Stem Cell Niches in Drosophila


Adult stem cells supply a continual source of highly differentiated cells throughout the life of an organism. They are able to maintain an undifferentiated state and possess unlimited proliferation capacity. Many stem cells reside in a special microenvironment known as a niche that specifies stem cell identity and protects them from differentiation by providing essential molecular signals. Because of its essential requirement to maintain stem cells, the stem cell niche also limits the number of stem cells, safeguarding against cancer. Drosophila melanogaster has served as an ideal model system to study stem cells and their niches, thanks to the well‐understood signalling pathways, elegant genetics and relatively simple anatomy. Studies in Drosophila have provided a fundamental framework for understanding mammalian stem cells and their niches. Here, I give an overview of how stem cells are regulated by their niches in Drosophila.

Key concepts

  • Adult stem cells: Cells found in adult tissues that are capable of proliferation over a prolonged time period (throughout the life of the organism) and of further differentiation to produce various types of differentiated cells in the tissue.

  • Self‐renewal: The phenomenon by which stem cells produce stem cells on cell division. Stem cell characteristics, including undifferentiated state, proliferative potential and developmental potential to differentiate, are maintained.

  • Niche: A microenvironment in which stem cell characteristics (such as stem cell identity and proliferation potential) are maintained.

  • Asymmetric stem cell division: A form of stem cell division in which one stem cell and one differentiated cell are created, thereby maintaining stem cell number.

Keywords: adult stem cells; niche; self‐renewal; asymmetric division; BMP signalling; Jak‐STAT pathway

Figure 1.

Stem cells and their niches. After stem cell division, the daughter cell either self‐renews to maintain stem cell identity or commits to differentiation. Many stem cells reside in a microenvironment called the stem cell niche, which sends out signals that specify stem cell identity. Cells that leave the niche initiate differentiation.

Figure 2.

The Drosophila (GSC) niche and asymmetric stem cell division. (a) Female GSC niche: GSCs are attached to cap cells via adherens junctions. GSCs divide asymmetrically to self‐renew and produce a differentiating cell (cystoblast). Dpp signalling controls GSC identity by suppressing Bam, a master regulator of differentiation. The mitotic spindle is oriented towards the cap cells via anchoring of one spindle pole to the spectrosome, which localizes consistently to the apical side of GSCs. Green lines, spindle microtubules. (b) Male GSC niche: GSCs are attached to hub cells via adherens junctions. GSCs divide asymmetrically to self‐renew and to produce a differentiating cell (gonialblast). Upd ligand is secreted from hub cells to activate the JAK‐STAT pathway in GSCs to specify stem cell identity. The mitotic spindle is oriented towards the hub cells via positioning of the centrosome, and the mother centrosome is consistently positioned close to the hub cells. Spectrosomes in male GSCs are not oriented with respect to the hub cells during interphase, but associate with the distal spindle pole in mitosis (our unpublished results).

Figure 3.

Niche‐independent, asymmetric stem cell division of Drosophila neuroblasts. In Drosophila neuroblasts, the spindle is oriented perpendicular to the apical crescent (light green line) that contains the BazPar6aPKC complex, as well as Pins, Insc and Gαi, leading to asymmetric stem cell division. The apical crescent is required for spindle orientation, basal crescent formation and spindle size asymmetry (the apical half is larger than the basal half). The basal crescent (yellow line) contains fate determinants such as Numb, Miranda and Prospero that promote or allow differentiation. Green line, spindle microtubules.


Further Reading

Clarke MF and Fuller M (2006) Stem cells and cancer: two faces of eve. Cell 124: 1111–1115.

Gonzalez C (2007) Spindle orientation, asymmetric division and tumour suppression in Drosophila stem cells. Nature Reviews. Genetics 8: 462–472.

Knoblich JA (2008) Mechanisms of asymmetric stem cell division. Cell 132: 583–597.

Martinez‐Agosto JA, Mikkola HK, Hartenstein V and Banerjee U (2007) The hematopoietic stem cell and its niche: a comparative view. Genes & Development 21: 3044–3060.

Morrison SJ and Kimble J (2006) Asymmetric and symmetric stem‐cell divisions in development and cancer. Nature 441: 1068–1074.

Morrison SJ and Spradling AC (2008) Stem cells and niches: mechanisms that promote stem cell maintenance throughout life. Cell 132: 598–611.

Ohlstein B, Kai T, Decotto E and Spradling A (2004) The stem cell niche: theme and variations. Current Opinion of Cell Biology 16: 693–699.

Spradling A, Drummond‐Barbosa D and Kai T (2001) Stem cells find their niche. Nature 414: 98–104.

Yamashita YM and Fuller MT (2008) Asymmetric centrosome behavior and the mechanisms of stem cell division. Journal of Cell Biology 180: 261–266.

Yamashita YM, Fuller MT and Jones DL (2005) Signaling in stem cell niches: lessons from the Drosophila germline. Journal of Cell Science 118: 665–672.

Yu F, Kuo CT and Jan YN (2006) Drosophila neuroblast asymmetric cell division: recent advances and implications for stem cell biology. Neuron 51: 13–20.

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Yamashita, Yukiko M(Dec 2009) Stem Cell Niches in Drosophila. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0021854]