Old Friends with a New Job

Abstract

The paper by Kobayashi et al. triggered fond memories and curious questions, as one might expect when meeting a couple of old, almost forgotten friends. As a post doc in Larry Zipursky's laboratory, I worked in a team trying to understand how Boss/Sevenless signaling directs the presence of one and only one R7 cell in each ommatidium of the fly eye. Almost 20 years later, an odd sense of ownership contributed to my first knee-jerk reaction to the title of the paper claiming a role for Boss and Sevenless in early male gonads: Those mutants are fertile! How, then, could either Boss or Sevenless be important for the niche in which male germline stem cells reside? But, thinking back, neither boss nor sevenless mutants are blind, and yet they told us a lot about cell fate decisions in the fly visual system. Actually reading the paper, I was drawn into a fascinating story of how, early in the male embryonic gonads, Boss/Sevenless signaling helps in determining the number of somatic niche cells. This decision, much less flexible than one might expect, carries forward into the adult male, where niche size appears to determine the number of germline stem cells. This PaperPick refers to Boss/Sev Signaling from Germline to Soma Restricts Germline-Stem-Cell-Niche Formation in the Anterior Region of Drosophila Male Gonads, by Y. Kitadate, S. Shigenobu, K. Arita, and S. Kobayashi, published in July 2007. Video Abstract Drs. Yu Kitadate and Satoru Kobayashi describe their work, building on the original Developmental Cell paper, showing that primordial germ cells use receptor tyrosine kinase ligands to activate a negative feedback mechanism in the embryonic niche. This feedback positions the niche and restricts its size to ensure the appropriate organization and numbers of germline stem cells in the adult fly.