The effect of 5-bromodeoxyuridine on chick embryo limb bud mesenchyme in organ culture

The thymidine analogue 5-bromodeoxyuridine (BrdU) prevents chondrogenesis in organ cultures of limb bud mesenchyme of 3 1/2 day chick embryos. The biologically active levels of BrdU inhibit both DNA and RNA synthesis, but the synthesis of methylated RNA is inhibited less than that of unmethylated RNA. If cell division is partially synchronized the ratio of incorporation of BrdU to thymidine is greater during the first few minutes of the S period than for unsynchronized cells. The results suggest that BrdU may be preferntially incorporated into the starting points of replicons and that this may affect subsequent transcription necessary for chondrogenesis.