Whole body distribution of the regulatory peptide 26RFa in male and female mice.

26RFa is a regulatory peptide initially isolated from the brain. 26RFa was found to be involved in the regulation of vital functions such as the regulation of energy and glucose metabolism. However, the whole distribution of 26RFa in the organs/tissues of the organism remains fragmentary although it represents a crucial step to discover novel physiological functions for this regulatory peptide. To this aim, we have generated a mouse line that expresses the fluorescent protein tdTomato in 26RFa-expressing cells, and visualization of tdTomato immunostaining in toto was performed using the tridimensional imaging approach. Our observations reveal that 26RFa is largely distributed among the organism of male and female mice. 26RFa-expressing cells were notably found in numerous regions of the central nervous system including the olfactory bulbs, the cortex, the hippocampus, the hypothalamus, the cerebellum, the brainstem and the spinal cord. At the periphery, 26RFa-expressing structures were detected all along the gastrointestinal tract, in the liver, the white adipose tissue, the kidney, the adrenal gland, the lungs, the male and female reproductive tracts, the striated muscles, the thymus and a number of exocrine glands such as the salivary glands, the prostate, the seminal vesicles. In conclusion, the present anatomical observations are in agreement with the main physiological functions previously reported for 26RFa such the regulation of energy and glucose metabolism or the control of the hypothalamo-pituitary-gonadal or adrenal axis. However, 26RFa is present in other organs/tissues in which its physiological relevance is totally unknown opening therefore a new field of research for this regulatory peptide.