And unique gene in chordates with no Met-Enkephalin homologues found in lower species such as flies or worms [1]. With adiponectin and other members of the C1q/TNF-related protein (CTRP) family Cthrc1 shares the presence of a short N terminal collagen domain but it lacks the characteristic C1q domain that defines the CTRP familyof proteins [9]. Cthrc1 and adiponectin are similar in molecular mass, 243 and 244 amino acids, respectively. Like adiponectin, we demonstrate here that Cthrc1 is a circulating hormone that forms high molecular weight complexes [10,11], although the significance of the different Cthrc1 molecular weight complexes needs to be determined. Yamamoto et al. [2] reported an interaction of Cthrc1 with the planar cell polarity pathway (PCP) of non-canonical WNT signaling. The authors’ reasoning for investigating an involvement of Cthrc1 in the PCP pathway was based on the fact that theFigure 9. Cthrc1 detection in human plasma. A pull-down assay with monoclonal Cthrc1 antibody coupled to magnetic beads was performed on human plasma samples (#1?4). (A) The eluate was analyzed 
by Western blotting with HRP-conjugated anti-Cthrc1 antibody, conditioned medium from hCthrc1 expressing CHO-K1 cells was used as a positive control. No Cthrc1 was detectable in the unbound plasma fraction (note absence of non-specific bands). (B) The eluates from plasma samples #2?4 were immunoblotted with biotin-conjugated anti-Cthrc1 antibody followed by HRP-conjugated streptavidin. doi:10.1371/journal.pone.0047142.gHormonal Functions of CthrcCthrc1 gene is located adjacent to the Frizzled6 gene, which is a WNT binding receptor. The targeted replacement of the first 16574785 exon of the Cthrc1 gene by a LacZ reporter gene in mice was reported to demonstrate expression of Cthrc1 in inner ear hair cells [2]. Abnormalities in inner ear development occurred when Cthrc1 null mice were crossed with mice carrying one mutant allele of Vangl2, but these abnormalities were only observed when these compound mutants were on a specific mixed genetic background and not when the mutants were crossed with outbred mice [2]. With our antibodies we have been unable to detect expression of Cthrc1 in inner ear hair cells and auditory testing did not reveal any hearing abnormalities in our mutant mice (data not shown). The use of LacZ expression as a surrogate for endogenous Cthrc1 localization has obvious limitations when the endogenous protein is released into the circulation. Yamamoto et al. [2] performed most of their Cthrc1 protein interaction studies in HEK293T cells. Unlike Cthrc1 transfected CHO-K1 cells, which secrete Cthrc1 readily into the medium, Cthrc1 cannot be detected in the medium of transfected HEK293T cells (Fig. 10). This raises the question of suitability of the HEK293T cell line for studying Cthrc1 in vitro. Detection of Cthrc1 in plasma implies that it is secreted from cells. In the neurosecretory nuclei of the hypothalamus (Fig. 6A ) and the paraventricular cells shown in Fig. 6M, we observed immunoreactivity with granular appearance restricted to the cytoplasm and axon of the cell. This is suggestive of Cthrc1 packaging in secretory granules, a characteristic of a regulated 35013-72-0 biological activity release mechanism that has been described for the release of neuropeptides from neuroendocrine cells [12]. A role for carboxypeptidase E (CPE) in the transport of peptide hormonecontaining vesicles to the site of release has been demonstrated in this process [13]. An interaction of Cthrc1 with CPE.And unique gene in chordates with no homologues found in lower species such as flies or worms [1]. With adiponectin and other members of the C1q/TNF-related protein (CTRP) family Cthrc1 shares the presence of a short N terminal collagen domain but it lacks the characteristic C1q domain that defines the CTRP familyof proteins [9]. Cthrc1 and adiponectin are similar in molecular mass, 243 and 244 amino acids, respectively. Like adiponectin, we demonstrate here that Cthrc1 is a circulating hormone that forms high molecular weight complexes [10,11], although the significance of the different Cthrc1 molecular weight complexes needs to be determined. Yamamoto et al. [2] reported an interaction of Cthrc1 with the planar cell polarity pathway (PCP) of non-canonical WNT signaling. The authors’ reasoning for investigating an involvement of Cthrc1 in the PCP pathway was based on the fact that theFigure 9. Cthrc1 detection in human plasma. A pull-down assay with monoclonal Cthrc1 antibody coupled to magnetic beads was performed on human plasma samples (#1?4). (A) The eluate was analyzed by Western blotting with HRP-conjugated anti-Cthrc1 antibody, conditioned medium from hCthrc1 expressing CHO-K1 cells was used as a positive control. No Cthrc1 was detectable in the unbound plasma fraction (note absence of non-specific bands). (B) 
The eluates from plasma samples #2?4 were immunoblotted with biotin-conjugated anti-Cthrc1 antibody followed by HRP-conjugated streptavidin. doi:10.1371/journal.pone.0047142.gHormonal Functions of CthrcCthrc1 gene is located adjacent to the Frizzled6 gene, which is a WNT binding receptor. The targeted replacement of the first 16574785 exon of the Cthrc1 gene by a LacZ reporter gene in mice was reported to demonstrate expression of Cthrc1 in inner ear hair cells [2]. Abnormalities in inner ear development occurred when Cthrc1 null mice were crossed with mice carrying one mutant allele of Vangl2, but these abnormalities were only observed when these compound mutants were on a specific mixed genetic background and not when the mutants were crossed with outbred mice [2]. With our antibodies we have been unable to detect expression of Cthrc1 in inner ear hair cells and auditory testing did not reveal any hearing abnormalities in our mutant mice (data not shown). The use of LacZ expression as a surrogate for endogenous Cthrc1 localization has obvious limitations when the endogenous protein is released into the circulation. Yamamoto et al. [2] performed most of their Cthrc1 protein interaction studies in HEK293T cells. Unlike Cthrc1 transfected CHO-K1 cells, which secrete Cthrc1 readily into the medium, Cthrc1 cannot be detected in the medium of transfected HEK293T cells (Fig. 10). This raises the question of suitability of the HEK293T cell line for studying Cthrc1 in vitro. Detection of Cthrc1 in plasma implies that it is secreted from cells. In the neurosecretory nuclei of the hypothalamus (Fig. 6A ) and the paraventricular cells shown in Fig. 6M, we observed immunoreactivity with granular appearance restricted to the cytoplasm and axon of the cell. This is suggestive of Cthrc1 packaging in secretory granules, a characteristic of a regulated release mechanism that has been described for the release of neuropeptides from neuroendocrine cells [12]. A role for carboxypeptidase E (CPE) in the transport of peptide hormonecontaining vesicles to the site of release has been demonstrated in this process [13]. An interaction of Cthrc1 with CPE.