Spatial and temporal expression of MFRP and its interaction with CTRP5.
OBJECTIVE
Mutations in the membrane frizzled-related protein (MFRP) gene cause nanophthalmos in humans, and a splice site mutation causes recessive retinal degeneration in the rd6 mouse. In human and mouse genomes, the MFRP gene lies adjoining to the complement 1q tumor necrosis factor-related protein 5 (CTRP5/C1QTNF5) gene involved in causing retinal degeneration and abnormal lens zonules in human. The purpose of this study was to characterize the spatial and temporal expression of the mouse Mfrp gene, determine tissue and subcellular localization of MFRP protein, and study its interaction with CTRP5.


METHODS
Expression of the Mfrp gene in the mouse was studied by quantitative (q)RT-PCR. MFRP protein expression and distribution were studied by Western blot analysis, immunohistochemistry, and immunoelectron microscopy. Interaction with CTRP5 was studied by immunoprecipitation and immunoblot analysis, using mouse eye and human retinal pigmented epithelium (RPE) choroid extracts and by expressing full-length CTRP5 and MFRP in a heterologous system.


RESULTS
The Mfrp gene is specifically expressed in RPE and ciliary body (CB), and its expression starts during early stages of embryogenesis. In the albino mouse eye, MFRP is localized to the apical and basal membranes of RPE and ciliary epithelium (CE). In addition, MFRP and CTRP5 were found to colocalize in RPE, CE, and MDCK cells, a general model of polarized epithelia. These proteins interact with each other in ocular tissues and also in a heterologous system.


CONCLUSIONS
MFRP is localized to the plasma membrane of CE and RPE, and colocalizes and interacts with CTRP5 indicating a functional relationship between these two proteins.
Mandal
Md Nawajes A
MN
Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA.
Vasireddy
Vidyullatha
V
Jablonski
Monica M
MM
Wang
Xiaofei
X
Heckenlively
John R
JR
Hughes
Bret A
BA
Reddy
G Bhanuprakash
GB
Ayyagari
Radha
R
D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D002924:Ciliary Body / Q000196:embryology / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology*; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016253:Microscopy, Immunoelectron; D010857:Pigment Epithelium of Eye / Q000196:embryology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D000099274:Frizzled-Related Proteins
D005136:Eye Proteins; D008565:Membrane Proteins; C516596:CTRP5 protein, mouse; C423368:Mfrp protein, mouse; D000099274:Frizzled-Related Proteins