[雙語翻譯]--醫(yī)學外文翻譯--ephrin-a5功能缺失阻斷晶狀體纖維細胞包裝導致白內(nèi)障的發(fā)生（原文）

1、Loss of ephrin-A5 function disrupts lens fiber cell packing and leads to cataractMargaret A. Coopera,1, Alexander I. Sona,1, Daniel Komlosb, Yuhai Suna, Norman J. Kleimanc, and Renping Zhoua,2aDepartment of Chemical Biol

2、ogy, Susan Lehman-Cullman Laboratory for Cancer Research, Ernest Mario School of Pharmacy, Rutgers University, Piscataway, NJ 08854; bDepartment of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Pisca

3、taway, NJ 08854; and cDepartment of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY 10032Communicated by Allan H. Conney, Rutgers, The State University of New Jersey, Pis

4、cataway, NJ, September 9, 2008 (received for review June 16, 2008)Cell–cell interactions organize lens fiber cells into highly ordered structures to maintain transparency. However, signals regulating such interactions ha

5、ve not been well characterized. We report here that ephrin-A5, a ligand of the Eph receptor tyrosine kinases, plays a key role in lens fiber cell shape and cell–cell interactions. Lens fiber cells in mice lacking ephrin-

6、A5 function appear rounded and irregular in cross-section, in contrast to their normal hexagonal appearance in WT lenses. Cataracts eventually develop in 87% of ephrin-A5 KO mice. We further demonstrate that ephrin-A5 in

7、ter- acts with the EphA2 receptor to regulate the adherens junction complex by enhancing recruitment of ?-catenin to N-cadherin. These results indicate that the Eph receptors and their ligands are critical regulators of

8、lens development and maintenance.?-catenin ? Eph receptor ? N-cadherinC ataract, or the opacification of the lens, is the leading cause of visual impairment and blindness worldwide (1). The molecular events underlying le

9、ns development and the processes by which the lens maintains transparency over a lifetime are unclear (2). In addition, the cellular and biochemical mecha- nisms underlying the pathological changes leading to cataract re

10、main poorly understood. The lens is composed of a single layer of epithelial cells on the anterior surface, which, over a lifetime, divide and differentiate into the underlying lens fiber cells that comprise the bulk of

11、the lens (3, 4). Initially during lens development, primary lens fiber cells differentiate and elongate from the posterior pole. In later embryogenesis and throughout life, secondary lens fiber cells differentiate from l

12、ens epithelial cells located at the equator. In cross section, the lens fiber cells resemble flattened hexagons with two broad and four short sides (3). These cells are organized in a highly ordered and closely packed ma

13、nner, and interact through extensive intercellular adhesion complexes including gap and adherens junctions (5). Fiber cell gap junctions are composed of connexins (Cx) 46 and 50 (6), inactivation of which leads to the de

14、generation of the inner fiber cells and the development of cataract in mice (7, 8). Mutations in human Cx genes have also been associated with cataractogenesis (9, 10). As the lens is completely enclosed by an acellular,

15、 avascular capsule, it is believed that these cell–cell junctions are critical for providing nutrient transport, removal of metabolic wastes, and maintenance of homeostasis (11, 12). In addition to gap junc- tions, wides

16、pread adherens junctions containing N-cadherin and its associated protein ?-catenin exist between lens fiber cells (13–16), and may play important roles in lens development and function. Although cell–cell interaction is

17、 critical for maintaining lens transparency, little is known about the molecular mechanisms underlying these interactions. We have identified an unexpected regulator of lens fiber cell–cell interaction, the axon guidance

18、 molecule ephrin-A5 (17–19), and have shown that the loss of its function leads to alterations of cell shape and severe cataracts in the adult mouse. Our studies identify a novel function of ephrin-A5 in lens development

19、 and suggest unique regulation ofdownstream signaling mechanisms. We show here that a disrup- tion in EphA2–ephrin-A5 interaction leads to the internalization of N-cadherin and a disruption in the binding of N-cadherin w

20、ith ?-catenin.Results and DiscussionEphrin-A5?/? Mice Develop Cataracts. Examination of ephrin- A5?/? mutant mice using slit-lamp biomicroscopy and Scheimp- flug imaging revealed large regions of opacification in the adu

21、lt mutant lenses (Fig. 1 A–D). Such cataracts developed in 87% of mutant mice older than 6 months (n ? 22), but not in any WT controls or heterozygous animals (n ? 24). The overall size and morphology of the heterozygous

22、 lenses were indistinguishable from that of the WT lens. In the mutant lens, histological analysis revealed ruptures of the posterior lens capsule and lens disrup- tions with varying degrees of severity in the mutant mic

23、e (Fig. 1 F, G, I, and J). In the most severe cases, the lens completely degenerated, leaving tissue remnants impinging against the retina and sometimes the iris.Loss of Cell Shape Control in Ephrin-A5?/? Lenses. To exam

24、ine the nature and timing of the initial defects, lenses from WT and ephrin-A5?/? mice were collected at various developmental stages (E14, E17, P0, P6, P21, P30, and P60), sectioned, and stained with H M.A.C., A.I.S., Y

25、.S., N.J.K.,and R.Z. performed research; D.K. and N.J.K. contributed new reagents/analytic tools;M.A.C., A.I.S., N.J.K., and R.Z. analyzed data; and M.A.C., A.I.S., N.J.K., and R.Z. wrote thepaper.The authors declare no

26、conflict of interest.1M.A.C. and A.I.S. contributed equally to this work.2To whom correspondence should be addressed. E-mail: rzhou@rci.rutgers.edu.This article contains supporting information online at www.pnas.org/cgi/

27、content/full/0808987105/DCSupplemental.© 2008 by The National Academy of Sciences of the USA16620–16625 ? PNAS ? October 28, 2008 ? vol. 105 ? no. 43 www.pnas.org?cgi?doi?10.1073?pnas.0808987105E-cadherin can also b

28、e internalized (30–32). Additionally, NMDA receptor activity increased N-cadherin turnover through endocytosis to modulate adhesion (33). Our observations here suggest that ephrin-A5 functions to promote N-cadherin mem-

29、brane localization during lens development.Decreased EphA2 Activation in Ephrin-A5?/? Lenses. To identify which Eph receptors mediate ephrin-A5 function in lens devel- opment, we examined the expression of Eph receptors

30、in WT lenses by PCR. Expression of EphA2, EphA3, EphA5, EphA7,EphA8, and all EphB receptors was detected (not shown). Examination of lenses from EphA3- (A. Brown, personal com- munication), EphA5-, and EphB1-null mice fa

31、iled to detect any morphological defects. Therefore, we proceeded to examine the expression of EphA2 in the developing lens. To determine where EphA2 protein was expressed, we performed double immuno- fluorescence studie

32、s for subcellular localization of both EphA2 receptor and ephrin-A5 proteins in the P21 lens. EphA2 protein was detected with a goat anti-EphA2 antibody coupled with a Cy3-conjugated anti-goat secondary antibody. For ana

33、lysis ofABBCCDDE‘‘‘Fig. 4. Both EphA2 and ephrin-A ligands are expressed at the cell junctions. (A) Phalloidin staining of WT lens shows lens fiber cell organization. (B and C) WT transverse sections of P21 lenses staine

34、d with anti-EphA2 and EphA3-Fc, respectively. Low-magnification images demonstrate that both EphA2 and A-ephrins are normally expressed at higher levels in the subcortical region. (D) EphA3-Fc staining on ephrin-A5?/? le

35、ns sections. Staining was mostly lost on mutant lenses indicating that the subcortical signals were a result of ephrin-A5 expression. (B?–D?) High-magnification confocal images of B–D. Note that WT EphA2 receptor (B?) an

36、d ephrin-A5 (C?) expression is the highest at the cell–cell junctions. (E) WT control without primary antibody. Images were collected with equal exposure times. Arrows in A denote the subcortical (sc) lens fiber region f

37、or A–E. (Scale bar in top left, 20 ?m; top right, 5 ?m.)A BFig. 3. Change in N-cadherin localization in ephrin-A5?/? lens. (A) Altered patterns of expression of N-cadherin and the gap junction protein ZO-1 in ephrin-A5?/

38、? lenses. P21 WT and ephrin-A5?/? lens cryosections were prepared (10 ?m thick) and stained with anti–N-cadherin and anti–ZO-1 antibodies. (B) Fractions of N-cadherin signals detected in the cytoplasm in P21 WT and ephri

39、n-A5?/? lenses. The fractions were obtained by dividing the fluorescent signals in the cytoplasm by the signals of the entire cell. Cell boundaries are defined by staining with Alexa Fluor 546-phalloidin. *Significant at