Biology subjects

Nandy, N.

Publications and source records attributed to Nandy, N..

3 recordsLinked to original sources

bioRxiv2024

Ovarian germline stem cell dedifferentiation is cytoneme-dependent

Progenitor cell dedifferentiation is important for stem cell maintenance during tissue repair and age-related stem cell decline. Here, we use the Drosophila ovary as a model to study the role of cytonemes in BMP signalling-directed germline stem cell (GSC) maintenance and dedifferentiation of germ cells to GSCs. We provide evidence that differentiating germ cell cysts extend longer cytonemes that are more polarised towards the niche during dedifferentiation to reactivate BMP signalling. The presence of additional somatic cells in the niche is associated with a failure of germ cell dedifferentiation, consistent with the formation of a physical barrier to cytoneme-niche contact and outcompetition of germ cells for BMP. Using BMP beads in vitro, we show that these are sufficient to induce cytoneme-dependent contacts in Drosophila tissue culture cells. We demonstrate that the Enabled (Ena) actin polymerase is localised to the tips of germ cell cytonemes and is necessary for robust cytoneme formation, as its mislocalisation reduces the frequency, length and directionality of cytonemes. During homeostasis, specifically perturbing cytoneme function through Ena mislocalisation impairs GSC fitness by reducing GSC BMP signalling and niche occupancy. Disrupting cytonemes by targeting Ena during dedifferentiation reduces germ cell BMP responsiveness and the ability of differentiating cysts to dedifferentiate. Overall, our results provide evidence that cytonemes play a fundamental role in establishing polarised signalling and niche occupancy during stem cell maintenance and dedifferentiation. Significance StatementFertility depends not only on germline stem cell (GSC) maintenance during homeostasis, but also on the ability of germ cells to reverse their developmental programme and dedifferentiate during ageing- or stress-induced GSC loss. Here, using the Drosophila ovary as a model, we show that cytonemes are required for GSC asymmetric signalling, niche occupancy and fitness during homeostasis. During dedifferentiation, we demonstrate that cytonemes are necessary for differentiating germ cells to re-access the self-renewal signal and establish polarised signalling, recolonise an empty niche and dedifferentiate to germline stem cells. Our data identify cytonemes as a novel target for strategies aimed at improving stem cell fitness or dedifferentiation, which has huge therapeutic potential for the regeneration of damaged tissues.

developmental biology↗

bioRxiv2021

Rab11 negatively regulates Wingless preventing JNK mediated apoptosis in Drosophila epithelium during embryonic dorsal closure

Cell signaling pathways involved in epithelial wound healing, show a lot of complexities when it comes to their regulation. Remarkably, a large proportion of these signaling pathways are triggered at the time of morphogenetic events which usually involve epithelial sheet fusions during embryonic development, such as the event of dorsal cloure in Drosophila embryos. One such conserved pathway in the wound healing process is the JNK-Dpp signaling pathway. Recent observations suggest that one such upstream regulator of JNK mediated apoptosis could be Rab11, a small Ras like GTPase, which is functionally associated with the membrane and cortical cytoskeletal organization of epithelial cells. Using Drosophila embryonic dorsal closure as a model of wound healing, we observed that a targeted expression of a Rab11 loss of function mutant in the dorso-lateral epidermis of fly embryos (tissue which extends contra-laterally in order to fill the intervening gap) undergoing dorsal closure leads to an ectopic expression of Caspase-3 and a concomitant up-regulation of the JNK-Dpp signaling. This resulted in the death of the dorso-lateral epithelial cells with a consequent embryonic lethality due to dorsal closure defects. Interestingly, a simultaneous knockdown of wingless (another developmentally conserved gene) in Rab11 mutants resulted in a rescue of the lethal phenotype and also a significant level of successful completion of the dorsal closure process. In our experiments we suggest Rab11 could promote cross talk between the JNK-Dpp pathway and the canonical wingless pathway in the regulation of apoptosis in the dorsolateral epithelium of fly embryos undergoing dorsal closure. One Sentence SummaryRab11 functions through a conserved Wingless mediated JNK-Dpp pathway during embryonic dorsal closure.

developmental biology↗

bioRxiv2019

Rab11 is essential for lgl mediated JNK-Dpp signaling in dorsal closure and epithelial morphogenesis in Drosophila

Dorsal closure in Drosophila provides a robust genetic platform providing deep insights into the basic cellular mechanisms that govern epithelial wound healing and morphogenesis. As dorsal closure proceeds, the adjacent epithelia advance contra-laterally involving coordinated cell shape changes in order to successfully accomplish the process. The JNK-Dpp signaling in these cells plays an instrumental role in guiding their fate as gastrulation completes. A huge number of genes have been reported to be involved in the regulation of this core signaling pathway, yet the mechanisms by which they do so is hitherto unclear, which forms the objective of our present study. Here we show that lgl, which is a potent tumour suppressor gene, conserved across the phyla till humans, regulates the JNK-Dpp pathway in the dorsal closure and epithelial morphogenesis process where in ectopic knockdown of this gene results in the failure of dorsal closure. Interestingly, we also find Rab11 to be interacting with lgl as they together regulate the core JNK-Dpp signaling pathway during dorsal closure and also during pupal thorax closure process. Using the robust Gal4-UAS system of targeted gene expression, we show here that Rab11 and lgl synergize to successfully execute the dorsal closure and the similar thorax closure process, ensuring proper spatio-temporal JNK-Dpp signaling.

developmental biology↗