ABSTRACT. The entire cDNA sequences were determined by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) techniques for equine copper/zinc superoxide dismutase (Cu/Zn-SOD) and manganese superoxide dismutase (Mn-SOD) through the use of total RNA extracted from the testis of an adult Thoroughbred. The results revealed a protein coding region for equine Cu/Zn-SOD with bases totaling 465 bp, accompanied by an estimated 154 residues of amino acids. As for equine Mn-SOD, its coding region contained a total of 669 bp and an estimated 222 residues of amino acids. Further, the expression of Cu/Zn-SOD and Mn-SOD genes were confirmed in the equine tissues by RT-PCR and in situ hybridization. -KEY WORDS: equine, in situ hybridization, RT-PCR, SOD.J. Vet. Med. Sci. 61(3): 291-294, 1999 confirmed by RT-PCR and in situ hybridization. Total RNAs for RT-PCR were extracted from the nine tissues; testis, adrenal gland, spleen, cerebrum, cerebellum, heart, thyroid gland, kidney, and liver. For in situ hybridization, the clones of equine Cu/Zn-SOD and Mn-SOD genes were digested with the restriction enzyme Spe I. In vitro transcription was conducted to produce RNA probes using a DIG-RNA Labeling Kit SP6/T7 (Boehringer Mannheim, Tokyo). In situ hybridization was conducted using a deparaffinated pieces of spleen tissue and these probes. Compared with other mammalian species, an 83% homology was found in the Cu/Zn-SOD cDNA sequence for both equine genes with humans [23] [7]. In mammals, the presence of the following three types of SOD has been confirmed: Cu/Zn-SOD found in the cytoplasm [17], Mn-SOD in the mitochondria [20], and EC-SOD in serum [16]. The cDNA sequences of these enzymes in humans have already been determined [2,6,23]. In this study, to allow us to carry out our basic research and enable clinical application regarding the role of active oxygen and antioxidative enzymes in equine biological functions, the cDNA sequences of Cu/Zn-SOD and Mn-SOD genes were first determined. Based on this data, the sequences of amino acids were then deduced. At the same time, the expressions of SOD genes in equine tissues were investigated by RT-PCR and in situ hybridization.Total RNA from the testis of an adult Thoroughbred was extracted by guanidinium/cesium chloride ultracentrifugation [4,21], and used in cDNA synthesis with RNA PCR Kit (Takara, Kyoto) using random primer. For both Cu/Zn-SOD and Mn-SOD, RT-PCR was performed using primers designed by referring to highly conserved regions of cDNA sequences between humans [2, 23] and mice [3,9]. The PCR products were cloned to T-vector (pCR TM II, Invitrogen, San Diego), and these cDNA sequences were determined by the dideoxy chain termination method [22]. Based on the cDNA sequences identified using the RT-PCR products, new PCR primers were designed. The entire cDNA sequences of equine Cu/Zn-SOD and Mn-SOD genes were then determined by 5' RACE and 3' RACE methods [8] using a 5'/3' RACE Kit (Boehringer Mannheim, Tokyo). The expressions of ...