Fig. 2.

A, The genomic organization of the Atp2b2 (PMCA2) gene at splice site A is illustrated with the alternatively spliced variants PMCA2w and PMCA2z shown below. RT-PCR was performed with primers (represented by arrows) flanking the splice site. B, RT-PCR was performed on RNA from mammary glands of mice at the developmental stages noted in the figure. Mouse brain RNA served as a control for the PMCA2z splice variant (the brain sample was run on a different gel). PCR products were of the predicted sizes for either the w splice variant (377 bp) or the PMCA2z splice variant (244 bp), but PCR products were sequenced to confirm their identity. Throughout postnatal development, the mouse mammary gland expresses only the PMCA2w variant of splice site A. C and D, Immunofluorescent staining for PMCA2 in mammary tissue from a lactating mouse (d 12) demonstrated that it was located at the apical plasma membrane. E, An electron micrograph of lactating mammary tissue stained for PMCA2 using immunoperoxidase techniques confirmed the apical membrane localization. There was no PMCA2 staining in secretory vesicles or other intracellular compartments.