BACKGROUND: In the honeybee Apis mellifera, female larvae destined to become a 
queen are fed with royal jelly, a secretion of the hypopharyngeal glands of 
young nurse bees that rear the brood. The protein moiety of royal jelly 
comprises mostly major royal jelly proteins (MRJPs) of which the coding genes 
(mrjp1-9) have been identified on chromosome 11 in the honeybee's genome.
RESULTS: We determined the expression of mrjp1-9 among the honeybee worker caste 
(nurses, foragers) and the sexuals (queens (unmated, mated) and drones) in 
various body parts (head, thorax, abdomen). Specific mrjp expression was not 
only found in brood rearing nurse bees, but also in foragers and the sexuals.
CONCLUSIONS: The expression of mrjp1 to 7 is characteristic for the heads of 
worker bees, with an elevated expression of mrjp1-4 and 7 in nurse bees compared 
to foragers. Mrjp5 and 6 were higher in foragers compared to nurses suggesting 
functions in addition to those of brood food proteins. Furthermore, the 
expression of mrjp9 was high in the heads, thoraces and abdomen of almost all 
female bees, suggesting a function irrespective of body section. This completely 
different expression profile suggests mrjp9 to code for the most ancestral major 
royal jelly protein of the honeybee.