bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methylation levels of maternal and paternal genomes during preimplantation development
Authors: HOWLETT SARAH K. , REIK WOLF 
Published: April 2021

ABSTRACT
The methylation status of three highly repeated sequences was studied in sperm, eggs and preimplantation embryos with different combinations of parental chromosomes. High levels of methylation of the IAP and MUP sequence families were found in sperm and in eggs, whereas the LI repeat was found to be highly methylated in sperm but only about 42 % methylated in eggs. To assess how the two parental genomes behaved during preimplantation development, normal, fertilised embryos were compared with parthenogenetic embryos where the chromosomes are exclusively of maternal origin. It was observed that the high levels of methylation at the IAP and MUP sequences were retained through early development, with the first signs of demethylation at the IAP sequences apparent on both parental chromosomes in the blastocyst. Methylation at the sperm-derived LI sequences dropped to about the same level as that of the egg-derived sequences by the late 2-cell stage, both then remain at this intermediate level until around the time of cavitation when levels fell to about 10 % in the blastocyst. High levels of DNA methylase were detected in germinal vesicle and metaphase II oocytes; these high levels were maintained in fertilised and parthenogenetic embryos through into the morula and then declined to be undetectable in the blastocyst. Our comparison of maternal and paternal genomes suggests that methylation levels at repeat sequences are remarkably similar at the time of fertilization or, as in the case of the LI sequences, they become so during the first few cell cycles. Hence, there do not appear to be global methylation differences between the genomes that are retained through preimplantation development. The marked loss of methylation from sperm-derived LI sequences during the first two cell cycles may be indicative of the re-modelling of paternal chromosomes in the egg.
Sex chimaerism, fertility and sex determination in the mouse
Authors: Patek C. E. , Kerr J. B. , Gosden R. G. , Jones K. W. , Hardy K. , Muggleton-Harris A. L. , Handyside A. H. , Whittingham D. G. , Hooper M. L. 
Published: April 2021

Abstract
Adult intraspecific mouse chimaeras, derived by introducing male embryonal stem cells into unsexed host blastocysts, were examined to determine whether gonadal sex was correlated with the sex chromosome composition of particular cell lineages. The fertility of XX↔XY and XY↔XY male chimaeras was also compared. The distribution of XX and XY cells in 34 XX↔XY ovaries, testes and ovotestes was determined by in situ hybridisation using a Y-chromosome-specific probe. Both XX and XY cells were found in all gonadal somatic tissues but Sertoli cells were predominantly XY and granulosa cells predominantly XX. The sex chromosome composition of the tunica albuginea and testicular surface epithelium could not, in general, be fully resolved, owing to diminished hybridisation efficiency in these tissues, but the ovarian surface epithelium (which like the testicular surface epithelium derives from the coelomic epithelium) was predominantly XX. These findings show that the claim that Sertoli cells were exclusively XY, on which some previous models of gonadal sex determination were based, was incorrect, and indicate instead that in the mechanism of Sertoli cell determination there is a step in which XX cells can be recruited. However, it remains to be established whether the sex chromosome constitution of the coelomic epithelium lineage plays a causal role in gonadal sex determination.
Male chimaeras with XX↔XY testes were either sterile or less fertile than chimaeras with testes composed entirely of XY cells. This impaired fertility was associated with the loss of XY germ cells in atrophic seminiferous tubules. Since this progressive lesion was correlated with a high proportion of XX Leydig cells, we suggest that XX Leydig cells are functionally defective, and unable to support spermatogenesis.
N-CAM alterations in splotch neural tube defect mouse embryos
Authors: Moase Connie E. , Trasler Daphne G. 
Published: April 2021

ABSTRACT
The splotch (Sp) mouse is a model for both neurulation defects and defects in neural crest cell (NCC) derivatives. Since neurulation and NCC emigration from the neural tube occur at similar times in development, we suggest that these two events share a mechanism that, if disrupted, leads to malformations in both developmental pathways. Previous studies have shown that the underlying defect in these mutants may involve a mechanism that alters cellular organization and communication. Cell adhesion molecules (CAMs) have been linked with such interactions and because some, including N-CAM, are involved in neural development, we were interested in their pattern of expression in the splotch mutant. Immunolocalization studies showed similar temporospatial distributions of N-CAM antibody in embryonic day 9 mutants and controls. However, mutant embryos had a much higher intensity of anti-N-CAM fluorescence compared to controls. Further characterization using immunoblot analysis revealed that Sp mutants have an altered N-CAM polypeptide profile. Two N-CAM isoforms (Mr 140K and 180K, K=103) are normally present at this time of development. However, extracts from Sp embryos display a heavier N-CAM species (Mr 200K), as well as an altered 140K isoform. Heterozygotes also exhibit a different N-CAM profile, displaying a band between 180K and 200K in addition to the normal 180K and 140K species. Microheterogeneity was also observed in mutant and heterozygous embryos carrying Spd, an allele of Sp. However, these differences were less dramatic than that of Sp. The Sp locus may be involved in post-translational modification of N-CAM. An aberration in N-CAM processing could be the primary target of the mutation that leads to the developmental abnormalities observed in this mouse mutant.
Developmental analysis of the retinoic acid-inducible RAR-βJ2 promoter in transgenic animals
Authors: Mendelsohn C. , Ruberte E. , Lemeur M. , Morriss-Kay G. , Chambon P. 
Published: April 2021

Abstract
Retinoic acid (RA) is a signalling molecule important for pattern formation during development. There are three known types of nuclear receptors for RA in mammals, RAR-α, RAR-β and RAR-γ, which transduce the RA signal by inducing or repressing the transcription of target genes. Here we describe the developmental expression pattern of the mouse RAR-β2 promoter. Independent lines of transgenic animals expressing RAR-β2 promoter sequences fused to the E. coil β- galactosidase gene were examined throughout the course of embryogenesis and found to exhibit reproducible and specific patterns of β-galactosidase expression in a majority of sites that have been shown previously to contain mRAR-β transcripts. In the limbs, mRAR-β2 promoter activity and mRAR-β transcripts were both excluded from precartilagenous condensations; interestingly, mRAR-β2 promoter activity was observed in the apical ectodermal ridge (AER) where mRAR-β transcripts could not be detected, while no mRAR-β2 promoter activity or mRAR-β transcripts were associated with the limb region that contains the zone of polarizing activity (ZPA). Analysis of the lacZ expression pattern in embryos from mothers treated with teratogenic doses of RA, indicated that mRAR-β2 promoter is selectively induced in a manner suggesting that overexpression of the mRAR-β2 isoform is involved in RA-generated malformations. The normal and induced expression pattern of the mRAR-β2 promoter suggests several possible roles for mRAR-β2 in development of the limbs, as an inhibitor of cartilage formation, in programmed cell death and in the formation of loose connective tissue.
The genes encoding the major 42S storage particle proteins are expressed in male and female germ cells of Xenopus laevis
Authors: Abdallah Bassima , Hourdry Jacques , Deschamps Stephane , Denis Herman , Mazabraud Andre 
Published: April 2021

ABSTRACT
As components of the 42S storage particles (thesauri-somes), thesaurin a and thesaurin b are involved in the long-term storage of tRNA and 5S RNA in previtello-genic oocytes of Xenopus laevis. Thesaurin a and thesaurin b are among the most abundant proteins in previtellogenic oocytes. We show here that the mRNAs encoding thesaurin a and thesaurin b are present not only in previtellogenic oocytes but also in pre-meiotic germ cells (oogonia). These mRNAs can also be detected in spermatogonia and early spermatocytes, and are translated into protein in testis, as they are in ovary. We conclude that male germ cells mimic female germ cells in several aspects of gene activity related to RNA accumu-lation and metabolism.
Regulated expression and growth inhibitory effects of transforming growth factor-β isoforms in mouse mammary gland development
Authors: Robinson Stephen D. , Silberstein Gary B. , Roberts Anita B. , Flanders Kathleen C. , Daniel Charles W. 
Published: April 2021

ABSTRACT
Transforming Growth Factor-βl (TGF-β1) was pre-viously shown to inhibit reversibly the growth of mouse mammary ducts when administered in vivo by miniature slow-release plastic implants. We now report a compara-tive analysis of three TGF-β isoforms with respect to gene expression and localization of protein products within the mouse mammary gland. Our studies revealed overlapping expression patterns of TGF-β 1, TGF-β 2 and TGF-β 3 within the epithelium of the actively-growing mammary end buds during branching morpho-genesis, as well as within the epithelium of growth-quiescent ducts. However, TGF-J83 was the only isoform detected in myoepithelial progenitor cells (cap cells) of the growing end buds and myoepithelial cells of the mature ducts. During pregnancy, TGF-β2 and TGF-β 3 transcripts increased to high levels, in contrast to TGF-β1 transcripts which were moderately abundant; TGF-β2 was significantly transcribed only during pregnancy. Molecular hybridization in situ revealed overlapping patterns of expression for the three TGF-β isoforms during alveolar morphogenesis, but showed that, in contrast to the patterns of TGF-β1 and TGF-β2 expression, TGF-β3 is expressed more heavily in ducts than in alveoli during pregnancy. Developing alveolar tissue and its associated ducts displayed striking TGF-β3 immunoreactivity which was greatly reduced during lactation. All three isoforms showed dramatically reduced expression in lactating tissue.
The biological effects of active, exogenous TGF-β 2 and TGF-β3 were tested with slow-release plastic implants. These isoforms, like TGF-β1, inhibited mam-mary ductal elongation in situ by causing the disappear-ance of the proliferating stem cell layer (cap cells) and rapid involution of ductal end buds. None of the isoforms were active in inhibiting alveolar morphogenesis. We conclude that under the limited conditions of these tests, the three mammalian isoforms are functionally equival-ent. However, striking differences in patterns of gene expression and in the distribution of immunoreactive peptides suggest that TGF-β isoforms may have distinct roles in mammary growth regulation, morphogenesis and functional differentiation.
Differential expression of R- and N-cadherin in neural and mesodermal tissues during early chicken development
Authors: Inuzuka Hiroyuki , Redies Christoph , Takeichi Masatoshi 
Published: April 2021

ABSTRACT
R-cadherin is a newly identified member of the cadherin family of cell adhesion receptors. The expression of R-cadherin in early chicken embryos was studied using affinity-purified antibodies to this molecule, comparing it with that of N-cadherin. Inununoblot analysis of various organs of 10.5-day embryos showed that R-cadherin is most abundantly expressed in the retina and brain. Immunostaining of the cervical and thoracic regions of embryos revealed that R- and N-cadherin are expressed in all neural tissues. In the neural tube, R-cadherin appears at around stage 21, although N-cadherin expression begins at a much earlier stage. The distribution of R-cadherin in the neural tube differs from that of N-cadherin; for example, some regions of the tube express only R-cadherin, and other regions only N-cadherin. In the peripheral ganglia, these two cadherins are also expressed in different patterns which change during development. Some mesenchymal tissues including the notochord, the myotome, myotubes and perichondria also express these cadherins, again in different patterns. Thus, R- and N-cadherin are differentially expressed in all the tissues examined, and they may contribute to the spatial segregation of heterogeneous cells in a tissue.
Associations between transforming growth factor β1 RNA expression and epithelial – mesenchymal interactions during tooth morphogenesis
Authors: Vaahtokari Anne , Vainio Seppo , Thesleff Irma 
Published: April 2021

ABSTRACTWe have studied the expression of transforming growth factor beta-1 (TGF-β1) RNA during mouse tooth development, using in situ hybridization and experimental tissue recombinations. Analysis of the serial sections revealed the appearance of local expression of TGF-β1 RNA in the dental epithelium at bud-staged teeth (13day embryos). Just before transition to the cap stage, TGF-β1 RNA expression rapidly increased in the epithelial bud, and it also extended to the condensed dental mesenchyme. At cap stage (14- and 15-day embryos), there was an intense expression of TGF-β1 RNA in the morphologically active cervical loops of the dental epithelium.During early bell stage (16- and 17-day embryos), TGF-β1 RNA expression was detected in the inner enamel epithelium where it subsequently almost disappeared (18-day embryos). After birth TGF-β1 transcripts transiently appeared in these cells when they were differentiating into ameloblasts (1-day mice). The transcripts were lost from the ameloblasts when they became secretory (4-day mice), but the expression continued in ameloblasts in enamel-free areas. Transient expression of TGF-β1 RNA was also detected in epithelial stratum intermedium cells at the time of ameloblast differentiation. In the mesenchyme, TGF-β1 RNA was not detected during bell stage until it appeared in differentiated odontoblasts (18-day embryos). The secretory odontoblasts continued to express TGF-β1 RNA at all stages studied including the odontoblasts of incisor roots.Analysis of the distribution of bromodeoxyuridine (BrdU) incorporation indicated apparent correlations between TGF-β1 RNA expression and cell proliferation at the bud and cap stages but not at later stages of tooth development. Tissue recombination experiments of bud-staged (13-day embryos) dental and non-dental tissues showed that tooth epithelium, when cultured together with tooth mesenchyme, expressed TGF-β1 RNA. When the tooth epithelium was combined with non-dental jaw mesenchyme, TGF-β1 transcripts were not expressed. However, TGF-β1 RNA expression was seen in oral epithelium cultured with dental mesenchyme, while no expression of TGF-β1 transcripts was seen in the oral epithelium during normal development. Thus, TGF-β1 RNA expression seems to be regulated by epithelial– mesenchymal interactions.
Macromere cell fates during sea urchin development
Authors: Cameron R. Andrew , Fraser Scott E. , Britten Roy J. , Davidson Eric H. 
Published: April 2021

ABSTRACT
This paper examines the cell lineage relationships and cell fates in embryos of the sea urchin Strongylocentrotus purpuratus leading to the various cell types derived from the definitive vegetal plate territory or the veg2 tier of cells. These cell types are gut, pigment cells, basal cells and coelomic pouches. They are cell types that constitute embryonic structures through cellular migration or rearrangement unlike the relatively non-motile ectoderm cell types. For this analysis, we use previous knowledge of lineage to assign macromeres to one of four types: VOM, the oral macromere; VAM, the aboral macro-mere, right and left VLM, the lateral macromeres. Each of the four macromeres contributes progeny to all of the cell types that descend from the definitive vegetal plate. Thus in the gut each macromere contributes to the esophagus, stomach and intestine, and the stripe of labeled cells descendant from a macromere reflects the re-arrangement of cells that occurs during archenteron elongation. Pigment cell contributions exhibit no consistent pattern among the four macromeres, and are haphazardly distributed throughout the ectoderm. Gut and pigment cell contributions are thus radially symmetrical. In contrast, the VOM blastomere contributes to both of the coelomic pouches while the other three macromeres contribute to only one or the other pouch. The total of the macromere contribution amounts to 60 % of the cells constituting the coelomic pouches.
Target sequences for hunchback in a control region conferring Ultrabithorax expression boundaries
Authors: Zhang Cheng-Cai , Müller Jürg , Hoch Michael , Jäckle Herbert , Bienz Mariann 
Published: April 2021

ABSTRACT
Boundaries of Ultrabithorax expression are mediated by long-range repression acting through the PBX or ABX control region. We show here that either of these control regions confers an early band of β-galactosidase expression which is restricted along the anteroposterior axis of the blastoderm embryo. This band is succeeded by a stripe pattern with very similar anteroposterior limits. Dissection of the PBX control region demonstrates that the two patterns are conferred by distinct cis-regulatory sequences contained within separate PBX subfragments. We find several binding sites for hunchback protein within both PBX subfragments. Zygotic hunchback function is required to prevent ectopic PBX expression. Moreover, the PBX pattern is completely suppressed in embryos containing uniformly distributed maternal hunchback protein. Our results strongly suggest that hunchback protein directly binds to the PBX control region and acts as a repressor to specify the boundary positions of the PBX pattern.
Selective expression of an acetylcholine receptor–lacZ transgene in synaptic nuclei of adult muscle fibers
Authors: Sanes Joshua R. , Johnson Yvette R. , Kotzbauer Paul T. , Mudd Jacqueline , Hanley Theresa , Marttnou Jean-Claude , Merlie John P. 
Published: April 2021

ABSTRACT
Acetylcholine receptors (AChRs) are highly concentrated in the postsynaptic membrane at the neuromuscular junction. To investigate mechanisms that lead to the formation or maintenance of this synaptic specialization, we generated transgenic mice in which regulatory elements from the AChR α- or ϵ-subunit genes are linked to a gene for a reporter protein that is targeted to the nucleus (nlacZ). Both transgenes were selectively expressed and developmentally regulated in muscle; nuclei in both extrafusal (ordinary) and intrafusal (spindle) muscle fibers were labeled. Within individual muscle fibers from є-nlacZ mice, nuclei near synaptic sites were nlacZ-positive, whereas extrasynaptic nuclei were nlacZ-negative. In contrast, nlacZ was expressed in both synaptic and extrasynaptic nuclei when under the control of regulatory elements from the AChR α-subunit gene; however, synaptic nuclei were somewhat more intensely stained than extrasynaptic nuclei in a minority of muscle fibers from these mice. Together, our results provide direct evidence for molecular differences between synaptic and extrasynaptic nuclei within a single cytoplasm, and suggest that the motor nerve regulates synapse formation by selectively affecting transcription in synaptic nuclei.
Expression of the zebrafish paired box gene pax[zf-b] during early neurogenesis
Authors: Krauss Stefan , Johansen Terje , Korzh Vladimir , Fjose Anders 
Published: April 2021

ABSTRACT
The paired box-containing (pax) gene family encodes a group of putative transcription factors differentially expressed during embryonic development. In this study, we describe the cloning and expression of a zebrafish gene pax[zf-b], which most probably is a direct homologue to the mouse Pax2 gene. The putative protein encoded by pax[zf-b] contains a paired box, an octapeptide, but no homeobox. However, a region of homology to the N-terminal half of paired-type homeoboxes is detected C-terminal to the pax[zf-b] paired domain. In zebrafish embryos, pax[zf-b] transcripts are first seen during the formation of the neural keel. At 9–10 h of development, two laterally located transverse stripes of cells expressing the gene appear in the rostral 1/3 of the embryo. The two areas sub
sequently move towards the midline and form the posterior portion of the midbrain. In the following stages of development, at 10–12 h, transcripts are detected in the otic placode, the Wolffian duct including the nephritic primordium and in the optic stalk. At a later time point, beginning at 14 –15 h, single cells along the spinal cord, presumably interneurons, start to express the gene. The characteristic expression pattern of pax[zf-b] in the neural tube suggests an involvement of this gene in the regionalization of the midbrain as well as in the specification of neuronal cell fates at early embryonic stages.
Segmental origin and migration of neural crest cells in the hindbrain region of the chick embryo
Authors: Lumsden Andrew , Sprawson Nicola , Graham Anthony 
Published: April 2021

ABSTRACT
A vital dye analysis of cranial neural crest migration in the chick embryo has provided a positional fate map of greater resolution than has been possible using labelled graft techniques. Focal injections of the fluorescent membrane probe DiI were made into the cranial neural folds at stages between 3 and 16 somites. Groups of neuroepithelial cells, including the premigratory neural crest, were labelled by the vital dye. Analysis of whole-mount embryos after 1–2 days further development, using conventional and intensified video fluorescence microscopy, revealed the pathways of crest cells migrating from mesencephalic and rhombencephalic levels of the neuraxis into the subjacent branchial region. The patterns of crest emergence and emigration correlate with the segmented disposition of the rhomben-cephalon. Branchial arches 1, 2 and 3 are filled by crest cells migrating from rhombomeres 2, 4 and 6 respectively, in register with the cranial nerve entry/exit points in these segments. The three streams of ventrally migrating cells are separated by alternating regions, rhombomeres 3 and 5, which release no crest cells. Rostrally, rhombomere 1 and the caudal mesencephalon also contribute crest to the first arch, primarily to its upper (maxillary) component. Both r3 and r5 are associated with enhanced levels of cell death amongst cells of the dorsal midline, suggesting that crest may form at these levels but is then eliminated. Organisation of the branchial region is thus related by the dynamic process of neural crest immigration to the intrinsic mechanisms that segment the neuraxis.