Anterior Pole of the Lens

2020 ◽  
Author(s):  
Keyword(s):  
Anterior Pole

Anterior Movement of the Crystalline Lens in the Process of Accommodation in Children

2007 ◽  
Vol 17 (4) ◽  
pp. 515-520 ◽  
Author(s):  
B.J. Kaluzny
Keyword(s):  
Refractive Error ◽  
Axial Length ◽  
Crystalline Lens ◽  
Posterior Pole ◽  
Anterior Pole ◽  
Forward Movement ◽  
Ophthalmic Examination ◽  
Lens Thickness ◽  
Lens Position ◽  
Refractive Status

Purpose To investigate changes of crystalline lens position during accommodation in children with emmetropia, myopia, and hyperopia. Methods A total of 188 children (372 eyes) from 4 to 19 years old (mean age 11.3±4.43) with cycloplegic refractive error within a range +9.00 D to −9.00 D were enrolled. After a general ophthalmic examination, ultrasound biometry was performed, with the eye at a maximal accommodative effort. Cycloplegia was induced by triple installation of 1% tropicamide drops and 30 minutes later the biometric examination was repeated. Results In emmetropic eyes in the process of accommodation, the anterior pole of the crystalline lens moved forward by 0.144±0.14 mm (p ≤ 0.001); the position of the posterior pole did not change. In myopic eyes, the anterior pole moved forward by 0.071±0.13 mm (p≤0.001) and the posterior pole moved backward by 0.039±0.10 mm (p=0.003). In hyperopic eyes, the whole lens translocated anteriorly: anterior pole moved forward by 0.242±0.16 mm (p≤ 0.001) and posterior pole moved forward by 0.036±0.09 mm (p≤0.001). Differences among emmetropia, myopia, and hyperopia were statistically significant. Forward movement of the posterior pole correlated with a low axial length of the eye, and also with plus refractive error and with a smaller accommodative increase of lens thickness. Conclusions In children, accommodative changes of the crystalline lens position depend on refractive status.

Induction of primitive streak and Hensen's node by the posterior marginal zone in the early chick embryo

Development ◽  
1998 ◽  
Vol 125 (17) ◽  
pp. 3521-3534 ◽  
Author(s):  
R.F. Bachvarova ◽  
I. Skromne ◽  
C.D. Stern
Keyword(s):  
Chick Embryo ◽  
Marginal Zone ◽  
Lower Layer ◽  
Primitive Streak ◽  
Normal Embryo ◽  
Anterior Pole ◽  
Posterior Edge ◽  
Amphibian Embryo ◽  
Midline Cells ◽  
Marginal Zones

In the preprimitive streak chick embryo, the search for a region capable of inducing the organizer, equivalent to the Nieuwkoop Center of the amphibian embryo, has focused on Koller's sickle, the hypoblast and the posterior marginal zone. However, no clear evidence for induction of an organizer without contribution from the inducing tissue has been provided for any of these structures. We have used DiI/DiO labeling to establish the fate of midline cells in and around Koller's sickle in the normal embryo. In the epiblast, the boundary between cells that contribute to the streak and those that do not lies at the posterior edge of Koller's sickle, except at stage X when it lies slightly more posteriorly in the epiblast. Hypoblast and endoblast (a second lower layer formed under the streak) have distinct origins in the lower layer, and goosecoid expression distinguishes between them. We then used anterior halves of chick prestreak embryos as recipients for grafts of quail posterior marginal zone; quail cells can be identified subsequently with a quail-specific antibody. Anterior halves alone usually formed a streak, most often from the posterior edge. Quail posterior marginal zones without Koller's sickle were grafted to the anterior side of anterior halves. These grafts were able to increase significantly the frequency of streaks arising from the anterior pole of stage X-XI anterior halves without contributing to the streak or node. Stage XII anterior halves no longer responded. A goosecoid-expressing hypoblast did not form under the induced streak, indicating that it is not required for streak formation. We conclude that the marginal zone posterior to Koller's sickle can induce a streak and node, without contributing cells to the induced streak.

Instability of the anteroposterior axis in spontaneous double abdomen (sda), a genetic variant of Chironomus samoensis (Diptera, Chironomidae)

Development ◽  
1987 ◽  
Vol 101 (3) ◽  
pp. 591-603 ◽  
Author(s):  
K.L. Kuhn ◽  
J. Percy ◽  
M. Laurel ◽  
K. Kalthoff
Keyword(s):  
Genetic Variant ◽  
Laboratory Strain ◽  
Posterior Pole ◽  
Mirror Image ◽  
Anterior Pole ◽  
Spontaneous Formation ◽  
Pole Cells ◽  
Anterior Segments ◽  
Egg Polarity

We have isolated a laboratory strain of Chironomus samoensis in which determination of the anteroposterior egg polarity is disturbed. Most conspicuous is the spontaneous formation of ‘double abdomen’ embryos where head and thorax are replaced by a mirror image of the abdomen. Such double abdomens are found in about half of the egg clusters in this strain, which we call the spontaneous double abdomen (sda) strain as opposed to the normal (N) strain. Also observed in the sda strain, although less frequently, are ‘double cephalon’ embryos showing a mirror-image duplication of cephalic segments in the absence of thorax and abdomen. Moreover, embryos from the sda strain tend to form cells at the anterior pole resembling the pole cells at the posterior pole. Reciprocal crossings between the sda and the N strain indicate that the sda trait is inherited maternally. Spontaneous double abdomen formation is correlated with signs of disturbed egg architecture, including extruded yolk and detached cells. Double cephalons can also be generated by centrifuging embryos from the N strain, whereas centrifugation of sda embryos produces mostly double abdomens. Double abdomen formation can be induced experimentally by anterior u.v. irradiation of embryos from either strain. The sda trait and u.v. irradiation act in a synergistic fashion. The data suggest that the sda trait may be caused by one or more genomic mutations interfering indirectly with the activity of anterior determinants, i.e. cytoplasmic RNP particles necessary for the development of anterior segments. The sda defects may be ascribed to alterations in cytoskeletal components involved in anchoring anterior determinants and segregating them into anterior blastoderm cells.

scholarly journals Optical Coherence Tomography Reveals New Insights into the Accommodation Mechanism

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Mahmoud Mohamed Farouk ◽  
Takeshi Naito ◽  
Kayo Shinomiya ◽  
Hiroshi Eguchi ◽  
Khulood Mohammed Sayed ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Outcome Measures ◽  
Anterior Segment ◽  
Case Series ◽  
Optical Coherence ◽  
Anterior Pole ◽  
Forward Movement ◽  
Anterior Segment Oct ◽  
Lens Thickness ◽  
Significant Difference

Purpose. To evaluate the movement of the anterior and posterior lens poles during naturally stimulated accommodation in children using anterior segment optical coherence tomography (OCT).Methods. This is a prospective, observational, noncomparative case series including 18 eyes of nine children. Analysis of the anterior segment in the accommodated and unaccommodated state (with cycloplegia) was done using anterior segment OCT. The main outcome measures were the position of the anterior and posterior lens poles (in relation to the cornea) and lens thickness (LT).Results. A Statistically significant forward movement of the anterior lens pole and backward movement of the posterior lens pole with an increase in LT were found during accommodation (P<0.001). There was no significant difference between the degree of movement of the anterior lens pole and the posterior lens pole during accommodation (P=0.944).Conclusions. Anterior segment OCT provides a rapid noncontact method for studying accommodation in children. The backward movement of the posterior lens pole during accommodation nearly equals the forward movement of its anterior pole. These data minimize the theoretical hydraulic effect of the vitreous during accommodation, adding more support to the capsular theory of Helmholtz.

scholarly journals The Microtubule Cytoskeleton during the Early Drosophila Spermiogenesis

Cells ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 2684
Author(s):  
Maria Giovanna Riparbelli ◽  
Veronica Persico ◽  
Giuliano Callaini
Keyword(s):  
Basal Body ◽  
Anterior Pole ◽  
Microtubule Cytoskeleton ◽  
Nuclear Shaping ◽  
Pericentriolar Material ◽  
Centriole Adjunct ◽  
Shed Light

Sperm elongation and nuclear shaping in Drosophila largely depends on the microtubule cytoskeleton that in early spermatids has centrosomal and non-centrosomal origins. We report here an additional γ-tubulin focus localized on the anterior pole of the nucleus in correspondence of the apical end of the perinuclear microtubules that run within the dense complex. The perinuclear microtubules are nucleated by the pericentriolar material, or centriole adjunct, that surrounds the basal body and are retained to play a major role in nuclear shaping. However, we found that both the perinuclear microtubules and the dense complex are present in spermatids lacking centrioles. Therefore, the basal body or the centriole adjunct seem to be dispensable for the organization and assembly of these structures. These observations shed light on a novel localization of γ-tubulin and open a new scenario on the distribution of the microtubules and the organization of the dense complex during early Drosophila spermiogenesis.

Mutations in the Drosophila gene bullwinkle cause the formation of abnormal eggshell structures and bicaudal embryos

Development ◽  
1995 ◽  
Vol 121 (9) ◽  
pp. 3023-3033 ◽  
Author(s):  
K.R. Rittenhouse ◽  
C.A. Berg
Keyword(s):  
Cell Migration ◽  
Cell Fate ◽  
Germ Line ◽  
Follicle Cell ◽  
Posterior Pole ◽  
Mirror Image ◽  
Follicle Cells ◽  
Anterior Pole ◽  
Posterior Group ◽  
General Transport

Subcellular localization of gene products and cell migration are both critical for pattern formation during development. The bullwinkle gene is required in Drosophila for disparate aspects of these processes. In females mutant at the bullwinkle locus, the follicle cells that synthesize the dorsal eggshell filaments do not migrate properly, creating short, broad structures. Mosaic analyses demonstrate that wild-type BULLWINKLE function is required in the germ line for these migrations. Since the mRNA for gurken, the putative ligand that signals dorsal follicle cell fate, is correctly localized in bullwinkle mutants, we conclude that our bullwinkle alleles do not affect the dorsoventral polarity of the oocyte and thus must be affecting the follicle cell migrations in some other way. In addition, the embryos that develop from bullwinkle mothers are bicaudal. A KINESIN:beta-GALACTOSIDASE fusion protein is correctly localized to the posterior pole of bullwinkle oocytes during stage 9. Thus, the microtubule structure of the oocyte and general transport along it do not appear to be disrupted prior to cytoplasmic streaming. Unlike other bicaudal mutants, oskar mRNA is localized correctly to the posterior pole of the oocyte at stage 10. By early embryogenesis, however, some oskar mRNA is mislocalized to the anterior pole. Consistent with the mislocalization of oskar mRNA, a fraction of the VASA protein and nanos mRNA are also mislocalized to the anterior pole of bullwinkle embryos. Mislocalization of nanos mRNA to the anterior is dependent on functional VASA protein. Although the mirror-image segmentation defects appear to result from the action of the posterior group genes, germ cells are not formed at the anterior pole. The bicaudal phenotype is also germ-line dependent for bullwinkle. We suspect that BULLWINKLE interacts with the cytoskeleton and extracellular matrix and is necessary for gene product localization and cell migration during oogenesis after stage 10a.

Differentiation within the gonads of Drosophila revealed by immunofluorescence

Development ◽  
1981 ◽  
Vol 63 (1) ◽  
pp. 233-242
Author(s):  
Danny L. Brower ◽  
R. J. Smith ◽  
Michael Wilcox
Keyword(s):  
Epithelial Cells ◽  
Hybrid Cell ◽  
Proximal Part ◽  
Follicular Epithelium ◽  
Follicle Development ◽  
Nurse Cells ◽  
Border Cells ◽  
Anterior Pole ◽  
Posterior Pair ◽  
Adult Ovary

The antibody produced by the hybrid cell line DA.1B6 binds to the diploid epithelial cells of Drosophila. In this paper, we describe the immunofluorescence-binding pattern of the antibody to the gonads. A bright sheath of fluorescence extends from the seminal vesicle onto the most proximal part of the adult testis. The only other significant binding to the organ is to the apical cells of the germinal proliferation centre, which fluoresce brightly in testes from adults and from third instar larvae. In the adult ovary, there is strong binding to the cells of the follicular epithelium, although this binding is reduced in the latter stages of follicle development. Soon after the formation of a follicle, a pair of epithelial cells at each pole of the follicle can be seen to fluoresce much more brightly than the other cells. This early differentiation is reflected in the morphogenetic behaviour of these polar cells as the follicle develops. The anterior pair are among the ‘border cells’ which migrate between the nurse cells to the anterior pole of the developing oocyte; and, when the follicular epithelium around the oocyte becomes columnar, the posterior pair of cells do not elongate as much as the surrounding cells.

RNA regulatory element BLE1 directs the early steps of bicoid mRNA localization

Development ◽  
1993 ◽  
Vol 118 (4) ◽  
pp. 1233-1243 ◽  
Author(s):  
P.M. Macdonald ◽  
K. Kerr ◽  
J.L. Smith ◽  
A. Leask
Keyword(s):  
Untranslated Region ◽  
Regulatory Element ◽  
Essential Element ◽  
Mrna Localization ◽  
Morphogen Gradient ◽  
Anterior Pole ◽  
Functional Elements ◽  
Cis Acting ◽  
Localization Signal ◽  
Drosophila Embryos

Deployment of the bicoid morphogen gradient in early Drosophila embryos requires the prelocalization of bicoid mRNA to the anterior pole of the egg. This anterior localization is mediated by a cis-acting localization signal contained within the 3′ untranslated region of the bicoid mRNA. Here we use a series of bicoid transgenes carrying small deletions in the 3′ untranslated region to survey for functional elements that constitute the localization signal. We identify and characterize one essential element, BLE1, which specifically directs the early steps of localization. In addition, we find that many deletions within the bicoid mRNA 3′ untranslated region impair but do not prevent localization. One such deletion specifically interferes with a later step in localization. Thus the bicoid mRNA localization signal appears to consist of multiple different elements, each responsible for different steps in the localization process.

The development of Drosophila embryos after partial u.v. irradiation

Development ◽  
1976 ◽  
Vol 36 (2) ◽  
pp. 395-408
Author(s):  
M. Bownes ◽  
K. Sander
Keyword(s):  
Low Frequency ◽  
Anterior Pole ◽  
Drosophila Embryos

U.v. irradiation of the anterior pole of nuclear multiplication stage Drosophila eggs produces embryos with defective anterior structures. At a low frequency embryos resembling some phenotypes of the bicaudal syndrome of Drosophila were observed. These embryos had no head or thorax and the eight abdominal segments were spread to the anterior of the embryo. Sometimes spiracles, characteristic of the most posterior embryonic segment were observed at the anterior of the embryo. The development of these embryos was followed, and abnormalities occurred as early as blastoderm formation. The extent of the blastoderm defects correlated well with the final abnormality in the embryo.

In vivo analyses of cytoplasmic transport and cytoskeletal organization during Drosophila oogenesis: characterization of a multi-step anterior localization pathway

Development ◽  
1998 ◽  
Vol 125 (18) ◽  
pp. 3655-3666 ◽  
Author(s):  
W.E. Theurkauf ◽  
T.I. Hazelrigg
Keyword(s):  
Laser Scanning ◽  
Fluorescent Protein ◽  
Drosophila Embryo ◽  
Nurse Cells ◽  
Anterior Pole ◽  
Microtubule Organization ◽  
Microtubule Network ◽  
Cytoplasmic Transport ◽  
Anterior Patterning

Anterior patterning of the Drosophila embryo depends on localization of bicoid (bcd) mRNA to the anterior pole of the developing oocyte, and bcd mRNA localization requires both the exuperantia (exu) gene and an intact microtubule cytoskeleton. To gain insight into the mechanism of anterior patterning, we have used time lapse laser scanning confocal microscopy to analyze transport of particles containing a Green Fluorescent Protein-Exu fusion (GFP-Exu), and to directly image microtubule organization in vivo. Our observations indicate that microtubules are required for three forms of particle movement within the nurse cells, while transport through the ring canals linking the nurse cells and oocyte appears to be independent of both microtubules and actin filaments. As particles enter the oocyte, a final microtubule-dependent step directs movement to the oocyte cortex. However, our observations and previous studies suggest that the polarity of the oocyte microtubule network is not in itself sufficient to generate anterior asymmetry, and that additional factors are required to restrict morphogens to the anterior pole. Based on these observations, we propose a multi-step anterior localization pathway.

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