[Latent TGF-beta 1 binding protein (LTBP-1); a new marker for intra-and extraocular PEX deposits]

BACKGROUND

Pseudoexfoliation (PEX) syndrome is a generalized process of the extracellular matrix characterized by the accumulation of an abnormal pathognomonic material in various intraocular and extraocular tissues. Whereas the intraocular manifestations can be directly diagnosed by biomicroscopic observations, the extraocular manifestations can presently only be diagnosed by electron microscopic methodology. In order to better evaluate the distribution and precise localization of PEX deposits in the various organ systems, we searched for a relatively specific immunohistochemical marker for PEX material on the light microscopic level.

MATERIAL AND METHODS

Eyes and tissue specimens of various organ systems (skin, heart, lungs, liver, kidney, abdominal aorta, cerebral artery, plexus choroideus, meninges) obtained from 4 organ donors with ocular PEX syndrome and age-matched control tissues were investigated by electron microscopy and immunohistochemistry using antibodies against various elastic microfibrillar components.

RESULTS

Out of a panel of antibodies tested, the immunolabeling of both intra- and extraocular PEX deposits with antibodies against latent TGF-beta 1 binding protein (LTBP-1) was particularly prominent. In addition to the known intraocular sites of PEX material accumulations, focal plaque-like LTBP-1 positive deposits could be observed in the conjunctival stroma, optic nerve meninges, skin, heart muscle, lungs, kidney as well as in the adventitia of the aorta and cerebral artery from donors with PEX syndrome; such plaque-like deposits positive for LTBP-1 were not present in the control tissues. Transmission electron microscopy confirmed the presence of typical fibrillar PEX aggregates in the respective tissues.

CONCLUSIONS

Antibodies against LTBP-1 provide a new and relatively specific marker for PEX deposits both in intraocular and extraocular locations. Systematic screening of PEX accumulations in a larger number of extraocular tissue specimens obtained from PEX patients may help to elucidate the functional implications and consequences of the systemic manifestations.

Identification of androgen, estrogen and progesterone receptor mRNAs in the eye

PURPOSE

Previous research has demonstrated that sex steroids exert a significant influence on the structure and function of numerous ocular tissues. To begin to explore the underlying basis of this hormone action, we examined whether various anterior and posterior tissues of the eye contain androgen, estrogen and progesterone receptor mRNAs.

METHODS

Tissue samples were obtained from adult male and female rats, rabbits and humans, processed for the isolation of total RNA and analyzed by RT-PCR, agarose gel electrophoresis and Southern blot hybridization. All PCR amplifications included positive and negative controls.

RESULTS

Our findings showed that androgen, estrogen and/or progesterone receptor mRNAs are present in the lacrimal gland, lacrimal gland acinar epithelial cells, meibomian gland, lid, palpebral and bulbar conjunctivae, cornea, iris/ciliary body, lens, retina/uvea, retina/choroid and retinal pigment epithelial cells of rats, rabbits or humans.

CONCLUSIONS

Our findings demonstrate that sex steroid receptor mRNAs exist in a variety of ocular tissues and suggest that these sites may represent target organs for androgens, estrogens and/or progestins.

Trk neurotrophin receptor-like proteins in the teleost Dicentrarchus labrax

In recent years, data have accumulated suggesting that the role of neurotrophins and Trk receptors may not be limited to the nervous system, and the presence of these substances has been detected in a variety of vertebrate and invertebrate non-nervous tissues. This study was designed to map the expression of immunoreactivity (IR) for Trk-like proteins in alevins of the teleost Dicentrarchus labrax, with particular emphasis on non-nervous structures. We used antibodies against specific epitopes of the intracellular domain of these proteins, a region that is highly conserved in phylogeny. Trk-like IR was seen in segregate cell populations of the nervous system, and non-nervous tissues. In the central nervous system TrkA-like and TrkC-like IR was abundant, whereas TrkB-like IR was restricted to a low number of brain areas. Expression of Trk-like protein IR was observed in the peripheral nervous system and sensory organs, with the exception of the lateral line organ. Outside the nervous system, TrkA-like IR was mainly found in different epithelia, TrkB-like IR in the endocrine and digestive system, and TrkC-like IR in the cardiovascular and immune systems. The gills showed IR for all three Trk-like proteins, whereas they were absent from the gonads. Furthermore, scattered cells positive for Trk-like proteins were found in most of the investigated tissues. The distribution of Trk-like IR in this teleost is compared with that of mammals and birds, which it often paralleled, and the possible role of neurotrophins and Trk-like receptor proteins in different non-neuronal tissues is discussed.

Primary structure of CHH/MIH/GIH-like peptides in sinus gland extracts from Penaeus vannamei

Peptides belonging to the CHH/MIH/GIH-family of crustacean hormones were isolated from acetic acid extracts of sinus glands isolated from eyestalks of the shrimp, Penaeus vannamei. The peptides were isolated by chromatography and molecular weights determined by MALDI mass spectrometry. Peptides in the range of 7-9 kDa and containing three disulfide bridges were selected for amino acid sequence analysis. Three peptides with the requisite properties were present in sufficient amounts for sequence analysis. Two peptides had unique sequences similar to CHH/MIH/GIH peptides from other crustaceans. A third peptide seemed to be a truncated form of one of the previous sequences.

Two opsin genes from the vetch aphid, Megoura viciae

The cDNAs of two opsins (Megopsin1 and Megopsin2) from the vetch aphid, Megoura viciae, have been sequenced and encoded for gene products with 378 and 371 amino acid residues, respectively. Phylogenetic analysis reveals that Megopsin1 falls into the insect long-wavelength opsin group and Megopsin2 is a member of the insect UV-wavelength opsins. Both opsins share the key features of G-protein-coupled receptors and the specific motifs of photopigments. In situ hybridization demonstrated that the transcripts of Megopsin1 and Megopsin2 were expressed in the retinula cells of the compound eyes.

Distribution of lead and transthyretin in human eyes

BACKGROUND

The retinal pigment epithelium serves as a defensive barrier to the retina in the same way that the choroid plexus functions in the brain. Previous studies have shown that lead sequestration in the choroid plexus reduces the production and secretion of transthyretin by the choroid plexus. The purpose of this study was to investigate the distribution of lead and transthyretin in human eyes and to explore the potential effect of lead on transthyretin in human eyes.

METHODS

Eight pairs of human eyes were obtained from the New York City Eyebank within 24 hours of postmortem. The eyes were dissected to obtain the aqueous, vitreous, retina, and choroid. Lead and transthyretin concentrations in ocular tissues and liquids were determined by atomic absorption spectrophotometry for lead and radioimmunoassay for transthyretin. Lead accumulated in the retina at concentrations that were 166, 739, and 5 times higher than those in the aqueous, vitreous, and choroid, respectively (p < 0.05 for all comparisons). Lead concentrations in ocular tissues or intraocular liquids did not change as a function of age or gender. The concentration of transthyretin in the vitreous (14.4 +/- 5.1 SE microg/mL) was twice as much as in the aqueous (7.0 +/- 1.1SE microg/mL) and was significantly correlated to that in the retina (r = 0.93, p < 0.005).

CONCLUSIONS

This study indicates that lead accumulates in human ocular tissues, particularly in the retina. The markedly elevated retina lead level and its relationship to ocular transthyretin and other macromolecules bear further investigation.

Zinc concentration of selected ocular tissues in zinc-deficient rats

A study was performed to determine the effect of zinc deficiency on the zinc concentration of the retina, lens, and the retinal pigment epithelium and choroid. Weanling, male Sprague-Dawley rats were fed ad libitum modified AIN-93 diets containing 3 mg zinc/kg diet (-Zn; n = 10) for 6 wk. Control animals were pair-fed (+ZnPF; n = 10) or fed ad libitum (+ZnAL; n = 10) diets containing 100 mg zinc/kg diet. At 6 wk, plasma and tibia zinc were measured by flame atomic absorption spectrophotometry to confirm zinc deficiency. The zinc concentration of ocular tissues was measured by inductively coupled plasma-mass spectrometry. Mean (+/- SEM) lens zinc concentration was significantly depressed in the zinc-deficient group as compared to that of pair-fed or ad libitum-fed controls, suggesting that the role of zinc in cataract formation should be investigated. The zinc concentration of total neural retina was preserved in zinc deficiency. Previously reported deterioration of retinal function in zinc deficiency may be the result of a decline in the zinc concentration of a specific cell layer of the retina that cannot be detected on gross analysis of the entire retina.

Characterization of alpha(1)-adrenoceptor subtypes in the eye

The presence of the alpha(1)-adrenoceptor subtypes in various parts of the pig and rabbit eyes was investigated using [(3)H]-prazosin radioligand binding. The characterization of the subtypes was achieved by performing competition experiments with various subtype selective drugs. In the pig retina, both alpha(1A)- and alpha(1B)-adrenoceptors were detected and the proportion of sites was 70% alpha(1A)- and 30% alpha(1B)-adrenoceptors, respectively. In the pig iris, ciliary body and choroid, which are melanin-rich tissues, the non-specific binding of [(3)H]-prazosin was too high to detect any of the alpha(1)-adrenoceptor subtypes. However, in the albino rabbit iris, ciliary body and retina both alpha(1A)- and alpha(1B)-adrenoceptors were detected. The proportion of sites in the iris was 60 % alpha(1A)- and 40% alpha(1B)-adrenoceptors, respectively. In the ciliary body and rabbit retina the proportion of sites were 70% alpha(1A)- and 30% alpha(1B)-adrenoceptors. Only the alpha(1A)-adrenoceptor subtype was detected in the rabbit choroid.

Identification of androgen receptor protein and 5alpha-reductase mRNA in human ocular tissues

BACKGROUND/AIMS

Androgens have been reported to influence the structural organisation, functional activity, and/or pathological features of many ocular tissues. In addition, these hormones have been proposed as a topical therapy for such conditions as dry eye syndromes, corneal wound healing, and high intraocular pressure. To advance our understanding of androgen action in the eye, the purpose of the present study was twofold: firstly, to determine whether tissues of the anterior and posterior segments contain androgen receptor protein, which might make them susceptible to hormone effects following topical application; and, secondly, to examine whether these tissues contain the mRNA for types 1 and/or 2 5alpha-reductase, an enzyme that converts testosterone to the very potent metabolite, dihydrotestosterone.

METHODS

Human ocular tissues and cells were obtained and processed for histochemical and molecular biological procedures. Androgen receptor protein was identified by utilising specific immunoperoxidase techniques. The analysis of type 1 and type 2 5alpha-reductase mRNAs was performed by the use of RT-PCR, agarose gel electrophoresis, and DNA sequence analysis. All immunohistochemical evaluations and PCR amplifications included positive and negative controls.

RESULTS

These findings show that androgen receptor protein exists in the human lacrimal gland, meibomian gland, cornea, bulbar and forniceal conjunctivae, lens epithelial cells, and retinal pigment epithelial cells. In addition, our results demonstrate that the mRNAs for types 1 and 2 5alpha-reductase occur in the human lacrimal gland, meibomian gland, bulbar conjunctiva, cornea, and RPE cells.

CONCLUSION

These combined results indicate that multiple ocular tissues may be target sites for androgen action.

[The physical and chemical changes in the eye structure after sulfurhexafluoride injection into the rabbit vitreous]

AIM

The aim of our paper was to observe the physical and chemical changes in the aqueous humor, lens, gelatous and fluid part of the vitreous body after the sulfurhexafluoride injection into the vitreous body.

MATERIAL AND METHODS

The New Zealand rabbits were randomized into the control and experimental group which were injected the gas into the vitreous body. The interesting samples were investigated during the 2nd, 7th and 14th day of the experiment. We estimated the volume of the fluid part of the vitreous body, its electrical resistance, the whole protein concentration (in the aqueous humor, lens and vitreous), and electrolite concentration (in the aqueous humor and fluid part of the vitreous body).

RESULTS

We observed the increase of the fluid fraction in the vitreous body with the increasing of the whole protein concentration, changes in the K+ concentration and decrease of the electrical resistance in the vitreous fluid fraction.

CONCLUSION

On the basis of our experimental results we can assume that expanding sulfurhexafluoride gas could mechanically disrupt the vitreous structure. Moreover, the rapid intrabulbar pressure increase after the injection can cause the cilliary body ischaemia and the eye barrier collapse.

Human ocular drusen possess novel core domains with a distinct carbohydrate composition

Ocular drusen are extracellular deposits that form between the retinal pigmented epithelium (RPE) and Bruch's membrane. Although the presence of large and/or numerous drusen in the macula is a significant risk factor for development of age-related macular degeneration (AMD), a major cause of irreversible blindness, little is known about their origin or composition. We have expanded on our previous investigations related to drusen-associated glycoconjugates by examining lectin binding patterns after removal of terminal sialic acid residues. Strikingly, intense and distinct labeling of drusen subdomains is revealed by Arachea hypogea agglutinin (PNA) after neuraminidase treatment. PNA binding is confined to discrete domains within both hard and soft drusen. These "cores" are positioned centrally within drusen and are typically juxtaposed to Bruch's membrane. Only one core per druse is observed. PNA labeling of drusen cores does not co-localize with associated lipids and is abrogated by digestion with O-glycosidase but not N-glycosidase. The association of cores with small drusen suggests that they may participate in drusen biogenesis. (J Histochem Cytochem 47:1533-1539, 1999)

[A brief review of recent achievements concerning biochemistry and physiology of prostaglandins in the eye]

Two prostaglandin molecules have important physiological and pathophysiological role in the tissues of the eye. Prostaglandin F2 alpha takes part in mediating intraocular pressure, prostaglandin E2 is the mediator of inflammation. In case of increased intraocular pressure, latanoprost a derivative of prostaglandin F2 alpha can be applied. Numerous data are available on the favourable intraocular pressure lowering effect of latanoprost. It can be applied as a single hypotensive or it can be combined with eye-drops currently used in glaucoma. It exerts its therapeutic effect by increasing uveoscleral outflow. Inflammation in the eye can be diminished by nonsteroidal anti-inflammatory drugs similarly to inflammations in other tissues of the organism. Literature on nonsteroidal anti-inflammatory drugs is enormous. Molecules of different structures inhibit the synthesis of prostaglandins. Primarily they are useful anti-inflammatory agents, reduce intraocular pressure in secundary glaucoma, inhibit intraocular miosis and prevent development of cystoid macula oedema. Nonsteroidal anti-inflammatory drugs do not exert their effects on prostaglandins themselves, but inhibit their synthesis. Hence the use of both, latanoprost and nonsteroidal anti-inflammatory drugs simultaneously, improves safety of therapy in case of patients prone to uveitis.

Pretreatment methods to improve nerve immunostaining in corneas from long-term fixed embryonic quail eyes

Pretreatment methods were used to improve neurofilament immunostaining in corneas from embryonic day 16 Japanese quail corneas that had been stored in fixative solution for several months. A sequential combination of the following three pretreatments: brief microwave heating in saline, followed by extraction with sodium dodecyl sulfate (SDS) at 37 degrees C, followed by digestion with hyaluronidase at 37 degrees C, produced significantly increased antibody staining of corneal neurofilament proteins, compared with embryonic corneas subjected to no prior pretreatments or to single or two-step protocols. After applying the sequence of all three pretreatments, darkest nerve staining and increased numbers of fine branches were observed, together with lower background staining. Thus, the result of applying the three-step pretreatment sequence is better than that of applying any of its component single pretreatments or even combinations of any two of them. These findings therefore suggest that each of these three pretreatments causes a unique effect, beneficial to immunostaining of neurofilament proteins, and that their individual effects are independent and additive. In addition to embryonic corneas, the three-step procedure also may be useful for immunostaining of nerves in other very delicate, highly-hydrated tissues containing an abundance of extracellular matrix.

Novel genes expressed in the developing medial cortex

Two cDNAs, M1 and M2, recently isolated by the differential display method from embryonic rat cerebral hemisphere were characterized and their patterns of spatiotemporal expression analysed in developing rat forebrain by in situ hybridization histochemistry and correlative immunocytochemistry. Neither gene bears any sequence homology to other known genes. Both genes are particularly expressed in medial regions of the cerebral hemisphere and M2 in the roof of the adjacent diencephalon. M1 expression is highly localized and confined to the neuroepithelium of the hippocampal rudiment from embryonic day (E) 12 onward. Its location corresponds to the fimbrial anlage, and immunocytochemical localization of M1 protein indicates its expression in radial glial cells. M2 expression at E12 is more extensive in the medial cerebral wall, extending into the preoptic region and beyond the hippocampus into dorsal hemisphere and into the dorsal diencephalon, with caudal extension along the dorsal midline and in the zona limitans intrathalamica. Later, M2 expression is found in association with the corpus callosum, hippocampal commissure, fimbria, optic nerve, stria medullaris, mamillothalamic tract and habenulopeduncular tract. M1 and M2 expression domains corresponding to the locations of fiber tracts are present prior to the arrival of the earliest axons, as identified by neuron specific markers. These findings suggest M1 and/or M2 genes are involved in early regional specification of the hippocampus and related structures in paramedian regions of the forebrain, and that cell populations expressing these genes in advance of developing axonal pathways may be involved in the early specification of tract location.

The transcription factor, Pax6, is required for cell proliferation and differentiation in the developing cerebral cortex

The cerebral cortex develops from the dorsal telencephalon, at the anterior end of the neural tube. Neurons are generated by cell division at the inner surface of the telencephalic wall (in the ventricular zone) and migrate towards its outer surface, where they complete their differentiation. Recent studies have suggested that the transcription factor Pax6 is important for regulation of cell proliferation, migration and differentiation at various sites in the CNS. This gene is widely expressed from neural plate stage in the developing CNS, including the embryonic cerebral cortex, where it is required for radial glial cell development and neuronal migration. We report new findings indicating that, in the absence of Pax6, proliferative rates in the early embryonic cortex are increased and the differentiation of many cortical cells is defective. A major question concerns the degree to which cortical defects in the absence of Pax6 are a direct consequence of losing the gene function from defective cells themselves, rather than being secondary to abnormalities in other cells. Cortical defects in the absence of Pax6 become much more pronounced later in cortical development, and we propose that many result from a compounding of abnormalities in proliferation and differentiation that first appear at the onset of corticogenesis.

Quantitative autoradiographic visualization and pharmacology of FP-prostaglandin receptors in human eyes using the novel phosphor-imaging technology

Quantitative autoradiographic visualization of FP prostaglandin receptors was determined in postmortem human eye sections using [3H]PGF2alpha and the novel phosphor-imaging technology coupled with computerized image analysis. Densitometric analysis of digital images obtained after a 19-day screen-exposure revealed FP receptors to be highly concentrated in the longitudinal ciliary muscle (12,741 digital light units [DLU/mm2]), iris sphincter muscle (19,261 DLU/mm2) and retina (9,544 DLU/mm2), with lesser amounts (1,558-3,776 DLU/mm2) in five other ocular structures (n = 3-4 donors). The highest percentage specific binding was in the iris sphincter and longitudinal ciliary muscle (78-73%) and lowest in the lens (12%). Binding of [3H]PGF2alpha to the longitudinal ciliary and iris sphincter muscles and retina was concentration-dependently and potently displaced by known FP-receptor-selective compounds such as cloprostenol (Ki = 13-37 nM), fluprostenol (Ki = 56-98 nM), PHXA85 (Ki = 181-206 nM) and latanoprost (isopropyl ester of PHXA85; Ki = 0.43-4.5 microM) (from up to 4 donor eyes). These quantitative phosphor-imaging autoradiography data provide further evidence for the presence of FP receptors in human longitudinal ciliary muscle, one of the tissues involved in the intraocular pressure lowering effects of FP-class prostaglandins. The quantitative localization of FP receptors in the human iris, iris sphincter muscle, and retina represent interesting new observations.

Purification and characterization of an isoform of crustacean hyperglycemic hormone from the eyestalk of Macrobrachium rosenbergii

Isolation of the crustacean hyperglycemic hormone (CHH) from the eyestalk of the giant freshwater prawn Macrobrachium rosenbergii was performed using 5,000 ground eye-stalks extracted in methanol-acetic acid-water (90:1:9). After the extract was partially purified using C18 cartridges, it was further purified by eight steps of RP-HPLC using four kinds of columns: C18, C8, cyano and phenyl, and three solvent systems: acetonitrile (ACN)/trifluoroacetic acid, ACN/heptafluoroacetic acid and ACN/triethylammonium acetate. The bioassay of CHH during purification was done by injection of eluate fractions into eyestalk-ablated prawns and determination of the ability of the fractions to elevate glucose in the haemolymph. A complete amino acid sequence analysis was performed on one isoform of CHH (Mar-CHH-1), consisting of 71 residues. The sequence of Mar-CHH-1 shows considerable similarity (45-68%) to CHHs reported in other crustaceans. It is expected that there might be more than one isoform of CHH in M. rosenbergii.

A scanning transmission microscopy and energy-dispersive X-ray microanalysis of idiopathic ocular calcification and oxalosis in AIDS patients

In a series of 98 consecutive eyeballs enucleated at postmortem from 86 patients dying with AIDS, the incidence of calcium deposits was 14 and 18.6%, respectively, for oxalates and calcium hydroxyapatite. The calcific eyes were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray microanalysis to confirm the elemental nature of the precipitates. Transmission electron microscopy was used in 2 of the cases with oxalosis. Oxalates with a free end exhibited a plate-like shape at SEM and appeared acicular at TEM, due to the reduced thickness of ultrathin sections. Crystals that were embedded in tissues such as the sclera or degenerate detached retinal tissue formed either spherules or plates at SEM. No clear relationship with intracellular structures could be found at TEM, possibly due to postmortem autolysis phenomena. Calcium hydroxyapatite deposits appeared at SEM as fine granules distributed over the collagen fibers of the corneal and conjunctival stroma and the scleral lamellae, but were also present intracellularly, both in the nucleus and cytoplasm of epithelial cells.

The expression of tenascin-X in developing and adult rat and human eye

Tenascin-X has been studied in developing and adult rat eye and in foetal and adult human eyes, using immunohistochemistry and frozen sections. The data were compared with the distribution of tenascin-C. The immunoreactivity for tenascin-X was seen in a basement membrane-like feature in different structures of embryonic (E) day 16-17 rat eyes. Postnatal (P) day 2 and older rat eyes showed immunoreactivity for tenascin-X in different connective tissues. In the epithelial basement membrane zone of the cornea, immunostaining was positive in P5 eyes, negative in P10 and P15 eyes and again positive in P30 and adult eyes. In the 20-week-old human foetus, immunoreactivity for the tenascin was seen in the posterior parts of the conjunctival stroma adjacent to the sclera and in a basement membrane-like fashion in anterior conjunctiva. In the adult human eye, immunoreactivity for tenascin-X was seen in the anterior one-third stroma of cornea as thin fibrils, in the stroma of the limbus and conjunctiva, and in blood vessels. Immunostaining for tenascin-C was seen in the posterior aspect of the further cornea, and in mesenchyme adjacent to cornea in E1617 rat eyes. Corneal keratocytes and Descemet's membrane showed immunoreactivity for tenascin-C in P2-P15 rat eyes. Sclera and the junction of the cornea, and sclera expressed tenascin-C in P2 and older rat eyes. In human foetal eyes, immunostaining for tenascin-C was seen in the anterior parts of the corneal stroma, in the basement membrane zone and Bowman's membrane of the corneal epithelium, in the posterior one-fifth of the corneal stroma and the sclera starting from the junction of the cornea and sclera. In normal human adult eyes, immunostaining for tenascin-X was seen in the anterior one-third stroma of cornea, in the stroma of limbus and conjunctiva, and in blood vessels. The association of tenascin-X and basement membranes in early development evokes a question of its potential function in the development of the basement membrane. The results also suggest the association of tenascin-X with connective tissue development as well as the association of tenascin-C with the migration of keratocytes during the development of the corneal stroma.

Colchicine causes excessive ocular growth and myopia in chicks

Colchicine has been reported to destroy ganglion cells (GCs) in the retina of hatchling chicks. We tested whether colchicine influences normal ocular growth and form-deprivation myopia, and whether it affects cells other than GCs. Colchicine greatly increased axial length, equatorial diameter, eye weight, and myopic refractive error, while reducing corneal curvature. Colchicine caused DNA fragmentation in many GCs and some amacrine cells and photoreceptors, ultimately leading to the destruction of most GCs and particular sub-sets of amacrine cells. Colchicine-induced ocular growth may result from the destruction of amacrine cells that normally suppress ocular growth, and corneal flattening may result from the destruction of GCs whose central pathway normally plays a role in shaping the cornea.

CNK, a RAF-binding multidomain protein required for RAS signaling

Kinase suppressor of ras (ksr) is required for efficient signal transmission within the RAS/MAPK cascade. A screen for mutations that modify a ksr-dependent phenotype identified a novel gene, connector enhancer of ksr (cnk), that functions upstream or in parallel to RAF in the RAS pathway. cnk encodes a protein containing several protein-protein interaction domains, suggesting that it brings different signaling molecules together. CNK is required in multiple receptor tyrosine kinase pathways where it appears to be a tyrosine phosphorylation target. Finally, CNK physically interacts with RAF and appears to localize to cell-cell contact regions. Together, these findings suggest that CNK is a novel component of a RAS-dependent signaling pathway that regulates RAF function and/or targets RAF to a specific subcellular compartment upon RAS activation.

Molecular cloning of XNLRR-1, a Xenopus homolog of mouse neuronal leucine-rich repeat protein expressed in the developing Xenopus nervous system

We report the isolation and characterization of a Xenopus sequence, XNLRR-1, that is closely related to a gene for mouse neuronal leucine-rich repeat protein (NLRR-1). The cDNA clone is 4179 bp long and encodes a putative transmembrane glycoprotein of 718 amino acids, containing 12 leucine-rich repeats followed by one C2-type immunoglobulin-like domain and one fibronectin type-III repeat. XNLRR-1 is transcribed mainly in the developing eye area and the ventricular zone from diencephalon to hindbrain and slightly in spinal cord in Xenopus tadpoles. The similarity of the XNLRR-1 gene to other known cell adhesion molecules, together with the expression pattern, suggests that XNLRR-1 is involved in interactions at the neuronal cell surface.