Fig. 1

Cxcl12 subfunctionalization affects gene expression and chemotactic activity of Cxcl12. (A,B) Zebrafish cxcl12a and cxcl12b mRNA expression patterns as detected by in situ hybridization using probes of identical length and identical staining duration to allow direct expression level comparison at late gastrula stage (A) and at the onset of somitogenesis (B). (C) During early somitogenesis stages, the primordial germ cells (PGCs, brown) clearly reside outside of regions of high cxcl12b expression (blue). (D,E) At 22 hpf, the PGC positions correlate only with cxcl12a expression. Insets show magnified views of the developing gonads. Arrow, gonad region. (F) Knockdown of Cxcl12a, but not of Cxcl12b, expression results in strong PGC migration defects. (G) Quantitation of the results presented in F. (H) cxcl12b-expressing tissues attract PGCs in embryos knocked down for Cxcl12a. Shown is the percentage of embryos with more than three PGCs at cxcl12b-expressing tissues. (I) PGCs (nos1, blue) normally reach cxcl12a-expressing domains (top), but arrive at regions expressing cxcl12b when Cxcl12a is knocked down (middle), or are located randomly when both chemokines are knocked down (bottom). Arrowheads, PGCs located in cxcl12b expression domains. (J) Percentage of PGCs attracted by Cxcl12a-expressing or Cxcl12b-expressing transplanted cells. (K,L) The percentage of PGCs attracted by Cxcl12a-expressing (red in L) or Cxcl12b-expressing (blue in L) co-transplanted cells. Arrows indicate the movement of the marked cells (asterisks) (see Movie 1 in the supplementary material). Error bars depict s.e.m.; n, the number of embryos analyzed. *, P<0.05 compared with control (t-test).