RNA-seq and Ribosome immunoprecipitation results from purified Drosophila male secondary cells

Even in well-characterized genomes, many transcripts are considered non-coding RNAs (ncRNAs) simply due to the absence of large Open Reading Frames (ORFs). However, it is now becoming clear that many small ORFs (smORFs) produce peptides with important biological functions. In the process of characterizing the ribosome-bound transcriptome of an important cell type of the seminal fluid producing accessory gland of Drosophila melanogaster, we detected an RNA, previously thought to be non-coding called, male specific abdominal (msa). Notably, msa is nested in the HOX gene cluster of the Bithorax complex and is known to contain a micro RNA within one of its introns. We find that this RNA encodes a novel “micropeptide“ (9 or 20 amino acids, MSAmiP) that is expressed exclusively in the secondary cells of the male accessory gland, where it seems to accumulate in nuclei. Importantly, loss of function of this micropeptide causes defects in sperm competition. In addition to bringing new insights into the biology of a rare cell type, this work underlines the importance of small peptides, a class of proteins now emerging as important actors in complex biological processes.