Stem cell chicken and egg debate moves to unlikely arena: ...( LA JOLLA CA Logic says it has to be...)

LA JOLLA, CA Logic says it has to be the niche. As air and water preceded life, so the niche, that hospitable environment that shelters adult stem cells in many tissues and provides factors necessary to keep them young and vital, must have emerged before its stem cell dependents.

A team of scientists at the Salk Institute for Biological Studies led by Leanne Jones, Ph.D., assistant professor in the Laboratory of Genetics, now suggests that this is not always the case. They report in the July 20 advance online edition of the journal Nature that the cells that comprise a specialized niche in the testis of fruit flies actually emerge from adult stem cells, a finding with implications for regenerative medicine, aging research, and cancer therapeutics.

Previously, investigators thought that a fruit fly's allotment of testis niche cells was handed out at birth and meant to last a lifetime. "What this paper demonstrates is that once a fly becomes an adult, some stem cells that function in spermatogenesis start making the very cells that support them," said Jones. "Once a fly develops into an adult, some of these niche cells can be replaced."

Using microscopy and fluorescent markers enabling them to image specific cell types over time, Jones' group, led by first author Justin Voog, actually caught a testis stem cell population in the act of turning into their own niche, known in the fly testis as the hub.

"We used a detailed lineage tracing strategy to differentiate between single somatic stem cells (SSCs) and hub cells," said Voog, an M.D./Ph.D. student in Jones' lab. The hub contains approximately 10 cells that secrete factors promoting self-renewal of two neighboring stem cell populations germline stem cells, which become sperm, and SSCs, which develop into a structure that encapsulates maturing sperm. "We tracked cells over a period of days and saw that SSCs can generate not only other immature SSCs but their nic
'/>"/>