Expression patterns of platypus defensin and related venom genes across a range of tissue types reveal the possibility of broader functions for OvDLPs than previously suspected Camilla M. Whittington a , Anthony T. Papenfuss b , Philip W. Kuchel c , Katherine Belov a, * a Faculty of Veterinary Science, RMC Gunn B19, University of Sydney, NSW 2006, Australia b Bioinformatics Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC 3050, Australia c School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia article info Article history: Received 21 May 2008 Received in revised form 28 June 2008 Accepted 1 July 2008 Available online 9 July 2008 Keywords: Platypus venom Ornithorhynchus anatinus Defensin-like peptides OvDLP Defensins abstract The platypus, as an egg-laying mammal, displays an unusual mixture of reptilian and mammalian characteristics. It is also venomous, and further investigations into its little- studied venom may lead to the development of novel pharmaceuticals and drug targets and provide insights into the origins of mammalian venom. Here we investigate the expression patterns of antimicrobial genes called defensins, and also the venom peptides called defensin-like peptides (OvDLPs). We show, in the first expression study on any platypus venom gene, that the OvDLPs are expressed in a greater range of tissues than would be expected for genes with specific venom function, and thus that they may have a wider role than previously suspected. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Since its discovery in 1798, the platypus (Ornithorhyn- chus anatinus) has remained an enigma. At first, it was thought to be the trick of a taxidermist, and even once it was proven to be real, early taxonomists had difficulty clas- sifying the animal because of its unusual mixture of reptilian and mammalian characteristics. It has fur, but its skeleton has several reptilian features (Grant, 1995). It possesses (in its bill) a complex system of electro- and mechano-receptors, found only in monotremes, fish and amphibians, which allow it to locate its prey underwater (Pettigrew, 1999). It regulates its body temperature, but at a much lower level (32  C) than other mammals (Grant, 1995), and not only does it lay eggs and suckle young from milk patches rather than nipples, but it is also venomous (Grant, 1995). The unique characteristics of this mammal make it an intriguing resource for genomic studies, and the recent publication of the platypus genome sequence (Warren et al., 2008) affords an unprecedented opportunity to do this. Adult male platypuses possess keratinous spurs on each hind leg, each of which is connected by a duct to a venom gland on the dorsal surface of the thigh (Grant, 1995). This system is known as the crural system. The spurs can be held erect for envenomation, when the animal drives its spurs into the victim, injecting 0.2– 4 mL of venom (Temple-Smith, 1973). Spurs are not retained in female platypuses, and it is thought that the platypus has no native predators, making it likely that the crural system is used for intraspecific aggression during the breeding season rather than for defence * Corresponding author. Tel.: þ61 2 9351 3454; fax: þ61 2 9351 3957. E-mail address: kbelov@vetsci.usyd.edu.au (K. Belov). Contents lists available at ScienceDirect Toxicon journal homepage: www.elsevier.com/locate/toxicon 0041-0101/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.toxicon.2008.07.002 Toxicon 52 (2008) 559–565