The number of Follicle Stem Cells in a Drosophila ovariole

Abstract

SummaryA paper by Reilein et al (2017) presented several fundamental new insights into the behavior of adult Follicle Stem Cells (FSCs) in the Drosophila ovary, including evidence that each ovariole hosts a large number of FSCs (14-16) maintained by population asymmetry (Reilein et al., 2017), rather than just two FSCs, dividing with largely individually asymmetric outcomes, as originally proposed (Margolis and Spradling, 1995; Nystul and Spradling, 2007). Fadiga and Nystul (2019) contest some of these conclusions on the basis of their repetition of a multicolor lineage strategy used by Reilein et al (2017) and repetition of earlier single-color lineage analysis. Here we outline a number of shortcomings in the execution and interpretation of those experiments that, in our opinion, undermine their conclusions. The central issue of general relevance concerns the importance of comprehensively analyzing all stem cell lineages, independent of any pre-conceptions, in order to identify all constituents and capture heterogeneous behaviors.

Determination of expression profiles for Drosophila ovarian Follicle Stem Cells (FSCs) using single-cell RNA sequencing

“…The assignment of a group of scRNA expression profiles to FSCs is not precise for a number of reasons, including imperfect and limited depth of RNA profiles, latitude in spatial correspondence according to RNA in situs , and the systematic limitation that FSCs become ECs or FCs within a few hours and therefore inevitably have strong similarities to those neighboring derivatives. Nevertheless, the results of this study have the unique virtue that the approximately-defined FSC group of cells is in accord with current understanding of FSC numbers and locations determined by thorough functional analyses (2, 9, 13, 17, 58-60). FSC behavior is guided by a number of external signals but with prominent roles for two graded signaling pathways, Wnt and JAK-STAT (13, 17).…”