Insulin-like growth factor II may play a local role in the regulation of ocular size

The Effects of Long-term Growth Hormone Treatment on Ocular Findings

PURPOSE

This study aimed to examine the long-term changes in anterior chamber depth (ACD), central corneal thickness (CCT), axial length (AxL), peripapillary retinal nerve fibre layer thickness (RNFLT), peripapillary ganglion cell layer - inner plexiform layer (GCL-IPL) thickness, and peripapillary choroidal thickness (ChT) after rhGH replacement treatment in paediatric patients with IGHD, compared to healthy controls.

METHODS

Twenty-two children with IGHD including 12 girls and 10 boys were enrolled in the study group, and 30 (16 girls, 14 boys) healthy children composed the control group. A detailed ophthalmological examination was performed for each participant. ACD, CCT, AxL, peripapillary RNFLT, GCL-IPL thickness and ChT measurements were performed before the rhGH replacement treatment and in the 12th month of the post-treatment period, as well as the corresponding visits in the control group. AxL ultrasound pachymetry (CCT), peripapillary RNFL thickness, peripapillary RNFLT, GCL-IPL thickness, and peripapillary ChT parameters were measured by spectral-domain optical coherence tomography.

RESULTS

The mean age of the groups were similar (p = 0.143). 12-month CCT, ACD, and AxL measurements of the study group showed significantly higher results than the pre-treatment measurements (p = 0.005, p = 0.024, and p = 0.002, respectively). Similarly, the mean RNFLT and ChT measurements of the study group obtained from all sectors were significantly higher in the 12th-month visit (p < 0.001 for both) other than the RNFLT, and GCL-IPL thickness measurements (p > 0.05 for all). However, all these parameters were similar at pre- and post-treatment visits in the control group (p > 0.05 for all). The mean pre-treatment values of all these parameters were significantly lower in the study group compared to the control group (p < 0.05 for all), other than the RNFLT, GCL-IPL thickness measurements (p > 0.05 for all), while the mean post-treatment values of all these parameters in both groups were similar at month 12 (p > 0.05 for all).

CONCLUSION

GH replacement treatment in childhood may play an important role in the development of the neural retina and can be effective on the anterior segment, RNFLT and ChT measurements.

Emmetropization and nonmyopic eye growth

Most eyes start with a hypermetropic refractive error at birth, but the growth rates of the ocular components, guided by visual cues, will slow in such a way that this refractive error decreases during the first 2 years of life. Once reaching its target, the eye enters a period of stable refractive error as it continues to grow by balancing the loss in corneal and lens power with the axial elongation. Although these basic ideas were first proposed over a century ago by Straub, the exact details on the controlling mechanism and the growth process remained elusive. Thanks to the observations collected in the last 40 years in both animals and humans, we are now beginning to get an understanding how environmental and behavioral factors stabilize or disrupt ocular growth. We survey these efforts to present what is currently known regarding the regulation of ocular growth rates.

Topographic and specular microscopic evaluation of cornea and meibomian gland morphology in children with isolated growth hormone deficiency

PURPOSE

To evaluate whether the anterior segment topographic measurements, meibomian gland (MG), and non-invasive tear film break-up time (NITFBUT) differ between healthy children and children with isolated growth hormone deficiency (GHD).

METHODS

A total of 74 eyes of 37 children with GHD and 84 eyes of 42 age- and sex-matched healthy children were included in the study. The spherical equivalence (SE), mean keratometry (Km), corneal thickness, corneal volume (CV), anterior chamber depth (ACD), topographic NITFBUT, qualitative and quantitative MG measurements, corneal endothelial cell density (CD), and proportion of hexagonal cells (HG) were analysed.

RESULTS

The mean SE level of GHD group was similar between groups (p = 0.017). Back Km values were insignificantly steep in children with GHD (p = 0.004, with Bonferroni correction). Specular microscopy analysis was not different between groups. MG loss of GHD group were higher than control group (p < 0.001). The MG morphology analysis and distortion grade were not different between groups (p > 0.05).

CONCLUSIONS

Our results showed that the growth hormone (GH) may have an important role on the anterior segment parameters; however, it is not clear that this misregulation leads to a clinical scenario in childhood. Future studies investigating GHD and/or GH therapy on the ocular surface system are required to clearly demonstrate basic mechanism of GH action.

Evaluation of anterior segment parameters in patients with Turner syndrome using Scheimpflug imaging

PURPOSE

To compare the anterior segment parameters in patients with Turner syndrome (TS) as measured by the Pentacam HR-Scheimpflug imaging system with those of healthy control subjects.

METHODS

This cross-sectional prospective study included 35 patients with TS and 30 age-matched controls. Corneal topographic analysis was performed using the Pentacam HR-Scheimpflug imaging system (Oculus, Wetzlar, Germany). The power of the corneal astigmatism, mean keratometry (Km) values for the both front and back surfaces of the cornea, maximum keratometry (Kmax), central corneal thickness (CCT), corneal volume (CoV), white-to-white diameter (WTW), chamber volume (CaV), angle and anterior chamber depth (ACD) values were recorded.

RESULTS

The mean age of TS subjects was 17.2 ± 6.1 years; of controls, 16.4 ± 5.7 years. All participants were female. There was a significant difference in the mean values of WTW (11.3 ± 0.5 mm vs 12.0 ± 0.4 mm [P < 0.001]), CaV (148.4 ± 33.5 mm³ vs 191.9 ± 27.6 mm³ [P < 0.001]), and ACD (2.8 ± 0.3 mm vs 3.1 ± 0.2 mm [P < 0.001]) between TS versus group and the control group. The mean values of the power of the corneal astigmatism, Km values for the both front and back of the corneal surface, Kmax, CCT, CoV, and angle values were similar between groups (P > 0.05 for each one).

CONCLUSIONS

There was a reduction in CaV, ACD, and WTW measurements in TS patients compared with controls.

Choroidal thickness measurements in children with isolated growth hormone deficiency

PurposeThe aim of this study was to determine the choroidal thickness measurement values in cases with isolated growth hormone deficiency (IGHD), to compare them with the healthy control group by using enhanced depth imaging optical coherence tomography (EDI-OCT), and to evaluate the effect of growth hormone (GH) treatment on choroid.Patients and methodsIn this study, 23 cases who were diagnosed with IGHD as a study group and 46 healthy subjects as a control group were included. All patients and controls underwent a complete ophthalmologic examination, including an examination with EDI-OCT. Choroidal thickness (CT) was measured at the fovea and at 1000 μm intervals from the foveal center in both temporal and nasal directions.ResultsThe mean subfoveal choroidal thickness (SFCT) was 329.04±88.49 μm in the cases with IGHD and 365.35±50.48 μm in the control group (P=0.033). The mean CT at temporal 1 and 2 mm were thinner in the IGHD group than that of control group (P=0.033 and P=0.043, respectively). Nasal quadrant measurements were also found to be thinner in the IGHD cases than that of control group, but the difference was not statistically significant. We found a significant positive correlation between pubertal staging and SFCT (r_s=0.607, P=0.006). There was no statistically significant difference in CT values of the study group between before and 12 months after GH treatment (P>0.05).ConclusionThis study shows patients with IGHD has a thinner CT when compared with healthy pediatric cases. GH treatment seems to be not associated with the choroidal development.

Ocular findings in adult subjects with an inactivating mutation in GH releasing hormone receptor gene

OBJECTIVE

Ocular function is fundamental for environmental adaptation and survival capacity. Growth factors are necessary for a mature eyeball, needed for adequate vision. However, the consequences of the deficiency of circulating growth hormone (GH) and its effector insulin-like growth factor I (IGF-I) on the physical aspects of the human eye are still debated. A model of untreated isolated GH deficiency (IGHD), with low but measurable serum GH, may clarify this issue. The aim of this study was to assess the ocular aspects of adult IGHD individuals who have never received GH therapy.

DESIGN

Cross sectional study.

METHODS

Setting: University Hospital, Federal University of Sergipe, Brazil.

PATIENTS

Twenty-five adult (13 males, mean age 50.1years, range 26 to 70years old) IGHD subjects homozygous for a null mutation (c.57+1G>A) in the GHRH receptor gene, and 28 (15 males, mean age 51.1years, range 26 to 67years old) controls were submitted to an endocrine and ophthalmological assessment. Forty-six IGHD and 50 control eyes were studied.

MAIN OUTCOME MEASURES

Visual acuity, intraocular pressure, refraction (spherical equivalent), ocular axial length (AL), anterior chamber depth (ACD), lens thickness (LT), vitreous depth (VD), mean corneal curvature (CC) and central corneal thickness (CCT).

RESULTS

IGHD subjects exhibited unmeasurable serum IGF-I levels, similar visual acuity, intraocular pressure and LT, higher values of spherical equivalent and CC, and lower measures of AL, ACD, VD and CCT in comparison to controls, but within their respective normal ranges. While mean stature in IGHD group was 78% of the control group, mean head circumference was 92% and axial AL was 96%.

CONCLUSIONS

These observations suggest mild ocular effects in adult subjects with severe IGF-I deficiency due to non-treated IGHD.

Abnormal vascular and neural retinal morphology in congenital lifetime isolated growth hormone deficiency

OBJECTIVE

Experimental models demonstrate an important role of GH in retinal development. However, the interactions between GH and the neuro-vascularization of the human retina are still not clear. A model of untreated congenital isolated GH deficiency (IGHD) may clarify the actions of GH on the retina. The purpose of this work was to assess the retinal neuro-vascularization in untreated congenital IGHD (cIGHD).

DESIGN

In a cross sectional study, we performed an endocrine and ophthalmological assessment of 25 adult cIGHD subjects, homozygous for a null mutation (c.57+1G>A) in the GHRH receptor gene and 28 matched controls. Intraocular pressure measurement, retinography (to assess the number of retinal vascular branching points and the optic disc and cup size), and optical coherence tomography (to assess the thickness of macula) were performed.

RESULTS

cIGHD subjects presented a more significant reduction of vascular branching points in comparison to controls (91% vs. 53% [p=0.049]). The percentage of moderate reduction was higher in cIGHD than in controls (p=0.01). The percentage of individuals with increased optic disc was higher in cIGHD subjects in comparison to controls (92.9% vs. 57.1%). The same occurred for cup size (92.9% vs. 66.7%), p<0.0001 in both cases. There was no difference in macula thickness.

CONCLUSIONS

Most cIGHD individuals present moderate reduction of vascular branching points, increase of optic disc and cup size, but have similar thickness of the macula.

Corneal thickness in children with growth hormone deficiency: the effect of GH treatment

OBJECTIVE

The eye represents a target site for GH action, although few data are available in patients with GH deficiency (GHD). Our aim was to evaluate central corneal thickness (CCT) and intraocular pressure (IOP) values in GHD children to assess the role played by GHD or GH treatment on these parameters.

DESIGN

In 74 prepubertal GHD children (51M, 23F, aged 10.4±2.4years) we measured CCT and IOP before and after 12months of treatment. A baseline evaluation was also made in 50 healthy children matched for age, gender and body mass index. The study outcome considered CCT and IOP during treatment and their correlations with biochemical and auxological data.

RESULTS

No difference in CCT and IOP between GHD children at baseline and controls was found (all p>0.005). GHD children after 12months of therapy showed greater CCT (564.7±13.1μm) than both baseline values (535.7±17μm; p<0.001) and control subjects (536.2±12.5μm; p<0.001), with a concomitantly higher corrected mean IOP (15.6±0.7mmHg; p<0.001) than both baseline (12.5±0.8mmHg; p<0.001) and controls (12.3±0.5mmHg; p<0.001), without correlation with auxological and biochemical parameters.

CONCLUSIONS

12months of GH treatment in children with GHD, regardless of auxological and biochemical data, affect CCT and IOP. Our findings suggest careful ocular evaluation in these patients to prevent undesirable side effects during the follow-up.

Insulin-like growth factor-2 antisense oligonucleotides inhibits myopia by expression blocking of retinal insulin-like growth factor-2 in guinea pig

OBJECTIVE

  To clarify the role of IGF-2 on the development of myopia, the dynamic expression of IGF-2 was investigated in the FD eyes' retina, and the effects of intravitreous injection with IGF-2 ASON was studied on the diopter and axial eye length of FD eyes.

METHODS

  64 guinea pigs were divided into 2 groups. In group A (n = 24), the right eyes were covered. On days 7, 14 and 21, the diopter, axial eye length and level of IGF-2 of both eyes were measured in every 8 guinea pigs. In group B (n = 40), the right eyes were covered. On day 1, the right eyes were received intravitreal injection with 40 µg IGF-2SON, 10 µg, 20 µg or 40 µg IGF-2 ASON. The diopter, axial eye length and level of IGF-2 were measured on day 14.

RESULTS

  FD eyes showed myopic shift, axial length enlongation, and up-regulation in retinal IGF-2 from day 7 to day 21. The level of retinal IGF-2 in FD eyes was higher than that in non-FD eyes. Compare with FD eyes without injection, the myopia diopter of FD eyes decreased in received intravitreous injection with IGF-2 ASON, axial length shortened, and down-regulated with retinal IGF-2. With the increase dose of IGF-2 ASON, the change of myopic diopter, axial length, and level of retinal IGF-2 were showed more and more significant.

CONCLUSIONS

  FD is effective to up-regulate the level of retinal IGF-2 expression in guinea pig. Intravitreous injection with IGF-2 ASON can inhibit the development of myopia.

Central corneal thickness in children with growth hormone deficiency

PURPOSE

  To evaluate central corneal thickness (CCT), intraocular pressure (IOP) and eye refraction in patients with congenital growth hormone (GH) deficiency.

METHODS

Retrospective case series. Forty-five patients with growth defect treated with recombinant GH and 45 healthy children underwent ophthalmological examination, including CCT measurements, applanation tonometry and cycloplaegic refraction.

RESULTS

The average CCT in the GH deficiency group was 570.6μm [standard deviation (SD) 37.4]. In the control group, it was 546.0 (SD 24.9). The average IOP in the GH deficiency group was 18.2mmHg (SD 3.4). In the control group, it was 14.6 (SD 2.0). The mean refractive error (spherical equivalent) in the GH deficiency group was 0.59D (SD 1.9). In the control group, it was 0.11 (SD 2.1).

CONCLUSION

  GH and insulin-like growth factor 1 are involved in ocular growth by influencing the synthesis of the extracellular matrix of the sclera. Children with congenital GH deficiency or insensitivity have a mean hyperopic defect related to a shorter axial length. A number of studies have demonstrated that CCT in newborns is significantly greater than in adults; a decrease in CCT is closely correlated with an increase in corneal diameter. This finding suggests that the growth of the eye, with possible remodelling and stretching of collagen fibres, may play an important role in the reduction of corneal thickness in the first years of life. Therefore, we conclude that a greater CCT can represent a sign of a delayed growth of the eye in patients with GH deficiency. Finally, our study confirms the influence of corneal thickness on IOP measures, and the prevalence of hyperopia among children with growth defect.

N-myc coordinates retinal growth with eye size during mouse development

Myc family members play crucial roles in regulating cell proliferation, size, differentiation, and survival during development. We found that N-myc is expressed in retinal progenitor cells, where it regulates proliferation in a cell-autonomous manner. In addition, N-myc coordinates the growth of the retina and eye. Specifically, the retinas of N-myc-deficient mice are hypocellular but are precisely proportioned to the size of the eye. N-myc represses the expression of the cyclin-dependent kinase inhibitor p27Kip1 but acts independently of cyclin D1, the major D-type cyclin in the developing mouse retina. Acute inactivation of N-myc leads to increased expression of p27Kip1, and simultaneous inactivation of p27Kip1 and N-myc rescues the hypocellular phenotype in N-myc-deficient retinas. N-myc is not required for retinal cell fate specification, differentiation, or survival. These data represent the first example of a role for a Myc family member in retinal development and the first characterization of a mouse model in which the hypocellular retina is properly proportioned to the other ocular structures. We propose that N-myc lies upstream of the cell cycle machinery in the developing mouse retina and thus coordinates the growth of both the retina and eye through extrinsic cues.

Congenital growth hormone deficiency and eye refraction: a longitudinal study

The aim of this study was to study the influence of growth hormone deficiency (GHD) on emmetropization and to evaluate the effect of growth hormone replacement therapy on eye refraction. Twenty-eight children affected by congenital GHD and undergoing substitutive therapy (group 1), and 28 healthy subjects (group 2), were prospectively studied. All patients had a thorough eye examination, including cycloplegic refraction and axial length measurement (only GHD children). After 2 years, we found in both groups a reduction of the dioptric power of the eye. A t test for paired data showed statistically significant differences in both groups (p<0.001), but the change of refraction was higher in group 2 (p<0.01). Axial length showed a statistically significant increase, according to the myopic shift (p<0.001). The change of the refraction found in GHD children could be related to the somatic growth and partially induced by growth hormone therapy. The difference between the two groups could be explained with the late beginning of the therapy in GHD children. It is possible to form the hypothesis that a correct and well-timed substitutive therapy could permit a normal emmetropization process.

The cellular and molecular bases of vertebrate lens regeneration

Lens regeneration takes place in some vertebrates through processes of cellular dedifferentiation and transdifferentiation, processes by which certain differentiated cell types can give rise to others. This review describes the principal forms of lens regeneration that occur in vivo as well as related in vitro systems of transdifferentiation. Classic experimental studies are reviewed that define the tissue interactions that trigger these events in vivo. Recent molecular analyses have begun to identify the genes associated with these processes. These latter studies generally reveal tremendous similarities between embryonic lens development and lens regeneration. Different models are proposed to describe basic molecular pathways that define the processes of lens regeneration and transdifferentiation. Finally, studies are discussed suggesting that fibroblast growth factors play key roles in supporting the process of lens regeneration. Retinoids, such as retinoic acid, may also play important roles in this process.

Visual deprivation stimulates the exchange of the fibrous sclera into the cartilaginous sclera in chicks

Form deprivation myopia in chicks is a widely accepted model to study visually-regulated postnatal ocular growth. The chick sclera has a cartilaginous layer as well as the fibrous layer found in mammals. It appears that a dynamic relationship exists between these two layers during visual deprivation-induced growth. The changes in the fibrous sclera of myopic eyes, however, have not been previously described. This investigation is focused on the comparative morphological analyses of the cartilaginous and fibrous scleral changes in myopic chick eyes. The fibrous scleral changes in the posterior segment of myopic eyes were examined in detail using light and electron microscopy, and the expression of growth factors was analysed by immunohistochemistry. In the posterior segment of myopic eyes the border between the cartilaginous and fibrous layers was indistinct because of collagen bundles of the fibrous sclera that spread into the cartilaginous sclera, whereas in control eyes the distinction was clear. Various types of transitional cells, from fibroblast-like mesenchymal cells to chondrocytes, were found in the border between the cartilaginous and fibrous layers. Collagen fibrillar diameters of the fibrous sclera in the posterior segment of myopic eyes were smaller than in control, whereas those in the equatorial segment were almost the same in myopic and control eyes although the distribution of sizes was obviously different. Thus, changes in the fibrous sclera in myopic eyes of chicks seem to be similar to scleral changes in myopic eyes of mammals. The cells in the posterior sclera of myopic eyes were more intensely immunostained for TGF-beta and IGF-II than control, whereas no immunoreaction of TGF-alpha could be detected in either control or myopic eyes. These results suggest that the structural characteristics of the posterior sclera are different from those of the anterior and equatorial segments. Undifferentiated mesenchymal cells might be concentrically distributed exclusively in the innermost layer of posterior fibrous sclera. TGF-beta and IGF-II might influence cell growth, differentiation, and migration in the exaggerated scleral growth accompanying myopia.

Influence of destruction of retina-RPE complex on the proliferation of scleral chondrocytes in chicks

We studied the role of the retina-retinal pigment epithelium (RPE) complex in the proliferation of scleral chondrocytes in chicks. Seventy-two chicks were allocated to one of four groups: intravitreal gentamicin (400 microg) injection (destruction of retina-RPE complex); intravitreal gentamicin injection with goggling; goggling only (form-deprivation myopia); and intravitreal saline injection (control). The chicks were killed and retina-RPE complexes were harvested under a microscope. Retina-RPE complexes were then co-cultured with primary culture of first day scleral chondrocytes in Transwell-COL co-culture systems (Costar), with two different pore sizes (0.4 and 3.0 microm) and serum-deprivation medium. An MTT assay was performed at A550 after 4 days. In the 0.4 microm pore size system, the absorbency at A550 showed no differences between groups. However, in the 3.0 microm pore size system, the absorbency at A550s in the intravitreal gentamicin groups was significantly lower than in the control and the goggle groups (p<0.05), indicating that destruction of the retina-RPE complex inhibited chondrocyte proliferation. The absorbency in the goggle group was higher than in the control group (p<0.05). These results indicate that the retina-RPE complex exerts a positive effect on the proliferation of scleral chondrocytes via a molecule sized between 0.4.and 3.0 microm in diameter.

Mouse mutant embryos overexpressing IGF-II exhibit phenotypic features of the Beckwith-Wiedemann and Simpson-Golabi-Behmel syndromes

In mice, the imprinted Igf2 gene (expressed from the paternal allele), which encodes a growth-promoting factor (IGF-II), is linked closely to the reciprocally imprinted H19 locus on chromosome 7. Also imprinted (expressed from the maternal allele) is the Igf2r gene on chromsome 17 encoding the type 2 IGF receptor that is involved in degradation of excess IGF-II. Double mutant embryos carrying a deletion around the H19 region and also a targeted Igf2r allele, both inherited maternally, have extremely high levels of IGF-II (7- and 11-fold higher than normal in tissues and serum, respectively) as a result of biallelic Igf2 expression (imprint relaxation by deletion of H19-associated sequence) in combination with lack of the IGF2R-mediated IGF-II turnover. This excess of IGF-II causes somatic overgrowth, visceromegaly, placentomegaly, omphalocele, and cardiac and adrenal defects, which are also features of the Beckwith-Wiedemann syndrome (BWS), a genetically complex human disorder associated with chromosomal abnormalities in the 11p15.5 region where the IGF2 gene resides. In addition, the double mutant mouse embryos exhibit skeletal defects and cleft palate, which are manifestations observed frequently in the Simpson-Golabi-Behmel syndrome, another overgrowth disorder overlapping phenotypically, but not genetically, with BWS.

Developmental regulation of insulin-like growth factor binding protein-2 in chick embryo serum and vitreous humor

The chick embryo is a useful vertebrate model for studying developmental embryogenesis. Insulin-like growth factor I (IGF-I), a potent mitogen, is thought to contribute to the general growth of the embryo as an endocrine factor, and as a paracrine factor to the development of the early embryo and of specific organs such as the eye. Recent data suggest that a family of at least six IGF binding proteins (IGFBPs) complex IGF-I and modulate its biological actions. In the present study, we examine the expression of IGFBPs in chicken serum and vitreous humor at different stages of embryonic development, and compare it with that of IGF-I. As determined by ligand blotting, the predominant IGFBP in chick serum and vitreous humor between embryonic days 4 and 22 (E4-E22) is a 30 kDa IGFBP. This IGFBP was specifically immunoprecipitated by a polyclonal antiserum raised against rat IGFBP-2, the predominant IGFBP in fetal human and rat serum. Although IGFBP-2 is present in both chick fluids at all times examined, serum IGFBP-2 increased progressively between E10-E22, whereas vitreous IGFBP-2 was highest during eye organogenesis (E4-E8). This suggests that vitreous IGFBP-2 is synthesized locally. Like serum IGFBP-2, levels of immunoreactive IGF-I in serum are higher in the second week of embryogenesis than the first. Despite this correlation, changes in IGFBP-2 do not appear to be regulated by IGF-I: (a) serum IGF-I decreases after day 15, whereas IGFBP-2 levels remain stable until hatching; (b) vitreous IGF-I, like serum IGF-I, is higher in the second week of embryogenesis, whereas vitreous IGFBP-2 is highest in the first week; (c) embryos cultured ex ovo express IGFBP-2 at E15-E19, although they lack the normal mid-embryogenesis surge in IGF-I. We conclude that vitreous IGFBP-2 is synthesized locally in the eye, and that the expression of IGFBP-2 in chick embryos is not directly regulated by IGF-I.

Growth factor-induced retinal regeneration in vivo

It is apparent from a number of studies that the RPE has a remarkable ability to regenerate neural retina. While retinal regeneration from the RPE has not been reported in adult vertebrates, with the exception of the newt, there is evidence that many vertebrate species have the ability to regenerate a new neural retina during the early development. Studies of retinal regeneration in the chicken embryo have provided some insight into the requirements for this process. Recent investigations using copolymer implants as an intraocular delivery system for growth factors have demonstrated that the state of differentiation of RPE cells in the stage 22-24 chicken embryo can be altered in vivo by specific growth factors, aFGF and bFGF. These results raise the distinct possibility that variations in the local production of FGFs and their receptors in the eye during development may, in part, regulate the pathway of differentiation of RPE and neural retina precursors. Further research on the role of FGFs and their receptors in retinal development and regeneration will not only contribute to our understanding of how the differentiated state is achieved and maintained but may provide a foundation for future attempts to develop methods of treatment for various degenerative and proliferative diseases of the eye.

Capacity to form choroid plexus-like cells in vitro is restricted to specific regions of the mouse neural ectoderm

Neural ectoderm was dissected from 9.5-day and 8.5-day gestation mouse embryos and divided into forebrain, midbrain, hindbrain and spinal cord regions. Forebrain and hindbrain material from 9.5-day neural ectoderm was further divided into presumptive choroid plexus regions and regions that would normally form nervous tissue in vivo. All tissues were plated onto a basement membrane substratum for culture in vitro. It was found that explants of neural ectoderm that would normally form choroid plexus in vivo, readily differentiated to form choroid plexus-like cells in culture. Cells from hindbrain segments and forebrain regions, which would normally form nervous tissue, also had the potential to differentiate into cells resembling the choroid plexus epithelium in culture, provided that the normal cell-cell interactions were disrupted. Cells from the midbrain neuromeres of 9.5-day embryos, which do not form a choroid plexus in vivo, did not form this lineage in vitro. However, cells cultured from the earlier head-fold stage midbrain neural ectoderm could develop into choroid plexus epithelium. There was no evidence that neural ectoderm from the spinal cord had the developmental potential to form choroid plexus epithelial cells at either of these two developmental stages. These studies show that the restrictions in the potential of neural ectoderm stem cells to form different lineages proceeds according to morphological divisions that appear along the anterior-posterior axis during the early stages of brain development. These results suggest that the division of neural ectoderm into segments which contain discrete stem cell populations may be a general feature of the early phase of development of the central nervous system.

Neonatal eye growth and emmetropisation--a literature review

The refractive development of the neonatal eye has been the subject of much study and debate. In this paper the hypothetical mechanisms of emmetropisation and their relationship to the development of refractive errors will be reviewed. The evidence supporting visual feedback control of eye growth will be described, and the role of ocular accommodation will be discussed.

The role of growth factors in the embryogenesis and differentiation of the eye

The vertebrate eye is composed of a variety of tissues that, embryonically, have their derivation from surface ectoderm, neural ectoderm, neural crest, and mesodermal mesenchyme. During development, these different types of cells are subjected to complex processes of induction and suppressive interactions that bring about their final differentiation and arrangement in the fully formed eye. With the changing concept of ocular development, we present a new perspective on the control of morphogenesis at the cellular and molecular levels by growth factors that include fibroblast growth factors, epidermal growth factor, nerve growth factor, platelet-derived growth factor, transforming growth factors, mesodermal growth factors, transferrin, tumor necrosis factor, neuronotrophic factors, angiogenic factors, and antiangiogenic factors. Growth factors, especially transforming growth factor-beta, have a crucial role in directing the migration and developmental patterns of the cranial neural-crest cells that contribute extensively to the structures of the eye. Some growth factors also exert an effect on the developing ocular tissues by influencing the synthesis and degradation of the extracellular matrix. The mRNAs for the growth factors that are involved in the earliest aspects of the growth and differentiation of the fertilized egg are supplied from maternal sources until embryonic tissues are able to synthesize them. Subsequently, the developing eye tissues are exposed to both endogenous and exogenous growth factors that are derived from nonocular tissues as well as from embryonic fluids and the systemic circulation. The early interaction between the surface head ectoderm and the underlying chordamesoderm confers a lens-forming bias on the ectoderm; later, the optic vesicle elicits the final phase of determination and enhances differentiation by the lens. After the blood-ocular barrier is established, the internal milieu of the eye is controlled by the interactions among the intraocular tissues; only those growth factors that selectively cross the barrier or that are synthesized by the ocular tissues can influence further development and differentiation of the cells. An understanding of the tissue interactions that are regulated by growth factors could clarify the precise mechanism of normal and abnormal ocular development.

Expression of insulin and insulin-like growth factor receptors and binding proteins by retinal pigment epithelium

Insulin-like growth factors (IGFs) I and II are mitogenic polypeptides structurally homologous to insulin, which are thought to mediate important neurobiologic actions in the CNS. The purpose of this study was to determine if cultured bovine retinal pigment epithelial cells (RPE) express IGF receptors and secrete soluble IGF binding proteins, and to characterize these receptors and binding proteins. We also characterized the soluble IGF binding proteins present in juvenile and adult rat vitreous and serum, as well as those in fetal bovine vitreous and serum, in order to facilitate identification of the RPE IGF binding protein, and to determine potential destinations for this protein once produced. Affinity labeling was used to characterize insulin, IGF-I and IGF-II receptors. Western radioligand blotting and immunoprecipitation were used to characterize IGF binding proteins. We found that RPE cells in culture express virtually no insulin receptors, and only modest amounts of IGF-I receptors. IGF-II receptors were abundantly expressed. Additionally, RPE cells secrete a soluble IGF binding protein which is immunologically related to IGFBP-2, the primary IGF binding protein produced in the central nervous system. Bovine vitreous was found to contain a mixture of IGF binding proteins (IGFBP). The most prominent IGFBP in this mixture is immunologically related to IGFBP-2. Likewise, juvenile and adult rat vitreous contained only one IGF binding protein that was shown to be immunologically related to IGFBP-2. Juvenile rat vitreous contained more binding activity corresponding to IGFBP-2 than did adult vitreous, suggesting developmental regulation. These data suggest that IGF's and their binding proteins may have important, and as yet undefined, roles in retinal neurophysiology.

Growth factors in the eye

In this review we report the distribution and functional significance of growth factors in the eye. Representatives of the major growth factor families are found in the eye: fibroblast growth factor, insulin and insulin-like growth factor, transforming growth factor-beta, platelet-derived growth factor, nerve growth factor, epidermal growth factor and colony-stimulating factor. There are numerous examples of their actions on ocular tissues in vitro and in some cases in vivo. The findings presented clearly illustrate that a growth factor can elicit different responses depending on the context of its action; the cell type involved, the concentration of the growth factor and the presence or absence of other growth factors can all influence the cellular response both quantitatively and qualitatively. The results of these studies in the eye are of general significance to our understanding of the role of growth factors in biological processes.