Localization and Structural Organization of the Goat Serum Amyloid A (SAA) Gene Cluster

The goat Serum Amyloid A (SAA) gene family comprises 5 tightly linked genes clustered on chromosome 29 (Chi29). Screening of a bacterial artificial chromosome (BAC) library constructed by Schibler et al. (1998), allowed isolating 3 overlapping BAC clones, ranging in size between 35 and 170 kb, spanning the goat SAA locus. These 3 BAC clones were sequenced. The goat SAA gene family encompasses ca. 85 kb and genes are in the following order: SAA3-SAA1-SAA2-SAA4-SAA3.2 adopting the same nomenclature as in cattle. The organization is very similar in both ruminant species. SAA3 and SAA1 are 15-kb apart and transcribed in the same direction. SAA1 and SAA2 are 9-kb apart and divergently transcribed. SAA4 is 11 kb downstream SAA2 and 14-kb apart from SAA3.2. These 3 genes are transcribed in the same direction. The genes encoding goat SAAs map to chromosome 29, as in cattle, in a region which is syntenic with human chromosome 11 (Hsa11) and mouse chromosome 7 (Mmu7). However, TPH1 a gene encoding the tryptophan hydroxylase which is flanking the SAA locus in humans and mouse was located on chromosome 15, as in cattle (Bta15). The 5 genes encode pre-proteins of which M_r range between 14.3 and 14.9 KDa. We also investigated the expression of the goat SAA3 and SAA3.2 at the transcriptional level in the mammary epithelium and in several tissues and we observed very high contents in both SAA3 and SAA3.2 mRNA, in the mammary gland.