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BMP Expression in Duck Interdigital Webbing: A Reanalysis

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Science  10 Oct 1997:
Vol. 278, Issue 5336, pp. 305
DOI: 10.1126/science.278.5336.305

In 1996, two of us (H.Z. and L.N.) reported that expression of a dominant-negative form of BMP receptor (dnBMPR-IB) in the embryonic chick hindlimb inhibited interdigital apoptosis and led to webbing of the digits (1) (BMPs are signaling molecules of the transforming growth factor–β superfamily). The importance of BMP signaling in regulating interdigital cell death has recently been confirmed by the use of an activated BMPR-IB retrovirus (2) and by application of BMP protein (3, 4).

It was also stated in this report (1) that BMP2,4, and 7 RNA expression was not detected in the duck interdigit. This result implied that the webbing in the hindlimb of ducks is a consequence of the absence of BMP expression in the duck embryo. After publication of the report (1), to explore this issue further, subsequent in situ hybridizations were carried out with the use of a modification (5) of an existing whole mount, in situ protocol. Results from our two different laboratories now indicate that BMP2, 4, and 7 are in fact expressed in the duck interdigit in a pattern similar to that of the chick interdigit (Fig. 1). The in situ protocol we used, in contrast with the protocol followed in the original study (1), included use of (i) a higher proteinase K concentration (30 to 70 μg/ml rather than 5 μg/ml), (ii) BCIP/NBT (6) as a color detection substrate rather than Boehringer-Mannheim purple AP substrate, and (iii) a TWEEN-20 concentration of 1% rather than 0.1% during the color substrate reaction. In combination, these modifications resulted in a greater sensitivity in detecting interdigital expression of BMP2,4, and 7 in late-stage embryonic limbs. This result has been confirmed for BMP7 by nonradioactive in situ hybridization to frozen tissue sections (7). Therefore, we (H.Z. and L.N.) must withdraw the earlier finding that the duck interdigit lacks BMP expression and regret any inconvenience the earlier conclusions may have caused.

Figure 1

Expression of BMP2, 4, and7 in the interdigital regions of chick and duck limbs. Expression of each gene was detected by whole mount in situ hybridization to stage 28/29 and to stage 31 chick (8) and stage-equivalent duck embryos, as indicated. In each case, wing and leg buds were removed from the embryos after completion of the whole mount procedure and photographed from a dorsal view.

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