Evolution of the Yellow/Major Royal Jelly Protein family and the emergence of social behavior in honey bees.

The genomic architecture underlying the evolution of insect social behavior is largely a mystery. Eusociality, defined by overlapping generations, parental brood care, and reproductive division of labor, has most commonly evolved in the Hymenopteran insects, including the honey bee Apis mellifera. In this species, the Major Royal Jelly Protein (MRJP) family is required for all major aspects of eusocial behavior. Here, using data obtained from the A. mellifera genome sequencing project, we demonstrate that the MRJP family is encoded by nine genes arranged in an approximately 60-kb tandem array. Furthermore, the MRJP protein family appears to have evolved from a single progenitor gene that encodes a member of the ancient Yellow protein family. Five genes encoding Yellow-family proteins flank the genomic region containing the genes encoding MRJPs. We describe the molecular evolution of these protein families. We then characterize developmental-stage-specific, sex-specific, and caste-specific expression patterns of the mrjp and yellow genes in the honey bee. We review empirical evidence concerning the functions of Yellow proteins in fruit flies and social ants, in order to shed light on the roles of both Yellow and MRJP proteins in A. mellifera. In total, the available evidence suggests that Yellows and MRJPs are multifunctional proteins with diverse, context-dependent physiological and developmental roles. However, many members of the Yellow/MRJP family act as facilitators of reproductive maturation. Finally, it appears that MRJP protein subfamily evolution from the Yellow protein family may have coincided with the evolution of honey bee eusociality.

A cis-regulatory sequence within the yellow locus of Drosophila melanogaster required for normal male mating success.

Drosophila melanogaster males perform a courtship ritual consisting of a series of dependent fixed-action patterns. The yellow (y) gene is required for normal male courtship behavior and subsequent mating success. To better characterize the requirement for y in the manifestation of innate male sexual behavior, we measured the male mating success (MMS) of 12 hypomorphic y mutants and matched-outbred-background controls using a y+ rescue element on a freely segregating minichromosome. We found that 4 hypomorphs significantly reduced MMS to varying degrees. Reduced MMS was largely independent of adult pigmentation patterns. These mutations defined a 300-bp regulatory region upstream of the transcription start, the mating-success regulatory sequence (MRS), whose function is required for normal MMS. Visualization of gene action via GFP and a Yellow antibody suggests that the MRS directs y transcription in a small number of cells in the third instar CNS, the developmental stage previously implicated in the role of y with regard to male courtship behavior. The presence of Yellow protein in these cells positively correlates with MMS in a subset of mutants. The MRS contains a regulatory sequence controlling larval pigmentation and a 35-bp sequence that is highly conserved within the genus Drosophila and is predicted to bind known transcription factors.

A novel hypothesis on the biochemical role of the Drosophila Yellow protein.

In Drosophila melanogaster, the protein product of the yellow gene is necessary for normal pigmentation and male sexual behavior. Although one of the best characterized loci from a genetic standpoint, the function of the Yellow protein in the development of either phenotype is unknown. Here I propose that Yellow acts as a growth factor- or hormone-like molecule in the development of pigmentation and sexual behavior, and discuss the consistency of this theory with experimental observations in flies and humans.

A gene necessary for normal male courtship, yellow, acts downstream of fruitless in the Drosophila melanogaster larval brain.

The fruitless (fru) gene is a member of the Drosophila melanogaster somatic sex determination genetic pathway. Although it has been hypothesized that the primary function of fru is to regulate a genetic hierarchy specifying development of adult male courtship behavior, genes acting downstream of fru have not yet been identified. Here we demonstrate that the yellow (y) gene is genetically downstream of fru in the 3(rd)-instar larval brain. Yellow protein is present at elevated levels in neuroblasts, which also show expression of male-specific FRU proteins, compared to control neuroblasts without FRU. A location for y downstream of fru in a genetic pathway was experimentally demonstrated by analysis of fru mutants lacking transcription of zinc-finger DNA binding domains, and of animals with temporal, spatial, or sexual mis-expression of male-specific FRU. A subset of fru and y mutants is known to reduce levels of a specific behavioral component of the male courtship ritual, wing extension, and FRU and Yellow were detected in the general region of the brain whose maleness is necessary for development of that behavior. We therefore hypothesized that ectopic expression of Yellow in the 3(rd)-instar brain, in a y null background, would rescue low levels of wing extension and male competitive mating success, and this was found to be the case. Overall, these data suggest that y is a downstream member of the fru branch of the D. melanogaster sex determination hierarchy, where it plays a currently unknown role in the development of adult male wing extension during courtship.

Immunohistochemical colocalization of Yellow and male-specific Fruitless in Drosophila melanogaster neuroblasts.

The Drosophila melanogaster fruitless gene encodes multiple male-specific transcription factors that are hypothesized to regulate a hierarchy of genes responsible for the development of male courtship behavior. Here we show that there are dramatically increased levels of the protein product of the male courtship behavior gene yellow associated with male-specific Fruitless protein in a subset of neuroblasts in third-instar larval male brains. We hypothesize that yellow is downstream of fruitless in a male courtship behavior developmental genetic pathway.