Novel tissue preservative and tissue fixative for comparative pathology and animal research

Aim: To determine whether universal molecular fixative (UMFIX), a novel human tissue fixative, could also be used as an animal tissue fixative for histomorphology and a preservative of RNA at subtropical temperatures. Cat, dog, mouse, pigeon, rabbit and rat tissue, as well as ant, beetle, earthworm and lizard were collected. Tissue was fixed in UMFIX for up to a week at room or ambient temperatures, processed and paraffin embedded. Histomorphology and RNA quality were evaluated and compared to formalin-fixed and fresh frozen tissue. Results: Animal tissue fixed in UMFIX at room temperature or high ambient temperature (30-34 °C) provides similar histomorphology. Comparable to other alcohol-based fixatives, UMFIX produces a histomorphology similar but not identical to formalin. All minor histopathological differences, however, in no way interfere with establishing the correct diagnostic conclusion. Whereas RNA extracted from animal tissue fixed in formalin was completely degraded, tissue fixed up to 1 week in UMFIX at high ambient temperatures rendered completely intact RNA. Conclusions: UMFIX represents a new class of preservative/fixative that protects RNA and provides acceptable histomorphology. Tissue fixation and preservation of RNA can be achieved at high ambient temperatures. This allows collection of animal tissue in field research without the need for immediate freezing of tissue and also provides histomorphology comparable to formalin-fixed tissue. Furthermore, as RNA is also preserved in UMFIX preserved paraffin-embedded tissue, if amount of tissue is limited the same tissue that is used to determine histomorphology can be used to extract RNA.