RESEARCH ARTICLE Molecular Reproduction & Development (2015) Molecular Cloning and Partial Characterization of a Low-Density Lipoprotein Receptor-Related Protein 13 (Lrp13) Involved in Vitellogenin Uptake in the Cutthroat Trout (Oncorhynchus clarki) YUJI MUSHIROBIRA, 1 HIROKO MIZUTA, 1 WENSHU LUO, 1 TAKASHI TODO, 2 AKIHIKO HARA, 2 BENJAMIN J. READING, 3 CRAIG V. SULLIVAN 4 , AND NAOSHI HIRAMATSU 2 * 1 Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Japan 2 Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan 3 Department of Applied Ecology, North Carolina State University, Raleigh, North Carolina 4 Carolina AquaGyn, Raleigh, North Carolina SUMMARY Multiple ovarian membrane proteins that bind vitellogenin (Vtg) have been detected in teleosts. One of these Vtg receptors was recently identified as low-density lipoprotein receptor-related protein 13 (lrp13/Lrp13) in perciform species, but little is known about this Vtg receptor in salmonid fish. In this study, a cDNA encoding a putative Vtg receptor with 13þ1 ligand binding repeats (lr13þ1) was cloned from the ovary, and identified as an lrp13 ortholog for cutthroat trout (Oncorhynchus clarki). This lrp13 was predominantly expressed in the pre-vitellogenic stage ovary, and its expression decreased during vitellogenesis. Ovarian localization of Lrp13 was observed by immunohistochemistry using specific antiserum against recombinant Lrp13. Lrp13 immunoreactivity was observed at the oolemma, throughout the zona radiata, and within the perivitelline space between the zona radiata and granulosa cells in ovarian follicles at both the lipid-droplet and vitellogenic stages of growthan expression pattern that mimics that of a lr8/LR8-type Vtg receptor in this species and of lrp13/Lrp13 in Morone species. Six discrete Vtg-binding proteins were detected in cutthroat trout ovarian membrane proteins when probing with a digoxygenin-labeled salmonid A-type Vtg (VtgAs) followed by chemiluminescent ligand detection. West- ern blotting using the anti-Lrp13 serum revealed a broad signal consisting of two proteins with masses ranging from 190 to 210 kDa, which corresponded with some of the VtgA-binding proteins. These findings suggest that, in addition to lr8/LR8, lrp13/Lrp13 acts as a VtgA receptor in trout. Mol. Reprod. Dev. 2015. ß 2015 Wiley Periodicals, Inc. Received 1 May 2015; Accepted 30 August 2015  Corresponding author: Faculty of Fisheries Sciences Hokkaido University 3-1-1 Minato, Hakodate Hokkaido, 041-8611, Japan E-mail: naoshi@fish.hokudai.ac.jp Grant sponsor: The Grant-in-Aid for JSPS Fellows; Grant numbers: 24-1961, 24- 2064; Grant sponsor: The Grant-in-Aid for Scientific Research; Grant number: 22380103; Grant sponsor: Japan Science and Technology Agency; Grant number: AS231Z00518E; Grant sponsor: North Carolina Sea Grant Program; Grant number: R/12- SSS-3; Grant sponsor: Carolina AquaGyn Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mrd.22579 INTRODUCTION Teleost eggs contain a substantial yolk mass, which serves as a source of nutrients for embryonic development Abbreviations: LDLa, low-density lipoprotein receptor domain class A; LDLR, low-density lipoprotein receptor; LR [7, 8, or 13þ1], low-density lipopro- tein receptor ortholog with [7, 8, or 13þ1] repeats; LRP, low-density lipoprotein receptor-related protein; VLDLR, very-low-density lipoprotein receptor; Vtg (Aa, Ab, As, C), vitellogenin (Aa-type, Ab-type, salmonid A-type, C-type); Vtgr, vitellogenin receptor ß 2015 WILEY PERIODICALS, INC.