Molecular evolution of epididymal lipocalin genes localized on mouse chromosome 2

We previously identified two murine secretory proteins, mE-RABP(Lcn5) and mEP17(Lcn8), belonging to the lipocalin family and specifically expressed in the epididymis. The genes are contiguous and localized on mouse chromosome 2. We now show that five other related lipocalin genes, Lcn9, Lcn10, Lcn11, Lcn12, and Lcn13, that evolved by in situ tandem duplication are present on the same locus. Lcn9, Lcn10, Lcn12, and Lcn13 genes, like Lcn5 and Lcn8 genes, are specifically expressed in the mouse epididymis. However, each gene has a distinct spatial expression within the epididymis and different regulation. Analysis of the human genome sequence shows the presence of genes encoding lipocalins with genomic organization, chromosomal arrangement, and orientation similar to that of the corresponding murine genes, indicating that the epididymal cluster is evolutionary conserved. A phylogenetic analysis of the new epididymal proteins reveals their spread position in the lipocalin protein family tree. This suggests the preservation of the regulatory sequences, while protein sequences have greatly diverged, reflecting functional diversity and possibly multifunctionality. In terms of the cluster ancestry, epididymal expression possibly appeared in a PGDS-like lipocalin in amniotes, and the duplications generating the cluster occurred at least in the common ancestor of rodents and primates. The presence and conservation of a cluster of five genes encoding epididymal lipocalins, differently regulated and regionalized in the epididymis, strongly suggests that these proteins may play an important role for male fertility.