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Abstract
Members of the bone morphogenetic protein (BMP) class of transforming growth factor
beta (TGF beta)-related molecules have been implicated in a variety of inductive processes
throughout vertebrate development. The 60A subclass of BMPs contains at least four
vertebrate members, BMPs 5-8. We have shown by library screening and in situ hybridization
that of these four genes, BMP 7 is expressed earliest, in gastrulating embryos. Furthermore,
BMP 7 transcripts are present at diverse sites throughout development, in a pattern
consistent with a role in a variety of inductive interactions. Recent studies have
shown that BMP 2/7 heterodimers have unique activities compared to the corresponding
homodimers. For this reason, we compared the patterns of expression of BMP 2 and BMP
7 using in situ hybridization. Our results demonstrate that these BMPs are coexpressed
in a number of tissues that are known to be the source of inductive signals, including
the zone of polarizing activity and apical ectodermal ridge of the developing limb
and the notochord, raising the possibility that BMP 2/7 heterodimers may mediate aspects
of these tissue interactions. We also show that BMP 2 transcripts are restricted within
the developing gut to dorsal endoderm, whereas sonic hedgehog has been localized to
ventral and medial regions of the developing gut endoderm. These markers provide the
first molecular evidence for dorsal/ventral polarity in the developing gut.