RT-PCR analysis of bmp2a (top panel) and bmp2b (middle panel) in late-stage zebrafish (5.3–5.7 mm). Column 1 contains a 100 bp ladder (New England BioLabs, Cat. No. N3231S) with 400 and 500 bp bands marked at left. Column 2 shows RT-PCR results with no template added to the reaction mix (negative control). Column 3, with 36 hpf whole embryos (Martinez-Barbera et al., 1997), and the bottom panel, with constitutively expressed ef-1α (Nordnes et al., 1994), were used as positive controls. Columns 4–9 show presence and relative levels of amplified RNA for caudal fin rays, caudal hypurals, neural and hemal arches and spines, distal anal fin fold, proximal anal fin tissue, and lens. Although bmp2a is detected by RT-PCR in caudal hypurals, this is most likely due to the presence of proximal fin ray tips, which are closely apposed to the distal hypurals. Note the absence of RNA for bmp2a and bmp2b in distal anal fin fold tissue, while proximal anal fin tissue (composed of distal radial cartilage and proximal fin ray tips) strongly expresses both genes. bmp2a levels are relatively high in the lens, bmp2b lens RNA is barely detectable.

Expression of bmp2a in the median fins, neural and hemal arches and spines, and lens of late-stage zebrafish. Arrows mark fin rays, arrowheads mark radials/hypurals. Black patches are melanophores. Anterior is to the left and dorsal to the top. The image of the dorsal fin in panel C was flipped vertically to maintain consistent orientation (dorsal at bottom only in this panel). Faint parallel stripes of expression can be observed in presumptive fin ray tissue within the anal fin fold (5.2 mm NL) (A). Radials, not in this plane of section, but see inset, do not express bmp2a (A). Expression in the fin rays is stronger later in their development (5.5 mm); radials do not express bmp2a (B). Fin ray is maintained during segmentation (6.2 mm). The ZS in a radial is marked by an asterisk (C). The distal radials have completely segmented from the proximal radials by 6.7 mm and bmp2a expression is no longer detected (D). Expression is not observed in hypertrophic or proliferative chondrocytes of the five caudal hypurals (6.5 mm), but it is observed at the segment boundaries of the fin rays (inset) (E). bmp2a sense probe exhibits no distinct pattern (5.8 mm) (F). bmp2a antisense probe stains neural spines after exposure to BM Purple for 48 h (5.0 mm NL) (G). Ossified neural spines () and posterior tip of notochord (right edge of image) are artifactually labeled with bmp2a sense probe after exposure to BM Purple for 72 h (5.0 mm NL) (H). Expression is observed in the lens (4.5 mm NL) (I). Scale bars equal 0.05 mm.

Expression of bmp2b in the median fins of late-stage zebrafish. Arrows mark fin rays, arrowheads mark radials/hypurals. Black patches are melanophores. Anterior is to the left and dorsal to the top. Presumptive fin ray tissue within the anal fin fold expresses bmp2b, distal to the muscle buds () (5.2 mm NL) (A). Radials, not in this plane of section, but see inset, do not express bmp2b at this stage (A). Fin ray expression is maintained and a new domain of expression in the ZS (*) of the anal and dorsal fins is observed (5.5 mm) (B). A third domain of bmp2b expression in the maturing and hypertrophic chondrocytes (X) of the anal and dorsal fin radials develops in larger specimens; fin ray and ZS expression is maintained (6.0 mm) (C). By 7.3 mm, expression in the fin rays, ZS, and hypertrophic chondrocytes of the anal and dorsal fins is no longer detected (D). bmp2b expression is observed in caudal fin rays and in hypertrophic chondrocytes of the caudal fin supports, but not in mesenchyme or proliferative chondrocytes (6.6 mm) (E). No cells are distinctly labeled by bmp2b sense probe (6.6 mm) (F). Scale bars equal 0.05 mm.