We previously reported that CORS26 gene, isolated from C3H10T1/2 cells treated with transforming growth factor-beta1, was predominantly expressed in cartilage. Because the gene product is a kind of secretory protein produced by cartilage tissue, we named it "cartducin". Cartducin shares a similar modular organization to adipocyte-derived hormone, adiponectin. In this study, we investigated cartducin function during chondrogenesis and cartilage development. In situ hybridization analysis showed that cartducin transcripts were restricted to the proliferating chondrocytes in the growth plate cartilage. Whole-mount in situ hybridization revealed that the first significant induction of cartducin expression occurred in the sclerotome, which contains a chondrogenic cell lineage between days 9.5 and 10.5 postcoitus (p.c.) during mouse embryogenesis. Chondrogenic differentiation by combined treatment with bone morphogenetic protein-2 and insulin induced cartducin expression along with type II and IX collagen expression in chondrogenic progenitor N1511 cells. To elucidate the direct action of cartducin on the cells, recombinant cartducin protein was expressed in and purified from Escherichia coli. The recombinant cartducin potentially forms homo-oligomers and promoted the proliferation of chondrogenic progenitor N1511 cells, and chondrocytic HCS-2/8 cells in a dose-dependent manner. On the other hand, cartducin did not affect the production of sulfated glycosaminoglycan (sGAG) in these cells. These findings indicate that cartducin is a novel growth factor and plays important roles in regulating both chondrogenesis and cartilage development by its direct stimulatory action on the proliferation of chondrogenic precursors and chondrocytes.

CTRP3/cartducin, a novel secretory protein, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. CTRP3/cartducin gene is transiently up-regulated in a balloon-injured rat carotid artery tissue. In this study, we report a new function of CTRP3/cartducin as a regulator of angiogenic processes. CTRP3/cartducin promoted proliferation and migration of mouse endothelial MSS31 cells in a dose-dependent manner. Further, stimulation of MSS31 by CTRP3/cartducin led to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). MAPK/ERK kinase 1/2 (MEK1/2) inhibitor, U0126, and p38 MAPK inhibitor, SB203580, blocked the CTRP3/cartducin-induced cell proliferation, and migration was blocked by U0126, but not the SB203580. Taken together, these results suggest that CTRP3/cartducin may be involved as a novel angiogenic factor in the formation of neointima following angioplasty.

Cartilage formation is driven by mesenchymal chondroprogenitor cells that proliferate and differentiate into chondrocytes. The molecular mechanisms by which growth factors regulate the fate of these cells are not well defined. We recently discovered a secretory protein, cartducin, which is an 27 kDa polypeptide containing an N-terminal signal peptide, a short variable domain, a collagen-like domain, and a C-terminal C1q-like globular domain. Its mRNA is predominantly and highly expressed in developing cartilages [1]. Interestingly, cartducin has structural homology with a 30 kDa serum protein Acrp30 ⁄ adiponectin, which is exclusively and highly expressed in differentiated adipocytes [2], and has been shown to be dysregulated in various forms of obesity in mice and humans [3,4]. Because cartducin is a paralog of Acrp30 ⁄ adiponectin, cartducin is a novel member of a newly designated C1q family of proteins [5,6]. The

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Subplate (SP) neurons are among the earliest-born neurons in the cerebral cortex and heterogeneous in terms of gene expression. SP neurons consist mainly of projection neurons, which begin to extend their axons to specific target areas very early during development. However, the relationships between axon projection and gene expression patterns of the SP neurons, and their remnant layer 6b (L6b) neurons, are largely unknown. In this study, we analyzed the corticocortical projections of L6b/SP neurons in the mouse cortex and searched for a marker gene expressed in L6b/SP neurons that have ipsilateral inter-areal projections. Retrograde tracing experiments demonstrated that L6b/SP neurons in the primary somatosensory cortex (S1) projected to the primary motor cortex (M1) within the same cortical hemisphere at postnatal day (PD) 2 but did not show any callosal projection. This unilateral projection pattern persisted into adulthood. Our microarray analysis identified the gene encoding a β subunit of voltage-gated potassium channel ( Kcnab1 ) as being expressed in L6b/SP. Double labeling with retrograde tracing and in situ hybridization demonstrated that Kcnab1 was expressed in the unilaterally-projecting neurons in L6b/SP. Embryonic expression was specifically detected in the SP as early as embryonic day (E) 14.5, shortly after the emergence of SP. Double immunostaining experiments revealed different degrees of co-expression of the protein product Kvβ1 with L6b/SP markers Ctgf (88%), Cplx3 (79%), and Nurr1 (58%), suggesting molecular subdivision of unilaterally-projecting L6b/SP neurons. In addition to expression in L6b/SP, scattered expression of Kcnab1 was observed during postnatal stages without layer specificity. Among splicing variants with three alternative first exons, the variant 1.1 explained all the cortical expression mentioned in this study. Together, our data suggest that L6b/SP neurons have corticocortical projections and Kcnab1 expression defines a subpopulation of L6b/SP neurons with a unilateral inter-areal projection.