Dolphins and terrestrial mammals: similarities in milk

Breast milk is not merely a source of nourishment, but a complex biological fluid that contains molecules involved in the regulation of various cellular and physiological processes. These include microRNAs (miRNAs), small RNAs capable of regulating gene activity, already widely studied in human milk and in the milk of several domestic species, but until now never characterised in the milk of marine mammals.

A new study carried out by researchers from the Department of Agronomy, Food, Natural Resources, Animals and Environment and the Department of Biology of the University of Padua, published in the journal PLOS One, analysed for the first time the miRNAs present in the milk of the bottlenose dolphin (Tursiops truncatus), combining bioinformatic genome analyses and microRNA sequencing.

The results show that, despite the profound evolutionary adaptations of cetaceans to aquatic life, the milk of the bottlenose dolphin contains some of the main miRNA families already identified in the milk of other mammals. Among the most abundant are miR-148 and let-7, also detected in human milk and in donkey, goat, sheep and bovine milk.

The study was carried out on an aggregated sample obtained from 76 milk collections gathered from two females at different stages of lactation, as part of the routine veterinary and welfare monitoring activities conducted by the ASL and the Istituto Zooprofilattico Sperimentale del Lazio e della Toscana.

“This study arose from the idea of extending to marine mammals a line of research that we had already developed by studying the milk of several terrestrial species,” explains Filippo Cendron, first author of the study and researcher at the Department of Agronomy, Food, Natural Resources, Animals and Environment of the University of Padua. “The main value of the work lies in having opened up a new line of research and created a knowledge base that can be expanded to better understand the biology of lactation in cetaceans and its evolution in mammals.”

The presence in the dolphin of the same miRNA families typical of terrestrial mammals therefore represents a finding of particular evolutionary interest, suggesting the conservation of important regulatory components of milk despite the profound transformations undergone by cetaceans.

“The collaboration between veterinarians and researchers has made it possible to achieve an important result: the first characterisation of these RNAs in the milk of a marine mammal. There are still many aspects to be explored, including the possibility that the observed similarities also correspond to conserved biological functions. This study opens up new research perspectives and lays the groundwork for further investigations,” concludes Umberto Rosani, corresponding author and researcher at the Department of Biology of the University of Padua.