Biology subjects

Nystul, T.

Publications and source records attributed to Nystul, T..

6 recordsLinked to original sources

bioRxiv2025

Ecdysone Receptor autonomously controls germ cell differentiation in the Drosophila ovary

In the Drosophila ovary, the steroid hormone ecdysone controls germline stem cell (GSC) maintenance and germ cell differentiation. Prior studies demonstrated that ecdysone regulates germ cell differentiation non-autonomously via the nuclear receptor Ecdysone Receptor (EcR) in ovarian somatic cells. Although EcR is also expressed in GSCs and their differentiating daughters, potential direct roles for EcR in GSCs independent of the soma have not been examined. Here, we demonstrate that EcR functions autonomously in GSCs and cystoblasts to control germline differentiation. While depletion of EcR from GSCs mildly reduces GSC self-renewal, over-expression of EcR specifically in GSCs and cystoblasts impedes germ cell differentiation, phenotypically resembling bag of marbles loss-of-function and Bone Morphogenetic Protein signaling constitutive activation. We propose that while low levels of EcR are essential to maintain GSC self-renewal and permit initial differentiation, higher levels of EcR accumulate in differentiated germ cells to promote transcription of maternal genes, providing temporal control over germline differentiation. These data support the model that stem cells harbor unique mechanisms to integrate signals from multiple cell sources that safeguard their self-renewal in response to local and physiological cues. SUMMARY STATEMENTThe nuclear receptor EcR modulates stem cell maintenance and differentiation in ovarian germ cells.

developmental biology↗

bioRxiv2023

Arp2/3 Complex Activity Enables Nuclear YAP for Naive Pluripotency of Human Embryonic Stem Cells

Our understanding of transitions of human embryonic stem cells between distinct stages of pluripotency relies predominantly on regulation by transcriptional and epigenetic programs with limited insight on the role of established morphological changes. We report remodeling of the actin cytoskeleton of human embryonic stem cells (hESCs) as they transition from primed to naive pluripotency that includes assembly of a ring of contractile actin filaments encapsulating colonies of naive hESCs. Activity of the Arp2/3 complex is required for the actin ring, uniform cell mechanics within naive colonies, nuclear translocation of the Hippo pathway effectors YAP and TAZ, and effective transition to naive pluripotency. RNA-sequencing analysis confirms that Arp2/3 complex activity regulates Hippo signaling in hESCs, and impaired naive pluripotency with inhibited Arp2/3 complex activity is rescued by expressing a constitutively active, nuclear-localized YAP-S127A. These new findings on the cell biology of hESCs reveal a mechanism for cytoskeletal dynamics coordinating cell mechanics to regulate gene expression and facilitate transitions between pluripotency states.

cell biology↗

bioRxiv2022

Single-cell RNA sequencing identifies regulators of differentiation and nutritional cues in Drosophila female germ cells

Drosophila ovarian germline stem cells (GSCs) are powerful model for stem cell research. However, due to the scarcity of GSCs in ovarian tissue, it is difficult to obtain the transcriptional profile of GSCs and identify novel GSC markers. In this study, we took advantage of single cell RNA sequencing (scRNA-seq) to profile the germline cells and somatic cells in wild type Drosophila ovary. We then performed an in vivo RNAi screen and network analysis to identify genes that are involved in the early stages of germ cell differentiation. We identified 33 genes with limited expression during early germ cell development and identified 19 genes that potentially regulate germ cell differentiation. Among these, an uncharacterized gene, which we named eggplant (eggpl), is highly expressed in GSC and downregulated in early daughter cells. Upon RNAi knockdown of eggpl, we observed an increase in germ cell proliferation, an accumulation of cysts in the early mitotic (2- and 4-cell) stages and an increase in overall ovary size compared to control when flies were maintained on a standard diet. In flies fed a rich yeast diet, the expression of eggpl was significantly lower and the effects of eggpl RNAi were suppressed, suggesting that downregulation of eggpl may link nutritional status to germ cell proliferation and differentiation. We also found that the matrix metalloproteases, Mmp1 and Mmp2 as well as the tissue inhibitor of metalloproteases (Timp) are additional regulators of eggpl. Collectively, this study provides new insight into the signaling networks that regulate early germ cell development and identifies eggpl as a key player in this process.

genetics↗

bioRxiv2021

Intracellular pH dynamics regulates intestinal stem cell fate

Intracellular pH (pHi) dynamics is increasingly recognized to regulate myriad cell behaviors, including proliferation, migration, differentiation, and transformation. Here we report a new finding that pHi dynamics also regulates adult stem cell lineage specification. In mouse small intestinal organoids, we identify a pHi gradient along the crypt axis, lower at the crypt base and higher toward the villus, and find that dissipating this gradient by inhibiting Na+-H+ exchanger 1 (NHE1) activity genetically or pharmacologically abolishes crypt budding. Using single-cell RNA sequencing and lineage tracing we demonstrate that pHi dynamics acts downstream of ATOH1, with increased pHi promoting differentiation toward the secretory lineage, while reduced pHi biases differentiation into the absorptive lineage. Consistent with these results, disrupting the pHi gradient blocks new Paneth cell differentiation. Paneth cells provide an essential WNT signal to ISCs in organoids, and we find that the loss of crypt budding with inhibiting NHE1 activity is rescued with exogenous WNTs. Our findings indicate that pHi dynamics is tightly regulated in the ISC lineage and that an increase in pHi is required for the specification of secretory lineage, including Paneth cell differentiation that contributes to crypt maintenance. These observations reveal a previously unreported role for pHi dynamics in cell fate decisions within an adult stem cell lineage.

cell biology↗

bioRxiv2021

Fly Cell Atlas: a single-cell transcriptomic atlas of the adult fruit fly

The ability to obtain single cell transcriptomes for stable cell types and dynamic cell states is ushering in a new era for biology. We created the Tabula Drosophilae, a single cell atlas of the adult fruit fly which includes 580k cells from 15 individually dissected sexed tissues as well as the entire head and body. Over 100 researchers from the fly community contributed annotations to >250 distinct cell types across all tissues. We provide an in-depth analysis of cell type-related gene signatures and transcription factor markers, as well as sexual dimorphism, across the whole animal. Analysis of common cell types that are shared between tissues, such as blood and muscle cells, allowed the discovery of rare cell types and tissue-specific subtypes. This atlas provides a valuable resource for the entire Drosophila community and serves as a comprehensive reference to study genetic perturbations and disease models at single cell resolution.

genomics↗

bioRxiv2018

Drosophila anion exchanger 2 is required for proper ovary development and oogenesis

Understanding how cell fate decisions are regulated is a central question in stem cell biology. Recent studies have demonstrated that intracellular pH (pHi) dynamics contribute to this process. Indeed, the pHi of cells within a tissue is not simply a consequence of chemical reactions in the cytoplasm and other cellular activity, but is actively maintained at a specific setpoint in each cell type. We found previously that the pHi of cells in the follicle stem cell (FSC) lineage in the Drosophila ovary increases progressively during differentiation from an average of 6.8 in the FSCs, to 7.0 in newly produced daughter cells, to 7.3 in more differentiated cells. Two major regulators of pHi in this lineage are Drosophila sodium-proton exchanger 2 (dNhe2) and a previously uncharacterized gene, CG8177, that is homologous to mammalian anion exchanger 2 (AE2). Based on this homology, we named the gene ae2. Here, we generated null alleles of ae2 and found that homozygous mutant flies are viable but have severe defects in ovary development and adult oogenesis. Specifically, we find that ae2 null flies have smaller ovaries, reduced fertility, and impaired follicle formation. In addition, we find that the follicle formation defect can be suppressed by a decrease in dNhe2 copy number and enhanced by the overexpression of dNhe2, suggesting that this phenotype is due to the dysregulation of pHi. These findings support the emerging idea that pHi dynamics regulate cell fate decisions and our studies provide new genetic tools to investigate the mechanisms by which this occurs.

developmental biology↗