#stem cell differentiation

Stem Cell -l

Which of the following stem cells has the narrowest differentiation potential?

Differentiation potential hierarchy is conventionally ordered conceptually from broadest to narrowest developmental outcome: totipotent covering entire organism plus supportive extraembryonic membranes, pluripotent covering all embryonic germ layers ectoderm mesoderm endoderm, multipotent covering multiple related types within a tissue system like blood, oligopotent covering few types, and unipotent covering single type such as muscle satellite cell generating myocyte or spermatogonial stem cell generating spermatozoon while still retaining long-term self-renewal capacity. Hence unipotent cells exhibit most restricted fate scope, although they remain bona fide stem cells due to maintenance capability and transplantation reconstitution ability over lifetime.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Unipotent narrowest differentiation potential hierarchy definition.

View Details

Stem Cell -l

A significant difference between pluripotent and totipotent stem cells is:

Totipotent cells, by forming trophectoderm lineage and primitive endoderm plus embryonic lineages, robustly support full fetal development including formation of placenta and yolk sac membranes essential for maternal-fetal nutrient exchange, gas exchange, and immunoprotection during implantation. Pluripotent cells, such as inner cell mass-derived embryonic stem cells cultured in vitro, efficiently form ectoderm, mesoderm, endoderm derivatives like neurons, muscle, gut epithelium, but contribute poorly to extraembryonic trophoblast without genetic manipulation or forced Cdx2 expression. This molecular restriction reflects epigenetic silencing of trophoblast program via Oct4-mediated repression of Cdx2, illustrating progressive narrowing of fate potential as development proceeds forward.

Ref: Rossant, Stem Cells 2008; Gilbert, Chapter 5: Totipotent extraembryonic capability versus pluripotent restriction difference.

View Details

Stem Cell -ll

Which type of chromatin modification is associated with stem cell differentiation?

Stem cell differentiation is accompanied by dramatic widespread chromatin reorganization from open to restrictive configuration. Pluripotent cells exhibit globally open euchromatin enriched in activating H3K9 acetylation and H3K4 trimethylation marks, maintaining accessibility of self-renewal genes like Nanog. Upon lineage commitment, histone deacetylases remove acetyl groups, H3K27 methyltransferase EZH2 component of PRC2 deposits repressive marks, DNA methyltransferases methylate CpG islands of Oct4 and Nanog promoters, and heterochromatin protein 1 consolidates constitutive heterochromatin foci at repeats. These coordinated modifications collectively silence pluripotency program and permanently lock lineage-specific expression patterns essential for stability.

Ref: Bernstein et al., Cell 2006; Spivakov & Fisher, Nat Rev Genet 2007: Chromatin modifications differentiation bivalency.

View Details

Stem Cell -ll

Which of the following stem cells has the narrowest differentiation potential?

Potency terminology precisely reflects developmental latitude and epigenetic restriction history. Totipotent cells like zygote generate embryonic plus extraembryonic tissues covering entire conceptus including placenta and yolk sac. Pluripotent cells like embryonic stem cells produce all embryonic germ layers but fail to contribute to placenta efficiently. Multipotent cells such as mesenchymal or hematopoietic stem cells generate several related differentiated types within a single tissue lineage. Unipotent cells such as spermatogonial stem cells, basal keratinocytes, or satellite muscle progenitors produce single differentiated progeny while still self-renewing, representing narrowest potential compatible with stem cell definition functionally.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Unipotent narrowest potency stem cell classification standard.

View Details

Stem Cell -ll

Which one of the following stem cells is multipotent?

Somatic stem cell classification relies strictly on breadth of lineage contribution observed in vivo and transplantation. Inner cell mass is pluripotent, zygote totipotent, spermatogonia unipotent. Hematopoietic stem cells give rise to all blood lineages including myeloid, erythroid, megakaryocytic, and lymphoid branches, yet do not generate neurons or skeletal muscle, exemplifying multipotency defined as generation of multiple distinct cell types within one germ layer family. Therefore hematopoietic stem cells are canonical multipotent adult stem cells extensively studied for transplantation therapies and clonal lineage tracing analysis.

Ref: Seita & Weissman, Wiley Stem Cell 2010; Gilbert, Chapter 6: Multipotent hematopoietic stem cells definition.

View Details

Stem Cell -lll

Which factor prevents differentiation in Drosophila GSCs?

In Drosophila ovary, cap cells located at terminal filament tip secrete Decapentaplegic, activating BMP pathway in adjacent germline stem cells to maintain identity. Phosphorylated Mad-Medea complex directly silences transcription of bag-of-marbles, encoding differentiation-promoting factor required for cyst formation and meiosis entry. High local BMP concentration sustains self-renewal, prevents premature differentiation, and represses bam via heterochromatin modulation. Daughter cells displaced from niche experience BMP attenuation, de-repress Bam, and initiate four synchronous transit-amplifying divisions leading to oocyte and nurse cells, constituting bistable switch.

Ref: Song et al., Development 2004; Gilbert, Chap 6: BMP signaling represses Bam preventing GSC differentiation Drosophila.

View Details

Stem Cell -lll

What is the correct order of lineage commitment in hematopoietic differentiation?

Developmental potency narrows progressively through epigenetic restriction and lineage priming. Zygote and early blastomeres up to two to four cell stage are totipotent, able to produce embryonic plus extraembryonic placenta and yolk sac membranes. Inner cell mass subsequently restricts to pluripotent state, generating ectoderm, mesoderm, endoderm but not trophoblast under normal conditions. Subsequently hematopoietic stem cells become multipotent within blood lineages only, and committed progenitors become unipotent forming one mature type such as erythrocyte or spermatogonium. This hierarchy underlies stepwise differentiation trajectories and transplantation potential.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Potency hierarchy Totipotent to Unipotent progressive restriction.

View Details