bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vitro development of murine T cells from prethymic and preliver embryonic yolk sac hematopoietic stem cells
Authors: Liu Chih-Pin , Auerbach Robert 
Published: April 2021

ABSTRACT
Mature T cells are derived from prethymic stem cells, which arise at one or more extrathymic sites and enter and differentiate in the thymus. The nature of these prethymic stem cells is a critical factor for the formation of the T-cell repertoire. Although the bone marrow of adult mice can provide such stem cells, their origin during murine embryogenesis is still undetermined. Among potential sites for these progenitor cells are the fetal liver and the embryonic yolk sac. Our studies focus on the yolk sac, both because the yolk sac appears earlier than any other proposed site, and because the mammalian yolk sac is the first site of hematopoiesis. Although it has been shown that the yolk sac in midgestation contains stem cells that can enter the thymic rudiment and differentiate toward T-cell lineage, our aim was to analyze the developmental potential of cells in the yolk sac from earlier stages, prior to the formation of the liver and any other internal organ. We show here that the yolk sac from 8- and 9-day embryos (2–9 and 13–19 somites, respectively) can reconstitute alymphoid congenie fetal thymuses and acquire mature T-cell-specific characteristics. Specifically, thymocytes derived from the early embryonic yolk sac can progress to the expression of mature T lymphocyte markers including CD3/T-cell receptor (TCR), CD4 and CD8. In contrast, we have been unable to document the presence of stem cells within the embryo itself at these early stages. These results support the hypothesis that the stem cells capable of populating the thymic rudiment originate in the yolk sac, and that their presence as early as at the 2-to 9-somite stage may indicate that prethymic stem cells found elsewhere in the embryo at later times may have been derived by migration from this extra-embryonic site. Our experimental design does not exclude the possibility of multiple origins of prethymic stem cells of which the yolk sac may provide the first wave of stem cells in addition to other later waves of cells.
The branchial Hox code and its implications for gene regulation, patterning of the nervous system and head evolution
Authors: Hunt Paul , Whiting Jenny , Nonchev Stefan , Sham Mai-Har , Marshall Heather , Graham Anthony , Cook Martyn , Allemann Rudolf , Rigby Peter W. J. , Gulisano Massimo , Faiella Antonio , Boncinelli Edoardo , Krumlauf Robb 
Published: April 2021

Abstract
In this study we have examined the expression of murine Hox homeobox containing genes by in situ hybridisation in the branchial region of the head. Genes from the Hox complexes display segmentally restricted domains of expression in the developing hindbrain, which are correlated with similar restricted domains in the neural crest and surface ectoderm of the branchial arches. Comparison of related genes from the different clusters shows that subfamily members are expressed in identical rhombomeres and branchial arches. These patterns suggest a combinatorial system for specifying regional variation in the head, which we refer to as a Hox code. The Hox genes also display dynamic dorso-ventral (D-V) restrictions in the developing neural tube which mirror the timing and spatial distributions of the birth of major classes of neurons in the CNS. Genes in the Hox-2 cluster all have a similar D-V distribution that differs from that of genes from the other Hox clusters, and suggests that members of a subfamily may be used to specify positional values to different subsets of cells at the same axial level. These results are discussed in terms of a system for patterning the branchial regions of the vertebrate head, and evolution of head structures.
We have also examined aspects of the transcriptional regulation of Hox-2 genes in transgenic mice using a lacZ reporter gene. We have been able to reconstruct the major pattern of the Hox-2.6 gene on the basis of identical expression of the transgene and the endogenous gene with respect to timing, spatial restrictions and tissue-specific distributions. Deletion analysis has enabled us to identify three regions involved in generating this pattern. Two of these regions have the properties of enhancers which are capable of imposing spatially-restricted domains of expression on heterologous promoters. We have generated similar Hox-lacZ fusions that reconstruct the highly restricted patterns of the Hox-2.1 and Hox-2.8 genes in the developing nervous system, supporting our in situ analysis and the idea of a Hox code. These transgenic experiments are a useful step in examining regulation in the Hox cascade.
Organogenesis in Drosophila melanogaster. embryonic salivary gland determination is controlled by homeotic and dorsoventral patterning genes
Authors: Panzer Scott , Weigel Detlef , Beckendorf Steven K. 
Published: April 2021

ABSTRACT
We have investigated Drosophila salivary gland determination by examining the effects of mutations in pattern forming genes on the salivary gland primordium. We find that the anterior-posterior extent of the primordium, a placode of columnar epithelial cells derived from parasegment 2, is established by the positive action of the homeotic gene Sex combs reduced (Scr). Embryos mutant for Scr lack a detectable placode, while ectopic Scr expression leads to the formation of ectopic salivary glands. In contrast, the dorsal-ventral extent of the placode is regulated negatively. Functions dependent on the decapentaplegic product place a dorsal limit on the placode, while dorsal-dependent genes act to limit the placode ventrally. We propose a model in which these pattern forming genes act early to determine the salivary gland anlage by regulating the expression of salivary gland determining genes, which in turn control genes that are involved in salivary gland morphogenesis.
The giant gene of Drosophila encodes a b-ZIP DNA-binding protein that regulates the expression of other segmentation gap genes
Authors: Capovilla Maria , Eldon Elizabeth D. , Pirrotta Vincenzo 
Published: April 2021

ABSTRACT
The sequence of a cDNA from the giant gene of Drosophila shows that its product has a basic domain followed by a leucine zipper motif. Both features contain characteristic conserved elements of the b-ZIP family of DNA-binding proteins. Expression of the gene in bacteria or by in vitro translation yields a protein that migrates considerably faster than the protein extracted from Drosophila embryos. Treatment with phosphatase shows that this difference is due to multiple phosphorylation of the giant protein in the embryo. Ectopic expression of the protein in precellular blastoderm embryos produces abnormal phenotypes with a pattern of segment loss closely resembling that of Krüppel mutant embryos. Immunological staining shows that giant, ectopically expressed from the hsp70 promoter, represses the expression of both the Krüppel and knirps segmentation gap genes. The analysis of the interactions between Krüppel, knirps and giant reveals a network of negative regulation. We show that the apparent positive regulation of knirps by Krüppel is in fact mediated by a negative effect of Krüppel on giant and a negative effect of giant on knirps. giant protein made in bacteria or in embryos binds in vitro to the Krüppel regulatory elements CD1 and CD2 and recognizes a sequence resembling the binding sites of other b-ZIP proteins.
Mechanism of anteroposterior axis specification in vertebrates Lessons from the amphibians
Authors: Slack J. M. W. , Tannahill D. 
Published: April 2021

ABSTRACT
Interest in the problem of anteroposterior specification has quickened because of our near understanding of the mechanism in Drosophila and because of the homology of Antennapedia-like homeobox gene expression patterns in Drosophila and vertebrates. But vertebrates differ from Drosophila because of morphogenetic movements and interactions between tissue layers, both intimately associated with anteroposterior specification. The purpose of this article is to review classical findings and to enquire how far these have been confirmed, refuted or extended” by modern work.
The “pre-molecular” work suggests that there are several steps to the process: Formation of anteroposterior pattern in mesoderm during gastrulation with posterior dominance.Regional specific induction of ectoderm to form neural plate.Reciprocal interactions from neural plate to mesoderm.Interactions within neural plate with posterior dominance.
Unfortunately, almost all the observable markers are in the CNS rather than in the mesoderm where the initial specification is thought to occur. This has meant that the specification of the mesoderm has been assayed indirectly by transplantation methods such as the Einsteckung.
New molecular markers now supplement morphological ones but they are still mainly in the CNS and not the mesoderm. A particular interest attaches to the genes of the Antp-like HOX clusters since these may not only be markers but actual coding factors for anteroposterior levels.
We have a new understanding of mesoderm induction based on the discovery of activins and fibroblast growth factors (FGFs) as candidate inducing factors. These factors have later consequences for anteroposterior pattern with activin tending to induce anterior, and FGF posterior structures.
Recent work on neural induction has implicated cAMP and protein kinase C (PKC) as elements of the signal transduction pathway and has provided new evidence for the importance of tangential neural induction. The regional specificity of neural induction has been reinvestigated using molecular markers and provides conclusions rather similar to the classical work.
Defects in the axial pattern may be produced by retinoic acid but it remains unclear whether its effects are truly coordinate ones or are concentrated in certain regions of high sensitivity.
In general the molecular studies have supported and reinforced the “pre-molecular ones”. Important questions still remain: How much pattern is there in the mesoderm (how many states?)How is this pattern generated by the invaginating organizer?Is there one-to-one transmission of codings to the neural plate?What is the nature of the interactions within the neural plate?Are the HOX cluster genes really the anteroposterior codings?
Embryonic stem cell-derived cystic embryoid bodies form vascular channels: an in vitro model of blood vessel development
Authors: Wang Rong , Clark Rebecca , Bautch Victoria L. 
Published: April 2021

ABSTRACT
Murine embryonic stem cells can differentiate in vitro to form cystic embryoid bodies (CEB) that contain different structures and cell types. The blood islands are one such structure that consist of immature hematopoietic cells surrounded by endothelial cells, the first identifiable vascular cells. CEBs differentiated in vitro developed blood islands initially, and subsequently these blood islands matured to form vascular channels containing hematopoietic cells. Phase contrast microscopy demonstrated the presence of channels in mature CEBs grown in suspension culture, and high resolution light and electron microscopy showed that the cells lining these channels were endothelial cells. The channels appeared less organized than the vasculature of the mature yolk sac. The hematopoietic cells were occasionally seen ‘flowing’ through the CEB channels, although their numbers were reduced relative to the yolk sac. Analysis of primary CEB cultures showed the presence of cells with two characteristics of endothelial cells: approximately 30% of the cells labelled with fluorescent acetylated low density lipoprotein and a small number of cells were positive for von Willebrand’s factor by immunostaining. Thus we conclude that a primitive vasculature forms in CEBs differentiated in vitro, and that not only primary differentiation of endothelial cells but also some aspects of vascular maturation are intrinsic to this cell culture system. CEBs are therefore a useful model for the study of developmental blood vessel formation.
Avian neural crest cells express a melanogenic trait during early migration from the neural tube: observations with the new monoclonal antibody, “MEBL-1”
Authors: Kitamura Kunio , Takiguchi-Hayashi Keiko , Sezaki Mariko , Yamamoto Hiroaki , Takeuchi Takuji 
Published: April 2021

ABSTRACT
A new monoclonal antibody, MEBL-1, which specifically recognizes melanocytes and their precursors, was used to examine the differentiation of neural crest cells into melanocytes in situ. MEBL-l-positive precursors of melanocytes in the trunk were first detected in mesenchyme located above the neural tube at the level of a wing bud at stage 19, when active migration of neural crest cells along the ventral route was almost complete. DiO-labelled neural crest cells, which begin to emigrate from the neural tube at stages 17–18 and then migrate along the dorsolateral route, were found to become MEBL-l-positive. This indicates that MEBL-1 antigens are expressed by neural crest cells immediately following their emigration and neural crest cells become melanogenic. Expression of the MEBL-1 antigens was followed by decrease in, and finally the loss of, HNK-1 antigen expression.
At the cephalic level, MEBL-l-positive precursors of melanocytes were first detected in mesenchyme located above the dorsal side of the mesencephalic neural tube at stage 16. At the vagal level, the precursors were noted first in mesenchyme located above the dorsal side of the rhombencephallc neural tube at stage 18.
MEBL-1 reacted with the cell membrane and preme-lanosome-like granules in addition to the nuclear membrane, endoplasmic reticulum and Golgi apparatus of the migratory precursors. The antigens recognized by MEBL-1 were proteins with relative molecular masses of 135 × 103 and 115 × 103. We suggest that MEBL-1 may be the earliest marker for melanogenic neural crest cells.
The fate of medial edge epithelial cells during palatal fusion in vitro: an analysis by Dil labelling and confocal microscopy
Authors: Carette Martin J. M. , Ferguson Mark W. J. 
Published: April 2021

ABSTRACT
Fusion of bilateral shelves, to form the definitive mammalian secondary palate, is critically dependent on removal of the medial edge cells that constitute the midline epithelial seam. Conflicting views suggest that programmed apoptotic death or epithelial-mesenchymal transformation of these cells is predominantly involved. Due in part to the potentially ambiguous interpretation of static images and the notable absence of fate mapping studies, the process by which this is achieved has, however, remained mechanistically equivocal.
Using an in vitro mouse model, we have selectively labelled palatal epithelia with Dil and examined the fate of medial edge epithelial (MEE) cells during palatal fusion by localisation using a combination of conventional histology and confocal laser scanning microscopy (CLSM). In dynamic studies using CLSM, we have made repetitive observations of the same palatal cultures in time-course investigations.
Our results concurred with the established morphological criteria of seam degeneration; however, they provided no evidence of MEE cell death or transformation. Instead we report that MEE cells migrate nasally and orally out of the seam and are recruited into, and constitute, epithelial triangles on both the oral and nasal aspects of the palate. Subsequently these cells become incorporated into the oral and nasal epithelia on the surface of the palate. We hypothesize an alternative method of seam degeneration in vivo which largely conserves the MEE population by recruiting it into the nasal and oral epithelia.
Characterisation of dystrophin during development of human skeletal muscle
Authors: Clerk Angela , Strong Peter N. , Sewry Caroline A. 
Published: April 2021

ABSTRACT
Dystrophin, the 427 × 103Mr product of the Duchenne muscular dystrophy (DMD) gene, was studied in human foetal skeletal muscle from 9 to 26 weeks of gestation. Dystrophin could be detected from at least 9 weeks of gestation at the sarcolemmal membrane of most myotubes, though there was differential staining with antibodies raised to various regions of the protein. Dystrophin immunostaining increased and became more uniform with age and by 26 weeks of gestation there was intense sarcolemmal staining of all myotubes. On a Western blot, a doublet of smaller relative molecular mass than that seen in adult tissue was detected in all foetuses studied. There was a gradual increase in abundance of the upper band from 9 to 26 weeks, and the lower band, although present in low amounts in young foetuses, increased significantly between 20 and 26 weeks of gestation. These data indicate that there are several specific isoforms of dystrophin present in developing skeletal muscle, though the role of these is unknown.
Hair follicle differentiation: expression, structure and evolutionary conservation of the hair type II keratin intermediate filament gene family
Authors: Powell Barry , Crocker Lesley , Rogers George 
Published: April 2021

ABSTRACT
During hair follicle development several cell streams are programmed to differentiate from the cell population of the follicle bulb. In the hair cells, a number of keratin gene families are transcriptionally activated. We describe the characterization of the type II keratin intermediate filament (IF) gene family which is expressed early in follicle differentiation. In sheep wool, four type II IF proteins are expressed. One gene has been completely sequenced and the expression of three of the genes examined in detail. The sequenced gene encodes a 55 × 103Mr protein of the type II keratin IF protein family, designated KU-9 in the new nomenclature we have adopted and described in the Introduction. The gene has a similar exon/intron structure to the epidermal type II keratin IF genes. In situ hybridization experiments show that the genes are expressed in the hair cortical cells but not in the cells of the outer root sheath, inner root sheath or medulla. During hair keratinocyte differentiation the type II IF genes are sequentially activated and coexpressed in the same cells. Expression is first detected in cells in the middle of the follicle bulb located near the dermal papilla and, subsequently, two of the genes are transcriptionally activated in the differentiating keratinocytes as they migrate upwards, in the upper part of the bulb. A fourth type II IF gene is activated later. The genes with the same expression pattern are also closely related in sequence and a number of conserved elements are present in the promoters of those genes, including a novel element which is also found in the promoter of a coexpressed type I IF gene and three other hair keratin genes.
U-cadherin in Xenopus oogenesis and oocyte maturation
Authors: Müller A. H. J. , Angres B. , Hausen P. 
Published: April 2021

ABSTRACT
U-cadherin is a member of the cadherin family in Xenopus that participates in interblastomere adhesion in the early embryo from the first cleavage onwards. Though a maternal pool of U-cadherin is available in the egg, it is not present on the egg membrane (Angres et al., 1991. Development 111, 829-844). To assess the origin of this unexpected distribution in the egg, the accumulation and localization of the cadherin during oogenesis and oocyte maturation were investigated.
We report here that U-cadherin is present in Xenopus oocytes throughout oogenesis. It is localized at the oocyte-follicle cell contacts suggesting that it functions in the adhesion of the two cell types.
When oocytes mature and the contacts to the follicle cells break, U-cadherin disappears from the oocyte surface. Evidence for a translocation of U-cadherin from the membrane to the inside of the oocyte was obtained when the fate of membrane-bound U-cadherin, which was labelled on the surface of oocytes prior to maturation, was followed through maturation.
The total U-cadherin content of the oocyte increases during maturation. Metabolic labelling experiments indicate that at maturation the translation of U-cadherin is elevated well above the level that one would expect from the general increase in protein synthesis occurring during maturation. This enhanced synthesis is presumably the main source of the maternal pool of U-cadherin in the egg.
Localized enhancement and repression of the activity of the TGF-P family member, decapentaplegic, is necessary for dorsal-ventral pattern formation in the Drosophila embryo
Authors: Ferguson Edwin L. , Anderson Kathryn V. 
Published: April 2021

ABSTRACT
Seven zygotic.ally active genes are required for normal patterning of the dorsal 40% of the Drosophila embryo. Among these genes, decapentaplegic (dpp) has the strongest mutant phenotype: in the absence of dpp, all cells in the dorsal and dorsolateral regions of the embryo adopt fates characteristic of more ventrally derived cells (Irish and Gelbart (1987)Genes Dev. 1, 868-879). Here we describe the phenotypes caused by alleles of another of this set of genes, tolloid, and show that tolloid is required for dorsal, but not dorsolateral, pattern. Extragenlc suppressors of tolloid mutations were isolated that proved to be mutations that elevate dpp activity. We studied the relationship between tolloid and dpp by analyzing the phenotypes of tolloid embryos with elevated numbers of the dpp gene and found that doubling the dpp+ gene dosage completely suppressed weak tolloid mutants and partially suppressed the phenotypes of tolloid null mutants. We conclude that the function of tolloid is to increase dpp activity. We also examined the effect of doubling dpp+ gene dosage on the phenotypes caused by other mutations affecting dorsal development. Like tolloid, the phenotypes of mutant embryos lacking shrew gene function were suppressed by elevated dpp, indicating that shrew also acts upstream of dpp to increase dpp activity. In contrast, increasing the number of copies of the dpp gene enhanced the short gastrulation (sog) mutant phenotype, causing ventrola teral cells to adopt dorsal fates. This indicates that sog gene product normally blocks dpp activity ventrally. We propose that the tolloid, shrew and sog genes are required to generate a gradient of dpp activity, which directly specifies the pattern of the dorsal 40% of the embryo.
Cholinergic neuronal differentiation factors: evidence for the presence of both CNTF-like and non-CNTF-like factors in developing rat footpad
Authors: Rohrer H. 
Published: April 2021

ABSTRACTCatecholaminergic sympathetic neurons are able to change their transmitter phenotype during development and to acquire cholinergic properties. Cholinergic sympathetic differentiation is only observed in fibers innervating specific targets like the sweat glands in the rat footpad. A function for ciliary neurotrophic factor (CNTF) in this process has been implied as it is able to induce cholinergic properties (ChAT,VIP) in cultured chick and rat neurons. We show here that a CNTF-like, VIP-inducing activity is present in rat footpads and that it increases 6-fold during the period of cholinergic sympathetic differentiation. Immunohistochemical analysis of P21 rat footpads demonstrated CNTF-like immunoreactivity in Schwann cells but not in sweat glands, the target tissue of cholinergic sympathetic neurons. The expression of this factor in footpads seems to be dependent on the presence of intact nerve axons, as nerve transection results in a loss of CNTF-like cholinergic activity and immunoreactivity. Immunoprecipitation experiments with rat footpad extracts provided evidence for the presence of ChAT-inducing factors other than CNTF, which may independently or together with CNTF be involved in the determination of sympathetic neuron phenotype.