Results of RT-PCR and whole-mount in situ hybridization of CD41. (A) Shown is the analysis of the expression of CD41 mRNA in developing zebrafish embryos by RT-PCR. The CD41 transcript is first detected at 42 hpf. Dilutions (10 ×, 100 ×, and 1000 ×) of the cDNA preparation 2 dpf, with EF-1α as a control, indicated that CD41 transcript is at least 1000 × lower than EF-1α transcript. The expected PCR product for CD41 is 1237 bp and for EF-1α is 220 bp. (B-D) Shown also are results of whole-mount in situ hybridization of wild-type zebrafish embryos with zebrafish CD41 antisense cRNA. (B) In embryos 2 dpf, punctate purple CD41⁺ cells are present in the ventral region of the dorsal aorta. (C) In embryos 3 dpf, the number of CD41⁺ cells has increased and they appear in the circulation. (D) In embryos 5 dpf, more CD41⁺ cells are present in the circulation. The CD41 transcript is not detected in the spadetail (E) and cloche (F) embryos 3 dpf.