bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mouse Hox-1.4 gene: primary structure, evidence for promoter activity and expression during development
Authors: Galliot Brigitte , Dollé Pascal , Vigneron Marc , Featherstone Mark S. , Ron Agnes Ba , Duboule Denis 
Published: April 2021

ABSTRACT
This study reports the structure of the mouse homeobox-containing gene Hox-1.4 of the HOX-1 cluster, as well as its expression pattern during embryonic and fetal development. The overall structure of this gene includes two major exons, the second of which encodes the homeo-domain. The putative Hox-1.4 protein displays similarities with products of homologous genes located at the same relative positions in other HOX clusters. A fragment extending 360 base pairs (bp) upstream of a transcriptional start site was shown to be able to promote transcription in transfected cells. This fragment is GC-rich and contains binding sites for the Spl transcription factor. In situ hybridization studies revealed the Hox-1.4 expression pattern during development. As already reported for several other murine Hox genes, Hox-1.4 is expressed in the fetal central nervous system (CNS), in structures derived from somitic mesodermal condensations (sclerotomes, prevertebrae) as well as in several mesodermal components of various organs and structures such as lungs, gut, stomach, intestine and meso- and metanephros. This expression pattern is in good agreement with recent proposals concerning the involvement of such genes in the establishment of the vertebrate body plan as well as the relationship between the positions of these genes within their clusters and the anteroposterior restriction of their expression domains.
Nuclear transplantation of male primordial germ cells in the mouse
Authors: Tsunoda Y. , Tokunaga T. , Imai H. , Uchida T. 
Published: April 2021

ABSTRACT
We examined the developmental ability of enucleated eggs receiving embryonic nuclei and male primordial germ cells (PGCs) in the mouse. Reconstituted eggs developed into the blastocyst stage only when an earlier 2-cell nucleus was transplanted (36 %) but very rarely if the donor nucleus was derived from a later 2-cell, 8-cell, or inner cell mass of a blastocyst (0–3%). 54–100%, 11–67 %, 6–43 % and 6–20 % of enucleated eggs receiving male PGCs developed to 2-cell, 4-cell, 8-cell and blastocyst stage, respectively, in culture. The overall success rate when taking into account the total number of attempts at introducing germ cells was actually 0-6 %. Live fetuses were not obtained after transfer of reconstituted eggs to recipients, although implantation sites were observed.
The developmental ability of reconstituted eggs in relation to embryonic genome activation and genomic imprinting is discussed.
The human blastocyst: cell number, death and allocation during late preimplantation development in vitro
Authors: Hardy Kate , Handyside Alan H. , Winston Robert M. L. 
Published: April 2021

ABSTRACT
The development of 181 surplus human embryos, including both normally and abnormally fertilized, was observed from day 2 to day 5, 6 or 7 in vitro. 63/149 (42 %) normally fertilized embryos reached the blastocyst stage on day 5 or 6. Total, trophectoderm (TE) and inner cell mass (ICM) cell numbers were analyzed by differential labelling of the nuclei with polynucleotide specific fluorochromes. The TE nuclei were labelled with one fluorochrome during immunosurgical lysis, before fixing the embryo and labelling both sets of nuclei with a second fluorochrome (Handyside and Hunter, 1984, 1986). Newly expanded normally fertilized blastocysts on day 5 had a total of 58.3±8.1 cells, which increased to 84.4±5.7 and 125.5±19 on days 6 and 7, respectively. The numbers of TE cells were similar on days 5 and 6 (37.9±6.0 and 40.3±5.0, respectively) and then doubled on day 7 (80.6±15.2). In contrast, ICM cell numbers doubled between days 5 and 6 (20.4±4.0 and 41.9±5.0, respectively) and remained virtually unchanged on day 7 (45.6±10.2). There was widespread cell death in both the TE and ICM as evidenced by fragmenting nuclei, which increased substantially by day 7. These results are compared with the numbers of cells in morphologically abnormal blastocysts and blastocysts derived from abnormally fertilized embryos. The nuclei of arrested embryos were also examined. The number of TE and ICM cells allocated in normally fertilized blastocysts appears to be similar to the numbers allocated in the mouse. Unlike the mouse, however, the proportion of ICM cells remains higher, despite cell death in both lineages.
The zygotic control of Drosophila pair-rule gene expression: II. Spatial repression by gap and pair-rule gene products
Authors: Carroll Sean B. , Vavra Stephanie H. 
Published: April 2021

ABSTRACT
We examined gene expression patterns in certain single and double pair-rule mutant embryos to determine which of the largely repressive pair-rule gene interactions are most likely to be direct and which interactions are probably indirect. From these studies we conclude that: (i) hairy+ and even-skipped (eve+) regulate the fushi tarazu (ftz) gene; (ii) eve+ and runt+ regulate the hairy gene; (iii) runt+ regulates the eve gene; but, (iv) runt does not regulate the ftz gene pattern, and hairy does not regulate the eve gene pattern. These pair-rule interactions are not sufficient, however, to explain the periodicity of the hairy and eve patterns, so we examined specific gap gene mutant combinations to uncover their regulatory effects on these two genes. Our surprising observation is that the hairy and eve genes are expressed in embryos where the three key gap genes hunchback (hb), Krüppel (Kr), and knirps (kni) have been removed, indicating that these gap genes are not essential to activate the pair-rule genes. In fact, we show that in the absence of either hb+ or kni+, or both gap genes, the Kr+ product represses hairy expression. These results suggest that gap genes repress hairy expression in the interstripe regions, rather than activate hairy expression in the stripes. The molecular basis of pair-rule gene regulation by gap genes must involve some dual control mechanisms such that combinations of gap genes affect pair-rule transcription in a different manner than a single gap gene.
Dynamics of Drosophila eye development and temporal requirements of sevenless expression
Authors: Basler Konrad , Hafen Ernst 
Published: April 2021

ABSTRACT
The development of the compound eye of Drosophila consists of a linear, stereotyped program starting at the posterior end of the eye imaginal disc and progressing towards the anterior border. The determination of the R7 photoreceptor cells is part of this process and is dependent on the sevenless gene. In this study, we used a heat-shock-inducible sevenless gene as a conditional allele to determine the exact temporal requirements of sevenless gene expression and to reveal the stages of ommatidial development during which the presumptive R7 cell can respond to the presence of sevenless protein.
Our results indicate that sevenless gene function is only required during a brief, defined period for the initiation of R7 development; subsequently sevenless is dispensable for both differentiation and function of the R7 photoreceptors. Furthermore, using rescue of R7 cells as an internal marker to monitor the progression of eye development we could examine when and at what rate ommatidial columns form.
Myonuclear birthdates distinguish the origins of primary and secondary myotubes in embryonic mammalian skeletal muscles
Authors: Harris A. J. , Duxson M. J. , Fitzsimons R. B. , Rieger F. 
Published: April 2021

ABSTRACT
Myotubes were isolated from enzymically disaggregated embryonic muscles and examined with light microscopy. Primary myotubes were seen as classic myotubes with chains of central nuclei within a tube of myofilaments, whereas secondary myotubes had a smaller diameter and more widely spaced nuclei. Primary myotubes could also be distinguished from secondary myotubes by their specific reaction with two monoclonal antibodies (MAbs) against adult slow myosin heavy chain (MHC). Myonuclei were birthdated with [3H]thymidine autoradiography or with 2-bromo-5 ′-deoxyuridine (BrdU) detected with a commercial monoclonal antibody. After a single pulse of label during the 1 –2 day period when primary myotubes were forming, some primary myotubes had many myonuclei labelled, usually in adjacent groups, while in others no nuclei were labelled. If a pulse of label was administered after this time labelled myonuclei appeared in most secondary myotubes, while primary myotubes received few new nuclei. Labelled and unlabelled myonuclei were not grouped in the secondary myotubes, but were randomly interspersed. We conclude that primary myotubes form by a nearly synchronous fusion of myoblasts with similar birthdates. In contrast, secondary myotubes form in a progressive fashion, myoblasts with asynchronous birthdates fusing laterally with secondary myotubes at random positions along their length. These later-differentiating myoblasts do not fuse with primary myotubes, despite being closely apposed to their surface. Furthermore, they do not generally fuse with each other, as secondary myotube formation is initiated only in the region of the primary myotube endplate.
The function of PS integrins in Drosophila wing morphogenesis
Authors: Wilcox Michael , Diantonio Aaron , Leptin Maria 
Published: April 2021

ABSTRACT
Integrins are found on many cell types during the development of most organisms. In Drosophila their functions can be analysed genetically. An analysis of lethal mutations in a PS integrin gene showed that the integrins were required for muscle attachment and for certain cell sheet migrations during embryogenesis. In this paper we use viable mutations in integrin component genes to look at integrin function in the later stages of development of one adult structure, the wing. We show that two known viable mutations, one which has its primary effect on the fly’s escape response, the other on wing morphogenesis, are mutations in the ß and PS2α subunits, respectively, of the PS integrins. The mutation non-jumper (mysnj42) in the ß subunit leads to wasting of the thoracic jump muscles. Flies in which the dosage of this allele is reduced (and no wildtype copy is present) show defects also in wing morphogenesis. The two surfaces of the wing fail to connect properly, resulting in ‘blistering’ of the wing and the formation of extra crossveins. The mutation in the gene for the PS2α integrin subunit, inflated, also leads to a failure in wing surface apposition and consequent wing blistering. When the two mutations are combined, the mutant phenotype is greatly enhanced. Thus, one of the roles of the PS integrins in late Drosophila development is to ensure the correct apposition and patterning of the wing epithelia.
The role of retinoid-binding proteins in the generation of pattern in the developing limb, the regenerating limb and the nervous system
Authors: Maden M. , Ong D. E. , Summerbell D. , Chytil F. 
Published: April 2021

ABSTRACT
We summarise existing data and describe new information on the levels and distribution of cellular retinoic acid-binding protein (CRABP) and cellular retinol-binding protein (CRBP) in the regenerating axolotl limb, the developing chick limb bud and the nervous system of the chick embryo in the light of the known morphogenetic effects of retinoids on these systems. In the regenerating limb, levels of CRABP rise 3- to 4-fold during regeneration, peaking at the time when retinoic acid (RA) is most effective at causing pattern duplications. The levels of CRBP are low. The potency of various retinoids in causing pattern respecification correlates well with the ability of these compounds to bind to CRABP. In the chick limb bud, the levels of CRABP are high and the levels of CRBP are low. Again the binding of various retinoids to CRABP correlates well with their ability to cause pattern duplications. By immunocytochemistry, we show that CRABP is present at high levels in the progress zone of the limb bud and is distributed across the anteroposterior axis in a gradient with the high point at the anterior margin. In the chick embryo, CRABP levels are high and CRBP levels are low. By immunocytochemistry, CRABP is localised primarily to the developing nervous system, labelling cells and axons in the mantle layer of the neural tube. These become the neurons of the commissural system. Also sensory axons label intensely with CRABP whereas motor axons do not and in the mixed nerves at the brachial plexus sensory and motor components can be distinguished on this basis. In the neural tube, CRBP only stains the ventral floor plate. Since the ventral floor plate may be a source of chemoattractant for commissural axons, we suggest on the basis of these staining patterns that RA may fulfill this role and thus be involved morphogenetically in the developing nervous system.
The role of fibroblast growth factor in early Xenopus development
Authors: Slack J. M. W. , Darlington B. G. , Gillespie L. L. , Godsave S. F. , Isaacs H. V. , Paterno G. D. 
Published: April 2021

ABSTRACT
In early amphibian development, the mesoderm is formed around the equator of the blastula in response to an inductive signal from the endoderm. A screen of candidate substances showed that a small group of heparin-binding growth factors (HBGFs) were active as mesoderm-inducing agents in vitro. The factors aFGF, bFGF, kFGF and ECDGF all show similar potency and can produce inductions at concentrations above about 100 pM. The product of the murine int-2 gene is also active, but with a lower specific activity. Above the induction threshold there is a progressive increase of muscle formation with dose. Single blastula ectoderm cells can be induced and will differentiate in a defined medium to form mesodermal tissues. All inner blastula cells are competent to respond to the factors but outer cells, bearing oocyte-derived membrane, are not.
Inducing activity can be extracted from Xenopus blastulae and binds to heparin like the previously described HBGFs. Antibody neutralization and Western blotting experiments identify this activity as bFGF. The amounts present are small but would be sufficient to evoke inductions in vivo. It is not yet known whether the bFGF is localized to the endoderm, although it is known that inducing activity secreted by endodermal cells can be neutralized by heparin.
The competence of ectoderm to respond to HBGFs rises from about the 128-cell stage and falls again by the onset of gastrulation. This change is paralleled by a rise and fall of binding of 125I-aFGF. Chemical cross-linking reveals that this binding is attributable to a receptor of relative molecular mass about 130 ×103. The receptor is present both in the marginal zone, which responds to the signal in vivo, and in the animal pole region, which is not induced in vivo but which will respond to HBGFs in vitro.
In the embryo, the induction in the vicinity of the dorsal meridian is much more potent than that around the remainder of the marginal zone circumference. Dorsal inductions contain notochord and will dorsalize ventral mesoderm with which they are later placed in contact. This effect might be due to a local high bFGF concentration or, more likely, to the secretion in the dorsal region of an additional, synergistic factor. It is known that TGF-β-1 and -2 can greatly increase the effect of low doses of bFGF, although it has not yet been demonstrated that they are present in the embryo. Lithium salts have a dorsalizing effect on whole embryos or on explants from the ventral marginal zone, and also show potent synergism when applied together with HBGFs.
Neural expression of the Xenopus homeobox gene Xhox3: evidence for a patterning neural signal that spreads through the ectoderm
Authors: Altaba A. Ruiz i 
Published: April 2021

Abstract
The Xenopus laevis homeobox gene Xhox3 is expressed in the axial mesoderm of gastrula and neurula stage embryos. By the late neurula-early tailbud stage, mesodermal expression is no longer detectable and expression appears in the growing tailbud and in neural tissue. In situ hybridization analysis of the expression of Xhox3 in neural tissue shows that it is restricted within the neural tube and the cranial neural crest during the tailbudearly tadpole stages. In late tadpole stages, Xhox3 is only expressed in the mid/hindbrain area and can therefore be considered a marker of anterior neural development. To investigate the mechanism responsible for the anterior-posterior (A-P) regionalization of the neural tissue, the expression of Xhox3 has been analysed in total exogastrula. In situ hybridization analyses of exogastrulated embryos show that Xhox3 is expressed in the apical ectoderm of total exogastrulae, a region that develops in the absence of anterior axial mesoderm. The results provide further support for the existence of a neuralizing signal, which originates from the organizer region and spreads through the ectoderm. Moreover, the data suggest that this neural signal also has a role in A-P patterning the neural ectoderm.
Expression of nerve growth factor receptor mRNA during early development of the chicken embryo: emphasis on cranial ganglia
Authors: Hallböök Finn , Ayer-Lelièvre Christiane , Ebendal Ted , Persson Häkan 
Published: April 2021

Abstract
In situ hybridization with β-nerve growth factor receptor (NGF-R) oligonucleotide probes was used to study NGF-R mRNA expression in early chicken embryos. Sections through the region of the visceral arches showed high levels of NGF-R mRNA in mesenchyme of the visceral arches, neural tube and myotomes. Labelling was also seen over E3 primordium of the trigeminal ganglion (V) and in the placodal thickening of the petrosal (IX) and nodose (X) ganglionic primordia. In the E5 embryo, all cranial sensory ganglia (V, VII, VIII, IX, X) expressed NGF-R mRNA although at varying levels with higher levels in the ganglia of the Vth, IXth and Xth cranial nerves than in ganglia of the VIIth and the VIIIth nerves. Within ganglia of the Vth, IXth and Xth cranial nerves, levels of NGF-R mRNA were higher in regions containing placode-derived neurons, than in regions with neural-crest-derived neurons. The placode-derived nodose ganglion (X) expressed NGF-R mRNA at all stages of development. In the E15 embryo and later in development, two thirds of the large neuron-like cells expressed high levels of NGF-R mRNA. Our results show that expression of NGF-R mRNA, in peripheral neurons, is not restricted to cells of neural crest origin. We also show a transient expression of NGF-R mRNA early in development in a wide range of non-neuronal differentiating cells. The high level of NGF-R mRNA in early differentiating tissues suggest that the NGF-R plays a wider role during development than previously anticipated.
Genetic imprinting in clinical genetics
Authors: Clarke Angus 
Published: April 2021

ABSTRACT
Genetic, and indeed genomic, imprinting does occur in humans. This is manifest at the level of the genome, the individual chromosome, subchromosomal region or fragile site, or the single locus. The best evidence at the single gene level comes from a consideration of familial tumour syndromes. Chromosomal imprinting effects are revealed when uniparental disomy occurs, as in the Prader-Willi syndrome and doubtless other sporadic, congenital anomaly syndromes. Genomic imprinting is manifest in the developmental defects of hydatidiform mole, teratoma and triploidy. Fragile (X) mental retardation shows an unusual pattern of inheritance, and imprinting can account for these effects. Future work in clinical genetics may identify congenital anomalies and growth disorders caused by imprinting: the identification of imprinting effects for specific chromosomal regions in mice will allow the examination of the homologous chromosomal region in humans.
Mechanisms for the construction and developmental control of heterochromatin formation and imprinted chromosome domains
Authors: Tartof Kenneth D. , Bremer Marilyn 
Published: April 2021

ABSTRACT
The study of variegating position effects in Drosophila provides a model system to explore the mechanism and material basis for the construction and developmental control of heterochromatin domains and the imprinted genomic structures that they may create. The results of our experiments in this regard have implications for a diverse assortment of long-range chromosome phenomena related to gene and chromosome inactivation. Specifically, as a consequence of our studies on position effect variegation, we propose a simple mechanism of X-chromosome inactivation, suggest a purpose for genomic imprinting, and postulate a general means for regulating the time in development at which certain genes become heterochromatically repressed.
The evolution of genomic imprinting
Authors: Chandra H. Sharat , Nanjundiah Vidyanand 
Published: April 2021

ABSTRACT
We explore three possible pathways for the evolution of genomic imprinting. (1) Imprinting may be advantageous in itself when imprinted and unimprinted alleles of a locus confer different phenotypes. If a segment of DNA is imprinted in the gametes of one sex but not in those of the other, it might lead to effects correlated with sexual dimorphism. More fundamentally, in certain organisms, sex determination might have evolved because of imprinting. When imprinting leads to chromosome elimination or inactivation and occurs in some embryos but not in others, two classes of embryos, differing in the number of functional gene copies, would result. A model for sex determination based on inequality in the actual or effective copy-number of particular noncoding, regulatory sequences of DNA has been proposed (Chandra, Proc. natn. Acad. Sci. U.S.A. 82. 1165–1169 and 6947–6949, 1985). Maternal control of offspring sex is another possible consequence of imprinting; this would indicate a potential role for imprinting in sex ratio evolution. (2) Genes responsible for imprinting may have pleiotropic effects and they may have been selected for reasons other than their imprinting ability. Lack of evidence precludes further consideration of this possibility. (3) Imprinting could have co-evolved with other traits. For instance, gamete-specific imprinting could lead to a lowered fitness of androgenetic or gynogenetic diploids relative to the fitness of ‘normal’ diploids. This in turn would reinforce the evolution of anisogamy. The reversibility of imprinting raises the possibility of occassional incomplete or improper erasure. If the site of imprinting is the egg -as appears to be the case with the human X (Chandra and Brown, Nature 253. 165–168, 1975) -either improper imprinting or improper erasure could lead to unusual patterns of inheritance (as in the fragile-X syndrome) or fitness effects skipping generations.