Optic Primordia Research Articles

Retinoic acid-induced duplication of the zebrafish retina.

Exogenous treatment of zebrafish embryos with retinoic acid induces a duplication of the retinas during development. These effects occur only when retinoic acid is applied within a 2-hr period prior to and during the initial formation of the optic primordia, and they are concentration-dependent. Light microscopic examination reveals that the second retina derives from cells in the ventral region of the developing eyecup that normally become pigment epithelial cells. Two distinct ganglion cell fields are usually observed in eyes with duplicated retinas. Bundles of axons from each ganglion cell field join as they leave the eye and innervate the contralateral tectum.

Distribution of glycoconjugates in the optic vesicle and optic cup

Lectin histochemical methods and immunohistochemical techniques have been utilized to investigate and partially characterize glycoconjugates in the developing eye. Peanut-lectin-binding sites associated with radial glial cells were found in the diencephalon. In the optic primordia, binding sites associated with radial glia were masked by terminal sialic acid, and only reacted with peanut lectin when pretreated with sialidase. This finding indicates that glycoconjugates associated with diencephalic radial glia contain terminal galactose-beta-(1----3)N-acetyl galactosamine, but glycoconjugates associated with radial glia in the optic primordia contain sialic acid----galactose-beta(1----3)N-acetyl galactosamine. The selective distribution of galactose, N-acetyl galactosamine and fucose associated with radial glial cells has also been demonstrated. We postulate that these distributions mediate the shaping of the developing eye.

Proliferation pattern and early differentiation of the optic lobes in Drosophila melanogaster.

The larval and early pupal development of the optic lobes in Drosophila is described qualitatively and quantitatively using [3H]thymidine autoradiography on 2-μm plastic sections. The optic lobes develop from 30-40 precursor cells present in each hemisphere of the freshly hatched larva. During the first and second larval instars, these cells develop to neuroblasts arranged in two epithelial optic anlagen. In the third larval instar and in the early pupa these neuroblasts generate the cells of the imaginal optic lobes at discrete proliferation zones, which can be correlated with individual visual neuropils.The different neuropils as well as the repetitive elements of each neuropil are generated in a defined temporal sequence. Cells of the medulla are the first to become postmitotic with the onset of the third larval instar, followed by cells of the lobula complex and finally of the lamina at about the middle of the third instar. The elements of each neuropil connected to the most posterior part of the retina are generated first, elements corresponding to the most anterior retina are generated last.The proliferation pattern of neuroblasts into ganglion mother cells and ganglion cells is likely to include equal as well as unequal divisions of neuroblasts, followed by one or two generations of ganglion mother cells. For the lamina the proliferation pattern and its temporal coordination with the differentiation of the retina are shown.

Target recognition in retinotectal projection; Rotation experiment of optic tectum primordium

Target recognition in retinotectal projection; Rotation experiment of optic tectum primordium

Target recognition in retinotectal projection; Rotation experiment of optic tectum primordium

Target recognition in retinotectal projection; Rotation experiment of optic tectum primordium

Mediobasal prosencephalic defects, including holoprosencephaly and cyclopia, in relation to the development of the human forebrain

Four very early synophthalmic embryos were studied in serial sections and reconstructed graphically by the point-plotting method. Three belonged to stage 16 (5 weeks) and one to stages 19/20 (7 weeks). Recently completed accounts and reconstructions of the normal brains of staged human embryos served as controls for comparison with the abnormal examples. The embryos shared in common: holoprosencephaly, arhinencephaly sensu stricto (absence of olfactory nerve fibers, bulbs, and tracts), presence of a proboscis, synophthalmia with two lens vesicles, a retarded telencephalic wall, absence of the mediobasal part of the telencephalon (the future septal area and the commissural plate: future anterior commissure and corpus callosum), irregularity of the diencephalon, mensural changes in the brain, absence of the rostral part of the notochord and consequent cranial defects, and small ganglia of the cranial nerves. Where it could be determined (at least in the three less advanced specimens), the adenohypophysial primordium was either small and isolated or was absent; a tentorial condensation appeared to be missing; and disturbances of the primordia of the orbital muscles and their innervation were noted. The corpus striatum is single and corresponds to only the diencephalic part (medial eminence) of normal embryos. Interference with induction by the prechordal plate at or before stage 8 (18 days) would be expected to affect the future mediobasal part of the neural plate (median prosencephalic dysgenesis) and the future optic primordium (cyclopia sensu stricto). Insufficient formation of material from the prechordal plate would account for disorders of the orbital musculature and, possibly, for inadequacy of the tentorium cerebelli. Disturbance a couple of days later (stage 9) would result in synophthalmia. Cyclopia and synophthalmia entail arhinencephaly and holoprosencephaly, both of which may arise independently. Defective distribution of the cephalic mesenchyme points to a derangement of the mesencephalic neural crest (stages 10 and 11), causing such features as an incomplete chondrocranium and reduction in size of the ganglia of the cranial nerves. Failure of bilateral division of the telencephalon would occur at or before 4 weeks (stages 13 and 14). It is concluded that all the above conditions arise during the first 4 postovulatory weeks.

Postembryonic development of Arg-Phe-amide-like and cholecystokinin-like immunoreactive neurons in the blowfly optic lobe

The adult optic lobes of the blowfly Calliphora erythrocephala were found to be innervated by more than 2000 neurons immunoreactive to antisera raised against the neuropeptides FMRFamide, its fragment RFamide, and gastrin/cholecystokinin (CCK). All of the CCK-like immunoreactive (CCK-IR) neurons also reacted with antisera to RFamide, FMRFamide and pancreatic polypeptide. A few RFamide/FMRFamide-like immunoreactive (RF-IR) neurons did not react with CCK antisera; they reacted instead with antisera to Leu-enkephalin and Met-enkephalin-Arg6-Phe7. The RF-IR neurons are, thus, heterogeneous with respect to their contents of immunoreactive peptides. Two of the RF-IR neuron types innervating the adult optic lobes could be traced in their entirety only after following their postembryonic development, because of the complexity of the trajectories of the immunoreactive neuronal process in the adult insect. The majority of the cell bodies of the RF-IR and CCK-IR neurons lie within the optic lobes and are derived from imaginal neuroblasts of the inner and outer optic anlagen. Six of the peptidergic neurons are, however, metamorphosing larval neurons with their cell bodies in the central part of the protocerebrum. The full extent of immunoreactivitiy is not attained in some of the neurons until the late pupal or early adult stage. The larval optic center was also found to be innervated by neurons immuno-reactive with both RFamide and CCK antisera. The cell bodies of these RF-IR/CCK-IR neurons are located near the developing lamina (one on each side). In the 24 h pupa, the cell bodies of these neurons are still immunoreactive, but thereafter they cannot be immunolabeled apparently due to cell death or a change in transmitter phenotype.

CYCLOPIA

Cyclopia is a congenital defect in which the two orkits merge to form a single cavity containing one eye, which is likely to show more or less evidence of its origin by fusion of the right and left optic primordia. It is usually combined with cyclencephaly. It is usually described as synophthalmus.

Fetal alcohol syndrome. Eye malformations in a mouse model.

Acute maternal ethanol administration on gestational day 7 (gastrulation stage) in C57Bl/6J mice results in a spectrum of ocular malformations. A deficiency in the anterior neural plate observable within 24 hours of exposure results in corresponding defects in the optic sulcus and subsequent optic vesicle. Deficiency in the size of the lens vesicle induced by a small optic vesicle is demonstrable as microphakia in older embryos. Delayed detachment of the lens vesicle from the surface ectoderm manifests in the live offspring as progressive corneal opacification and vascularization related to defects in corneal endothelium and Descemet's membrane. Anterior segment dysgenesis results in persistent iridocorneal adhesions, dyscoria, and abnormal formation of the anterior chamber. In contrast, ethanol exposure on day 8 of gestation did not result in eye malformations. Thus, it appears that many of the ocular abnormalities associated with fetal alcohol syndrome may result from an acute insult to the optic primordia during a very specific period that corresponds to the third week after fertilization in the human.

Postembryonic development of serotonin-immunoreactive neurons in the central nervous system of the blowfly, Calliphora erythrocephala

The postembryonic development of serotonin-immunoreactive (5-HTi) neurons was studied in the optic lobe of the blowfly. In the adult fly there are 24 5-HTi neurons invading each optic lobe. The perikarya of two of these neurons are situated in the dorso-caudal part of the protocerebrum (LBO-5HT neurons; large bilateral optic lobe 5-HTi neurons). The cell bodies of the remaining 22 neurons are located anteriorly at the medial base of the medulla (2 innervating the lobula, LO-5HT neurons; and 20 neurons innervating the medulla, ME-5HT neurons). The two central neurons (LBO-5HT neurons) are derived from metamorphosing larval neurons, while the ME- and LO-5HT neurons are imaginai optic lobe neurons differentiating during pupal development. The 5-HTi neurons of the optic lobe seem to have different ancestors. The LBO-5HT neurons are probably derived from segmental protocerebral neuroblasts, whereas the ME-and LO-5HT neurons are most likely derived from the inner optic anlage. The first 5-HTi fibers to reach the imaginal optic lobes are seen in the late third instar larva and are derived from the LBO-5HT neurons. The first ME- and LO-5HT neurons become immunoreactive at 24 h (10%) pupal development. At about 96 h (40%) of pupal development all the 5-HTi neurons of the optic lobes have differentiated and attained their basic adult morphology. The further development mainly entails increase in volume of arborizations and number of finer processes. The differentiation and outgrowth of 5-HTi processes follows that of, e.g., columnar neurons in the optic lobe neuropils. Hence, 5-HTi processes invade neuropil relatively late in the differentiation of the optic lobe.

An in vitro study of teratogenicity in the rat due to antibody-induced yolk sac dysfunction : Identification of the yolk sac antigen involved.

An antiserum was prepared in rabbit against rat visceral yolk sac endoderm. The initial injection was of a ConA-Sepharose purified fraction of endoderm, and subsequent injections were of whole endoderm. The antiserum was found to be a potent rat teratogen in vivo, the most common defects observed being anophthalmia and hydrocephaly.Using rat whole embryo culture, the antiserum was demonstrated to induce dysmorphogenesis and growth retardation in a concentration dependent manner. The most frequent abnormalities were of the optic primordia, suggesting a similar embryonic response in vitro to that observed in vivo.In further culture experiments, the antiserum was shown to inhibit macromolecule (125I-labelled PVP) uptake by the visceral yolk sac, an essential process in embryonic nutrition. This effect of impaired yolk sac-mediated nutrition confirms previous observations using anti-whole yolk sac antiserum (Freeman et al. 1982), and it is proposed as the primary cause of teratogenesis.In order to identify the yolk sac antigen(s) involved in the teratogenic response, yolk sac endoderm peptides were separated by PAGE and electrophoretically transferred to nitrocellulose for analysis. With an enzyme linked immunoassay, the antiserum was observed to cross-react with a single 30 kd peptide, demonstrated by a ConA-binding technique to be a glycopeptide. Control serum showed no evidence of cross-reaction with yolk sac peptides.

The first appearance of the neural tube and optic primordium in the human embryo at stage 10.

Thirteen embryos of stage 10 (22 days) were studied in detail and graphic reconstructions of most of them were prepared. The characteristic feature of this stage is 4-12 pairs of somites. Constantly present are the prechordal and notochordal plates (the notochord sensu stricto is not yet apparent), the neurenteric canal or at least its site, the thyroid primordium, probably the mesencephalic and rhombencephalic neural crest and the adenohypophysial primordium. During this stage, the following features appear: terminal notch, optic sulcus, initial formation of neural tube, oropharyngeal membrane, pulmonary primordium, cardiac loop, aortic arches 1-3, intersegmental arteries, and laryngotracheal groove. The primitive streak is still an important feature. Graphic reconstructions have permitted the detection of the telencephalic portion of the forebrain, for the first time at such an early stage. It is proposed that the remainder of the forebrain comprises two subdivisions: D1, which becomes largely the optic primordium during stage 10, and D2, which is the future thalamic region. The optic sulcus is found in D1 but does not extent into D2, as has been claimed in the literature. An indication of invagination of the otic disc appears towards the end of the stage. As compared with the previous stage, the prosencephalon has increased in length, the mesencephalon has remained the same, the rhombencephalon has decreased, and the spinal part of the neural plate has increased fivefold in length. The site of the initial closure of the neural groove is rhombencephalic, upper cervical, or both. The neural plate extends caudally beyond the site of the neurenteric canal. Cytoplasmic inclusions believed to indicate locations of great activity were always detected in the forebrain (especially in the optic primordium), and also in the rhombencephalon, spinal part, and mesencephalon.

Computer simulation of organogenesis: An approach to the analysis of shape changes in epithelial organs

Embryonic development of epithelial organ primordia often involves changes in several parameters, such as cell height, cell width, cell volume, amount of extracellular space, and cell number. Since these changes often occur simultaneously, it becomes difficult to “separate out” the role that each plays in the developmental process. A computer program has been written that allows the shape of epithelial organs to be reproduced based upon measurements of the primordium. A developmental sequence can be simulated by changing the dimensions of the primordium based upon either measurements of the developmental stages or theoretical projections of changes. The primordium is divided into blocks representing groups of cells, based upon characteristics of the different cell groups. The program allows differences in cell height and circular and spiral curvatures of the primordium to be simulated. Analysis of the optic primordium using this method has allowed recognition of several regional changes during optic cup formation. These are sequential constriction of cell apices at the margin of the optic cup, expansion of the apical surface toward the center of the retinal disc, and spreading of the future pigmented layer. Simulation of other organs permits regions of morphogenetic activity to be identified.

Neural cell types surviving congenital sensory deprivation in the optic lobes of Drosophila melanogaster

Golgi staining of neuronal cell types in the optic lobe rudiments of adult eyeless flies of the sine oculis ( so) mutant of Drosophila melanogaster reveals partial independence of optic lobe's development from compound eye formation. (1) Differentiation and maintenance of many neuronal cell types of medulla and lobular complex do not require innervation of the medulla from the retina and the lamina. Neurons derived from the outer and inner optic anlage have been found in adult eyeless flies. (2) The rudiments of ipsilateral medulla, lobula, and lobular plate are isotopically connected with each other. (3) Stratification of the lobular complex is retained. (4) Equivalent parts of the dorsal lobulae are connected by heterolateral small field neurons. (5) The shapes of many tangential neurons of the medulla show sprouting and compensatory innervation of the lobular complex. The basic results reported here for eyeless flies have many parallels in what is known about anophthalmic mice.

The effect of inhibitors of glycoconjugate synthesis on optic cup formation in the chick embryo

Invagination of the optic primordium in the chick embryo coincides with the appearance of material at the apical cell surface that precipitates cetylpyridinium chloride. Since this precipitate is soluble only at high salt concentrations, it is suspected of being an acidic glycoconjugate. In order to test whether glycoconjugates play a role in optic cup formation, embryos were treated with drugs that interfere with glycoconjugate synthesis. 6-Diazo-5-oxo- l-norleucine was selected as a general inhibitor of glycoconjugates and tunicamycin as a specific inhibitor of asparagine-linked oligosaccharides. Both inhibitors prevented invagination of the optic vesicle and resulted in absence of a cetylpyridinium chloride precipitate at the apical cell surfaces. In addition to the effect within the cavity of the optic vesicle, both inhibitors also affected the attachment between the lens epithelium and the retinal disc. During normal development, the basal laminae of the lateral surface of the optic vesicle and the overlying ectoderm fuse to form a thickened basement membrane at the margin of the future retinal disc. As the retinal disc and lens epithelium invaginate, additional attachments form toward the center of the two folding layers. These attachments are perturbed by both diazo-oxo-norleucine and tunicamycin. However, the lens epithelium forms a vesicle even if the optic cup does not form. Since both inhibitors have been reported to affect processes in addition to glycoconjugate synthesis, the effect of tunicamycin on sugar, amino acid, and sulfate incorporation was studied. The inhibitor had a significant effect only on glucosamine incorporation and appeared to selectively inhibit an increase in incorporation that began in control heads at the time of invagination.

Abnormal differentiation of selected nuclear centers in the brain of a duck embryo associated with partial duplication of the primitive streak.

In a control set of duck embryos, an abnormal duck embryo of 16 days incubation was found which had two beaks as the only outward sign of duplication. The beaks were of equal size, each with upper and lower bills. Bill-clapping movements were absent. The embryo had two normal eyes placed one on either side of the head, and the rest of the body was normal in external appearance. Sections through the head revealed further duplication of the fore-, mid-, and hindbrain divisions. The medial half of each of the embryonic brain divisions, however, was greatly reduced. Two additional optic primordia were also noticed in sections, each of which was reduced to a mass of tissue representing a lens and a much-folded pigment epithelium. The orbital tissues associated with the rudimentary eyes were greatly disorganized. Abnormal differentiation associated with duplication of the brain divisions was determined by cell counts in selected nuclear centers. Cell numbers in each case appeared to be remarkably proportional to the size of the innervation field. Our data, based on cell counts in the nuclear centers chosen for this study in the abnormal embryo and normal control embryos of the same age, are consistent with the hypothesis that cell survival in related parts of the nervous system may be regulated by their peripheral field of innervation.

Differentiation of the optic cups from an anophthalmic murine strain, in culture and in intrafoetal grafts

The optic anlage of the anophthalmic murine strain ZRDCT/an has been studied. In this strain, 70% of the adults are anophthalmic, 30% are one-eyed. The eye primordium appears and starts to differentiate at day 9 of gestation, then it degenerates. At 13 days of gestation, it has practically disappeared. When isolated and cultured in vitro, the 10-day anophthalmic anlage develops in the same way as a control optic-cup culture from a Swiss or C57B16 mouse. When grafted in the back of a 15--17 day Swiss foetus, this 10-day anophthalmic anlage also develops: retina and lens differentiate, the structures which grow are very similar to those obtained when C57B16 optic cups are grafted in the same conditions. It appears from these results that the eye regression of the mutant in situ is not a process intrinsic to the anlage. If withdrawn from its local environmental influences, the eye primordium is able to express its aptitude for differentiation.

Fine structural aspects of the developing compound eye of the honey bee, apis mellifera L.

We studied the postembryonic development of the compound eye of the worker honey bee on the light and electron microscopy levels. During the late third and early fourth larval instars the cells of the optic primordium became organized into preommatidial cell clusters. Each cluster contained four prospective cone cells, nine prospective retinula cells (of which the ninth was centrally located and shorter than the other eight), and an undetermined number of prospective pigment cells. During ommatidial differentiation that was characterized by ommatidium and crystalline cone elongation, the ninth retinula cell moved laterally, and each retinula cell elaborated a rhabdomer. Possible roles of membrane junctional specializations and cytoplasmic microtubules in the processes of differentiation are discussed.

Grafting of additional periphery reduces embryonic loss of neurons

Effects of increased peripheral field of innervation on the magnitude of the spontaneously occurring embryonic cell death in the chick trochlear and isthmo-optic nuclei were examined. Grafting of an additional optic primordium and the surrounding mesoderm (which forms extraocular muscles) was performed at stage 11 (HH stage series). The grafted tissue is innervated by the appropriate neuron pool as revealed by the retrograde axonal flow of HRP. Cell counts of the trochlear nucleus on day 19 indicate a mean increase of 37% (range 19–62%) in the number of cells on the experimental side (contralateral to the graft) as compared to the ipsilateral control nucleus of the same embryos. Cell counts of the isthmo-optic nucleus on day 19 show an average increase of 35% (range 27–41%) on the experimental (contralateral) side over the ipsilateral control side. This increase in cell survival is not due to a stimulatory effect of grafting on cellular proliferation as revealed by the cell counts of trochlear and isthmo-optic nuclei on day 9 and 11 respectively. Thus, the increased cell survival is attributed solely to the reduction in the magnitude of the embryonic cell death. Whether this reducton in embyronic cell death is due to increased number of synaptic sites or increased amounts of trophic substances remains uncertain.

An SEM AND TEM study of suppression of eye development in eyeless mutant axolotls.

Morphology of the primary optic rudiment of normal eyed and mutant eyeless (e/e) axolotl embryos was studied at light. Tem and SEM levels. The presumptive eyeforming region of eyeless embryos differs from that of normal embryos in several important respects including premature formation of basal lamina, separation from overlying ectoderm by mesenchyme cells and persistence of granules in the interspace surrounding the optic anlage into relatively late developmental stages. These differences suggest that the gene that causes failure of eye formation in the mutant axolotls produces structural differences that interfer with normal physical and/or biochemical inductive interactions between neurectoderm and mesenchyme cells due primarily to the precocious development of basal lamina over the extermal surface of the optic primordia.