In captivity but not in the wild, black and Sumatran rhinos are susceptible to iron overload disorder while white and Indian rhinos are resistant.3,6 The difference in susceptibility aligns with wild forage diets, either browser or grazer, and may reflect evolutionary adaption to the low iron browser diet in the wild.4 Iron overload likely contributes to increased morbidity and premature death of affected rhinos in captivity. To date, one black rhino single nucleotide polymorphism (SNP), HFE S88T has been reported, the functional consequences of which remains undetermined.1 Our goal is to identify the iron regulatory differences underlying the observed species difference in susceptibility to iron overload.
The sequences of African white and black liver and spleen mRNAs were assembled using Trinity RNA-Seq software.2 The SIFT computer algorithm was used to compare rhino with human sequences and identify possible disease-causing mutations.5 Candidate SNPs were independently validated by genomic sequencing in four rhino species. Candidate mutations that may be associated with primary iron disorders or hemolytic anemias known to occur in black rhinos were identified in the following genes:
SLC28a2: Adenosine transporter may contribute to low erythrocyte ATP levels.
STEAP4: Metalloreductase—may contribute to metal homeostasis by reducing vacuolar iron and copper, thereby allowing their transfer across vacuolar membranes.
EPB41: Mutations are associated with hereditary hemolytic anemia.
The functional consequences of these candidate mutations are being determined.
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2. Grabherr, M.G., B.J. Haas, M. Yassour, J.Z. Levin, D.A. Thompson, I. Amit, X. Adiconis, L. Fan, R. Raychowdhury, Q. Zeng, Z. Chen, E. Mauceli, N. Hacohen, A. Gnirke, N. Rhind, F. di Palma, B.W. Birren, C. Nusbaum, K. Lindblad-Toh, N. Friedman, and A. Regev. 2011. Full-length transcriptome assembly from RNA-Seq data without a reference genome. Nat. Biotechnol. 29:644–652.
3. Paglia, D.E. and P. Dennis. 1999. Role of chronic iron overload in multiple disorders of captive Black rhinoceroses (Diceros bicornis). Proc. Am. Assoc. Zoo Vt. Annu. Meet. 163–171.
4. Paglia, D.E. and R.W. Radcliffe. 2000. Anthracycline cardiotoxicity in a black rhinoceros (Diceros bicornis): Evidence for impaired antioxidant capacity compounded by iron overload. Vet. Pathol. 37:86–88.
5. Prateek, K., S. Henikoff, and P.C. Ng. 2009. Predicting the effects of coding non-synonymous variants on protein function using the SIFT algorithm. Nat. Protoc. 4:107–31082.
6. Smith, J. E., P.S. Chavey and R.E. Miller. 1995. Iron metabolism in captive black (Diceros bicornis) and white Ceratotherium simum) rhinoceroses. J. Zoo Wildl. Med. 26:525–531.