Cell and species distribution of prolactin-inducible annexin I mRNA

The major prolactin-induced gene in the Columbid cropsac (cp35) is a unique member of the annexin (lipocortin/calpactin) gene family, most closely related to mammalian annexin I. Because no other annexins are known to be regulated by a specific hormonal signal, we have analyzed the distribution of annexin I mRNAs which hybridize to cp35 cDNA by comparing several tissue and cell systems. In addition we have used in situ hybridization to locate the expression of cp35 mRNA in the cropsac. Of nine separate organs extracted only cropsac, spleen, trachea, intestine, and lung expressed easily detectable levels of annexin I mRNA. Heart, liver, kidney, and skeletal muscle did not consistently express detectable annexin I. Prolactin (PRL) injection had no measurable effect on the mRNAs expressed in any of the tissues other than cropsac. Mammalian cell lines which respond to PRL (COMMA-D, HC11) were probed for expression of cp35-hybridizing mRNAs. These cell lines contained high levels of annexin I mRNA, but the mRNA level was not stimulated by PRL. Lactating mouse mammary gland did not contain measurable RNAs for either annexin I or II. In situ hybridization of cropsac sections showed that high-level expression of annexin I (cp35) mRNA was localized in the differentiating layer of the cropsac mucosal epithelium after PRL stimulation. It was not abundant in either the proliferating layer or the outermost desquamating layer of cells. These experiments argue that mRNAcp35 expression is a unique component of the PRL-induced differentiation response of cropsac and that closely related mRNAs are expressed in some, but not all, other tissues of the pigeon.