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PubMed2002

Expression of nerve growth factor during the development of nervous system in early chick embryo.

In the chick gastrula, nerve growth factor (NGF) is localized to the endoblast mesoblast presumptive head ectoderm but not in the presumptive neuroectoblast. During early morphogenesis the dorsal body ectoderm presumptive neural crest cells exhibit strong NGF positive cell surface reaction. NGF appears to be a marker of cells participating in morphogenetic movements but not early neural differentiation. NGF is localized where neural folds fuse and cells die allowing detachment of the neural tube from head ectoderm as well as in dead cells in the neurocoele. NGF reactivity in cells lining the evaginated extremities of the optic vesicle the floor of the neural tube the splanchnopleure heart primordia the inner outer surfaces of somites is suggestive of the role of NGF in primitive organ shaping.

Animals↗

PubMed2003

XMAN1, an inner nuclear membrane protein, antagonizes BMP signaling by interacting with Smad1 in Xenopus embryos.

A family of inner nuclear membrane proteins is implicated in gene regulation by interacting with chromatin, nuclear lamina and intranuclear proteins; however, the physiological functions of these proteins are largely unknown. Using a Xenopus expression screening approach with an anterior neuroectoderm cDNA library, we have identified an inner nuclear membrane protein, XMAN1, as a novel neuralizing factor that is encoded by the Xenopus ortholog of human MAN1. XMAN1 mRNA is expressed maternally, and appears to be restricted to the entire ectoderm at the early gastrula stage, then to the anterior neuroectoderm at the neurula stage. XMAN1 induces anterior neural markers without mesoderm induction in ectodermal explants, and a partial secondary axis when expressed ventrally by dorsalizing the ventral mesoderm. Importantly, XMAN1 antagonizes bone morphogenetic protein (BMP) signaling downstream of its receptor Alk3, as judged by animal cap assays, in which XMAN1 blocks expression of downstream targets of BMP signaling (Xhox3 and Msx1), and by luciferase reporter assays, in which XMAN1 suppresses BMP-dependent activation of the Xvent2 promoter. Deletion mutant analyses reveal that the neuralizing and BMP-antagonizing activities of XMAN1 reside in the C-terminal region, and that the C-terminal region binds to Smad1, Smad5 and Smad8, which are intracellular mediators of the BMP pathway. Interference with endogenous XMAN1 functions with antisense morpholino oligos leads to the reduction of anterior neuroectoderm. These results provide the first evidence that the nuclear envelope protein XMAN1 acts as a Smad-interacting protein to antagonize BMP signaling during Xenopus embryogenesis.

Amino Acid Sequence↗

PubMed2003

A novel NK-type homeobox gene, ENK (early embryo specific NK), preferentially expressed in embryonic stem cells.

In order to identify novel homeobox-containing genes involved in early embryonic development, we conducted a degenerate oligonucleotide polymerase chain reaction (PCR) screening of a murine embryonic stem (ES) cell cDNA library. ENK (early embryo specific expression NK family) was one of several genes isolated that was found to exhibit early embryo stage-specific expression. The full-length ENK cDNA was cloned and its genomic organization was characterized. Murine ENK spans 7.1 kb, encodes four exons and maps to mouse chromosome 6F2. Reverse transcriptase-PCR and Northern blot analyses show that ENK is preferentially expressed in pre-implantation mouse embryos and a higher level in blastocysts. Whole-mount in situ hybridization analysis further demonstrates that ENK mRNA is present predominantly in the inner cell mass of blastocysts. The expression of ENK is markedly higher in undifferentiated ES cells than in retinoic acid differentiated ES cells and embryonic bodies. ENK expression slightly decreased in early primitive ectoderm-like (EPL) cells and was absent after the 9.5-day embryo stages. ENK is one of the few homeobox-encoding genes preferentially expressed in ES cells during mammalian embryogenesis.

Amino Acid Sequence↗

PubMed1955

The nuclear envelope; its structure and relation to cytoplasmic membranes.

An electron microscope study of thin sections of interphase cells has revealed the following:- Circular pores are formed in the double nuclear envelope by continuities between the inner and outer membranes which permit contact between the nucleoplasm and the cytoplasm unmediated by a well defined membrane. The pores, seen in sections normal to the nuclear envelope, are profiles of the ring-shaped structures described by others and seen in tangential section. The inner and outer nuclear membranes are continuous with one another and enclose the perinuclear space. The pores contain a diffuse, faintly particulate material. A survey of cells of the rat derived from the embryonic ectoderm, mesoderm, and endoderm, and of a protozoan and an alga has revealed pores in all tissues examined, without exception. It is concluded that pores in the nuclear envelope are a fundamental feature of all resting cells. In certain cells, the outer nuclear membrane is continuous with membranes of the endoplasmic reticulum, hence the perinuclear space is continuous with cavities enclosed by those membranes. There are indications that this is true for all resting cells, at least in a transitory way. On the basis of these observations, the hypothesis is made that two pathways of exchange exist between the nucleus and the cytoplasm; by way of the perinuclear space and cavities of the endoplasmic reticulum and by way of the pores in the nuclear envelope.

Animals↗

PubMed2006

Connexin 26 (GJB2) mutations in two Swedish patients with atypical Vohwinkel (mutilating keratoderma plus deafness) and KID syndrome both extensively treated with acitretin.

Neuroectodermal syndromes involving the skin and inner ear may be associated with mutations in connexin proteins, which form gap junctions important for intercellular communication. Vohwinkel syndrome (keratodermia mutilans with hearing loss) and keratitis-ichthyosis-deafness (KID) syndrome are rare ectodermal dysplasias associated with dominant mutations in the GJB2 gene encoding connexin 26. We report here two patients, one with KID and one with Vohwinkel syndrome. Both displayed unusual clinical features and responded well to long-term treatment with oral retinoid. Mutation analysis revealed a novel GJB2 mutation p.Gly59Ser in the patient with Vohwinkel syndrome, whereas a recurrent mutation p.Asp50Asn was found in the patient with KID syndrome. The clinical features, particularly a proneness to skin cancer in the patient with Vohwinkel syndrome, are discussed in relation to the identified genotypes.

Acitretin↗

PubMed1993

Developmental patterns of two alpha 1(IX) collagen mRNA isoforms in mouse.

Northern blot hybridization, reverse-transcription polymerase chain reaction (RT-PCR), and RNase protection assays were used to examine the expression of two alpha 1(IX) collagen mRNA species (long and short form) in developing mouse tissues. Furthermore, in situ hybridization was used to identify cells expressing the Col9a1 gene during eye development. The results indicate that during embryonic development eye and heart preferentially express the short form; lung and cartilage express the long form; whereas liver expresses a very low level of long form alpha 1(IX) mRNA which can only be detected by RT-PCR. In situ hybridization demonstrated that at 10.5 day postcoitum (d.p.c.), the alpha 1(IX) collagen mRNAs were first expressed in optic cup (neural ectoderm) but not in lens vesicle (surface ectoderm). By 13.5 d.p.c., the cells that express the alpha 1(IX) mRNA progressively were concentrated toward the anterior part of the neural retina. By 16.5-18.5 d.p.c., the hybridization signals were found exclusively in the inner non-pigmented layer of the presumptive ciliary epithelium. As ciliary epithelial cells become well differentiated 3 weeks after birth, cells expressing the Col9a1 gene were limited to the junction between mature ciliary folds and the neural retina. No hybridization signal could be detected in ocular tissues of mouse older than 6 weeks. It is of interest to note that a hybridization signal was not detected in cornea at the various developmental stages examined, suggesting that mouse cornea does not significantly express alpha 1(IX) mRNA during embryonic development. This differs from that of chick cornea development. In summary, the expression of the Col9a1 gene shows a temporospatial pattern throughout mouse eye development.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed2005

Dlx gene expression during chick inner ear development.

Members of the Dlx gene family play essential roles in the development of the zebrafish and mouse inner ear, but little is known regarding Dlx genes and avian inner ear development. We have examined the inner ear expression patterns of Dlx1, Dlx2, Dlx3, Dlx5, and Dlx6 during the first 7 days of chicken embryonic development. Dlx1 and Dlx2 expression was seen only in nonneuronal cells of the cochleovestibular ganglion and nerves from stage 21 to stage 32. Dlx3 marks the otic placode beginning at stage 9 and becomes limited to epithelium adjacent to the hindbrain as invagination of the placode begins. Dlx3 expression then resolves to the dorsal otocyst and gradually becomes limited to the endolymphatic sac by stage 30. Dlx5 and Dlx6 expression in the developing inner ear is first seen at stages 12 and 13, respectively, in the rim of the otic pit, before spreading throughout the dorsal otocyst. As morphogenesis proceeds, Dlx5 and Dlx6 expression is seen throughout the forming semicircular canals and endolymphatic structures. During later stages, both genes are seen to mark the distal surface of the forming canals and display expression complementary to that of BMP4 in the vestibular sensory regions. Dlx5 expression is also seen in the lagena macula and the cochlear and vestibular nerves by stage 30. These findings suggest important roles for Dlx genes in the vestibular and neural development of the avian inner ear.

Amino Acid Sequence↗

PubMed1991

Specific expression of a retinoic acid-regulated, zinc-finger gene, Rex-1, in preimplantation embryos, trophoblast and spermatocytes.

We have previously isolated a cDNA clone for a gene whose expression is reduced by retinoic acid (RA) treatment of F9 embryonal carcinoma cells. The nucleotide sequence indicated that this gene, Rex-1, encodes a zinc-finger protein and thus may be a transcriptional regulator. The Rex-1 message level is high in two lines of embryonic stem cells (CCE and D3) and is reduced when D3 cells are induced to differentiate using four different growth conditions. As expected for a stem-cell-specific message, Rex-1 mRNA is present in the inner cell mass (ICM) of the day 4.5 mouse blastocyst. It is also present in the polar trophoblast of the blastocyst. One and two days later, Rex-1 message is found in the ectoplacental cone and extraembryonic ectoderm of the egg cylinder (trophoblast-derived tissues), but its abundance is much reduced in the embryonic ectoderm which is directly descended from the ICM. Rex-1 is expressed in the day 18 placenta (murine gestation is 18 days), a tissue which is largely derived from trophoblast. The only tested adult tissue that contains detectable amounts of Rex-1 mRNA is the testis. In situ hybridization and northern analyses of RNA from germ-cell-deficient mouse testis and stage-specific germ cell preparations suggest that Rex-1 expression is limited to spermatocytes (germ cells undergoing meiosis). These results suggest that Rex-1 is involved in trophoblast development and spermatogenesis, and is a useful marker for studies of early cell fate determination in the ICM.

Animals↗

PubMed1996

Cell allocation to the inner cell mass and the trophectoderm in bovine embryos cultured in two different media.

Data from other laboratories have shown that speed of bovine blastocyst development is higher when Ménézo B2 is used for coculture compared to TCM199. It was our purpose to investigate whether this early blastocyst formation was also indicative of embryo quality by studying the allocation of inner cells in embryos generated by B2-coculture and by TCM199-coculture. For this purpose, a differential staining technique was used. General embryo development was similar for TCM199- and B2-embryos expressed as rate of cleavage at day 3 and morula-blastocyst formation at day 8 (P > 0.05), but significantly different when expressed as number of eight-cell stages at day 3 and expanded or hatched blastocysts at day 8 (P < 0.01). B2-embryos cultured until day 5, 6, and 7 post insemination, had total cell numbers of 24, 65, and 109 respectively, which was significantly higher than the cell number of TCM199-embryos cultured over the same time period (18, 41, and 71 respectively, P < 0.001). Morphological differentiation was significantly more advanced for B2-embryos at day 7 and 8 (P < 0.0001 and P < 0.001, respectively). First presumptive inner cells appeared in eight- to 16-cell stages at day 3. Because the determination of inner cells by differential staining is depending upon the presence of functional tight junctions, we concluded that the establishment of the tight junction seal in B2-embryos differed from that in TCM199-embryos: Inner cells appeared 0.56 cell cycle later in B2-embryos (P < 0.001) and a larger variation existed in the number of ICM-cells in B2-blastocysts (P < 0.001). The higher total cell number of B2-expanded blastocysts was mainly acquired by trophectoderm growth (P < 0.06). These data indicate that the apparent better quality of B2-embryos (faster cleavage, earlier blastocyst formation) is not reflected in a reliable number of inner cells of B2-blastocysts.

Animals↗

PubMed2002

Systematic analysis of E-, N- and P-cadherin expression in mouse eye development.

Cadherins are a family of Ca(2+)-dependent cell adhesion molecules. Through their homophilic binding interactions, cadherins play important roles in tissue formation and maintenance during development. Here the authors compare the expression patterns of the three classical cadherins, E-, N- and P-cadherin, during mouse eye development from embryonic day 9.5 (E9.5) to adult. It was found that: (1) The expression patterns of N- and P-cadherin are mutually exclusive in most ocular tissues during development. N-cadherin mRNA is detected specifically in the lens placode during lens induction at E9.5, and is absent in the rest of the surface ectodermal tissues. In contrast, P-cadherin is expressed in the surface ectoderm but not in the lens vesicle. N-cadherin is expressed continuously in the lens pit, lens vesicle, and in the epithelial cells and newly differentiating fiber cells of the mature lens. P-cadherin is expressed in the epithelial cells of the cornea, eyelids and Harderian gland. Reciprocal expression patterns of N-and P-cadherins are also seen during retinal development. N-cadherin is initially expressed in both the inner and outer layers of the optic cup at E9.5. N-cadherin expression persists in the inner layer as it develops into neural retina, but is turned off in the outer layer where the cells differentiate into retinal pigment epithelial (RPE) cells and express P-cadherin. Reciprocal patterns of expression are also seen in the ciliary epithelium. N-cadherin is expressed in the inner layer and P-cadherin in the outer layer of the ciliary epithelium. (2) E- and P-cadherins are epithelial cadherins. Their expression patterns in the eye are not identical. Both cadherins are found in the epithelia of the cornea, eyelid and Harderian gland. In contrast, lens epithelial cells express E- but not P-cadherin, and RPE cells express P- but not E-cadherin. (3) In addition to its high expression in surface ectoderm-derived tissues, E-cadherin mRNA was also detected in some of the retinal ganglion neurons at postnatal day 14 (P14). E-cadherin expression in the neural retina has not been reported before. This study shows that cell fate determination in the eye occurs in conjunction with distinct changes in the patterns of cadherin gene expression.

Animals↗

PubMed1993

Development of the eye in the North American opossum (Didelphis virginiana).

Marsupials are unique models for developmental biology-oriented research because of the immature state of their development at birth. The North American opossum (Didelphis virginiana) has several advantages over other marsupials, including large litter size, short prenatal period (12.5 d), an extended postnatal period while accessible in the pouch, and its ability to reproduce reliably in captivity. Studies of ocular development in this species have not been reported previously. The aim of the present investigation was therefore to document the major landmarks in prenatal and postnatal development of the cornea, lens, iris, ciliary body and retina. Fifteen embryos (10.5, 10.7 and 11 d postconception and 6 h after birth [12 d]) were studied by paraffin histology. Eyes of pouch young at 8 d, 2, 6, 9 and 13 wk were studied by transmission electron microscopy and light microscopy. The study revealed a similar pattern of ocular development in Didelphis to other metatherian and eutherian mammals. Differentiation of the eye is particularly rapid in the 2 d before birth. For example, although the lens vesicle separates from the surface ectoderm on d 10, by birth (2.5 d later) a primitive cornea and fused eyelids have formed, presumably to protect the eye during migration to the pouch. At birth the retinal pigment epithelium (RPE) contains melanin; however, the inner layer of the optic cup does not differentiate into an inner and outer neuroblastic layer until 8 d after birth. Around 6 wk after birth most components of the adult eye are identifiable, albeit in an immature form. These include the corneal layers, the iris (including the sphincter pupillae), ciliary processes, RPE tapetum, and a fully laminated retina with immature photoreceptors. A knowledge of the timing of major events in eye development in Didelphis and their comparison with equivalent events in human eye development should allow the appropriate choice of stages for any future experimental studies utilising this marsupial species.

Animals↗

PubMed1983

The chick epiblast: a model for examining epithelial morphogenesis.

The epiblast of early chick embryos is an important model system for examining morphogenesis. Five major morphogenetic processes can be readily examined by scanning electron microscopy of the epiblast: thickening of epithelial sheets by cell elongation, folding of epithelial sheets, fusion of epithelial sheets, cavitation of epithelial cords and dispersal of cell sheets during cell migration. The purpose of this paper is to describe these morphogenetic processes, showing examples of each type. Thickening of epithelial sheets occurs by cell elongation during formation of the neural plate. Folding then ensues to form the neural groove, which is flanked laterally by the neural folds. Fusion of the neural folds closes the neural groove and separates the incipient neural tube from the overlying surface ectoderm. The caudal part of the neural tube develops much differently. Cells derived from the tail bud cluster together as an epithelial medullary cord, the peripheral cells of this cord elongate, and, simultaneously, several small cavities appear at the inner ends of the peripheral cells. All of these cavities eventually coalesce, forming a single lumen. Thus, the neural tube can be formed by markedly different morphogenetic processes depending upon its particular craniocaudal level of origin. Cell migration is exhibited by neural crest cells. In chick embryos, these cells originate from the roof of the closed neural tube. They then migrate laterad to take up residence in a variety of new locations. Scanning electron microscopy has served as an important tool, aiding us greatly in visualizing complex spatial changes that occur during the morphogenesis of epithelia.

Animals↗

PubMed2001

Development of the membranous labyrinth of human embryos and fetuses using computer aided 3D-reconstruction.

The last detailed description of the development of the inner ear membranous labyrinth goes back to Streeter in 1918. This investigation can be regarded to be of outstanding scientific value. However, at that time no staging system of human embryos existed. In this respect, Streeter's work is outdated. It was the aim of this study to reinvestigate the development of the membranous labyrinth in human embryos and fetuses of which the developmental stages have been determined according to the Carnegie staging system and to compare the results with the literature. Serial histologic sections in the coronal or frontal plane of the heads of human embryos and fetuses of different developmental stages were used for computer aided 3D-reconstruction of the membranous labyrinth. From the obtained results, it is concluded that the endolymphatic duct develops earlier than previously described in the literature. The induction of the differentiation of the endolymphatic duct does not correspond with the superficial ectoderm because the endolymphatic duct develops medial of the otic vesicle. The membranous labyrinth determines the form of the petrosal bone as early as in stage 19 (47-48 days post conception).

Ear, Inner↗

PubMed1975

An ultrastructural study of adhesive junctions in reaggregates of unincubated chick embryos.

Cell suspensions obtained by the dissociation of unincubated chick embryo blastoderms were allowed to reaggregate on a gyratory shaker for 24-48 hours. The reaggregates which form during this period consist of an inner phase of tightly packed cohesive cells surrounded by an external phase of loosely packed cells. This sorted out arrangement achieves its definitive form between 24 and 48 hours of rotation culture. It was determined that the external phase consists of primitive ectoderm and that the internal phase consists of primitive endoderm. Both 24- and 48-hour reaggregates were examined in the electron microscope and observations were directed to areas of close membrane apposition between cells. In 48-hour reaggregates, primitive endoderm cells were joined by many specialized junctions (desmosomes). The formation of desmosomes in reaggregates of dissociated unincubated chick embryo cells was correlated with the sorting out process.

Animals↗

PubMed2003

Atlas of the embryonic brain in the pygmy squid, Idiosepius paradoxus.

Gross structural changes and neuropil formation in the brain during development were described in Idiosepius paradoxus, a sepioid that we chose as a model cephalopod. The brain originates in 4 pairs of ectodermal placodes, which occur separately in the embryonic surface undergoing epiboly. In the final period of epiboly, neuroblasts internalize from the placodes and gather into 4 pairs of ganglionic masses. The ganglionic masses assemble into a ring-like cluster encircling the inner yolk and the foregut anlage, gradually integrated into the 4 domains of a massive brain, a subesophageal mass (SBM), a supraesophageal mass (SPM), and a pair of optic lobes. In the early brain, neuropil forms a framework composed of a longitudinal ladder lying in the SBM, and a transverse arch standing on the lateral sides of the SBM and crossing the SPM. Differentiation of brain lobes proceeds from ventral to dorsal along this framework; first the magnocellular lobes and the posterior pedal lobe appear first in the SBM, the other lobes in the SBM and the basal lobes follow in the proximal region of the SPM, and the accessory lobes develop last in the most dorsal zone of the SPM. In the hatchlings, the brain lobes show almost the same arrangement as in the adults, but the accessory lobes, particularly the vertical lobe, are much smaller than those in the adults. Comparison of the present results with those in the teuthoid and the octopod indicates that developmental sequences of the brain are highly conserved in the coleoid cephalopods.

Animals↗

PubMed1978

[Formation and cellular structure of the lines of tension in the axial rudimenta of amphibian embryos].

The lines of mechanical tension (cross-lines) in axial rudiments of the amphibian embryo represent bands of polarized cells. They form in the inner layers of the rudiments as separate bundles of polarized cell which, then, merge, attain the external surface and gather in lengthy planes (cross-planes) and, later, degrade. The primary inductor induces the formation of cross-lines in the ventral ectoderm of the early gastrula. The growth of cross-lines in considered as one of the types of contact cells polarization. The morphogenetic role of contact polarization is discussed. The connection between the subsequent tension patterns is based on the fact that the lines of exit of the cross-planes on the surface of the embryo coincide with the direction of the previously established tensions.

Amphibians↗

PubMed1989

The extracellular matrix architecture relating to myotendinous pattern formation in the distal part of the developing chick limb: an ultrastructural, histochemical and immunocytochemical analysis.

In the later developmental stages (Hamburger and Hamilton, 25-34) the distal part of the chick leg possesses a distinctive extracellular matrix (ECM) architecture which relates to myotendinous patterning. There are two components: firstly, a system of dorsoventrally oriented fibrils which link the two ectodermal surfaces through the undifferentiated distal mesenchyme and secondly, a 'mesenchyme lamina' originates at the basement membrane distally, but proximally runs through the mesoderm, subjacent and parallel to the basement membrane. The 'mesenchyme lamina' appears to be a precursor of developing tendons and is spatially related to the distal tips of the myogenic blocks. As developing tendons form on the inner surface of the lamina at its proximal end, it becomes less distinct and disappears. Further dorsoventral fibrils run from the 'mesenchyme lamina' into the developing condensations and chondrogenic elements of the phalanges. The architecture of the ECM was revealed by silver and lectin staining (peanut and Ricinus communis agglutinins, PNA and RCA I), by immunocytochemistry (for fibronectin, tenascin, collagen type I) and by ultrastructural analysis. Both components stain with silver, PNA following neuraminidase digestion, RCA I, tenascin and collagen type I. However, the dorsoventral fibrils are positive for fibronectin and negative for PNA, while conversely the mesenchyme lamina is positive for PNA but much less so for fibronectin. Tenascin has been shown to be a specialized mesenchyme component of tendons and myotendinous junctions (Chiquet and Fambrough, 1984). Such a basement membrane forming a 'mesenchyme lamina' appears to be unique in epithelial-mesenchymal developing systems and points to an ectodermal role in tendon pattern formation within the mesenchyme. We discuss the possible role of mechanical force in converting the dorsoventral tenascin-positive fibrils into the localized pattern of tendon insertions into the proximal parts of the phalanges. Distally the dorsoventral fibrils may shape the digital plate by pulling together the two ectodermal surfaces. A similar ECM architecture is found in corresponding stages in the developing wing.

Animals↗

PubMed1983

Spontaneous high expression of heat-shock proteins in mouse embryonal carcinoma cells and ectoderm from day 8 mouse embryo.

When submitted to a heat-shock, mouse embryonal carcinoma (EC) and fibroblast cells show very different behavior. All the EC cells so far analyzed express very high levels of several heat-shock proteins (HSP) in the absence of stress and independent of their origin and culture conditions. In such cells, the 89-kd, 70-kd and 59-kd HSP are the most prominent proteins after actin. In addition, the 89-kd and 59-kd HSP are not stimulated by an arsenite shock in contrast to what is observed with fibroblasts or cells of the parietal yolk sac type. Arsenite induces the synthesis of a 105-kd polypeptide in fibroblasts but not in EC cells. In vitro differentiation of F9 cells induced by retinoic acid and dibutyryl cAMP is accompanied by a decrease in the spontaneous relative abundance of HSP and restores the arsenite-induced synthesis of the 105-kd polypeptide. EC cells are usually believed to be similar to inner cell mass cells of mouse blastocyst. Furthermore, data in the literature together with our own results suggest that the same three HSP are also spontaneously expressed in high amounts in the early mouse embryo.

Animals↗