44. The following are certain statements regarding stem cells:
    (A) All types of stem cells have the ability to give rise to a complete embryo.
    (B) Multipotent stem cells are those whose commitment is limited to a relatively small subset
    of all possible cell types.
    (C) Stem cell niches allow controlled self-renewal and also survival of the cells that leave the niche.
    (D) The pluripotency of the stem cells in an embryo is essentially maintained by Fgf8, Nanog and TGFβ.
    (E) Adult cells may be reprogrammed to gain pluripotency by modifying the following genes: Oct 3/4, sox2, c-Myc, Klf-4.
    Which one of the following combinations of statements is correct?
    (1) A,B and D (2) B and E
    (3) C and E                                                              (4) A, C and D

Stem cells reside within specialized microenvironments known as niches that critically regulate their behavior, including self-renewal and differentiation. These niches provide a supportive habitat integrating signals from cellular and acellular components, coordinating with stem cells to maintain tissue homeostasis over an organism’s lifetime.

A fundamental function of the stem cell niche is to promote controlled self-renewal, ensuring stem cells can divide to retain their population without uncontrolled expansion that could lead to tumorigenesis. The niche also provides biochemical and physical cues that influence whether stem cells remain quiescent, proliferate, or differentiate.

Another important role of the niche is ensuring the survival of stem cells, including those that leave the niche. While some stem cells leave the niche to differentiate, the niche’s signals can support their viability to maintain regenerative potential or direct lineage-specific maturation.

This intricate balance between self-renewal and survival mediated by the niche microenvironment is essential for normal development, tissue repair, and aging.

Regarding the statements given:

• Statement (C) “Stem cell niches allow controlled self-renewal and also survival of the cells that leave the niche” is true.

• Statement (E) “Adult cells may be reprogrammed to gain pluripotency by modifying genes Oct3/4, Sox2, c-Myc, Klf-4” is a well-established fact related to induced pluripotent stem cells.

Thus, the correct combination of statements is:

(3) C and E

Understanding stem cell niches and reprogramming factors informs therapeutic strategies in regenerative medicine, offering avenues for tissue engineering and treatment of degenerative diseases.

Answer: (3) C and E