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Establishing Prokaryotic Expression System of Angiotensin- Converting Enzyme 2 (ACE2) gene in pigs Abstract In this paper, ACE2 gene of pigs was cloned and the purified protein was obtained via 12 the prokaryotic expression system. Polyclonal antibody of high titer and sensitivity 13 was obtained using Wastar rats immunization method and is then used to determine of 14 the expression of ACE2 using immunohistochemistry. The sequence of ACE2 in pigs 15 covered 2418 nucleotides and coded 805 amino acid (aa) residues. Sequence 16 homology analysis showed that the ACE2 sequence in pigs is highly conserved 17 among species at the nucleotide and amino acid levels. Genetic evolution analysis 18 revealed that ACE2 gene in pigs has the shortest genetic distance with that in goats 19 while residing in a totally different branch from that in zebra fishes. Analysis of 20 protein structure predicted that ACE2 protein is a transmembrane secreted protein 21 with high hydrophilicity, containing a signal peptide sequences locating between 1aa 22 to 17aa. The ACE2 fusion protein expressed (under the induction with 1.0 mmol/L 23 IPTG for 10 h) was of approximately 100 kDa and mainly existed in inclusion body. Wastar rats immunization showed that the titer of the anti-ACE2 antiserum in rats was The renin-angiotensin system (RAS) is an importance regulator of 34 cardiovascular and renal function, both under physiological and pathological 35 conditions (Tipnis et al., 2000) . Angiotensin converting enzyme 2 (ACE2) was 36 discovered as a new member of the RAS system in 2000. Earlier studies showed that 37 ACE2 in rats or humans was highly expressed in the kidney, heart and testicle tissues, 38 and was later confirmed existence in the lungs, brain, and the intestines and other The ACE2 genes in human, rat and mouse have been located on the X chromosome. So far, the research on ACE2 has been focused on rodents and human beings. 53 The research gaps in other animals, especially production animals, such as cattle, 54 sheep, pigs still need to be filled. Particularly, GenBank still lacks the information of The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint 61 polyclonal antibody was obtained and the expression distribution of ACE2 was 62 determined. We hope to be able to provide the whole sequence of ACE2 gene and other 63 related information for Genbank. 75 The Healthy newborn piglets were terminally anesthetized via an intraperitoneal 76 (ip.) injection of 20% urethane (5 mL/kg body weight), were decapitated within 15 77 min after anesthesia took effect (i.e. animals lost conciseness and whole body muscle 78 relaxation was observed), and all tissues including heart, liver, hung, kindey, stomach 79 and soon were collected and frozen immediately in liquid nitrogen and then stored at 80 -80°C , Part of tissues were fixed immediately with 4% buffered paraformaldehyde 81 for 24 hours, then transferred to 20% sucrose solution for 3 h. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint Freund's adjuvant. Serum was collected from heart method and stored at −80 o C. 152 The protein of heart, spleen, kidney, liver, duodenum, liver of pig, and also liver 153 and kidney tissue of chicken were extracted from Roe. The protein concentration of 154 each tissue was measured by BCA kit(Beyotime Biotechnology, China). The IPEC-J2 cells were cultured in 6 orifice plates with cell crawling slices. After being placed in 37°C and 5%CO 2 incubators to 70% of fusion degree, After 177 washing with PBS for 2 times, then 4% polyformaldehyde was used to fix 15 min, between 82.0%~90.0%, and the lowest homology with zebrafish was less than 50%. reached over 80%, and the lowest homology with zebrafish was 46.8% (Fig. 2-A) . From the tree of genetic evolution (Figure 52-B) , the fragment is in the same 237 evolutionary group with the ACE2 amino acid sequence of goats and cattle, and the 238 zebrafish is in a completely different 2 branch, and the genetic evolution is consistent . CC-BY 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint 239 with the evolution of amino acid. proteins, such as people and sheep, were the same. Among them, part 1~739aa is the 245 extracellular part, and there is a transmembrane helix between 740~762 aa, and the 246 763~805 AA is the intracellular part (Fig. 3-A) . The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint pET-32a-ACE2 recombinant plasmid was successfully constructed. Results as shown in Figure 7 , the serum dilution ratio of the positive serum OD 450 was 288 about 1, and the P/N value (P: the mean OD 450 value of the positive hole, the mean 289 value of the negative pore, OD 450 ) was the best serum dilution degree, that was 3200. The rat anti ACE2 serum was prepared with the best multiple dilution as a single 292 antibody, and the Sheep anti rat IgG-HRP was used as a two antibody. The purified 293 fusion protein, pig heart, spleen, kidney, liver, duodenum, sheep liver, rat liver, rat 294 liver and chicken liver and kidney tissue protein were analyzed by Western blot. The 295 results showed the fusion protein and pig heart. There was a specific binding protein 296 in the size of 100 kDa in the viscera, spleen, kidney, liver and duodenum (Fig. 8) , and 297 the rest did not appear. The results show that the ACE2 polyclonal antibody can 298 identify the fusion protein and the ACE2 protein in the pig tissues, but the ACE2 . CC-BY 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint 299 protein in other species can not be combined, that is, the ACE2 polyclonal antibody 300 against the pig's mouse has good immune response and specificity. 301 3.11 Anti ACE2 serum specificity in mice by immunofluorescent 302 The mouse anti ACE2 serum was diluted by multiple 1:600 as one antibody, the 303 fluorescent enzyme labeled Sheep anti mouse IgG-HRP was two resistance, and the 304 final concentration was 100 ng/mL DAPI for 5 minutes. The immunofluorescence 305 analysis of the pig intestinal epithelial cells, as shown in Figure 9 , that the mouse anti 306 ACE2 could specifically identify the ACE on the membrane of the pig small intestinal 307 epithelial cells. The 2 protein, that is, the polyclonal antibody of pig anti mouse ACE2 308 prepared, has better immunoreactivity. 310 As shown in Figure 10 , the proteins extracted from pig spleen, kidney, liver, lung, 311 pancreas, lymph node, stomach, duodenum, jejunum, ileum, colon, rectum and cecum 312 were analyzed by Western blotting, and the rat anti porcine polyclonal antibody was 313 diluted with 1: 3200 as one resistance, and the IgG of sheep resistant to HRP was two. Resistance, the results showed that the tissue protein extracted from pig kidney, 315 jejunum and rectum had obvious bands at 92 kDa, and the highest content in kidney, 316 but not in other tissues. Under the same condition, the Sheep anti rabbit polyclonal 317 antibody was diluted with 1:1000 multiple as a single antibody, and the HRP labeled 318 Goat anti rabbit IgG was two. The results showed that the tissue protein extracted 319 from pig spleen, kidney, lung, pancreas, lymph node, stomach, duodenum, jejunum, 320 ileum, colon, rectum, and cecum was marked at 92 kDa. The results showed that the 321 sensitivity of mouse against polyclonal antibody was poor. The cellular localization of ACE2 in porcine tissues was analyzed after dilution 325 of 1:600 prepared by anti ACE2 serum. The criterion is that if Brown is positive, the 326 result is shown in Fig. 11 . As can be seen from figure 3-21, ACE2 protein exists in 327 various tissues and organs of the pig, mainly expressed in the mucosa of the gastric 328 fundus (Fig. 11-A) , the myometrium of the small intestine, serous layer, and villi In this study, the pig ACE2 gene was cloned, analyzed and prokaryotic expressed 362 successfully, and the polyclonal antibody of mouse ACE2 was prepared. The whole 363 gene sequence of ACE2 in pig was 2418 bp and 805 amino acids were encoded. Homology analysis on GenBank found that the cloned ACE2 gene were above 99% 365 similar to other porcine ACE2 genes, which shows that the pig ACE2 gene cloning 366 was successful. The full-length gene sequence of pig ACE2 gene was provided to 367 GenBank database., It is deduced that the pig ACE2 protein belongs to the type I 368 secretory transmembrane protein and its signal peptide sequence is located between 369 1~17 AA, which is similar to that of goats (1~18 AA) (Yang et al,. 2016 ). In conclusion, In this paper, the basic information of porcine ACE2 protein was 371 provided and the specific anti-porcine polyclonal antibody was successfully, which The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint 471 tissue protein of chicken. Figure 9 . Immunofluorescence analysis of specificity of polyclonal antibody. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.03.12.988634 doi: bioRxiv preprint