bluuebunny/crossref_metadata_2025 huggingface dataset:
The fine structure of the elasmobranch renal tubule: Intermediate, distal, and collecting duct segments of the little skate
Authors: Lacy E. R. , Reale E.
Published: February 2005

Sharks, skates, and rays (Elasmobranchii) have evolved unique osmoregulatory strategies to survive in marine habitats. These adaptations include a complex renal countercurrent system for urea retention. The fine structure of the complete renal tubular epithelium has yet to be elucidated in any species of cartilagenous fish. The present study, which is a companion to our recent paper describing the ultrastructure of the neck and proximal segments of the elasmobranch nephron, uses thin sections and freeze‐fracture replicas to elucidate the fine structural organization of the intermediate, distal, and collecting duct segments of the little skate, Raja erinacea, renal tubule.

The epithelium of the intermediate, distal, and collecting duct segments consists of two major cell types: nonflagellar cells, the major epithelial cell type; and flagellar cells, described elsewhere.

The intermediate segment consists of six subdivisions lined by cuboidal–‐columuar cells with variously elaborated microvilli and interdigitations of lateral and basal cell plasma membranes, as well as some subdivisions with distinctive vesicles and granules.

The distal segment consists of two subdivisions, both of which are lined by a simple epithelium, and are distinguished from each other by their distinctive contents; dense bodies and granules.

The collecting duct segment also has two subdivisions, the first lined by a simple columnar epithelium and the second by a stratified columnar epithelium. Both subdivisions have apical secretory granules.

The present findings show a more highly specialized and diverse epithelium lining the renal tubule of these cartilagenous fish than is found in either of the “adjacent” phylogenetic taxa, Agnatha or Ostheichthyes, suggesting significant differences among these groups in transepithelial transport mechanisms and renal function.
Pattern of glucose transporter (Glut 1) expression in embryonic brains is related to maturation of bood‐brain barrier tightness
Authors: Dermietzel R. , Krause D. , Kremer M. , Wang C. , Stevenson B.
Published: February 2005

A constant supply of blood‐borne glucose is vital to cerebral metabolism. Although transport of glucose into the nervous tissue, effectively separated from the blood by a functional barrier (the blood‐brain barrier, BBB), is one of the essential properties of the cerebral endothelium, little is known about its metabolic regulation and developmental expression in the BBB. In this study we provide evidence by immunocytochemistry that the pattern of the brain endothelial glucose transporter in rat brains (BBB‐GT), immunologically homologous with the human hepatoma (G2), human erythrocyte transporter (Glut 1), changes with BBB maturation. While the neuroepithelium at embryonic days 12 and 13 shows a high incidence of immuno‐detectable BBB‐GT, vascularisation of the cerebral anlage and subsequent development of vascular tightness, as evidenced by intravascularly applied horseradish peroxidase and fluorescinated dextrans, is accompanied by a significant reduction BBB‐GT expression in neuroepithelial cells and confinement of BBB‐GT expression to the cerebral endothelium. Immunoblots and Northern blots of embryonic brain homogenates corroborate this change in BBB‐GT expression in the brain anlage at the time of BBB maturation. However, low molecular weight glucose transporters, presumed to be of non‐endothelial origin, are less dramatically reduced. The development of BBB tightness, therefore, seems to play a pivotal role in the pattern of BBB‐GT expression during brain differentiation.
Effects of tunicamycin on retinoic acid induced respecification of positional values in regenerating limbs of the larval axolotl, Ambystoma mexicanum
Authors: Johnson Keith J. , Scadding Steven R.
Published: February 2005

Urodele amphibians possess a remarkable ability to regenerate limbs following experimental or accidental amputation. Since only those parts of the limb distal to the plane of amputation usually regenerate, this suggests the existence of level‐specific positional values within the cells of the limb. Vitamin A and other retinoids respecify the positional values of regenerating limbs such that structures proximal to the actual plane of amputation are formed in the regenerating limb producing proximodistal duplications. Regenerating limbs of larval axolotls (Ambystoma mexicanum) treated with sufficient retinoic acid to induce proximodistal duplication were also treated via implantation with tunicamycin, a drug which blocks the synthesis of glycoproteins by blocking N‐glycosylation of proteins. Tunicamycin was shown to inhibit the proximalizing effects of retinoic acid. This indicates that asparaginelinked glycoproteins may be essential to the process through which retinoic acid induces these effects in the regenerating limb and that glycoproteins may be responsible for specifying positional values in regeneration blastema cells.
JunB does not inhibit the induction of c‐Jun during the retinoic acid induced differentiation of F9 cells
Authors: Kwon Moosik , Oshima Robert G.
Published: February 2005

JunB, a member of the jun gene family of transcription factors, is distinguished from c‐Jun by its differential activity on certain arrangements of promoter regulatory elements and the ability of JunB to inhibit the action of cJun in both transforming and trans‐activating assays. We have tested the potential negative regulatory role of JunB during the retinoic acid induced differentiation of F9 murine embryonal carcinoma cells. Constitutive expression of high levels of JunB in F9 cells failed to inhibit the differentiation dependent induction of c‐Jun or the coincident expression of differentiation markers keratin 8 and 18, tissue plasminogen activator, and laminin Bl. Among these marker genes, keratin 18, has been shown to contain an AP‐1 binding site, TGA(C/G)TCA, which is essential for high level, differentiation dependent expression and which is transactivated by Jun and Fos proteins. These results suggest that JunB does not play a major negative or positive regulatory role during the retinoic acid induced differentiation of F9 cells.
Positional control of mesoderm movement and fate during avian gastrulation and neurulation
Authors: Garcia‐Martinez Virginio , Schoenwolf Gary C.
Published: February 2005

Segments of primitive streak from donor quail embryos at stages of gastrulation and neurulation were transplanted heterotopically and isochronically to primitive streaks of host chick embryos. The subsequent movement and fate of grafted cells was determined using the quail nucleolar marker to define grafted cells. The pattern of movement of grafted cells depended on their new position within the primitive streak, not on their original position. When cells of cranial regions were placed more caudally, they moved to mesodermal subdivisions that were located lateral to those they would have populated if left in their original position. When caudal segments were placed more cranially, they moved to more medial mesodermal subdivisions. Whether the fate of grafted cells corresponded to their original location or their new location depended on both their level of origin and their new position. Cells from heterotopically transplanted Hensen's nodes, which migrated to the somitic and more lateral mesoderm, self‐differentiated notochords. Similarly, in some cases, heterotopically transplanted prospective somitic cells, which migrated to lateral plate mesoderm, formed ectopic somites. In other cases, however, grafted cells contributed to the host's somites, intermediate mesoderm, and lateral plate mesoderm. Moreover, prospective somitic cells, which migrated to the extraembryonic lateral plate mesoderm, changed their fate and formed extraembryonic lateral plate mesoderm; and prospective lateral plate mesoderm cells, which migrated to the somitic mesoderm, formed somites as well as intermediate mesoderm and lateral plate mesoderm. These results suggest that the movement of primitive streak cells to various mediolateral subdivisions of the mesodermal stream is determined solely by their craniocaudal position within the streak, but that determination of cell fate involves a combination of self‐differentiation and positional regulation. Cells from cranial levels of the primitive streak exhibit a considerably greater potential to self‐differentiate than those from more caudal levels, and cranial cells are more likely to migrate as a coherent group, unlike more caudal cells, which tend to freely disperse within host structures. © 1992 Wiley‐Liss, Inc.
Retinoic acid‐induced change in anteroposterior positional identity in regenerating axolotl limbs is dose‐dependent
Authors: Monkemeyer Jon , Ludolph David C. , Cameron Jo Ann , Stocum David L.
Published: February 2005

Retinoic acid (RA) induces pattern duplication in the proximodistal (PD) axis of axolotl limb regenerates. The effect is dose‐dependent, with the maximum extent of duplication being evoked at a dose of 150 μ RA/g body weight, The same dose of RA induces maximum pattern completion in the anteroposterior (AP) axis of regenerating anterior half or double anterior half limbs. RA inhibits the regeneration of posterior half or double posterior half limbs (Kim, W.S., and Stocum, D.L. [1986] Dev Biol 114:170–179). The effects of lower doses of RA on the AP axis of limb regenerates have not been tested and thus it is not known whether the effects of RA on positional identity in this axis are dose‐dependent or are all‐or‐none. To answer this question, we examined the effects of a range of doses of RA on AP positional identity in regenerating double anterior and double posterior axolotl forelimbs and hindlimbs constructed by exchanging the anterior and posterior halves of right and left zeugopodia as either autografts or homografts. Ten days after the exchange, the double half zeugopodia were amputated through their distal ends. At 4 days postamputation, the animals were injected intraperitoneally with 20, 50, 75, or 100 μg RA/g body weight and the constructs allowed to regenerate for at least 6 weeks. Control double anterior forelimbs and hindlimbs formed symmetrical regenerates with an average of two and 1.8 anterior digits, respectively. RA treatment induced the blastema of double anterior zeugopodia to regenerate missing posterior structures in mirror‐image patterns and to duplicate zeugopodial and stylopodial elements in the PD axis. The extent of posterior regeneration and PD duplication was proportional to dose. Control double posterior forelimbs and hindlimbs produced symmetrical regenerates with an average of 2.4 and 3.3 posterior digits, respectively. Regeneration was inhibited at 100% frequency at doses above 50 μg of RA, but regeneration took place with increasing frequency at the 50 and 20 μg doses. We conclude from these data that RA posteriorizes AP positional identity in a dose‐dependent way, analogous to the dose‐dependent proximalization of positional identity reported previously for the PD axis. © 1992 Wiley‐Liss, Inc.
Mullerian inhibiting substance binding and uptake
Authors: Catlin E. A. , Ezzell R. M. , Donahoe P. K. , Manganaro T. F. , Ebb R. G. , MacLaughlin D. T.
Published: February 2005

Mullerian inhibiting substance (MIS) is a 140,000 Mr Sertoli cell derived glycoprotein with a critical regulatory role in the male fetus initiated presumably by ligand binding with receptor. To localize this binding species we performed time course incubations of cultured fetal rat lungs or control tissues with MIS, applied rabbit anti‐MIS IgG, and fluorescein conjugated antirabbit IgG, and examined specimens with laser confocal microscopy. Punctate surface fluorescence followed by cytosolic and nuclear localization in lung consistent with specific adsorptive endocytosis was seen. Confocal imaging also detected MIS binding to the Mullerian duct in the urogenital ridge. Crosslinking of 125I‐MIS with plasma membranes revealed a high molecular mass binder with signal displaceable by excess unlabeled ligand. These data support the hypothesis that a specific plasma membrane binding protein for MIS exists. © 1992 Wiley‐Liss, Inc.
Effect of systemic calcium deficiency on the expression of transforming growth factor‐β in chick embryonic calvaria
Authors: Sato Tomotaro , Tuan Rocky S.
Published: February 2005

The developmental process of intramembranous ossification involves bone formation directly from mesenchymal differentiation without a cartilage intermediate. We have previously observed that systemic calcium deficiency in the developing chick embryo, produced by long‐term shell‐less culture, results in the appearance of chondrocyte‐like cells in the calvarium, a parietal bone which normally develops via intramembranous ossification. This investigation aims to analyze the mechanism underlying this calcium deficiency–related, aberrant appearance of cartilage phenotype in the chick embryonic calvarium. In view of the reported involvement of transforming growth factor β (TGF‐β) in osteogenesis and chondrogenesis, we have examined and compared here the expression of TGF‐β in the chick embryonic calvaria of normal (in ovo development, NL), shell‐less (SL), and calcium‐supplemented SL (SL + Ca) embryos. TGF‐β expression was analyzed at the mRNA level by blot and in situ cDNA hybridization, and at the protein level by immunohistochemistry and immunoblotting. The results presented here indicate that: (1) TGF‐β is expressed in the chick embryonic calvarium by both periosteal cells and osteocytes, as revealed by in situ hybridization and immunohistochemistry; (2) TGF‐β expression is significantly increased in SL calvarium compared to NL calvarium, at both protein and mRNA levels; (3) the number of TGF‐β expressing cells increases in the SL calvarium, particularly along the central, subcambial core region of the bone; and (4) exogenous calcium repletion to the SL embryo affects the expression of TGF‐β such that the pattern approaches that in the NL embryo. Taken together, these results indicate that altered TGF‐β expression accompanies the aberrant appearance of cartilage phenotype caused by systemic calcium deficiency. We postulate that normal cellular differentiation along the osteogenic pathway during embryonic intramembranous ossification is crucially dependent on regulated TGF‐β expression. © 1992 Wiley‐Liss, Inc.
Sense and antisense TGFβ3 mRNA levels correlate with cardiac valve induction
Authors: Potts J. D. , Vincent E. B. , Runyan R. B. , Weeks D. L.
Published: February 2005

The formation of the valves in the heart is a spatially and temporally controlled process. A tissue interaction between the endothelium and its adjacent myocardium initiates the transformation of the endothelium into the mesenchymal precursors of the heart valve. One or more of the molecules implicated as critical for valve formation are members of the transforming growth factor β family of molecules. Presented here is a spatial and temporal analysis of TGFβ and TGFβ3 in the chick heart during valve formation. We show that TGFβ mRNA is concentrated in AV canal tissue where valve formation will occur, consistent with previous observations that TGFβ3 production is critical during valve formation. Additionally, an RNA complementary to TGFβ3 encoding mRNA is present in the heart. The temporally controlled appearance of RNA complementary to TGFβ3 suggests that this molecule may play a role in the regulation of TGFβ3 production in the heart. © 1992 Wiley‐Liss, Inc.
Differences in the histogenesis of EDL and diaphragm in rat
Authors: Yiping Ling , Appelt Denah , Kelly Alan M. , Franzini‐Armstrong Clara
Published: February 2005

We have examined the histogenesis of the diaphragm and extensor digitorum muscle in rat embryos, with the aim of defining differences in developmental patterns that can be related to the functional requirements of these muscles during and after development.

Patterns of interactions between myotubes and other cells, and frequency of gap junctions are quite different in the two muscles. In diaphragm, primary myotubes (at day 16 in utero) are closely associated with each other, forming parallel sheets or palisades and communicating by gap junctions. Secondary myotubes have formed by day 18, but are immature, and the frequency of gap junctions is lower. The arrangement in palisades is maintained even after fibers are separated from each other by their individual basal lamina. In EDL primary fibers at day 16 have fewer gap junctions, and the peak in communication occurs after the appearance of secondary myotubes (day 18 and 21). Secondary myotubes are more mature than in diaphragm at day 18. © 1992 Wiley‐Liss, Inc.
Embryonic expression and functional analysis of a Xenopus activin receptor
Authors: Hemmati‐Brivanlou Ali , Wright David A. , Melton Douglas A.
Published: February 2005

We report the isolation and characterization of a Xenopus activin receptor (XAR1). The amino acid sequence of this protein shows extensive homology with a murine activin receptor. The mRNA is expressed maternally and is ubiquitously distributed during the early stages of embryogenesis. Consistent with a possible role in mesoderm induction and patterning, interference with the normal expression of the receptor by overexpression in the early embryo results in the formation of ectopic dorsal axial structures. During neurulation the XAR1 mRNA is expressed predominantly in the presumptive brain and spinal cord, suggesting an additional function for XAR1 in neurogenesis. © 1992 Wiley‐Liss, Inc.
Effects of lithium chloride and retinoic acid on the expression of genes from the Xenopus laevis Hox 2 complex
Authors: Leroy Pascale , de Robertis Eddy M.
Published: February 2005

We show that Xenopus laevis has a Hox 2 complex, and that this complex is strongly conserved with the mammalian one, both in structure and in the rules of spatial and temporal sequential expression of its genes during the early stages of development. Lithium chloride and retinoic acid, two reagents known to alter axial patterning of the body when applied to Xenopus embryos, produce, respectively, embryos with reduced posterior but exaggerated anterior structures and embryos with truncation of anterior structures. We report here on the effect of these reagents on the expression of Hox 2 genes in the Xenopus embryo. LiCl has a dramatic effect on Hox genes, suppressing the expression of these genes during gastrulation and early neurulation. However, later on expression of these genes reaches significant levels, suggesting the existence of two phases in the control of Hox gene expression. Retinoic acid increases the steady state level of transcripts from Hox genes with the greatest effect on Hox 2.7, the most anterior of the genes studied. This suggests that the results obtained in EC cells (Simeone et al., 1990, 1991) reflect what occurs in vivo. Neither LiCl nor RA change the sequential order of the onset of expression of the genes, showing that these reagents do not perturb the molecular mechanisms used to establish the sequential activation of the genes of the Hox complexes. © 1992 Wiley‐Liss, Inc.
Molecular analyses of carbonic anhydrase‐II expression and regulation in the developing chicken lens
Authors: Buono Russell J. , Linser Paul J. , Cuthbertson R. Andrew , Piatigorsky Joram
Published: February 2005

The expression of carbonic anhydrase‐II (CA‐II) in the developing chicken lens was examined and compared with that in the retina of the chicken embryo. CA‐II expression was measured by immunohistochemistry and radioimmunoassay during development, and CA‐II mRNA was quantified by Northern blot and densitometric scanning and localized by in situ hybridization. A functional promoter of the chicken CA‐II gene was identified by transfection of primary embryonic chicken lens epithelial cells and analyzed in deletion mutants. The results establish that CA‐II makes up about 0.1% of the total soluble protein of the embryonic chicken lens, an amount insufficient to make it a candidate for an enzyme crystallin in this species. Lens fiber differentiation coincided with a loss of CA‐II mRNA and protein; by contrast, CA‐II persisted in the epithelial cells of the embryonic and mature lens. This and previous studies showed that CA‐II amounts to as much as 3% of the protein of the embryonic chicken retina and follows a different developmental time course of expression; like the lens, CA‐II decreases until day 10 in the embryonic retina, but, unlike the lens, it increases thereafter and plateaus at hatching. Progressive deletions of the 5′ flanking regions (from position −1314 to +32) of the CA‐II gene fused to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene resulted in a gradual loss of promoter activity, consistent with an additive effect of putative cis‐regulatory elements found in many crystallin genes. These experiments provide the foundation for a molecular analysis of the developmental and differential regulation of the CA‐II gene in lens and retina. © 1992 Wiley‐Liss, Inc.
Association interneurons of embryonic rat spinal cord transiently express the cell surface glycoprotein SNAP/TAG‐1
Authors: Vaughn J. E. , Phelps P. E. , Yamamoto M. , Barber R. P.
Published: February 2005

SNAP/TAG‐1 is a 135 kDa glycoprotein of the immunoglobulin superfamily that is transiently expressed upon the surfaces of developing axons. In the embryonic rodent spinal cord, this molecule is expressed by motor neurons, dorsal root ganglion cells, and commissural neurons (Yamamoto et al.: J. Neurosci. 6:3576–3594, 1986; Dodd et al.: Neuron 1:105–116, 1988). The commissural cells are a subset of early‐forming dorsal horn interneurons whose axons follow a circumferential course in the embryonic spinal cord. The axons of commissural neurons cross the developing ventral commissure to terminate on contralateral synaptic targets, whereas those of the other subset of circumferential cells, the association interneurons, remain on the same side of the spinal cord to form ipsilateral, terminal synaptic fields. The difference between the axonal trajectories of these two subsets of nerve cells raised the question of whether or not association interneurons would also express the SNAP/TAG‐1 epitope and, if so, how would this expression be related to that of the commissural cells. Immunocytochemistry for SNAP/TAG‐1 and choline acetyltransferase (ChAT) was used to answer these questions. The results indicated that association interneurons expressed SNAP/TAG‐1 epitopes and that this expression began later and lasted longer than that of the commissural neurons. Other new findings of this study included the identification of a lateral subgroup of commissural fibers that expressed SNAP/TAG‐1 later than their more medially located counterparts, and these lateral fibers were more pronounced in the thoracic spinal cord than at cervical levels. Furthermore, interesting developmental relationships were observed between SNAP/TAG‐1‐positive fibers and ChAT‐positive motor neurons in both cervical and thoracic spinal cord. Lastly, SNAP/TAG‐1 immunoreactivity was detected on the terminal collaterals of dorsal root ganglion fibers during the late prenatal period. While the function(s) of SNAP/TAG‐1 remains enigmatic, its expression in developmental time and space, along with the recent suggestion that a released form of this molecule might serve a substrate adhesion function (Furley et al.: Cell 61:157–170, 1990; Karagogeos et al.: Development 112:51–67, 1991), hint that SNAP/TAG‐1 might play a role in the migration of certain cholinergic neurons in the developing spinal cord. © 1992 Wiley‐Liss, Inc.
Talpid2 limb bud mesoderm does not express GHox‐8 and has an altered expression pattern of GHox‐7
Authors: Krabbenhoft Karen M. , Fallon John F.
Published: February 2005

We have studied the expression patterns of the chick homeobox‐containing genes, GHox‐7 and GHox‐8, in the talpid2 (ta2) chick mutant whose limbs have abnormal pattern. These studies provide new insight into how homeobox gene expression and limb patterning may be related. This is the first study demonstrating a natural change in GHox‐7 and GHox‐8 along the anteroposterior axis. While GHox‐7 is expressed asymmetrically in normal limb buds, it is expressed at a uniform level across the anteroposterior axis of ta2 limb buds. GHox‐8 is expressed in anterior mesoderm of normal limb buds, but is un‐detectable in ta2 limb bud mesoderm. These data are consistent with the subtle anteroposterior polarity in ta2 limbs, and allow us to propose that ta2 limb buds lack anterior positional information, but have a narrow range of posterior positional values. We suggest that in normal limb buds GHox‐8 may establish the anterior limb bud boundary. Furthermore, we point out that coexpression of GHox‐7 and GHox‐8 in normal anterior limb bud mesoderm can be correlated with the reduced apical ridge maintenance activity of this tissue, while the lack of coexpression in ta2 limb buds is correlated with the strong ridge maintenance activity in the mutant's anterior limb bud mesoderm. Last, ta2 limbs contain no dying cells in their anterior and posterior border mesoderm; nevertheless, they express GHox‐7 in these regions. These data challenge the proposal that this gene determines cell death. © 1992 Wiley‐Liss, Inc.
Distinct regions of human fibronectin are essential for fibril assembly in an in vivo developing system
Authors: Darribére Thierry , Koteliansky Victor E. , Chernousov Michael A. , Akiyama Steven K. , Yamada Kenneth M. , Thiery Jean Paul , Boucaut Jean‐Claude
Published: February 2005

In early vertebrate development, the proper assembly of fibronectin into fibrils is crucial for embryonic cells to adhere and to migrate on the extracellular matrix. The molecular mechanisms by which such a process occurs in vivo are poorly understood. In the amphibian embryo Pleurodeles waltl fibronectin fibrils appear first at the blastula stage. They form a fibrillar matrix on the basal surface of animal cells facing the blastocoel. Using competition and perturbation experiments with purified proteolytic fragments and domain‐specific monoclonal antibodies, we demonstrate that at least three fibronectin sites are essential for assembly of fibronectin fibrils in the blastula of Pleurodeles waltl. Two sites, the RGDS sequence and the synergistic domain in the 10th type III repeat, are both involved in receptor recognition. A third site that spans the 9th type I and 1st type III homology sequences is also likely to participate in fibronectin‐fibronectin interactions. © 1992 Wiley‐Liss, Inc.
A cyclical, developmentally‐regulated death phenomenon in a colonial urochordate
Authors: Lauzon Robert J. , Ishizuka Katherine J. , Weissman Irving L.
Published: February 2005

Botryllus schlosseri is a colonial ascidian whose asexually derived, clonally modular systems of zooids exhibit developmental synchrony. The blastogenic cycle culminates in a phase of programmed cell and zooid death called takeover, in which all functional zooids die over a 30 hr period, and are replaced by a new generation of individuals. Because of the weekly recurrence and magnitude of visceral death in this model organism, we have begun to characterize the mechanisms that govern takeover. Here we describe a monoclonal antibody (B3F12.9) that recognizes a novel 57 Kd polypeptide (under reducing conditions) localized to the perivisceral extracellular matrix (PVEM) of buds and zooids, as well as blood cells of Botryllus by immunofluorescence and immunogold labeling of tissue sections. During their active feeding phase, zooids exhibited a uniform labeling pattern of PVEM along their anteroposterior (A‐P) axis. At the onset of takeover (T = 3 hr), B3F12.9 immunostaining became diffuse or absent at the anterior end, which paralleled the axis of contraction of the dying zooid, whereas the posterior end retained its labeling integrity. During mid (T = 15 hr) to late (T = 28 hr) takeover, issue damage was extensive, large blood macrophages and other B3F12.9 immunoreactive blood cells invaded the peribranchial cavity, whereas PVEM labeling gradually disappeared along the entire A‐P axis. These findings indicate that takeover is a dynamic process in which extracellular matrix breakdown proceeds in a polarized fashion, beginning at the anterior end of each zooid and gradually propagating toward the posterior end. © 1992 Wiley‐Liss, Inc.
Coordinated induction of cell proliferation and syndecan expression in dental mesenchyme by epithelium: Evidence for diffusible signals
Authors: Vainio Seppo , Thesleff Irma
Published: February 2005

Epithelial–mesenchymal interactions induce the expression of syndecan, a cell surface proteoglycan, and tenascin, an extracellular matrix glycoprotein in the mesenchymal component of many organ rudiments including the tooth. Experimental recombination cultures of early dental epithelium and mesenchyme were analysed by double immunostaining to compare the distribution of syndecan, tenascin, and proliferating cells (BrdU incorporation) in the induced dental mesenchyme. After 5–9 hr in culture expression of syndecan and tenascin as well as an increase in BrdU incorporation were evident in the mesenchymal cells adjacent to the epithelium and the positive area enlarged with time. Syndecan and tenascin were colocalized only partially in some explants. The expression of syndecan and tenascin in the recombinants correlates with their stage‐dependent expression pattern during early tooth development in vivo (Vainio and Thesleff, 1992). The area of increased cell proliferation in the mesenchyme correlated closely with syndecan expression. In none of the explants was increased BrdU incorporation observed in syndecan negative areas. Epithelium induced also condensation of the mesenchymal cells. Induction and spread of the syndecan‐positive zone in the dental mesenchyme required close and continuous contact with the epithelium. The mechanism by which the induction of syndecan expression spreads in the mesenchyme was studied in rat‐mouse interspecies recombination cultures, using syndecan antibodies that recognize mouse but not rat syndecan. The rat mesenchyme and epithelium were first cultured in contact for 24 hr. Then the epithelium was removed and freshly dissected, “uninduced” mouse mesenchyme was placed in contact with different aspects of the rat mesenchyme. The rat mesenchymal cells that had located next to the epithelial tissue stimulated syndecan expression in adjacent mouse mesenchyme. The induction potential was gradually lost toward the periphery of the rat mesenchyme. Based on these findings we suggest that diffusible signal molecules mediate the spread of syndecan induction in the mesenchyme and that syndecan plays a role in the regulation of cell proliferation. © 1992 Wiley‐Liss, Inc.
Localization of type II collagen, long form α1(IX) collagen, and short form α1(IX) collagen transcripts in the developing chick notochord and axial skeleton
Authors: Swiderski Ruth E. , Solursh Michael
Published: February 2005

In this study we compare, by in situ hybridization, the spatial and temporal expression patterns of transcripts of avian type II collagen and the long and short forms of the (α1) chain of type IX collagen during the development of the notochord and axial skeleton. We observed type II collagen and short form type IX collagen transcripts in the developing (stage 25–28) nonchondrogenic notochord. Conversely, long form type IX transcripts were not detectable in the notochord or perinotochordal sheath. Interestingly, all three transcripts colocalized in the developing chondrogenic vertebrae of the axial skeleton as well as in the chondrocranium and Meckel's cartilage. The expression of the short form of type IX collagen in these regions was more restricted than that of the long form. This report provides additional support for a complex regulatory pathway of cartilage marker gene expression in chondrogenic vs. nonchondrogenic tissues during avian embryogenesis. © 1992 Wiley‐Liss, Inc.
Urokinase expression during the epithelial–mesenchymal transformation of the avian somite
Authors: McGuire Paul G. , Alexander Susan M.
Published: February 2005

Early events in the morphogenesis of the axial skeleton involve an epithelial‐mesenchymal transformation of the somites. Cells of the ventromedial wall of the somite (the sclerotome) migrate to regions surrounding the notochord and neural tube and condense to form the cartilage model of the vertebrae. Urokinase activity in the axial region of the quail embryo trunk was found to increase during these stages. In situ hybridization localized urokinase mRNA expression in this region and suggests an important role for this protease in the process of cell migration and matrix remodeling during development of the axial skeleton. © 1992 Wiley‐Liss, Inc.
Neuroblastoma × spinal cord (NSC) hybrid cell lines resemble developing motor neurons
Authors: Cashman Neil R. , Durham Heather D. , Blusztajn Jan Krzysztof , Oda Kenichiro , Tabira Takeshi , Shaw Ivan T. , Dahrouge Simone , Antel Jack P.
Published: February 2005

We have developed a series of mouse‐mouse neural hybrid cell lines by fusing the aminopterin‐sensitive neuroblastoma N18TG2 with motor neuron‐enriched embryonic day 12–14 spinal cord cells. Of 30 neuroblastoma‐spinal cord (NSC) hybrids displaying a multipolar neuron‐like phenotype, 10 express choline acetyltransferase, and 4 induce twitching in cocultured mouse myotubules. NSC‐19, NSC‐34, and their subclones express additional properties expected of motor neurons, including generation of action potentials, expression of neurofilament triplet proteins, and acetylcholine synthesis, storage, and release. In addition, NSC‐34 cells induce acetylcholine receptor clusters on cocultured myotubes, and undergo a vimentin‐neurofilament switch with maturation in culture, similar to that occurring in neuronal development. NSC cell lines appear to model selected aspects of motor neuron development in an immortalized clonal system. © 1992 Wiley‐Liss, Inc.
Id expression during mouse development: A role in morphogenesis
Authors: Wang Yaoqi , Benezra Robert , Sassoon David A.
Published: February 2005

We have characterized the spatial and temporal pattern of Id transcription during mouse embryogenesis. The Id gene encodes a helix–loop–helix (HLH) protein which can heterodimerize with the ubiquitously expressed HLH protein products of the E2A gene, and prevent them from binding DNA either alone or as a heterodimer with tissue specific HLH transcription factors such as the muscle determination gene, MyoD1 (Benezra et al., 1990: Cell 61:49–59). Since Id has been shown to be down‐regulated during induced differentiation in several cell lines, it has been postulated that Id plays a general inhibitory role in cell differentiation (Benezra et al., 1990). In situ analysis of Id mRNA expression in the mouse embryo was performed in order to determine whether the pattern of Id expression is consistent with this postulate. A detailed study throughout the entirety of mouse postimplantation development reveals that Id is expressed upon gastrulation at very high levels in almost all regions of the mouse embryo and expression declines as embryogenesis proceeds. In skeletal muscle, in which the inhibitory action of Id has been established in tissue culture models (Benezra et al., 1990), Id and the HLH myogenic factors are expressed in a mutually exclusive manner suggesting that myogenic precursors do not express both types of HLH gene products. In addition, Id colocalizes both spatially and temporally with Hox‐7.1, a murine homeobox gene which is associated with regions of high cell proliferation and positional fate assignment. © 1992 Wiley‐Liss, Inc.
Retinoic acid receptor β2 mRNA is elevated by retinoic acid in vivo in susceptible regions of mid‐gestation mouse embryos
Authors: Harnish Douglas C. , Jiang H. , Soprano Kenneth J. , Kochhar D. M. , Soprano Dianne Robert
Published: February 2005

Many of the biological effects of retinoic acid are mediated by its nuclear receptors (RAR‐α, RAR‐β, and RAR‐γ), and each of these three receptors exist in multiple isoforms. As a first step to identify if any of the receptor isoforms are involved in dysmorphogenesis which is induced in mouse embryos after treatment with retinoic acid (RA), we examined the levels of mRNA of several isoforms of each RAR in the limb buds and other embryonic regions of normal and RA‐treated embryos. Within 3 to 6 hr after treatment of mice on day 11 of gestation with RA, RAR‐β2 mRNA levels in the whole embryo increased 7‐fold while both RAR‐α2 and RAR‐γ1 mRNA levels were elevated only 2‐fold. Since RA treatment of day 11 embryos especially produces limb defects in virtually every embryo, we next examined individual embryonic regions separately. Limb buds showed the highest elevations in RAR‐β2 mRNA levels (12‐fold) compared to a moderate elevation in the head/craniofacial region (8‐fold) and a small elevation in the remainder of the body (4‐fold). In contrast, RAR‐α2 and RAR‐γ1 mRNA levels were elevated in all these tissues to a similar extent, which amounted to only about a 2‐fold increase. Retinol, the precursor of RA in the embryo, was also capable of elevating RAR‐β2 mRNA levels in the limb bud, but the increase was delayed, apparently indicating that metabolic conversion of retinol to RA preceded the effect on mRNA levels. Finally, treatment of dams on day 14 of gestation, a time when embryos are relatively insensitive to RA, resulted in no elevation in RAR‐α2 mRNA levels and a greatly reduced elevation (2‐ to 3‐fold in all embryonic regions) in RAR‐β2 mRNA levels. Therefore, the elevation in RAR‐β2 mRNA correlates well with regions of the embryo, e.g., limb buds, which are specific targets for RA‐induced teratogenesis. These results are consistent with the possibility that specific isoforms of the RARs, in particular RAR‐β2, may mediate the effects of RA during abnormal development. © 1992 Wiley‐Liss, Inc.
Proteoglycans and the modulation of cell adhesion by steric exclusion
Authors: Morris John E.
Published: February 2005

The hypothesis that cell aggregation may be driven by linear polymers in the matrix, particularly glycosaminoglycans, is revisited in light of more recent evidence. A model is proposed that extends the concept of steric exclusion to include a role in determining the directionality of cell migration and neurite extension. Recent literature is reviewed to support the conclusion that in living tissues the theoretical conditions for driving aggregation and migration by steric exclusion are met. The ability of a linear polymer to exclude cells is a function of its viscosity, which is optimum with glycosaminoglycans similar to chondroitin sulfate. It is ineffective with low viscosity glycosaminoglycans such as most heparin or heparan sulfate. Hyaluronic acid, a massive polymer, excludes cells poorly when present as an open matrix gel but forms an effective exclusion barrier when attached to the cell surface. According to a model for steric exclusion in organogenesis, when cells have a glycocalyx of linear polymer, they should disperse and migrate down a viscosity gradient of excluding matrix polymer; when they shed or internalize their surface coat in the continued presence of matrix, they should be excluded into a smaller volume and thus stimulated to aggregate. © 1993 wiley‐Liss, Inc.
5A11 antigen is a cell recognition molecule which is involved in neuronal‐glial interactions in avian neural retina
Authors: Fadool James M. , Linser Paul J.
Published: February 2005

In continuing efforts to identify cell‐surface molecules involved in cell‐cell interactions in the developing avian retina, we identified a monoclonal antibody, the 5A11 antibody, which possessed the ability to interfere with contact‐dependent glial cell maturation in vitro. We sought to determine the molecular and biochemical identity of the glycoprotein recognized by this antibody, and using additional criteria, establish whether the 5All antigen is indeed a cell‐recognition molecule in the developing retina. Immuno‐histochemical analyses demonstrate that in the hatchling chick retina and in live cultures of embryonic retina cells, the 5A11 antigen is predominantly associated with Müller glial cells whereas little is observed on neuronal elements. Microsequencing of the major component isolated by immunoaffinity chromatography identifies the HT7 antigen (Seulberger et al.: EMBO Journal 9:2151–2158, 1990), a unique member of the immunoglobulin super gene family (IGSF), as a homologous if not identical protein to the 5A11 antigen. The HT7 antibody, furthermore, recognizes affinity purified 5A11 antigen, and both the HT7 antibody and additional probes generated against the 5A11 antigen recognize a major polypeptide of 45.5 kDa and a minor band of 69 kDa on Western blots of membrane preparations from neural retina. To verify that the 5A11 antigen mediates cell‐cell recognition events in the developing neural retina, we examined the consequences of adding antibody to monolayer cultures of dissociated embryonic retina cells and to dissociated retina cells in rotation‐mediated suspension culture. Addition of the 5A11 antibody to monolayer cultures results in alteration in the development of the stereotypic arrangement of neurons and glia characterized by a reduction in the number and complexity of neural extensions upon the glial‐derived flat cells. Similarly, addition of antibodies generated against the 5A11 antigen to dissociated cells in rotation cultures significantly reduces retina cell reaggregation as monitored by computer‐assisted image analysis of cell aggregate size. These data and the identification of the 5A11 antigen as a member of the IGSF establish a role for the 5A11 antigen as a novel recognition molecule in the developing neural retina. © 1993 wiley‐Liss, Inc.
Region‐specific patterns of beta keratin expression during avian skin development
Authors: Knapp L. W. , Shames R. B. , Barnes G. L. , Sawyer R. H.
Published: February 2005

The transient embryonic layers primarily composed of a periderm and subperiderm cover most regions of the chick embryo and are the first suprabasal cell layers covering the body ectoderm. This study presents evidence for regional vriation in the expression of beta keratin in the embryonic layers. Here we show that the embryonic layers covering the anterior metatarsal region of the chicken hindlimb (scutate scale forming region) produce several members of the beta keratin family of polypeptides, designated beta (β) 1–7. These specific polypeptides are later expressed in this region exclusively in the thick, cornified beta strata of mature scutate scales. In contrast to this sequence of events, the embryonic layers overlying the epidermis of the ventral foot pad (reticulate scale‐forming region) and those covering the epidermis in apteric regions of the body produce beta keratin polypeptides β1–3 and β2,3, respectively, but no subsequent expression of these proteins occurs in the mature epidermises of these regions. Furthermore, we find that the embryonic layers of the skin overlying the anterior metatasal region of birds homozygous for the mutation “scaleless” (sc/sc), which completely lack scutate scales, produce the same members of the beta keratin family, β1–7, as the embryonic layers and beta strata of normal scutate scales.

Thus, the accumulation of specific beta keratin polypeptides in the developing anterior metatarsal region appears to occur in two distinct phases; first, an early region‐specific expression in cells of the embryonic layers followed by a second phase of expression which occurs in conjunction with appendage morphogenesis. The relationship between differentiation of embryonic skin and the expression of beta keratins is discussed. © 1993 wiley‐Liss, Inc.
Spatio‐temporal distribution of acidic and basic FGF indicates a role for FGF in rat lens morphogenesis
Authors: de Iongh R. , McAvoy J. W.
Published: February 2005

As part of an investigation into the role FGF in lens development, we have studied the distribution of both aFGF and bFGF during eye morphogenesis from embryonic days 10 to 18 (E10–E18) in the rat. For aFGF, reactivity was found only in ectoderm at E10, prior to contact between the optic vesicle and presumptive lens ectoderm. During lens placode formation (E11) there was a transient, diffuse reactivity for aFGF in anterior optic vesicle cells directly apposed to the labelled ectoderm of the lens placode. At E12 the diffuse reactivity of the lens placode had changed to a discrete localisation along the basolateral surfaces of differentiating cells in the lens pit. Similar reactivity was associated with neuroblasts along the inner margin of the optic cup. At the early lens vesicle stage (E13) the baso‐lateral aFGF‐like reactivity associated with elongating lens cells was more intense and extensive. From the late lens vesicle stage (E14) to E18, reactivity in the lens was increasingly restricted to the equatorial regions which incorporate the germinative and transitional zones. From E16 to E18, aFGF‐like reactivity in the retina was predominantly localised in the peripheral regions corresponding to the developing ciliary body and iris and in the central retina associated with ganglion cell axons. For bFGF, weak reactivity was detectable as early as E13 in the developing lens capsule and increased in intensity during lens development with the posterior capsule reacting more intensely than the anterior capsule. Retinal bFGF‐like reactivity was first detected at E14, associated with differentiating ganglion cells in the central retina. From E16 to E18 the retinal ganglion cells showed increasing reactivity and the pattern of reactivity followed the centro‐peripheral pattern of retinal development. Thus reactivity for aFGF is first detected in presumptive lens ectoderm and subsequently in optic vesicle cells which are closely associated with lens ectoderm. This raises the possibility that aFGF may be involved in inductive interactions between presumptive lens ectoderm and optic vesicle. Furthermore the localisation patterns established for both aFGF and bFGF during lens and retina morphogenesis suggest an important role for FGF in regulating their morphogenesis and growth. © 1993 Wiley‐Liss, Inc.