Biology subjects

Reilein, A.

Publications and source records attributed to Reilein, A..

7 recordsLinked to original sources

bioRxiv2025

Regulation of somatic stem cell and niche precursor fates and proliferation of by Wnt, JAK-STAT, Hedgehog and Hippo/Yorkie pathways during Drosophila pupal ovary development resembles the signaling framework organizing adult stem cell behavior.

Follicle Stem Cells (FSCs) in the Drosophila melanogaster ovary are maintained through independent regulation of division and differentiation to become proliferative Follicle Cells (FCs) to their posterior or quiescent Escort Cells (ECs) to their anterior. These behaviors are guided by graded extracellular Hedgehog (Hh) and Wnt signals emanating from cells anterior to FSCs and an inverse gradient of JAK-STAT pathway activity. Here, we used lineage analyses to investigate the development of ECs, FSCs and FCs from a common set of precursors during pupation. Previous studies found that the most anterior precursors divide slowest, with quiescence spreading from the anterior over time to include all ECs, that FSCs are specified simply by their location at eclosion, and that the first FCs derive from cells that accumulate posterior to the developing germline over the first 48h of pupation. We now provide evidence that those accumulating cells derive from migration out of the developing germarium. We found that Wnt pathway activity favored conversion of precursors to more anterior adult derivatives (ECs rather than FCs), while JAK-STAT pathway activity favored posterior outcomes. Posterior bias and faster division, explored by altering Cyclin E activity, both favored a precursor becoming an FSC. Both JAK-STAT and Hh signaling could increase precursor division rate. All of these characteristics resemble regulation of adult FSC behavior. We suggest that similar signaling networks and division rate dependence during maintenance and development may be general features for stem cells that are specified in parallel with tissue development and that exhibit division-independent differentiation. Article SummaryDrosophila ovarian Follicle Stem Cell (FSC) behavior and regulation by graded Hedgehog (Hh), Wnt and JAK-STAT signals is well understood, motivating us to study mechanisms guiding development of FSCs and the neighboring cell types they maintain. The marked progeny of single cells labeled at pupariation were compared in adults for lineages with genetic alterations affecting signal transduction. Wnt and JAK-STAT had strong opposing influences on the anterior-posterior location, and hence identity of derivatives, while JAK-STAT and Hh (via Yorkie) stimulated cell division. Conversion of precursors to FSCs was favored by higher division rates.

developmental biology↗

bioRxiv2022

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

Drosophila ovarian Follicle Stem Cells (FSC) present an excellent paradigm for understanding how a community of active stem cells maintained by population asymmetry is regulated. Here we describe single-cell RNA sequencing studies of a pre-sorted population of cells that include FSCs and the neighboring cell types, Escort Cells (ECs) and Follicle Cells (FCs), which they support. Cell-type assignment relies on anterior-posterior (AP) location within the germarium. We clarify the previously determined location of FSCs and use spatially targeted lineage studies as further confirmation. The scRNA profiles among four clusters are consistent with an AP progression from anterior ECs through posterior ECs and then FSCs, to early FCs. Several genes with graded profiles from ECs to FCs are highlighted as candidate effectors of the inverse gradients of the two principal signaling pathways, Wnt and JAK-STAT, that guide FSC differentiation and division.

developmental biology↗

bioRxiv2022

Spatial regulation of Drosophila ovarian Follicle Stem Cell division rates and cell cycle transitions

Drosophila ovarian Follicle Stem Cells (FSCs) present a favorable paradigm for understanding how stem cell division and differentiation are balanced in communities where they can be regulated independently. Many key extracellular signals for FSCs have been identified, including inversely graded Wnt and JAK-STAT pathway activators. FSCs also exhibit interesting functional spatial heterogeneity; posterior FSCs become proliferative Follicle Cells, while anterior FSCs become quiescent Escort Cells at a much lower rate. Here, by using live imaging and FUCCI cell-cycle reporters, we measured absolute division rates and found that posterior FSCs cycle 3-4 times faster than their anterior neighbors, matching their increased differentiation rate. We also found evidence for FSC G2/M cycling restrictions and G1/S restriction that increases more anteriorly, especially beyond the FSC domain. JAK-STAT signaling promotes both transitions but graded JAK-STAT signaling alone does not explain the graded cycling of FSCs. Genetic interaction tests and FUCCI reporter assays suggest that JAK-STAT signaling acts partly through Yorkie and can largely substitute for stimulation of division by Hh signaling. PI3 kinase signaling, in contrast to Hh signaling, acts largely independently of Yorkie induction and stimulates the G2/M transition.

developmental biology↗

bioRxiv2021

The number of Follicle Stem Cells in a Drosophila ovariole.

A 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.

developmental biology↗

bioRxiv2020

Follicle Stem Cells (FSCs) in the Drosophila ovary; a critique of published studies defining the number, location and behavior of FSCs

SummaryA paper by Reilein et al., (2017) presented several key new insights into the behavior of adult Follicle Stem Cells (FSCs) in the Drosophila ovary, including overwhelming evidence that each ovariole hosts a large number of FSCs (about 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). Here we provide further discussion asserting the merits of the conclusions of Reilein et al., (2017) and the deficiencies in the contrary assertions recently presented by Fadiga and Nystul (Fadiga and Nystul, 2019). The principles that we discuss here, particularly with regard to lineage tracing and population asymmetry, are common to the investigation of most types of adult stem cell and should therefore be instructive and of interest to investigators studying any type of adult stem cell. The improved understanding of FSC numbers, location and behavior afforded by Reilein et al., (2017) and Reilein et al., (2018) can only provide a firm foundation for future progress once they are widely appreciated and seen to be resistant to challenge, as described in detail here.Competing Interest StatementThe authors have declared no competing interest.View Full Text

developmental biology↗

bioRxiv2020

Gradual segregation of Adult Stem Cells and Niche cells during development from common precursors under the guidance of graded extracellular signals

Adult stem cell function relies on the prior development of appropriate numbers and spatial organization of stem cells and supportive niche cells. Drosophila Follicle Stem Cells (FSCs) present a favorable paradigm for understanding those developmental processes. About sixteen FSCs in an adult germarium produce transit-amplifying Follicle Cells (FCs) from their posterior face and quiescent Escort Cells (ECs) to their anterior. Both ECs and FCs also act as niche cells. Here we show that adult ECs, FSCs and FCs derive from common precursors intermingled with germline cells during pupal development, with progeny of a single precursor commonly including ECs and FSCs, FSCs and FCs, or all three adult cell types. Precursors posterior to germline cells become the first FCs and engulf a largely naked germline cyst projected out of the germarium to form the first egg chamber and set up a key posterior signaling center for regulating adult FSC behavior.

developmental biology↗

bioRxiv2017

Division-independent differentiation mandates proliferative competition among stem cells

Cancer-initiating gatekeeper mutations that arise in stem cells would be especially potent if they stabilize and expand an affected stem lineage (1, 2). It is therefore important to understand how different stem cell organization strategies promote or prevent variant stem cell amplification in response to different types of mutation, including those that activate stem cell proliferation. Stem cell numbers can be maintained constant while producing differentiated products through individually asymmetric division outcomes or by population asymmetry strategies, in which individual stem cell lineages necessarily compete for niche space. We considered alternative mechanisms underlying population asymmetry and used quantitative modeling to predict starkly different consequences of altering proliferation rate: a variant, faster-proliferating mutant stem cell should compete better only when stem cell division and differentiation are independent processes. For most types of stem cell it has not been possible to ascertain experimentally whether division and differentiation are coupled. However, Drosophila Follicle Stem Cells (FSCs) provided a favorable model system to investigate population asymmetry mechanisms and also for measuring the impact of altered proliferation on competition. We found from detailed cell lineage studies that FSC division and FSC differentiation are not coupled. We also found that FSC representation, reflecting maintenance and amplification, was highly responsive to genetic changes that altered only the rate of FSC proliferation. The FSC paradigm therefore provides definitive experimental evidence for the general principle that relative proliferation rate will always be a major determinant of competition among stem cells specifically when stem cell division and differentiation are independent.\n\nSIGNIFICANCEAdult stem cells support tissue maintenance throughout life but they also can be cells of origin for cancer, allowing clonal expansion and long-term maintenance of the first oncogenic mutations. We considered how a mutation that increases the proliferation rate of a stem cell would affect the probability of its competitive survival and amplification for different potential organizations of stem cells. Quantitative modeling showed that the key characteristic predicting the impact of relative proliferation rate on competition is whether differentiation of a stem cell is coupled to its division. We then used Drosophila Follicle Stem Cells to provide definitive experimental evidence for the general prediction that relative proliferation rates dictate stem cell competition specifically for stem cells that exhibit division-independent differentiation.

developmental biology↗