Insights into platypus crural gland transcriptomics – venom and beyond

The platypus (Ornithorhynchus anatinus) is one of 15 confirmed venomous mammals worldwide, and possesses a unique venom system, termed the crural system. Used for intraspecific competition, their sexually dimorphic and seasonal venom causes pain and functional impairment in envenomated individuals. Despite its unique nature, investigations into the platypus crural system are limited. Utilising the new platypus genome and a suite of transcriptomic data collected over the past 15 years, we investigate key genes, transcripts and proteins of importance to the platypus crural system. We generated a global transcriptome and a crural gland-specific transcriptome for the platypus, utilising the new platypus genome and 45 RNA-Seq samples collated from past studies. From this, we found 177 upregulated and crural gland-specific genes of importance. 13 key crural system proteins have been identified for the first time. 85% of these belong to protein families found in venoms and include kallikreins and secretoglobins key in mammalian venoms. Three kallikreins were identified as well as two additional proteins that may be influencing kallikrein activity in platypus venom. All three secretoglobins belong to an independent cluster of uteroglobin-like proteins and are unique to the platypus. New omics resources have allowed us to uncover new genes, transcripts and proteins of importance to platypus venom and their crural system. This work reinforces the importance of convergent recruitment in the toxin repertoires of venomous mammals through proteins such as kallikreins and secretoglobins. Our findings have enhanced knowledge of the platypus crural system and provided new insights into platypus venom composition.