This small cluster of 14 clones (# 296-309) was characterized by an over expression occurring earlier than for the genes belonging to cluster 3. Among those 14 clones, 12 belonged to a UniGene cluster and 11 had a significant hit in SwissProt (Table 4 ). Two clones (# 305 and 306) were most similar to rat and human aquaporin 4 (aqp4) respectively. These 2 clones belonged to the same UniGene cluster (Omy.23866). In addition, one clone (# 296) was most similar to mouse serine protease 23 (sp23). Within cluster 3, aqp4 and sp23 genes were kept for real-time PCR analysis. 