bluuebunny/crossref_metadata_2025 huggingface dataset:
The zebrafish buttonhead-like factor Bts1 is an early regulator ofpax2.1expression during mid-hindbrain development
Authors: Tallafuß Alexandra , Wilm Thomas P. , Crozatier Michèle , Pfeffer Peter , Wassef Marion , Bally-Cuif Laure
Published: April 2021

Little is known about the factors that control the specification of the mid-hindbrain domain (MHD) within the vertebrate embryonic neural plate. Because the head-trunk junction of the Drosophila embryo and the MHD have patterning similarities, we have searched for vertebrate genes related to the Drosophila head gap gene buttonhead (btd), which in the fly specifies the head-trunk junction. We report here the identification of a zebrafish gene which, like btd, encodes a zinc-finger transcriptional activator of the Sp-1 family (hence its name, bts1 for btd/Sp-related-1) and shows a restricted expression in the head. During zebrafish gastrulation, bts1 is transcribed in the posterior epiblast including the presumptive MHD, and precedes in this area the expression of other MHD markers such as her5, pax2.1 and wnt1. Ectopic expression of bts1 combined to knock-down experiments demonstrate that Bts1 is both necessary and sufficient for the induction of pax2.1 within the anterior neural plate, but is not involved in regulating her5, wnt1 or fgf8 expression. Our results confirm that early MHD development involves several genetic cascades that independently lead to the induction of MHD markers, and identify Bts1 as a crucial upstream component of the pathway selectively leading to pax2.1 induction. In addition, they imply that flies and vertebrates, to control the development of a boundary embryonic region, have probably co-opted a similar strategy: the restriction to this territory of the expression of a Btd/Sp-like factor.
Abnormal function of astroglia lackingAbrandBcrRacGAPs
Authors: Kaartinen Vesa , Gonzalez-Gomez Ignacio , Voncken Jan Willem , Haataja Leena , Faure Emmanuelle , Nagy Andre , Groffen John , Heisterkamp Nora
Published: April 2021

Experiments in cultured cells have implicated the molecular switch Rac in a wide variety of cellular functions. Here we demonstrate that the simultaneous disruption of two negative regulators of Rac, Abr and Bcr, in mice leads to specific abnormalities in postnatal cerebellar development. Mutants exhibit granule cell ectopia concomitant with foliation defects. We provide evidence that this phenotype is causally related to functional and structural abnormalities of glial cells. Bergmann glial processes are abnormal and GFAP-positive astroglia were aberrantly present on the pial surface. Older Abr;Bcr-deficient mice show spontaneous mid-brain glial hypertrophy, which can further be markedly enhanced by kainic acid. Double null mutant astroglia are hyper-responsive to stimulation with epidermal growth factor and lipopolysaccharide and exhibit constitutively increased phosphorylation of p38 mitogen-activated protein kinase, which is regulated by Rac. These combined data demonstrate a prominent role for Abr and Bcr in the regulation of glial cell morphology and reactivity, and consequently in granule cell migration during postnatal cerebellar development in mammals.
A role ofArabidopsisCOP9 signalosome in multifaceted developmental processes revealed by the characterization of its subunit 3
Authors: Peng Zhaohua , Serino Giovanna , Deng Xing-Wang
Published: April 2021

The COP9 signalosome is a highly conserved eight-subunit protein complex initially defined as a repressor of photomorphogenic development in Arabidopsis. It has recently been suggested that the COP9 signalosome directly interacts and regulates SCF type E3 ligases, implying a key role in ubiquitin-proteasome mediated protein degradation. We report that Arabidopsis FUS11 gene encodes the subunit 3 of the COP9 signalosome (CSN3). The fus11 mutant is defective in the COP9 signalosome and accumulates significant amount of multi-ubiquitinated proteins. The same mutant is specifically impaired in the 26S proteasome-mediated degradation of HY5 but not PHYA, indicating a selective involvement in protein degradation. Reduction-of-function transgenic lines of CSN3 produced through gene co-suppression also accumulate multi-ubiquitinated proteins and exhibit diverse developmental defects. This result substantiates a hypothesis that the COP9 signalosome is involved in multifaceted developmental processes through regulating proteasome-mediated protein degradation.
BMP and Ihh/PTHrP signaling interact to coordinate chondrocyte proliferation and differentiation
Authors: Minina Eleonora , Wenzel Hans Markus , Kreschel Conny , Karp Seth , Gaffield William , McMahon Andrew P. , Vortkamp Andrea
Published: April 2021

During endochondral ossification, two secreted signals, Indian hedgehog (Ihh) and parathyroid hormone-related protein (PTHrP), have been shown to form a negative feedback loop regulating the onset of hypertrophic differentiation of chondrocytes. Bone morphogenetic proteins (BMPs), another family of secreted factors regulating bone formation, have been implicated as potential interactors of the Ihh/PTHrP feedback loop. To analyze the relationship between the two signaling pathways, we used an organ culture system for limb explants of mouse and chick embryos. We manipulated chondrocyte differentiation by supplementing these cultures either with BMP2, PTHrP and Sonic hedgehog as activators or with Noggin and cyclopamine as inhibitors of the BMP and Ihh/PTHrP signaling systems. Overexpression of Ihh in the cartilage elements of transgenic mice results in an upregulation of PTHrP expression and a delayed onset of hypertrophic differentiation. Noggin treatment of limbs from these mice did not antagonize the effects of Ihh overexpression. Conversely, the promotion of chondrocyte maturation induced by cyclopamine, which blocks Ihh signaling, could not be rescued with BMP2. Thus BMP signaling does not act as a secondary signal of Ihh to induce PTHrP expression or to delay the onset of hypertrophic differentiation. Similar results were obtained using cultures of chick limbs.

We further investigated the role of BMP signaling in regulating proliferation and hypertrophic differentiation of chondrocytes and identified three functions of BMP signaling in this process. First we found that maintaining a normal proliferation rate requires BMP and Ihh signaling acting in parallel. We further identified a role for BMP signaling in modulating the expression of Ihh. Finally, the application of Noggin to mouse limb explants resulted in advanced differentiation of terminally hypertrophic cells, implicating BMP signaling in delaying the process of hypertrophic differentiation itself. This role of BMP signaling is independent of the Ihh/PTHrP pathway.
The role of effectors of the activin signalling pathway, activin receptors IIA and IIB, and Smad2, in patterning of tooth development
Authors: Ferguson Christine A. , Tucker Abigail S. , Heikinheimo Kristiina , Nomura Masatoshi , Oh Paul , Li En , Sharpe Paul T.
Published: April 2021

The gene for activin βA is expressed in the early odontogenic mesenchyme of all murine teeth but mutant mice show a patterning defect where incisors and mandibular molars fail to develop but maxillary molars develop normally. In order to understand why maxillary molar tooth development can proceed in the absence of activin, we have explored the role of mediators of activin signalling in tooth development. Analysis of tooth development in activin receptor II and Smad2 mutants shows that a similar tooth phenotype to activin βA mutants can be observed. In addition, we identify a novel downstream target of activin signalling, the Iroquois-related homeobox gene, Irx1, and show that its expression in activin βA mutant embryos is lost in all tooth germs, including the maxillary molars. These results strongly suggest that other transforming growth factor β molecules are not stimulating the activin signalling pathway in the absence of activin. This was confirmed by a non-genetic approach using exogenous soluble receptors to inhibit all activin signalling in tooth development, which reproduced the genetic phenotypes. Activin, thus, has an essential role in early development of incisor and mandibular molar teeth but this pathway is not required for development of maxillary molars.
TheMef2cgene is a direct transcriptional target of myogenic bHLH and MEF2 proteins during skeletal muscle development
Authors: Wang Da-Zhi , Valdez M. Renee , McAnally John , Richardson James , Olson Eric N.
Published: April 2021

Members of the MEF2 family of transcription factors are upregulated during skeletal muscle differentiation and cooperate with the MyoD family of myogenic basic helix-loop-helix (bHLH) transcription factors to control the expression of muscle-specific genes. To determine the mechanisms that regulate MEF2 gene expression during skeletal muscle development, we analyzed the mouse Mef2c gene for cis-regulatory elements that direct expression in the skeletal muscle lineage in vivo. We describe a skeletal muscle-specific control region for Mef2c that is sufficient to direct lacZ reporter gene expression in a pattern that recapitulates that of the endogenous Mef2c gene in skeletal muscle during pre- and postnatal development. This control region is a direct target for the binding of myogenic bHLH and MEF2 proteins. Mutagenesis of the Mef2c control region shows that a binding site for myogenic bHLH proteins is essential for expression at all stages of skeletal muscle development, whereas an adjacent MEF2 binding site is required for maintenance but not for initiation of Mef2c transcription. Our findings reveal the existence of a regulatory circuit between these two classes of transcription factors that induces, amplifies and maintains their expression during skeletal muscle development.
TheDrosophila daughterlessgene autoregulates and is controlled by both positive and negativecisregulation
Authors: Smith John E. , Cronmiller Claire
Published: April 2021

As the only class I helix-loop-helix transcription factor in Drosophila, Daughterless (Da) has generally been regarded as a ubiquitously expressed binding partner for other developmentally regulated bHLH transcription factors. From analysis of a novel tissue-specific allele, dalyh, we show that da expression is not constitutive, but is dynamically regulated. This transcriptional regulation includes somatic ovary-specific activation, autoregulation and negative regulation. Unexpectedly, the diverse functions of da may require that expression levels be tightly controlled in a cell and/or tissue-specific manner. Our analysis of dalyh identifies it as the first springer insertion that functions as an insulating element, with its disruptive activity mediated by the product of a fourth chromosome gene, Suppressor of lyh [Su(lyh)].
Patterning the optic neuroepithelium by FGF signaling and Ras activation
Authors: Zhao Shulei , Hung Fang-Cheng , Colvin Jennifer S. , White Andrew , Dai Weilie , Lovicu Frank J. , Ornitz David M. , Overbeek Paul A.
Published: April 2021

During vertebrate embryogenesis, the neuroectoderm differentiates into neural tissues and also into non-neural tissues such as the choroid plexus in the brain and the retinal pigment epithelium in the eye. The molecular mechanisms that pattern neural and non-neural tissues within the neuroectoderm remain unknown. We report that FGF9 is normally expressed in the distal region of the optic vesicle that is destined to become the neural retina, suggesting a role in neural patterning in the optic neuroepithelium. Ectopic expression of FGF9 in the proximal region of the optic vesicle extends neural differentiation into the presumptive retinal pigment epithelium, resulting in a duplicate neural retina in transgenic mice. Ectopic expression of constitutively active Ras is also sufficient to convert the retinal pigment epithelium to neural retina, suggesting that Ras-mediated signaling may be involved in neural differentiation in the immature optic vesicle. The original and the duplicate neural retinae differentiate and laminate with mirror-image polarity in the absence of an RPE, suggesting that the program of neuronal differentiation in the retina is autonomously regulated. In mouse embryos lacking FGF9, the retinal pigment epithelium extends into the presumptive neural retina, indicating a role of FGF9 in defining the boundary of the neural retina.
Sonic hedgehog is a survival factor for hypaxial muscles during mouse development
Authors: Krüger Marcus , Mennerich Detlev , Fees Stefan , Schäfer Ralf , Mundlos Stefan , Braun Thomas
Published: April 2021

Sonic hedgehog (Shh) has been proposed to function as an inductive and trophic signal that controls development of epaxial musculature in vertebrate embryos. In contrast, development of hypaxial muscles was assumed to occur independently of Shh. We here show that formation of limb muscles was severely affected in two different mouse strains with inactivating mutations of the Shh gene. The limb muscle defect became apparent relatively late and initial stages of hypaxial muscle development were unaffected or only slightly delayed. Micromass cultures and cultures of tissue fragments derived from limbs under different conditions with or without the overlaying ectoderm indicated that Shh is required for the maintenance of the expression of myogenic regulatory factors (MRFs) and, consecutively, for the formation of differentiated limb muscle myotubes. We propose that Shh acts as a survival and proliferation factor for myogenic precursor cells during hypaxial muscle development. Detection of a reduced but significant level of Myf5 expression in the epaxial compartment of somites of Shh homozygous mutant embryos at E9.5 indicated that Shh might be dispensable for the initiation of myogenesis both in hypaxial and epaxial muscles. Our data suggest that Shh acts similarly in both somitic compartments as a survival and proliferation factor and not as a primary inducer of myogenesis.
Activation of rabbit oocytes: the impact of the Ca2+ signal regime on development
Authors: Ozil Jean-Pierre , Huneau Daniel
Published: April 2021

Postfertilization manipulation of mammalian embryos results in various developmental alterations. To determine whether the manipulation of the Ca2+ regime causing oocyte activation is a valuable experimental means in helping understand the biological process by which embryos integrate signals from outside and later regulate gene expression, we linked Ca2+ signal parameters i.e. amplitude, number and frequency, with the efficiency and quality of postimplantation development. Freshly ovulated rabbit oocytes were subjected to repetitive and modulated Ca2+ influx. The results provide three major pieces of information. Firstly, the Ca2+ stimulus is the most efficient signal activating mammalian eggs when it is applied in a repetitive manner, the amplitude being the crucial factor.

Secondly, the dynamics of early cleavage does not appear to be determined by either the frequency or the amplitude of modulation of the Ca2+ signal that activates the oocyte. Thirdly, amplitude and temporal modulation of the Ca2+ signal in the early minutes influences the developmental performance and the morphology of the rabbit parthenogenetic conceptus at day 11.5 of pregnancy. The results demonstrate the importance of epigenetic events during postfertilization as well as the possible uses of Ca2+ modulation in studying long term developmental effects.
GAP-43 promoter elements in transgenic zebrafish reveal a difference in signals for axon growth during CNS development and regeneration
Authors: Udvadia Ava J. , Köster Reinhard W. , Skene J. H. Pate
Published: April 2021

A pivotal event in neural development is the point at which differentiating neurons become competent to extend long axons. Initiation of axon growth is equally critical for regeneration. Yet we have a limited understanding of the signaling pathways that regulate the capacity for axon growth during either development or regeneration. Expression of a number of genes encoding growth associated proteins (GAPs) accompanies both developmental and regenerative axon growth and has led to the suggestion that the same signaling pathways regulate both modes of axon growth. We have tested this possibility by asking whether a promoter fragment from a well characterized GAP gene, GAP-43, is sufficient to activate expression in both developing and regenerating neurons. We generated stable lines of transgenic zebrafish that express green fluorescent protein (GFP) under regulation of a 1 kb fragment of the rat GAP-43 gene, a fragment that contains a number of evolutionarily conserved elements. Analysis of GFP expression in these lines confirms that the rat 1 kb region can direct growth-associated expression of the transgene in differentiating neurons that extend long axons. Furthermore, this region supports developmental down-regulation of transgene expression which, like the endogenous gene, coincides with neuronal maturation. Strikingly, these same sequences are insufficient for directing expression in regenerating neurons. This finding suggests that signaling pathways regulating axon growth during development and regeneration are not the same. While these results do not exclude the possibility that pathways involved in developmental axon growth are also active in regenerative growth, they do indicate that signaling pathway(s) controlling activation of the GAP-43 gene after CNS injury differ in at least one key component from the signals controlling essential features of developmental axon growth.
The AP-2 transcription factor is required for joint formation and cell survival in Drosophila leg development
Authors: Kerber Birgit , Monge Ignacio , Mueller Martin , Mitchell Pamela J. , Cohen Stephen M.
Published: April 2021

Flies mutant for the Drosophila homologue of the mammalian transcription factor AP-2 show a severe reduction in leg length and fail to develop joint structures. Presumptive joint cells express dAP-2 in response to Notch signaling. dAP-2 is required for joint cell differentiation and can induce formation of supernumerary joints when misexpressed. Although dAP-2 is expressed only in presumptive joint cells, its activity is required to support cell survival in the entire leg segment. Taken together, our data indicate that dAP-2 is an important mediator of Notch activity in leg development.
Mesodermal patterning defect in mice lacking the Ste20 NCK interacting kinase (NIK)
Authors: Xue Yingzi , Wang Xiaozhong , Li Zhai , Gotoh Noriko , Chapman Deborah , Skolnik Edward Y.
Published: April 2021

We have previously shown that the Drosophila Ste20 kinase encoded by misshapen (msn) is an essential gene in Drosophila development. msn function is required to activate the Drosophila c-Jun N-terminal kinase (JNK), basket (Bsk), to promote dorsal closure of the Drosophila embryo. Later in development, msn expression is required in photoreceptors in order for their axons to project normally. A mammalian homolog of msn, the NCK-interacting kinase (NIK) (recently renamed to mitogen-activated protein kinase kinase kinase kinase 4; Map4k4), has been shown to activate JNK and to bind the SH3 domains of the SH2/SH3 adapter NCK. To determine whether NIK also plays an essential role in mammalian development, we created mice deficient in NIK by homologous recombination at the Nik gene. Nik−/− mice die postgastrulation between embryonic day (E) 9.5 and E10.5. The most striking phenotype in Nik−/− embryos is the failure of mesodermal and endodermal cells that arise from the anterior end of the primitive streak (PS) to migrate to their correct location. As a result Nik−/− embryos fail to develop somites or a hindgut and are truncated posteriorly. Interestingly, chimeric analysis demonstrated that NIK has a cell nonautonomous function in stimulating migration of presomitic mesodermal cells away from the PS and a second cell autonomous function in stimulating the differentiation of presomitic mesoderm into dermomyotome. These findings indicate that despite the large number of Ste20 kinases in mammalian cells, members of this family play essential nonredundant function in regulating specific signaling pathways. In addition, these studies provide evidence that the signaling pathways regulated by these kinases are diverse and not limited to the activation of JNK because mesodermal and somite development are not perturbed in JNK1-, and JNK2-deficient mice.
Molecular and functional evidence for early divergence of an endothelin-like system during metazoan evolution: analysis of the Cnidarian, hydra
Authors: Zhang Jinsong , Leontovich Alexey , Sarras Michael P.
Published: April 2021

A novel putative endothelin-converting enzyme (ECE) has been cloned from hydra, a freshwater invertebrate that belongs to the second oldest phylum of the animal kingdom. As an integral component of the endothelin system, vertebrate ECE functions in the activation of endothelin (ET) peptides. Vertebrate ETs are (1) the most potent vasoconstrictors known in mammals; and (2) function as essential signaling ligands during development of tissues derived from neural crest cells. To date, only a limited number of immunocytochemical studies have suggested the presence of endothelin-like peptides in invertebrates. Based on structural and functional analyses, we present evidence for a functional endothelin-like system in hydra that is involved in both muscle contraction and developmental processes. These findings indicate the broad use of endothelin systems in metazoans and also indicate that this type of signaling system arose early in evolution even before divergence of protostomes and deuterostomes.
The transcription factor Schnurri plays a dual role in mediating Dpp signaling during embryogenesis
Authors: Torres-Vazquez Jesus , Park Sangbin , Warrior Rahul , Arora Kavita
Published: April 2021

Decapentaplegic (Dpp), a homolog of vertebrate bone morphogenic protein 2/4, is crucial for embryonic patterning and cell fate specification in Drosophila. Dpp signaling triggers nuclear accumulation of the Smads Mad and Medea, which affect gene expression through two distinct mechanisms: direct activation of target genes and relief of repression by the nuclear protein Brinker (Brk). The zinc-finger transcription factor Schnurri (Shn) has been implicated as a co-factor for Mad, based on its DNA-binding ability and evidence of signaling dependent interactions between the two proteins. A key question is whether Shn contributes to both repression of brk as well as to activation of target genes. We find that during embryogenesis, brk expression is derepressed in shn mutants. However, while Mad is essential for Dpp-mediated repression of brk, the requirement for shn is stage specific. Analysis of brk; shn double mutants reveals that upregulation of brk does not account for all aspects of the shn mutant phenotype. Several Dpp target genes are expressed at intermediate levels in double mutant embryos, demonstrating that shn also provides a brk-independent positive input to gene activation. We find that Shn-mediated relief of brk repression establishes broad domains of gene activation, while the brk-independent input from Shn is crucial for defining the precise limits and levels of Dpp target gene expression in the embryo.
SEMAPHORE1 functions during the regulation of ancestrally duplicatedknoxgenes and polar auxin transport in maize
Authors: Scanlon Michael J. , Henderson David C. , Bernstein Brad
Published: April 2021

The expression of class 1 knotted1-like homeobox (knox) genes affects numerous plant developmental processes, including cell-fate acquisition, lateral organ initiation, and maintenance of shoot apical meristems. The SEMAPHORE1 gene product is required for the negative regulation of a subset of maize knox genes, the duplicated loci rough sheath 1 and gnarley1 (knox4). Recessive mutations in semaphore1 result in the ectopic expression of knox genes in leaf and endosperm tissue. Genetic analyses suggest that SEMAPHORE1 may regulate knox gene expression in a different developmental pathway than ROUGH SHEATH2, the first-identified regulator of knox gene expression in maize. Mutations at semaphore1 are pleiotropic, disrupting specific domains of the shoot. However, unlike previously described mutations that cause ectopic knox gene expression, semaphore1 mutations affect development of the embryo, endosperm, lateral roots, and pollen. Moreover, polar transport of the phytohormone auxin is significantly reduced in semaphore1 mutant shoots. The data suggest that many of the pleiotropic semaphore1 phenotypes result from defective polar auxin transport (PAT) in sem1 mutant shoots, and support models correlating down-regulated knox gene expression and PAT in maize shoots.
PTHrP and Indian hedgehog control differentiation of growth plate chondrocytes at multiple steps
Authors: Kobayashi Tatsuya , Chung Ung-il , Schipani Ernestina , Starbuck Michael , Karsenty Gerard , Katagiri Takenobu , Goad Dale L. , Lanske Beate , Kronenberg Henry M.
Published: April 2021

In developing murine growth plates, chondrocytes near the articular surface (periarticular chondrocytes) proliferate, differentiate into flat column-forming proliferating cells (columnar chondrocytes), stop dividing and finally differentiate into hypertrophic cells. Indian hedgehog (Ihh), which is predominantly expressed in prehypertrophic cells, stimulates expression of parathyroid hormone (PTH)-related peptide (PTHrP) which negatively regulates terminal chondrocyte differentiation through the PTH/PTHrP receptor (PPR). However, the roles of PTHrP and Ihh in regulating earlier steps in chondrocyte differentiation are unclear. We present novel mouse models with PPR abnormalities that help clarify these roles. In mice with chondrocyte-specific PPR ablation and mice with reduced PPR expression, chondrocyte differentiation was accelerated not only at the terminal step but also at an earlier step: periarticular to columnar differentiation. In these models, upregulation of Ihh action in the periarticular region was also observed. In the third model in which the PPR was disrupted in about 30% of columnar chondrocytes, Ihh action in the periarticular chondrocytes was upregulated because of ectopically differentiated hypertrophic chondrocytes that had lost PPR. Acceleration of periarticular to columnar differentiation was also noted in this mouse, while most of periarticular chondrocytes retained PPR signaling. These data suggest that Ihh positively controls differentiation of periarticular chondrocytes independently of PTHrP. Thus, chondrocyte differentiation is controlled at multiple steps by PTHrP and Ihh through the mutual regulation of their activities.
Neural crest progenitors of the melanocyte lineage: coat colour patterns revisited
Authors: Wilkie Alison L. , Jordan Siobhán A. , Jackson Ian J.
Published: April 2021

Neural crest-derived melanoblasts are the progenitors of melanocytes, the pigment cells of the skin, hair and choroid. Previous studies of adult chimaeric mice carrying different coat colour markers have suggested that the total melanocyte population is derived from a small number of melanoblast progenitors, each of which generates a discrete unilateral transverse band of colour. This work also suggested minimal mixing of cells between clones. We have used two complementary approaches to assess the behaviour of migrating clones of melanoblasts directly in the developing embryo. First, we made aggregation chimaeras between transgenic Dct-lacZ and non-transgenic embryos, in which lacZ is a marker for melanoblasts. Second, we generated transgenic mice carrying a modified lacZ reporter construct containing a 289 base pair duplication (laacZ) under the control of the Dct promoter. The laacZ transgene is normally inactive, but reverts to wild-type lacZ at low frequency, labelling a cell and all of its progeny at random. Mosaic embryos containing labelled melanoblast clones were generated. In contrast to previous data, chimaeric and mosaic embryonic melanoblast patterns suggest that: (1) there is a large number of melanoblast progenitors; (2) there is a pool of melanoblasts in the cervical region; (3) different cell dispersion mechanisms may operate in the head and trunk regions; and (4) there is extensive axial mixing between clones.
An essential role of aFoxDgene in notochord induction inCionaembryos
Authors: Imai Kaoru S. , Satoh Nori , Satou Yutaka
Published: April 2021

A key issue for understanding the early development of the chordate body plan is how the endoderm induces notochord formation. In the ascidian Ciona, nuclear accumulation of β-catenin is the first step in the process of endoderm specification. We show that nuclear accumulation of β-catenin directly activates the gene (Cs-FoxD) for a winged helix/forkhead transcription factor and that this gene is expressed transiently at the 16- and 32-cell stages in endodermal cells. The function of Cs-FoxD, however, is not associated with differentiation of the endoderm itself but is essential for notochord differentiation or induction. In addition, it is likely that the inductive signal that appears to act downstream of Cs-FoxD does not act over a long range. It has been suggested that FGF or Notch signal transduction pathway mediates ascidian notochord induction. Our previous study suggests that Cs-FGF4/6/9 is partially involved in the notochord induction. The present experimental results suggest that the expression and function of Cs-FGF4/6/9 and Cs-FoxD are not interdependent, and that the Notch pathway is involved in B-line notochord induction downstream of Cs-FoxD.
FGF3 and FGF8 mediate a rhombomere 4 signaling activity in the zebrafish hindbrain
Authors: Maves Lisa , Jackman William , Kimmel Charles B.
Published: April 2021

The segmentation of the vertebrate hindbrain into rhombomeres is highly conserved, but how early hindbrain patterning is established is not well understood. We show that rhombomere 4 (r4) functions as an early-differentiating signaling center in the zebrafish hindbrain. Time-lapse analyses of zebrafish hindbrain development show that r4 forms first and hindbrain neuronal differentiation occurs first in r4. Two signaling molecules, FGF3 and FGF8, which are both expressed early in r4, are together required for the development of rhombomeres adjacent to r4, particularly r5 and r6. Transplantation of r4 cells can induce expression of r5/r6 markers, as can misexpression of either FGF3 or FGF8. Genetic mosaic analyses also support a role for FGF signaling acting from r4. Taken together, our findings demonstrate a crucial role for FGF-mediated inter-rhombomere signaling in promoting early hindbrain patterning and underscore the significance of organizing centers in patterning the vertebrate neural plate.
Spatially specific expression ofHoxb4is dependent on the ubiquitous transcription factor NFY
Authors: Gilthorpe Jonathan , Vandromme Marie , Brend Tim , Gutman Alejandro , Summerbell Dennis , Totty Nick , Rigby Peter W. J.
Published: April 2021

Understanding how boundaries and domains of Hox gene expression are determined is critical to elucidating the means by which the embryo is patterned along the anteroposterior axis. We have performed a detailed analysis of the mouse Hoxb4 intron enhancer to identify upstream transcriptional regulators. In the context of an heterologous promoter, this enhancer can establish the appropriate anterior boundary of mesodermal expression but is unable to maintain it, showing that a specific interaction with its own promoter is important for maintenance. Enhancer function depends on a motif that contains overlapping binding sites for the transcription factors NFY and YY1. Specific mutations that either abolish or reduce NFY binding show that it is crucial for enhancer activity. The NFY/YY1 motif is reiterated in the Hoxb4 promoter and is known to be required for its activity. As these two factors are able to mediate opposing transcriptional effects by reorganizing the local chromatin environment, the relative levels of NFY and YY1 binding could represent a mechanism for balancing activation and repression of Hoxb4 through the same site.
Differential expression of a transcription regulatory factor, the LIM domain only 4 protein Lmo4, in muscle sensory neurons
Authors: Chen Hsiao-Huei , Yip Joseph W. , Stewart Alexandre F. R. , Frank Eric
Published: April 2021

In the stretch-reflex system, proprioceptive sensory neurons make selective synaptic connections with different subsets of motoneurons, according to the peripheral muscles they supply. To examine the molecular mechanisms that may influence the selection of these synaptic targets, we constructed single-cell cDNA libraries from sensory neurons that innervate antagonist muscles. Differential screening of these libraries identified a transcription regulatory co-factor of the LIM homeodomain proteins, the LIM domain only 4 protein Lmo4, expressed in most adductor but few sartorius sensory neurons. Differential patterns of Lmo4 expression were also seen in sensory neurons supplying three other muscles. A subset of motoneurons also expresses Lmo4 but the pattern of expression is not specific for motor pools. Differential expression of Lmo4 occurs early, as neurons develop their characteristic LIM homeodomain protein expression patterns. Moreover, ablation of limb buds does not block Lmo4 expression, suggesting that an intrinsic program controls the early differential expression of Lmo4. LIM homeodomain proteins are known to regulate several aspects of sensory and motor neuronal development. Our results suggest that Lmo4 may participate in this differentiation by regulating the transcriptional activity of LIM homeodomain proteins.
Modulation of the notch signaling byMash1andDlx1/2regulates sequential specification and differentiation of progenitor cell types in the subcortical telencephalon
Authors: Yun Kyuson , Fischman Seth , Johnson Jane , de Angelis Martin Hrabe , Weinmaster Gerry , Rubenstein John L. R.
Published: April 2021

Notch signaling has a central role in cell fate specification and differentiation. We provide evidence that the Mash1 (bHLH) andDlx1 and Dlx2 (homeobox) transcription factors have complementary roles in regulating Notch signaling, which in turn mediates the temporal control of subcortical telencephalic neurogenesis in mice. We defined progressively more mature subcortical progenitors (P1, P2 and P3) through their combinatorial expression of MASH1 and DLX2, as well as the expression of proliferative and postmitotic cell markers at E10.5-E11.5. In the absence ofMash1, Notch signaling is greatly reduced and `early' VZ progenitors(P1 and P2) precociously acquire SVZ progenitor (P3) properties. Comparing the molecular phenotypes of the delta-like 1 and Mash1 mutants, suggests that Mash1 regulates early neurogenesis through Notch-and Delta-dependent and -independent mechanisms. While Mash1 is required for early neurogenesis (E10.5), Dlx1 and Dlx2 are required to downregulate Notch signaling during specification and differentiation steps of `late' progenitors (P3). We suggest that alternate cell fate choices in the developing telencephalon are controlled by coordinated functions of bHLH and homeobox transcription factors through their differential affects on Notch signaling.
Organizer activity of the polar cells duringDrosophilaoogenesis
Authors: Grammont Muriel , Irvine Kenneth D.
Published: April 2021

Patterning of the Drosophila egg requires the establishment of several distinct types of somatic follicle cells, as well as interactions between these follicle cells and the oocyte. The polar cells occupy the termini of the follicle and are specified by the activation of Notch. We have investigated their role in follicle patterning by creating clones of cells mutant for the Notch modulator fringe. This genetic ablation of polar cells results in cell fate defects within surrounding follicle cells. At the anterior, the border cells, the immediately adjacent follicle cell fate, are absent, as are the more distant stretched and centripetal follicle cells. Conversely, increasing the number of polar cells by expressing an activated form of the Notch receptor increases the number of border cells. At the posterior, elimination of polar cells results in abnormal oocyte localization. Moreover, when polar cells are mislocalized laterally, the surrounding follicle cells adopt a posterior fate, the oocyte is located adjacent to them,and the anteroposterior axis of the oocyte is re-oriented with respect to the ectopic polar cells. Our observations demonstrate that the polar cells act as an organizer that patterns surrounding follicle cells and establishes the anteroposterior axis of the oocyte. The origin of asymmetry duringDrosophila development can thus be traced back to the specification of the polar cells during early oogenesis.
Immunohistological studies on the reconstitution of nephric tubules from dissociated cells
Authors: Okada T. S.
Published: April 2021

Dissociated cells of metanephri of 16-day chick embryos were reaggregated immediately or several days after culturing at a glass-medium interface to encourage spreading. The reaggregates were organ-cultured at the air-medium interface on nutrient agar for up to 4 days. They were examined immunohistologically using fluorescein conjugated antiserum-globulin directed against semi-purified ‘kidney-specific’ antigens. The specific antigens (‘K-antigens’) are localized only in the secretory tubules of kidney, and the conjugated antiserum stains only the cells originating from this particular tissue. In the reaggregates of fresh suspension, sorting out of the positive and negative cells started after 1 day in organ culture and the sorting out and selective localization were essentially completed after 4 days. Almost all of the positive cells were incorporated in the reconstituted tubular structures within the reaggregates, while the outer wall of the reaggregates consisted of fluorescence negative epithelial tissue. In the reaggregates of 30 hr. monolayer culture localization was somewhat less selective: Epithelial cells with positive fluorescence very often formed patches of epithelial tissue in the outer wall. Reconstitution of tubular structures hardly occurred in reaggregates after 96 hr. in monolayer. Almost all of the cells of the organ-cultured reaggregates were negative cells. The results indicate that fluorescent antibody technique can be a potent tool for identifying cells derived from a single tissue. The gradual loss of the histoformative capacity in monolayer culture was discussed in relation to the antigenic changes of the cells occurring in such culture conditions.
Genes and genotypes affecting the teeth of the mouse
Authors: Grüneberg Hans
Published: April 2021

This paper is dedicated in gratitude and affection to Professor Hans Nachtsheim on the occasion of his seventy-fifth birthday (13th June 1965).

The teeth of mammals have been studied in great detail both by palaeontologists and by taxonomists who are interested in differences between species or higher systematic categories which are ultimately genetic in nature. By contrast, little is known about intra-specific genetic variability of the dentition. An invitation to participate in an ‘Institute for Advanced Education in Dental Research’ sponsored by the American College of Dentists provided an occasion to explore the situation in the laboratory and, presently, in the wild house mouse. The main results of this search are given in this paper. The extent of the intra-specific variance discovered may help systematists in assessing how much importance to attach to the differences they encounter; and it will be shown how easily one can be misled, in a limited sample, as to what is ‘normal’. Two characteristic dental syndromes to be described pose a new kind of problem to dental pathology. The fact that their interpretation in developmental terms is far from obvious may act as a stimulus to further work on the embryology of both the dental crown and the roots. The material to be described in this paper offers opportunities for such an approach not hitherto available.
Submicroscopical observations on the differentiation of chick gonads
Authors: Narbaitz Roberto , Adler Ruben
Published: April 2021

The role of hormones in gonadal differentiation has not been fully elucidated. One of the main problems consists in determining the exact moment in which steroid synthesis begins. If, as has been claimed, sex hormones act as organizers and are responsible for the morphological changes which characterize gonadal differentiation, then they should appear before these changes take place.
Developmental regulatory mechanisms in the evolution of insect diversity
Authors: Carroll Sean B.
Published: April 2021

The major architectural differences between most Arthropod classes and orders involve variations in the number, type and pattern of body appendages. We have utilized the emerging knowledge of appendage formation in fruit flies to begin to address the developmental and genetic basis of morphological diversity among insects. Butterflies, for example, differ from fruit flies in possessing larval abdominal limbs, two pairs of adult wings, and a sophisticated system of wing color pattern formation. We have found that the genetic bases for these three major morphological features involve differences between flies and butterflies at three levels of genetic regulation during development.

First, we show that the presence of abdominal limbs in butterflies is associated with striking changes in the regulation of specific homeotic genes in the abdominal segments of the butterfly embryo. Second, we suggest that the twowinged state of the fruit fly and the distinct pattern of the butterfly hindwing are the consequence of many accumulated changes in the target genes regulated by the Ultra-bithorax homeotic gene. And finally, we demonstrate that a new genetic program, involving many of the same genes that specify the conserved global patterning coordinates of fruit fly and butterfly wings, has been superimposed onto the butterfly wing to create their unique color patterning system. These findings demonstrate how morphological diversity arises from the different ways in which conserved sets of regulatory genes are deployed during development.
Domain organizations of extracellular matrix proteins and their evolution
Authors: Engel Jürgen , Efimov Vladimir P. , Maurer Patrik
Published: April 2021

The astonishing diversity in structure and function of extracellular matrix (ECM) proteins originates from different combinations of domains. These are defined as autonomously folding units. Many domains are similar in sequence and structure indicating common ancestry. Evo lutionarily homologous domains are, however, often func tionally very different, which renders function prediction from sequence difficult. Related and different domains are frequently repeated in the same or in different polypeptide chains. Common assembly domains include α-helical coiled-coil domains and collagen triple helices. Other domains have been shown to be involved in assembly to other ECM proteins or in cell binding and cell signalling. The function of most of the domains, however, remains to be elucidated. ECM proteins are rather recent ‘inventions’, and most occur either in plants or mammals but not in both. Their creation by domain shuffling involved a number of different mechanisms at the DNA level in which introns played an important role.
Etude ultrastructurale de Fectoblaste chez l’embryon d’Urodèle normal ou traité par l’urée
Authors: Gallera J. , Baud C. A.
Published: April 2021

A preliminary description is given of the submicroscopic texture of the yolk platelets and of the membrane which surrounds them, as also of that of the hyaloplasm.

The ultrastructure of the cytoplasm of neurectoblast cells and of ventral epiblast cells from young neurulas is characterized by an obvious dorso-ventral orientation of the constituents (hyaloplasm and yolk platelets).

After treatment with urea these cells no longer show this orientation, and they then resemble normal ectoblast cells, but of a younger stage, at the beginning of gastrulation.

The modifications of ultrastructure are correlated with modifications of competence. The origin of these morphological and functional modifications is discussed.
Analyse de l’induction neurale chez les Amphibiens au moyen d’organisateurs marqués
Authors: Ficq Adrienne
Published: April 2021

The analysis of neural induction by means of organizers tagged by glycine and orotic acid has demonstrated the migration of radioactive substances during neuralization.

The incorporation of these precursors, both as regards proteins and nucleic acids, is greatest in regions undergoing active morphogenesis. It seems to be particularly intense in the nuclei.
The Effect of Three Antimetabolites on Sea-Urchin Development
Authors: Hörstadius Sven , Gustafson Tryggve
Published: April 2021

The metabolic background for morphogenesis has been the object of intense investigations during the past decades. As an approach to this problem the metabolic effects of the vegetalizing lithium ion and the animalizing thiocyanate ion have been investigated (cf. Lindahl, 1936, and Gustafson, 1952). The studies of antimetabolites (growth-factor analogues) during the last decade have opened pathways for interfering with the embryonic metabolism in a predictable way. Using the antimetabolites it is now possible to get a deeper insight into the relation between metabolic processes and different developmental trends.
Le pouvoir inducteur de l’endoblaste présomptif contenu dans la ligne primitive jeune de Poulet
Authors: Gallera J. , Nicolet G.
Published: April 2021

Dans deux notes publiées en 1964 et 1965, Vakaet conclut que la partie antérieure de la jeune ligne primitive, transplantée à la périphérie de l’aire pelIucide, ne peut induire que le cerveau, tandis que son segment moyen induit exclusivement la formation d’une nouvelle ligne primitive. Pourtant, Gallera (1968) a obtenu, dans quelques cas, l’induction d’un cerveau par le segment moyen de la jeune ligne primitive, si bien que la règle établie par Vakaet n’a pas une valeur aussi absolue qu’il le pense. Nous avons repris ces expériences systématiquement d’une part pour vérifier si la potentialité d’induire le cerveau et celle de provoquer la formation d’un nouveau centre gastruléen sont aussi strictement localisées que l’affirme Vakaet et d’autre part pour voir si la nature de la réponse de redoblaste de l’hôte ne dépend pas en partie de son âge, et, enfin, pour établir le rôle joué dans le processus d’induction par l’endoblaste présomptif contenu dans la ligne primitive.
Immunofluorescence studies on the distribution of mouse uterine epithelial antigen in foetal, immature and adult mice
Authors: Forsberg John-Gunnar , Nord Lennart
Published: April 2021

In an investigation of cellular differentiation processes, it is of great value to be able to study the appearance of specific cell products. Systems permitting this include pancreatic exocrine cells which make zymogen granules and amylase (Grobstein, 1964), the myoblast which produces myosin (Konigsberg, 1965), the chondrocyte which makes chondroitin and chondroitin synthesizing en-zymes (Lash, Glick & Madden, 1964), and the melanocyte which makes melanin (Wilde, 1961). In other cases, such well-defined products are not known or are difficult to obtain and it is therefore necessary to turn to other methods for investigations of specific cell changes. Histochemical methods have been widely used but frequently give unspecific results. Advantages are obtained by using immuno-chemical methods which can demonstrate the appearance of organ- or tissue-specific antigen (Dumonde, 1966). The differentiation of the lens has been extensively studied by immuno-histological methods (for reviews, see Halbert & Manski, 1963; Dumonde, 1966). The appearance of kidney-specific antigens during metanephros differentiation was studied by Lahti & Saxén (1966).