ABSTRACT. Slit, a secreted protein, functions as a chemorepellent factor in axon guidance and neuronal migration and as an inhibitor in leukocyte chemotaxis. In humans, slit2 protein attracts endothelial cells and promotes tube formation in the tumor angiogenic mechanism. In this study, we cloned a part of the canine slit subfamily and examined the expression of slit subfamily mRNAs in 3 normal canine mammary glands and 11 mammary tumor samples by RT-PCR. The cloned part of the slit gene sequences showed high similarity to those of the human, mouse, and rat. The mRNAs were expressed at low levels in the normal mammary gland. The expression levels of slit1 mRNA were low in both the normal and tumor tissues. In contrast, the expression of slit2 mRNA increased in most of the malignant mammary tumors, and an increase in slit3 mRNA expression was observed in 2 of the malignant mixed tumors. These results suggest that the expression of slit2 plays an important role in tumor angiogenesis in canine mammary gland tumors and that slit2 can be a putative marker for malignancy diagnosis of these tumors. KEY WORDS: canine mammary gland tumor, malignancy, robo, slit, tumor marker.

ABSTRACT. Human BRCA1 is familial breast cancer susceptibility gene. Recently, decreased BRCA1 mRNA and protein expression has been identified in sporadic breast tumors. In the reported human BRCA1 splicing variants, delta11b lacks the majority of exon11 and is suspected to have a distinct function in normal tissues. The splicing variants display a variety of expression pattern in breast cancer samples. Although mammary gland tumor is important disease in dog, there are few reports for BRCA1 in the canine tumors. In this study, we examined the relative amounts of BRCA1 splicing variants mRNA in canine normal and mammary tumor samples by RT-PCR to investigate whether there is the altered expression of variant mRNAs in the canine tumor as reported in human. The exon11b-defecting RT-PCR products were observed in all the normal tissues examined and the nucleotide sequence was quite similar to that of human BRCA1 delta11b. In some tumor samples, we did not detect the products targeted for exon10-13 and exon14-15, while these products were observed in all the normal samples examined. Especially, the relative amounts of the exon11-defecting products were remarkably decreased in most of the tumors (11/16). KEY WORDS: BRCA1, canine, mammary tumor, RT-PCR, splicing variant.