Mating-Induced Increase in Germline Stem Cells via the Neuroendocrine System in Female Drosophila
Authors: Ryusuke Niwa
Tomotsune Ameku
Journal: PLoS genetics (2016)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Mating; Gametogenesis; Germline stem cell; Drosophila melanogaster; Sex Peptide
Affiliations: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan., Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan., PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan.

Abstract:  Mating and gametogenesis are two essential components of animal reproduction. Gametogenesis must be modulated by the need for gametes, yet little is known of how mating, a process that utilizes gametes, may modulate the process of gametogenesis. Here, we report that mating stimulates female germline stem cell (GSC) proliferation in Drosophila melanogaster. Mating-induced increase in GSC number is not simply owing to the indirect effect of emission of stored eggs, but rather is stimulated by a male-derived Sex Peptide (SP) and its receptor SPR, the components of a canonical neuronal pathway that induces a post-mating behavioral switch in females. We show that ecdysteroid, the major insect steroid hormone, regulates mating-induced GSC proliferation independently of insulin signaling. Ovarian ecdysteroid level increases after mating and transmits its signal directly through the ecdysone receptor expressed in the ovarian niche to increase the number of GSCs. Impairment of ovarian ecdysteroid biosynthesis disrupts mating-induced increase in GSCs as well as egg production. Importantly, feeding of ecdysteroid rescues the decrease in GSC number caused by impairment of neuronal SP signaling. Our study illustrates how female GSC activity is coordinately regulated by the neuroendocrine system to sustain reproductive success in response to mating. 

Retracted: No

PubPeer comments:
 Malpe et al., 2020 was not capable of reproducing that female flies increase their GSC numbers and mitotic activity upon mating. Reference: https: www.biorxiv.org content 10.1101 2020.05.15.098509v1 , 
 #1 We did realize the bioRxiv preprint by Malpe and Shultz as well. Right now I and our co-authors do not have any ideas why Malpe and Shultz cannot detect the increase in GSC numbers in mated females. By our hands, the phenomenon is of course reproducible using many independent strains by multiple members in our lab. Moreover, after Ameku and Niwa (2016), we have published further data about molecular mechanisms regulating the mating-induced increase in GSCs, such as Ameku at al. PLOS Biology (2018) and in Yoshinari et al. bioRxiv (2020). Malpe and Shultz mentioned in Discussion that the discrepancy  could be due to fluctuations in the quality of the molecular tools, specifically the antibodies, or differences in human analysis and interpretation of the results. In addition, or alternatively, one factor influencing the different outcomes may be the number of germaria analyzed. To spread our results over as many females as possible, we analyzed a limited number of germaria per ovary, while it appears that Ameku and Niwa (2016) analyzed every germarium from only a few ovaries. Finally, it is possible that our fly strains behave differently due to intrinsic parameters, or that air pressure or other environmental factors in the different countries have impacted the results.u201d We also think that any of these factors may influence the results. In near future, we should further investigate which (uncharacterized, maybe environmental?) factors are important for mating-induced GSC increase. Best regards, Ryusuke Niwa , 
 #2 Both groups reported solid and interesting research, and this is a really important discussion topic for the Drosophila community. The results of the two studies showed phenotypic differences that likely resulted from differences in the genetic backgrounds of fly lines used by the two groups. These papers provide a great example of how differences between the genetic backgrounds of different labs fly strains need to be considered in comparing across studies. Ameku and Niwa (2016) reported that the genetic background of their control line as a yw mutant strain - I m not sure if the transgenic lines used in your work were backcrossed into the genetic background of this control line? In contrast, Malpe and Schulz (2020) reported using a w1118 mutant strain, OR, CS, and w1 mutant strain; the y locus was wild type, y+. All 4 lines were repeatedly isogenized. Mutation in y alters larval feeding-related behaviour; this will affect developmental progression and trajectory as compared to y+ wild type larvae. The Niwa group s previous work has clearly demonstrated the impact of feeding environment on ecdysteroid physiology and development, and showed in this article that ecdysteroids affect GSC proliferation. The w locus alters cGMP uptake (as noted by Malpe and Schulz); mutation in w prevents cellular cGMP uptake (Evans et al., 2008. doi: 10.1242 jeb.014837). Reduced cGMP uptake will alter the activity of cGMP-dependent protein kinase (PKG). PKG is a not-quite-but-nearly ubiquitous enzyme that is found in many parts of the larval and adult body, including the ovaries (Allen and Sokolowski, 2021. DOI: 10.1080 01677063.2021.1941946). Loss of w function in the ovaries could affect GSC function, and different w mutant alleles have different degrees of reduced function. A very important point to take from these articles is that differences in genetic background can significantly alter phenotype, and this is essential to remember when comparing across studies. This subject was well addressed by Ryusuke Niwa in his response (above) and by Malpe and Schulz in their discussion. ,