Stem Cell Niches, Activation, Therapies & Risks

Posted on Jan 11, 2026 in Biomedical Sciences

Drosophila Ovary — Germarium

Female (Ovary — Germarium)

Female (Ovary – Germarium):

In the Drosophila ovary, 2–3 germline stem cells (GSCs) are located at the anterior tip of the germarium. They physically attach to cap cells using E-cadherin–mediated adhesion. Cap cells act as the niche, producing key signals such as Dpp, Gbb, Hedgehog, and Piwi to maintain GSC self-renewal.

When a GSC divides, it undergoes asymmetric division: one daughter remains attached to cap cells and stays a stem cell, while the other daughter moves away from the niche and becomes a cystoblast, which further divides to form the 16-cell cyst and eventually the oocyte. Somatic cells around the GSCs include the terminal filament cells, cap cells, and inner germarial sheath cells, which together maintain stem cell fate and regulate differentiation.

Development, Activation, and Maintenance of Satellite Cells (5 marks)

Development, Activation, and Maintenance of Satellite Cells 5 marks

Satellite cells are the stem cells of skeletal muscle that normally remain quiescent, located beneath the basal lamina, and express Pax-7 and Foxk1. They originate from embryonic myoblast precursors, fetal myoblasts, and mesoangioblasts, all of which require Pax-7 activation for proper development.

After muscle injury, satellite cells become activated, increasing expression of MyoD, Myf-5, desmin, and Wnt5a/5b. Their activation is controlled mainly by the Notch pathway, while FGF, HGF, IGF-1 and other growth factors promote proliferation.

During the transition to differentiation, Pax-7 decreases and Myogenin and MRF-4 increase, driving myoblast formation and fusion into repairing or newly formed myofibers.

For maintenance, a portion of activated cells undergo asymmetric division and return to quiescence, preserving the satellite cell pool. The myofiber and M-cadherin–mediated adhesion form the key components of the satellite cell niche, supporting long-term self-renewal.

Applications of Neural Stem Cells (2 marks)

Write 4 applications of neural stem cell (2 marks)

  1. Treating stroke (hESC-derived NSCs).
  2. Treating glioma using genetically modified NSCs that target tumor cells.
  3. Treating ALS (Amyotrophic Lateral Sclerosis) through spinal cord injections of fetal-derived NSCs.
  4. Regenerating CNS tissues in brain or spinal cord injury.

Factors That Regulate the Stem Cell Niche (2 marks)

What are the factors the regulate the niche of the stem cell (2 marks)

  1. Cell–cell interactions between stem cells and neighboring niche cells.
  2. Adhesion molecules and ECM components, plus growth factors and cytokines.
  3. Physicochemical environment such as local pH.
  4. Signaling pathways, especially JAK-STAT and TGF-β in Drosophila.

Applications of Stem Cell Gene Therapy (2 marks)

Applications of stem cell gene therapy (2 marks)

  1. Treating blood disorders such as thalassemia, sickle cell disease, and hemophilia using corrected hematopoietic stem cells.
  2. Using stem cells for regeneration, such as iPSC-based therapy for Parkinson’s disease, spinal cord injury, autoimmune diseases, and metastatic cancers (HSC-based therapy).

How to Prepare a Neurosphere Culture (2 marks)

8. How to prepare a neurosphere culture (2 marks)

Neurosphere culture is prepared by first microdissecting a specific CNS region and dissociating the tissue mechanically or enzymatically to obtain single cells. These cells are then cultured in a defined serum-free medium supplemented with growth factors such as EGF and/or bFGF, which stimulate neural stem and progenitor cells to proliferate and form free-floating clusters called neurospheres within a few days.

miR-290–295 Regulation of Stem Cells (2 marks)

9. How does miR290-295 regulate stem cell ? ( 2 marks)

The miR-290–295 cluster promotes stem cell self-renewal by targeting RBL2, a repressor of DNMTs.

By inhibiting RBL2, DNMTs are active and methylate CpG islands, which maintains expression of pluripotency genes such as OCT4, preserving stem cell identity and preventing differentiation.

Drosophila Testes — Male

Male. In Drosophila testes, 7–9 GSCs are arranged around a cluster of hub cells, which function as the niche. GSCs attach to hub cells using E-cadherin, ensuring they remain in a stem cell state. Hub cells secrete signals such as JAK-STAT ligands that promote self-renewal. When a GSC divides, one daughter maintains attachment to the hub and stays a GSC, while the other becomes a gonialblast, which undergoes mitotic divisions to form sperm cells. Along with GSCs, somatic stem cells (SSCs) lie adjacent and divide to produce cyst cells that surround and support the developing germ cells.

Risks and Challenges of Stem Cell Therapies

  • Tumorigenicity and impurity – undifferentiated cells may cause tumors.
  • Mis-differentiation and cell death – difficulty controlling cell fate after transplantation.
  • Complexity of microenvironment interactions – poor understanding of how transplanted cells behave.
  • Immunogenicity – risk of rejection after transplantation.