New tools for studying osteoarthritis genetics in zebrafish

Abstract

Objective: Increasing evidence points to a strong genetic component to osteoarthritis (OA) and that certain changes that occur in osteoarthritic cartilage recapitulate the developmental process of endochondral ossification. As zebrafish are a well validated model for genetic studies and developmental biology, our objective was to establish the spatiotemporal expression pattern of a number of OA susceptibility genes in the larval zebrafish providing a platform for functional studies into the role of these genes in OA.

Design: We identified the zebrafish homologues for Mcf2l, Gdf5, PthrP/Pthlh, Col9a2, and Col10a1 from the Ensembl genome browser. Labelled probes were generated for these genes and in situ hybridisations were performed on wild type zebrafish larvae. In addition, we generated transgenic reporter lines by modification of bacterial artificial chromosomes (BACs) containing full length promoters for col2a1 and col10a1.

Results: For the first time, we show the spatiotemporal expression pattern of Mcf2l. Furthermore, we show that all six putative OA genes are dynamically expressed during zebrafish larval development, and that all are expressed in the developing skeletal system. Furthermore, we demonstrate that the transgenic reporters we have generated for col2a1 and col10a1 can be used to visualise chondrocyte hypertrophy in vivo.

Conclusion: In this study we describe the expression pattern of six OA susceptibility genes in zebrafish larvae and the generation of two new transgenic lines marking chondrocytes at different stages of maturation. Moreover, the tools used demonstrate the utility of the zebrafish model for functional studies on genes identified as playing a role in OA.

Fig. 1

Mcf2la is dynamically expressed during zebrafish development A phylogenetic tree to show that mcf2la clusters with mcf2l orthologues from vertebrate species, while mcf2lb is more derived. zf = zebrafish, ol = oryzias latipes {medaka}, bt = bos Taurus {cow}, hs = homo sapien {human}, mm = mus musculus {mouse}, xl = xenopus laevis {clawed frog}. B–F″ whole mount in situ hybridisation expression for mcf2la, B–E show whole mount images, while D′, D″, F–F″ show cryosections. 12G. Sense control for mcf2la. Anterior is to the left, with the exception of B–C where anterior is up. Ages are as follows 12s (B) 18s (C), 24 hpf (D–D″), 72 hpf (E–F″). Arrows in top panel indicate the muscle pioneers. Arrows in bottom panels point to chondrocytes (labelled c) or to cells surrounding the cartilage elements (sc).., ba = branchial arches kv = Kupffer'svesicle, jj = jaw joint, mp = muscle pioneers, cb = cerebellum, hbv = hindbrain vesicle, c = chondrocytes, op = operculum, pq = palatoquadrate, sc = surrounding cells (which include the perichondrial cells), ep = ethmoid plate, bh = basohyal, gc = ganglion cell layer, ac=amacrine cells.

Fig. 2

mRNA expression of pthlha, gdf5, col9a2 and col10a1 A phylogenetic tree to demonstrate that pthlha segregates with the vertebrate Pthlh genes h.s.=homo sapiens, m.m.=mus musculus, zf=zebrafish, x.l.=xenopus laevis, o.l.=oryzias latipes, b.t.=bos taurus. In situ hybridisation expression of (B–D′) pthlha, (E–E″)gdf5, (F–H′) Col9a2 and (I–J′) Col10a1 B, G, H, I and J show lateral views; B′, C′,G′,H, I″ and J′ ventral views. D–F″ are cryosections. All images are orientated with anterior to left. B,B′, G, G′, I and I′ are 72 hpf, E is 96 hpf, C–D′, E′–F′, H, H′, J and J′ are 120 hpf. Ba = branchial arches, cl = cleithrum, m = maxilla, ch = ceratohyal, op = operculum, ps = parasphenoid, pn = pronephros, 5ba = 5th branchial arch, mc = Meckel's cartilage, pf=pectoral fin.

Fig. 3

Col10a1, osterix and col2a1 transgenic reporter expression expression of tg(col10a1BAC:citrine) A, A′ B, C, E′, E″, F′ and F″, tg(col2a1BAC:mcherry) C, D, D″, E′ and E″ and Tg(OlSp7:mCherry)zf131 A′(A) Col10a1BAC:citrine reporter expression in live zebrafish at 72 hpf, (A,A′), 120 hpf (D–E″) and 14 dpf (B). B is of the vertebral column at the level of the cloaca. (F and F′) 96 hpf col2a1BAC:mCherry transgenic larvae fixed and labelled with anti-mCherry to detect transgene activity in green and with II–II3B3 antibody (DSHB) which detects type II collagen protein in red, green labelled cells with transgene activity are surrounded by matrix positive for collagen 2 protein. G) Fluorescent in situ for col10a1 mRNA detected with anti-digoxigenin rhodamine. G′) anti-GFP/citrine staining and G″ shows the overlay of G and G′, showing that all regions that stain for col10a1 mRNA are also positive for the fluorescent transgenic protein. A, A′, D–D″ F and G–G″ are lateral views and E–E″ and F′ are ventral. All are projections of confocal stacks, all presented with anterior facing left. cl = cleithrum, m = maxilla, ch = ceratohyal, op = operculum, mc = Meckel's cartilage, 5ba = 5th branchial arch and teeth, hs = hyosymplectic, br = branchiosteal rays, na = neural arches, ha = haemal arches.