MFG-E8 in the retina and retinal pigment epithelium of rat and mouse.
OBJECTIVE
To study the distribution of milk fat globule epidermal growth factor E8 (MFG-E8) in the rodent eye and to investigate a potential role for this molecule in the phagocytosis of photoreceptor outer segments (POS) by the retinal pigment epithelium (RPE).


METHODS
We have used immunohistochemistry, in situ hybridization, Northern and Western blotting to demonstrate the presence and distribution of MFG-E8 in the rat and mouse retina. siRNA technology was used to knock down MFG-E8 mRNA and to study the effect of such knockdown on the phagocytosis of POS by the RPE.


RESULTS
We identified a novel long form of this protein (MFG-E8L) in rat tissues, which contains a 56 amino acid insert that is rich in proline and threonine. This is the first demonstration that MFG-E8L is present in a species other than the mouse. Immunohistochemistry and in situ hybridization demonstrate that MFG-E8 is present in the retina and RPE. Northern blotting and PCR show that the short form of MFG-E8 (MFG-E8S) is present in both the retina and RPE, but MFG-E8L is found only in the RPE. Our results do not demonstrate a role for MFG-E8 in POS phagocytosis by cultured RPE cells.


CONCLUSIONS
In all tissues in which MFG-E8 has been localized, it has been shown to perform an important role in cell-cell binding, or in promoting phagocytosis. The localization of this glycoprotein in the retina and RPE, and particularly the specific localization of MFG-E8L in the RPE, suggests that this molecule may play an important, but as yet unknown role in retinal function.
Burgess
Barry L
BL
Jules Stein Eye Institute, UCLA Medical Center, Los Angeles, CA 90095-7000, USA.
Abrams
Toshka A
TA
Nagata
Shigekazu
S
Hall
Michael O
MO
D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002478:Cells, Cultured; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051379:Mice / Q000378:metabolism*; D008807:Mice, Inbred BALB C; D008894:Milk Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010587:Phagocytosis / Q000502:physiology; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism* / Q000473:pathology / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D034622:RNA Interference; D051381:Rats / Q000378:metabolism*; D011919:Rats, Inbred Strains; D011922:Rats, Mutant Strains; D012164:Retinal Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D012374:Rod Cell Outer Segment; D013194:Staining and Labeling
D000954:Antigens, Surface; C499941:MFGE8 protein, rat; C490919:Mfge8 protein, mouse; D008894:Milk Proteins; D020033:Protein Isoforms