The Wnt gene family encodes a set of intercellular signaling molecules implicated in the regulation of a wide range of basic developmental processes. Both spontaneous mutations and geneknockout studies have demonstrated the importance of a number of these in normal mouse development. Wnts are involved in the regulation of development of the midbrain, limbs, kidneys, and a number of other tissues (reviewed by Cadigan and Nusse 1997). Wnt genes are highly evolutionarily conserved and have been identified in a wide range of species. The best characterized Wnt is the Drosophila segment polarity gene wingless, the ortholog of Wnt1. The mouse Wnt gene family comprises at least 18 members, each of which encodes a secretory glycoprotein of between 350 and 380 amino acids in length and containing a characteristically spaced pattern of cysteine residues. Wnt genes have been classified into various subfamilies based largely on sequence homologies. Most of these subfamilies consist of pairs of Wnt genes more closely related to each other than to other Wnt genes. Thus, while members of the mouse Wnt gene family are typically around 40% identical to each other, homologies within the subfamilies are greater than 80%(see Cadigan and Nusse 1997). Expression patterns of some orthologous Wnt genes are conserved between species, lending strength to identifications based purely upon homology. Members of the Wnt8 subfamily have previously been described in Xenopus, zebrafish, chick, human, and mouse (see Cadigan and Nusse 1997 for references). Here, we describe the cloning and characterization of mouse Wnt8B.

A number of Wnt genes are expressed in the postnatal mammary gland. We used degenerate PCR on cDNA made from mRNA derived from 11-day lactating mouse mammary gland following the protocol described by Gavin and McMahon (1993). Primers were designed to correspond to the conserved amino acid motifs CKCHG [5-GGGGCTCGAGTG (CT) AA (AG) TG (CT) CA (CT) GG-3] and FHWCC [5-GGAATCTAGA (AG) CA (AG) CACCA (AG) TG (AG) AA-3]. This produced a fragment of approximately 410 bp which was digested with XhoI and XbaI and cloned into pBluescriptII. Sequence analysis revealed one insert that was most closely related to the Wnt8 subfamily. This was used