bluuebunny/crossref_metadata_2025_split huggingface dataset:
Segmental and neuronal architecture of the hindbrain of Krox-20 mouse mutants
Authors: Schneider-Maunoury Sylvie , Seitanidou Tania , Charnay Patrick , Lumsden Andrew 
Published: April 2021

ABSTRACT
The vertebrate hindbrain is transiently segmented during its early development with the formation of reiterated bulges, the rhombomeres (r). The Krox-20 gene, which encodes a zinc finger transcription factor, has been shown previously to be implicated in the maintenance of r3 and r5 (Schneider-Maunoury, S., Topilko, P., Seitanidou, T., Levi, G., Cohen-Tannoudji, M., Pournin, S., Babinet, C. and Charnay, P. (1993) Cell 75, 1199-1214; Swiatek, P. J. and Gridley, T. (1993) Genes Dev. 7, 2071-2084. However, it was not clear from these analyses how extensive the deletion of r3 and r5 was and whether the overall segmentation and internal architecture of the hindbrain was affected. We have now reinvestigated these issues by analysis of rhombomere boundaries, using both morphological and molecular markers, and of the fate of specific motor neuron populations, using retrograde and anterograde carbocyanine dye tracing. We conclude that r3 and r5 and their derivatives are completely eliminated in Krox-20−/ − embryos while overall hindbrain segmentation is maintained. In addition, we show that the disappearance of these territories has important consequences for even-numbered rhombomeres as well, in particular on axonal navigation: (i) a population of r6 motoneurons, presumably normally fated to join the glossopharyngeal nerve, has its axons misrouted toward the facial exit point in r4; (ii) the trigeminal motor axons are also misrouted, presumably because of the proximity of the trigeminal and facial exit points. They fasciculate with facial axons outside the neural tube and enter the second branchial arch instead of the first arch. This navigational error could explain the disappearance, at around 17.5 dpc, of the trigeminal motor nucleus in Krox-20−/ − embryos by inadequate supply of essential, possibly arch-specific survival factors.
Hedgehog activity, independent of Decapentaplegic, participates in wing disc patterning
Authors: Luis Mullor José , Calleja Manuel , Capdevila Javier , Guerrero Isabel 
Published: April 2021

ABSTRACT
In the Drosophila wing imaginal disc, the Hedgehog (Hh) signal molecule induces the expression of decapentaplegic (dpp) in a band of cells abutting the anteroposterior (A/P) compartment border. It has been proposed that Dpp organizes the patterning of the entire wing disc. We have tested this proposal by studying the response to distinct levels of ectopic expression of Hh and Dpp, using the sensory organ precursors (SOPs) of the wing and notum and the presumptive wing veins as positional markers. Here, we show that Dpp specifies the position of most SOPs in the notum and of some of them in the wing. Close to the A/P compartment border, however, SOPs are specified by Hh rather than by Dpp alone. We also show that late signaling by Hh, after setting up dpp expression, is responsible for the formation of vein 3 and the scutellar region, and also for the determination of the distance between veins 3 and 4. One of the genes that mediates the Hh signal is the zinc-finger protein Cubitus interruptus (Ci). These results indicate that Hh has a Dpp-independent morphogenetic effect in the region of the wing disc near the A/P border.
Determination of the unequal fate of cotyledons of a one-leaf plant, Monophyllaea
Authors: Tsukaya Hirokazu 
Published: April 2021

ABSTRACT
One-leaf plants, belonging to the family Gesneriaceae, were described for the first time more than 150 years ago. One such unusual plant, Monophyllaea, has only one leaf at maturity. Only one of the two cotyledons grows continuously, without the formation of true leaves, and this feature, known as anisocotyledonous development, has been repeatedly mentioned in textbooks of plant morphology. However, the mechanism for the determination of the one-leaf phenotype remains to be ascertained.
In this study, meristematic regions were identified, by monitoring DNA synthesis, at the base of both cotyledons just after germination, while no such regions were found in the shoot apex. Surgical experiments with seedlings and analysis of the anisocotyledonous development revealed that the fate of the cotyledons is determined during their growth. Anisocotyledonous development seems to be the result of competition between the two cotyledons. The mechanism that governs the development of the shoot in the genus Monophyllaea is discussed in relation to apical dominance, which is the common mechanism that regulates shoot development in many plants.
Loss of cerebum function ventralizes the zebrafish embryo
Authors: Fisher Shannon , Amacher Sharon L. , Halpern Marnie E. 
Published: April 2021

ABSTRACT
Recent studies implicate ventrally derived signals, in addition to dorsal ones emanating from the organizer, in patterning the vertebrate gastrula. We have identified five overlapping deficiencies that uncover the zebrafish cerebum locus and dramatically alter dorsal-ventral polarity at gastrulation. Consistent with the properties of experimentally ventralized amphibian embryos, cerebum mutants exhibit reduced neurectodermal gene expression domains and an increase in derivatives of ventral mesoderm. Structures derived from paraxial and lateral mesoderm also are reduced; however, dorsal axial mesodermal derivatives, such as the hatching gland and notochord, are largely spared. The pleiotropic action of cerebum deficiencies, and the differential response of affected tissues, suggest that the cerebum gene may normally function as an inhibitor of ven-tralizing signals, a function previously ascribed to Noggin and Chordin in Xenopus. Analysis of the cerebum phenotype provides genetic evidence for the existence of ventralizing signals in the zebrafish gastrula and for antagonists of those signals.
Lingual deficits in BDNF and NT3 mutant mice leading to gustatory and somatosensory disturbances, respectively
Authors: Nosrat Christopher A. , Blomlöf Johan , ElShamy Wael M. , Ernfors Patrik , Olson Lars 
Published: April 2021

ABSTRACT
A combination of anatomical, histological and physiological data from wild-type and null-mutated mice have established crucial roles for BDNF and NT3 in gustatory and somatosensory innervation of the tongue, and indeed for proper development of the papillary surface of the tongue. BDNF is expressed in taste buds, NT3 in many surrounding epithelial structures. Absence of BDNF in mice leads to severely malformed taste bud-bearing papillae and severe reduction of taste buds, a loss of proper innervation of remaining taste buds and a loss of taste discrimination although not of the suckling reflex per se. In contrast, absence of NT3 leads to a massive loss of somatosensory innervation of lingual structures. These findings demonstrate distinct roles for BDNF and NT3 in the establishment of the complex innervation apparatus of the tongue with non-overlapping roles for the lingual gustatory and somatosensory systems. The distinction between different sensory modalities, being dependent on either BDNF or NT3 may also have clinical implications.
A sensory axon repellent secreted from ventral spinal cord explants is neutralized by antibodies raised against collapsin-1
Authors: Shepherd Iain T. , Luo Yuling , Lefcort Frances , Reichardt Louis F. , Raper Jonathan A. 
Published: April 2021

ABSTRACT
During embryogenesis, different subclasses of sensory neurons extend central projections to specific locations in the spinal cord. Muscle and cutaneous afferents initially project to the same location in the dorsal cord. Later, specific muscle afferents leave other afferents behind and project into the ventral cord. Previous studies have shown that ventral spinal cord explants secrete a repellent for sensory neurites. We now find that antibodies to collapsin-1 neutralize this repellent activity. Additional data suggest that all afferents respond to collapsin-1 when they are first confined to the dorsal cord, but that ventrally projecting muscle afferents become collapsin-1 insensitive as they project into the ventral cord. Our results suggest that the transient dorsal expression of collapsin-1 prevents all efferents from entering the cord early and sustained ventral expression prevents dorsally terminating afferents from entering the ventral cord later.
The role of Pax-6 in eye and nasal development
Authors: Grindley Justin C. , Davidson Duncan R. , Hill Robert E. 
Published: April 2021

ABSTRACT
Small eye (Sey) mice homozygous for mutations in the Pax-6 gene have no lenses and no nasal cavities. We have examined the ontogeny of eye and nasal defects in Sey/Sey embryos and have related the defects seen to the pattern of Pax-6 mRNA expression in the mouse during normal eye and nasal development.
There are two principal components of the early eye, the neural ectoderm of the optic vesicle, which forms the retina, and the overlying surface ectoderm, which forms the lens and cornea. By studying these interacting tissues in normal and Sey/Sey embryos, we have identified processes for which Pax-6 is important and can thus suggest possible roles for the Pax-6 gene.
Pax-6 is essential for the formation of lens placodes from surface ectoderm. In normal development, early Pax-6 mRNA expression in a broad domain of surface ectoderm is downregulated, but expression is specifically maintained in the developing lens placode. Moreover, other Pax-6expressing tissues are frequently those that have can transdifferentiate into lens. Thus, phenotype and expression together suggest a role for Pax-6 in lens determination.
At least some functions of Pax-6 can be separated from the influence of other tissues. Early Sey/Sey optic vesicles are abnormally broad and fail to constrict proximally.
These defects occur prior to the time of lens placode formation and probably reflect a requirement for Pax-6 in neural ectoderm. In surface ectoderm domains, where Pax6 expression is known to be independent of the presence of an optic vesicle, Pax-6 function is required for the maintenance of its own transcription.
The mutual dependency of lens and optic vesicle development can also be studied using the Small eye mutation. Using region-specific markers we find that, in the morphologically abnormal Sey/Sey optic vesicles, aspects of normal proximo-distal specification nevertheless persist, despite the complete absence of lens.
Like the lens, the nasal cavities develop from ectodermal placodes that normally express Pax-6 mRNA, fail to form in Sey/Sey mice and show Pax-6-dependent Pax-6 mRNA regulation. Analysis of patterns of programmed cell death and absence of nasal region expression from an Msx-1 transgene in Sey/Sey embryos suggest a requirement for Pax-6 in the transition from presumptive nasal ectoderm to placode, and that Msx-1, or genes regulating it, are possible targets for Pax-6.
Left-right asymmetry of a nodal-related gene is regulated by dorsoanterior midline structures during Xenopus development
Authors: Lohr Jamie L. , Danos Maria C. , Yost H. Joseph 
Published: April 2021

ABSTRACT
Development of asymmetry along the left-right axis is a critical step in the formation of the vertebrate body plan. Disruptions of normal left-right patterning are associated with abnormalities of multiple organ systems, including significant congenital heart disease. The mouse nodal gene, and its homologues in chick and Xenopus, are among the first genes known to be asymmetrically expressed along the left-right axis before the development of organ asymmetry. Alterations in the expression pattern of mouse nodal and the chick homologue (cNR-1) have been associated with defects in the development of left-right asymmetry and cardiac looping (Levin, M., Johnson, R. L., Stern, C. D., Kuehn, M. and Tabin, C. (1995) Cell 82, 803-814; Collignon, J., Varlet, I. and Robertson, E. J. (1996) Nature 381, 155-158; Lowe, L. A., Supp, D. M., Sampath, K., Yokoyama, T., Wright, C. V. E., Potter, S. S., Overbeek, P. and Kuehn, M. R. (1996) Nature 381, 158-161). Here, we show that the normal expression patterns of the Xenopus nodal-related gene (Xnr-1) are variable in a large population of embryos and that Xnr-1 expression is altered by treatments that perturb normal left-right development. The incidence of abnormal Xnr-1 expression patterns correlates well with cardiac reversal rates in both control and experimentally treated Xenopus embryos. Furthermore, dorsal midline structures, including notochord and/or hypochord and neural floorplate, regulate Xnr-1 expression prior to the specification of cardiac left-right orientation by repression of Xnr-1 expression in the right lateral plate mesoderm during closure of the neural tube. The correlation of Xnr-1 expression and orientation of cardiac looping suggests that Xnr-1 is a component of the left-right signaling pathway required for the specification of cardiac orientation in Xenopus, and that dorsal midline structures normally act to repress the signaling pathway on the right side of the embryo.
The allocation of epiblast cells to the embryonic heart and other mesodermal lineages: the role of ingression and tissue movement during gastrulation
Authors: Tam Patrick P. L. , Parameswaran Maala , Kinder Simon J. , Weinberger Ron P. 
Published: April 2021

ABSTRACT
The cardiogenic potency of cells in the epiblast of the early primitive-streak stage (early PS) embryo was tested by heterotopic transplantation. The results of this study show that cells in the anterior and posterior epiblast of the early PS-stage embryos have similar cardiogenic potency, and that they differentiated to heart cells after they were transplanted directly to the heart field of the late PS embryo. That the epiblast cells can acquire a cardiac fate without any prior act of ingression through the primitive streak or movement within the mesoderm suggests that neither morphogenetic event is critical for the specification of the cardiogenic fate. The mesodermal cells that have recently ingressed through the primitive streak can express a broad cell fate that is characteristic of the pre-ingressed cells in the host when they were returned to the epiblast. However, mesoderm cells that have ingressed through the primitive streak did not contribute to the lateral plate mesoderm after transplantation back to the epiblast, implying that some restriction of lineage potency may have occurred during ingression. Early PS stage epiblast cells that were transplanted to the epiblast of the mid PS host embryos colonised the embryonic mesoderm but not the extraembryonic mesoderm. This departure from the normal cell fate indicates that the allocation of epiblast cells to the mesodermal lineages is dependent on the timing of their recruitment to the primitive streak and the morphogenetic options that are available to the ingressing cells at that instance.
Retinoid signaling is required for the establishment of a ZPA and for the expression of Hoxb-8, a mediator of ZPA formation
Authors: Lu Hui-Chen , Revelli Jean-Pierre , Goering Lisa , Thaller Christina , Eichele Gregor 
Published: April 2021

ABSTRACT
We show that retinoid receptor antagonists applied to the presumptive wing region block the formation of a zone of polarizing activity (ZPA). This suggests a direct relationship between retinoid signaling and the establishment of the ZPA. We provide evidence that the Hox gene, Hoxb-8, is a direct target of retinoid signaling since exogenously applied RA rapidly induces this gene in the absence of protein synthesis and, moreover, retinoid receptor antagonists down-regulate Hoxb-8 expression. In addition, we find that, in the lateral plate mesoderm, the domains of Hoxb-8 expression and of polarizing activity are coextensive. Taken together, these findings support the hypothesis that retinoids are required for the establishment of a ZPA, and that retinoids act, at least in part, through Hoxb-8, a gene associated with ZPA formation (Charité et al., 1994).
Requirement for engrailed and invected genes reveals novel regulatory interactions between engrailed/invected, patched, gooseberry and wingless during Drosophila neurogenesis
Authors: Bhat Krishna Moorthi , Schedl Paul 
Published: April 2021

ABSTRACT
During neurogenesis, the transmembrane protein Patched (Ptc) promotes a wingless (wg)-mediated specification of a neuronal precursor cell, NB4-2, by repressing gooseberry (gsb). In this study, novel interactions of these genes with engrailed (en) and invected (inv) during neurogenesis have been uncovered. While in row 4 cells Ptc represses gsb and wg, in row 5 cells en/inv relieve Ptc repression of gsb by a non-autonomous mechanism that does not involve hedgehog (hh). This differential regulation of gsb leads to the specification of NB5-3 and NB4-2 identities to two distinct neuroblasts. The uncoupling of the ptc-gsb regulatory circuit also enables gsb to promote Wg expression in row 5 cells. Our results suggest that the en/inv⟶ptc⟶gsb⟶wg pathway uncovered here and the hh⟶wg are distinct pathways that function to maintain wild-type level of Wg. Our results also indicate that Hh is not the only ligand for Ptc and similarly Ptc is not the only receptor for Hh.
Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resembles that of its segment-polarity homolog in Drosophila
Authors: Holland Linda Z. , Kene Mamata , Williams Nic A. , Holland Nicholas D. 
Published: April 2021

ABSTRACT
Vertebrate segmentation has been proposed as an evolutionary inheritance either from some metameric protostome or from a more closely related deuterostome. To address this question, we studied the developmental expression of AmphiEn, the engrailed gene of amphioxus, the closest living invertebrate relative of the vertebrates. In neurula embryos of amphioxus, AmphiEn is expressed along the anteroposterior axis as metameric stripes, each located in the posterior part of a nascent or newly formed segment. This pattern resembles the expression stripes of the segment-polarity gene engrailed, which has a key role in establishing and maintaining the metameres in embryos of Drosophila and other metameric protostomes. Later, amphioxus embryos express AmphiEn in non-metameric patterns — transiently in the embryonic ectoderm and dorsal nerve cord. Nerve cord expression occurs in a few cells approximately midway along the rostrocaudal axis and also in a conspicuous group of anterior cells in the cerebral vesicle at a level previously identified as corresponding to the vertebrate diencephalon. Compared to vertebrate engrailed expression at the midbrain/hindbrain boundary, AmphiEn expression in the cerebral vesicle is relatively late. Thus, it is uncertain whether the cerebral vesicle expression marks the rostral end of the amphioxus hindbrain; if it does, then amphioxus may have little or no homolog of the vertebrate midbrain. The segmental expression of AmphiEn in forming somites suggests that the functions of engrailed homologs in establishing and main- taining a metameric body plan may have arisen only once during animal evolution. If so, the protostomes and deuterostomes probably shared a common segmented ancestor.
5-HT2B receptor-mediated serotonin morphogenetic functions in mouse cranial neural crest and myocardiac cells
Authors: Choi Doo-Sup , Ward Simon J. , Messaddeq Nadia , Launay Jean-Marie , Maroteaux Luc 
Published: April 2021

ABSTRACT
During embryogenesis, serotonin has been reported to be involved in craniofacial and cardiovascular morphogenesis. The detailed molecular mechanisms underlying these functions, however remain unknown. From mouse and human species, we have recently reported the cloning of 5-HT2B receptors which share signal transduction pathways with other 5-HT2 receptor subtypes (5-HT2A and 5-HT2C). In addition to phospholipase C stimulation, it appears that these three subtypes of receptor transduce a common serotonin-induced mitogenic activity, which could be important for cell differentiation and proliferation. We have first investigated the expression of 5-HT2 receptor mRNAs in the mouse embryo. Interestingly, a peak of 5-HT2B receptor mRNA expression was detected 8-9 days postcoitum, whereas there was only low level 5-HT2A and no 5-HT2C receptor mRNA expression at this stage. Expression of this receptor was confirmed by binding assays using a 5-HT2-specific ligand which revealed a peak of binding to membrane preparations from 9 days post-coitum embryos. In addition, whole mount in situ hybridisation and immunohistochemistry on similar stage embryos detected 5-HT2B expression in neural crest cells, heart myocardium and somites. The requirement for functional 5-HT2B receptors between 8 and 9 days postcoitum is supported by culture of embryos exposed to 5-HT2-specific ligands; 5-HT2B high-affinity antagonist such as ritanserin, induced morphological defects in the cephalic region, heart and neural tube. These antagonistic treatments interfere with cranial neural crest cell migration, induce their apoptosis, and are responsible for abnormal sarcomeric organisation of the subepicardial layer and for the absence of the trabecular cell layer in the ventricular myocardium. This report indicates for the first time that 5-HT2B receptors are actively mediating the action of serotonin on embryonic morphogenesis, probably by pre-venting the differentiation of cranial neural crest cells and myocardial precursor cells.
Ethylene provides positional information on cortical cell division but is not involved in Nod factor-induced root hair tip growth in Rhizobium-legume interaction
Authors: Heidstra Renze , Yang Wei Cai , Yalcin Yesim , Peck Scott , Emons AnneMie , Kammen Ab van , Bisseling Ton 
Published: April 2021

ABSTRACT
Nod factors secreted by Rhizobium leguminosarum bv. viciae induce root hair deformation, involving a reinitiation of tip growth, and the formation of nodule primordia in Vicia sativa (vetch). Ethylene is a potent inhibitor of cortical cell division, an effect that can be counteracted by applying silver ions (Ag+) or aminoethoxy-vinylglycine (AVG). In contrast to the inhibitory effect on cortical cell division, ethylene promotes the formation of root hairs (which involves tip growth) in the root epidermis of Arabidopsis. We investigate the possible paradox concerning the action of ethylene, putatively promoting Nod factor induced tip growth whilst, at the same time, inhibiting cortical cell division.
We show, by using the ethylene inhibitors AVG and Ag+, that ethylene has no role in the reinitiation of root hair tip growth induced by Nod factors (root hair deformation) in vetch. However, root hair formation is controlled, at least in part, by ethylene. Furthermore, we show that ACC oxidase, which catalizes the last step in ethylene biosynthesis, is expressed in the cell layers opposite the phloem in that part of the root where nodule primordia are induced upon inoculation with Rhizobium. Therefore, we test whether endogenously produced ethylene provides positional information controlling the site where nodule primordia are formed by determining the position of nodules formed on pea roots grown in the presence of AVG or Ag+.