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Endogenous, very small embryonic-like stem cells: Critical review, therapeutic potential and a look ahead
Human Reproduction Update
  • Deepa Bhartiya, National Institute for Research in Reproductive Health India
  • Ambreen Shaikh, National Institute for Research in Reproductive Health India
  • Sandhya Anand, National Institute for Research in Reproductive Health India
  • Hiren Patel, National Institute for Research in Reproductive Health India
  • Sona Kapoor, National Institute for Research in Reproductive Health India
  • Kalpana Sriraman, National Institute for Research in Reproductive Health India
  • Seema Parte, National Institute for Research in Reproductive Health India
  • Sreepoorna Unni, Zayed University
Document Type
Article
Publication Date
1-1-2016
Abstract

© The Author 2016. BACKGROUND: Both pluripotent very small embryonic-like stem cells (VSELs) and induced pluripotent stem (iPS) cells were reported in 2006. In 2012, a Nobel Prize was awarded for iPS technology whereas even today the very existence of VSELs is not well accepted. The underlying reason is that VSELs exist in low numbers, remain dormant under homeostatic conditions, are very small in size and do not pellet down at 250-280g. The VSELs maintain life-long tissue homeostasis, serve as a backup pool for adult stem cells and are mobilized under stress conditions. An imbalance in VSELs function (uncontrolled proliferation) may result in cancer. SEARCH METHODS: The electronic database 'Medline/Pubmed' was systematically searched with the subject heading term 'very small embryonic-like stem cells'. OBJECTIVE AND RATIONALE: The most primitive stem cells that undergo asymmetric cell divisions to self-renew and give rise to progenitors still remain elusive in the hematopoietic system and testes, while the presence of stem cells in ovary is still being debated. We propose to review the available literature on VSELs, the methods of their isolation and characterization, their ontogeny, how they compare with embryonic stem (ES) cells, primordial germ cells (PGCs) and iPS cells, and their role in maintaining tissue homeostasis. The review includes a look ahead on how VSELs will result in paradigm shifts in basic reproductive biology. OUTCOMES: Adult tissue-specific stem cells including hematopoietic, spermatogonial, ovarian and mesenchymal stem cells have good proliferation potential and are indeed committed progenitors (with cytoplasmic OCT-4), which arise by asymmetric cell divisions of pluripotent VSELs (with nuclear OCT-4). VSELs are the most primitive stem cells and postulated to be an overlapping population with the PGCs. Rather than migrating only to the gonads, PGCs migrate and survive in various adult body organs throughout life as VSELs. VSELs express both pluripotent and PGC-specific markers and are epigenetically and developmentally more mature compared with ES cells obtained from the inner cell mass of a blastocyst-stage embryo. As a result, VSELs readily differentiate into three embryonic germ layers and spontaneously give rise to both sperm and oocytes in vitro. Like PGCs, VSELs do not divide readily in culture, nor produce teratoma or integrate in the developing embryo. But this property of being relatively quiescent allows endogenous VSELs to survive various kinds of toxic insults. VSELs that survive oncotherapy can be targeted to induce endogenous regeneration of non-functional gonads. Transplanting healthy niche (mesenchymal) cells have resulted in improved gonadal function and live births. WIDER IMPLICATIONS: Being quiescent, VSELs possibly do not accumulate genomic (nuclear or mitochondrial) mutations and thus may be ideal endogenous, pluripotent stem cell candidates for regenerative and reproductive medicine. The presence of VSELs in adult gonads and the fact that they survive oncotherapy may obviate the need to bank gonadal tissue for fertility preservation prior to oncotherapy. VSELs and their ability to undergo spermatogenesis/neo-oogenesis in the presence of a healthy niche will help identify newer strategies toward fertility restoration in cancer survivors, delaying menopause and also enabling aged mothers to have better quality eggs.

Publisher
Oxford University Press
Disciplines
Keywords
  • Cancer,
  • Cord blood,
  • Differentiation,
  • Embryonic stem cells,
  • Gametes,
  • Ovary,
  • Pluripotent stem cells,
  • Primordial germ cells,
  • Testis,
  • Very small embryonic-like stem cells
Scopus ID

85012069128

Indexed in Scopus
Yes
Open Access
Yes
Open Access Type
Hybrid: This publication is openly available in a subscription-based journal/series
https://doi.org/10.1093/humupd/dmw030
Citation Information
Deepa Bhartiya, Ambreen Shaikh, Sandhya Anand, Hiren Patel, et al.. "Endogenous, very small embryonic-like stem cells: Critical review, therapeutic potential and a look ahead" Human Reproduction Update Vol. 23 Iss. 1 (2016) p. 1 - 36 ISSN: <p><a href="https://v2.sherpa.ac.uk/id/publication/issn/1355-4786" target="_blank">1355-4786</a></p>
Available at: http://works.bepress.com/sreeporna-pramodh/4/