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Y. Luo, M. Fukuhara, L.J. Rizzolo; The expression of the Junction Adhesion Molecule (JAM) is transiently expressed before tight junctions are assembled in the retinal pigment epithelium . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3682.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: JAM is thought to play a role in the assembly of epithelial tight junctions. Because tight junctions form slowly during the development of chick RPE, this may be an ideal experimental model to examine the role of JAM. This study examines the pattern of expression of JAM and one of its ligands, AF–6, during RPE development. Methods: The mRNAs of JAM 1 and AF–6 were examined by real time, RT–PCR. RPE was isolated from chicken embryos on embryonic days 5 (E5), E6, E7, E8, E9, E10, E14 and E18. To control for variations in mRNA concentration, 18S rRNA was amplified using a mixture of primers and competing primers, as described by Ambion, Inc. Results: JAM 1 and AF–6 mRNAs were expressed by RPE during development. The expression of JAM 1 was highest during the early phase when claudins were beginning to be expressed and tight junctional strands were beginning to be assembled. JAM1 mRNA decreased after E9, just before the most active period of junctional strand assembly that occurs between E10 and E14. By contrast, the mRNA for AF–6 was low early in development, but increased between E10 and E18 in parallel with the most active period of junction assembly. The pattern of expression for AF–6 was in sharp contrast with the pattern for two other PDZ–domain proteins of the tight junction, ZO–1 and ZO–2. These proteins decreased steadily during development. Therefore, of these cytoplasmic scaffolding proteins, AF–6 most closely paralleled the assembly of strands. Conclusions: RPE expresses several tight junctional proteins in advance of the assembly of tight junctions. Accordingly, ZO–1, ZO–2, occludin and JAM 1 are all present when claudins, the major strand–former, first appear. The delayed increase in AF–6 expression more closely parallels the assembly of patches of strands into a network that can function as a permeability barrier. This experimental model will allow us to examine the roles JAM 1 and AF–6 play in the assembly of the network of tight junctional strands.
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