles for endothelins in the development of neural crestderived tissues. Endothelin converting enzyme-1 (ECE-1) catalyzes the proteolytic activation of big endothelin-1 to endothelin-1(ET-1) in vitro. However, the importance of ECE-1 cleavage in the multiple endothelin pathways in vivo is unknown. Here we generated a targeted null mutation in the mouse ECE-1 gene. ECE-1−/− term embryos exhibited craniofacial and cardiac abnormalities virtually identical to the defects seen in ET-1 and endothelin A receptor (ETA)deficient embryos. Epidermal melanocytes as well as enteric neurons of the distal gut were also absent in ECE-1−/− embryos, reproducing the developmental phenotype seen in ET-3−/− and endothelin B receptor (ETB)−/− mice. Surprisingly, large amounts of mature ET-1 peptide are found in ECE-1−/− embryos, indicating that non-ECE-1 protease(s) can activate ET-1 at certain sites. However, these enzymes cannot produce sufficient mature endothelin at the locations crucial for normal embryonic development. These findings reveal that ECE-1 is a bona fide activating protease for both big ET-1 and big ET-3 in vivo, and that the cell-cell communication pathways represented by the ET-1/ECE-1/ETA axis and the ET-3/ECE-1/ETB axis are each involved in the development of distinct subsets of neural crest cell lineages. Mutations in ECE-1 may cause developmental defects in humans, such as Hirschsprung disease, velocardiofacial syndrome and related neurocristopathies.
Xenopus Smad8 acts downstream of BMP-4 to modulate its activity during vertebrate embryonic patterning
Authors: Nakayama Takuya , Snyder Mark A. , Grewal Savraj S. , Tsuneizumi Kazuhide , Tabata Tetsuya , Christian Jan L. 
Published: April 2021

ABSTRACT
Bone morphogenetic proteins (BMPs) participate in the development of nearly all organs and tissues. BMP signaling is mediated by specific Smad proteins, Smad1 and/or Smad5, which undergo serine phosphorylation in response to BMP-receptor activation and are then translocated to the nucleus where they modulate transcription of target genes. We have identified a distantly related member of the Xenopus Smad family, Smad8, which lacks the C-terminal SSXS phosphorylation motif present in other Smads, and which appears to function in the BMP signaling pathway. During embryonic development, the spatial pattern of expression of Smad8 mirrors that of BMP-4. We show that an intact BMP signaling pathway is required for its expression. Overexpression of Smad8 in Xenopus embryos phenocopies the effect of blocking BMP- 4 signaling, leading to induction of a secondary axis on the ventral side of intact embryos and to direct neural induction in ectodermal explants. Furthermore, Smad8 can block BMP-4-mediated induction of ventral mesoderm- specific gene expression in ectodermal explants. Overexpression of Smad8 within dorsal cells, however, causes patterning defects that are distinct from those reported in BMP-4-deficient embryos, suggesting that Smad8 may interact with additional signaling pathways. Indeed, overexpression of Smad8 blocks expression of Xbra in whole animals, and partially blocks activin signaling in animal caps. In addition, Smad8 inhibits involution of mesodermal cells during gastrulation, a phenotype that is not observed following blockade of activin or BMPs in Xenopus. Together, these results are consistent with the hypothesis that Smad8 participates in a negative feedback loop in which BMP signaling induces the expression of Smad8, which then functions to negatively modulate the amplitude or duration of signaling downstream of BMPs and, possibly, downstream of other transforming growth factor-β (TGF-β) family ligands.
Auxin-induced developmental patterns in Brassica juncea embryos
Authors: Hadfi Katalin , Speth Volker , Neuhaus Gunther 
Published: April 2021

ABSTRACT
To investigate the mechanism of auxin action during pattern formation in dicot embryos, we tested the effects of the natural auxin indole-3-acetic acid (IAA), the auxin transport inhibitor N-(1-naphthyl)thalamic acid (NPA) and the antiauxin p-chlorophenoxyisobutyric acid (PCIB). In vitro treatments of isolated zygotic Brassica juncea embryos with these substances led to a wide range of morphogenetic alterations. Treatment of globular embryos with exogenous auxin (10-40 µM) either completely inhibited morphogenesis, resulting in ball-shaped embryos, or caused the development of egg- and cucumber-shaped embryos, which only consisted of a shortened hypocotyl without any apical structures. Axis duplication was observed sometimes after inhibition of auxin transport in globular embryos, and led to the development of twin embryos. During the transition from globular to heart stage, changes in auxin distribution or activity frequently caused the development of either split-collar or collar-cotyledons. Antiauxin inhibited cotyledon growth, leading to embryos with single or no cotyledons, or inhibited the development of the hypocotyl and the radicle. Inhibition of auxin transport in transition embryos sometimes led to axis broadening, which resulted in the development of two radicles. The described changes in embryo shapes represent arrests in different auxin-regulated developmental steps and phenocopy some Arabidopsis morphogenetic mutants.
Defined concentrations of a posteriorizing signal are critical for MafB/Kreisler segmental expression in the hindbrain
Authors: Grapin-Botton Anne , Bonnin Marie-Ange , Sieweke Michael , Douarin Nicole M. Le 
Published: April 2021

ABSTRACT
It has been shown by using the quail/chick chimera system that Hox gene expression in the hindbrain is influenced by positional signals arising from the environment. In order to decipher the pathway that leads to Hox gene induction, we have investigated whether a Hox gene regulator, the leucine zipper transcription factor MafB/Kr, is itself transcriptionally regulated by the environmental signals. This gene is normally expressed in rhombomeres (r) 5 and 6 and their associated neural crest. MafB/Kr expression is maintained in r5/6 when grafted into the environment of r3/4. On the contrary, the environment of rhombomeres 7/8 represses MafB/Kr expression. Thus, as previously shown for the expression of Hox genes, MafB/Kr expression is regulated by a posterior-dominant signal, which in this case induces the loss of expression of this gene. We also show that the posterior signal can be transferred to the r5/6 neuroepithelium by posterior somites (somites 7 to 10) grafted laterally to r5/6. At the r4 level, the same somites induce MafB/Kr in r4, leading it to behave like r5/6. The posterior environment regulates MafB/Kr expression in the neural crest as it does in the corresponding hindbrain level, showing that some positional regulatory mechanisms are shared by neural tube and neural crest cells. Retinoic acid beads mimic the effect produced by the somites in repressing MafB/Kr in r5/6 and progressively inducing it more rostrally as its concentration increases. We therefore propose that the MafB/Kr expression domain is defined by a molecule unevenly distributed in the paraxial mesoderm. This molecule would allow the expression of the MafB/Kr gene in a narrow window of concentration by activating its expression at a definite threshold and repressing it at higher levels, accounting for its limited domain of expression in only two rhombomeres. It thus appears that the regulation of MafB/Kr expression in the rhombomeres could be controlled by the same posteriorizing factor(s) as Hox genes.
The lines gene of Drosophila is required for specific functions of the Abdominal-B HOX protein
Authors: Castelli-Gair James 
Published: April 2021

ABSTRACT
The Hox genes encode homeobox transcription factors that control the formation of segment specific structures in the anterior-posterior axis. HOX proteins regulate the transcription of downstream targets acting both as repressors and as activators. Due to the similarity of their homeoboxes it is likely that much of the specificity of HOX proteins is determined by interaction with transcriptional cofactors, but few HOX cofactor proteins have yet been described. Here I present genetic evidence showing that lines, a segment polarity gene of Drosophila, is required for the function of the Abdominal-B protein. In lines mutant embryos Abdominal-B protein expression is normal but incapable of promoting its normal functions: formation of the posterior spiracles and specification of an eighth abdominal denticle belt. These defects arise because in lines mutant embryos the Abdominal-B protein cannot activate its direct target empty spiracles or other downstream genes while it can function as a repressor of Ultrabithorax and abdominal-A. The lines gene seems to be required exclusively for Abdominal-B but not for the function of other Hox genes.
Role of vascular endothelial-cadherin in vascular morphogenesis
Authors: Gory-Fauré Sylvie , Prandini Marie-Hélène , Pointu Hervé , Roullot Valérie , Pignot-Paintrand Isabelle , Vernet Muriel , Huber Philippe 
Published: April 2021

ABSTRACT
Vascular endothelial (VE)-cadherin is an adhesive transmembrane protein specifically expressed at interendothelial junctions. Its extracellular domain exhibits Ca2+-dependent homophilic reactivity, promoting cell-cell recognition. Mice deficient in VE-cadherin die at mid-gestation resulting from severe vascular defects. At the early phases of vascular development (E8.5) of VE- cadherin-deficient embryos, in situ differentiation of endothelial cells was delayed although their differentiation program appeared normal. Vascularization was defective in the anterior part of the embryo, while dorsal aortae and vitelline and umbilical arteries formed normally in the caudal part. At E9.25, organization of endothelial cells into large vessels was incomplete and angiogenesis was impaired in mutant embryos. Defects were more severe in extraembryonic vasculature. Blood islands of the yolk sac and clusters of angioblasts in allantois failed to establish a capillary plexus and remained isolated. This was not due to defective cell-cell recognition as endothelial cells formed intercellular junctions, as shown by electron microscopy. These data indicate that VE-cadherin is dispensable for endothelial homophilic adhesion but is required for vascular morphogenesis.