Published online: March 26, 2015 (Researchgate)
(IV) The magna-minuta/precyst classification in the light of Entamoeba invadens’ stem cell biology
Vladimir F. Niculescu
D-86420 Diedorf, Germany, Kirschenweg 1
From the time as the magna - minuta classification was still valid exists the conviction that only cells of the “minuta” form can encyst in vivo. According to this previous classification, Entamoeba would have only two vegetative cell forms. One of them is the commensal forma minuta, a small cell type living in the lumen of the large intestine (5-25µ in diameter) and the other the tissular forma magna (30-50µ in diameter). Minuta amoebae have a reduced motility, few phagocytic vacuoles and are capable to transform into cysts. Cysts are discharged with the feces for a long period of time (http://de.wikipedia.org/ wiki/ Entamoeba histolytica). Forma magna is a vegetative large tissue form which does not become encysted in vivo. They penetrate the colon tissue destroying them. Via the bloodstream they reach hostorgans producing abcesses. It is usually found in mucosanguineous stools of the host (http://health.wikinut. com/The-Clinical-and-Economic-Importance-of-Amoeba-in-Medicine-and-in-the-Human-Health/2_zzr.ne/). The mechanisms converting minuta to magna forms are not understand (http://www.uni-protokolle.de/Lexikon/Entamoeba_ histolytica.html)
Just ambiguous is the term precyst. Some studies equate precystic cells with minuta form and suggest, precysts are daughter cells that cease to grow. According to this definition (http://www.biologydiscussion.com/parasites) all mitotic arrested cells (MAP, MAS and MAT cells) would be precysts. This is incorrect. Other authors define pre-cysts as cells going through a hypoxic encystment process [1, 2]. They refer in particular to cells going through the process of ITD encystment that occur in encystment media after inducement. This definition is more realistic. In our opinion precysts are committed MAT/EP and MAS/EP cells that have passed the checkpoint of terminal differentiation and encyst. They are just transition stages of terminal differentiation.
After discovery of the stem cell lineage of E. invadens [3, 4] it became clear that multicellularity of Entamoebae is more complex as suggested by the simple minuta /magna/precyst classification. Entamoebae stem cell lineages contain in fact three stem cell lines (primary, secondary and tertiary lines, PST lineage) that produce by asymmetric cell division self renewing stem cells (SRP, SRS and SRT cells), reversible differentiated quiescent cells (MAP, MAS and MAT cells) and complementary cells such as MAS/EP and ISH cells [4], thus at least ten different cell types. Which of these cells correspond best to minuta and which to magna form? We see certain similarities between minuta and MAS cells and between magna and MAT cells. Concerning the minuta/magna transition it occurs by the conversion of the s-SRL cell line into a t-SRL stem cell line (S/T conversion).
In our experience [4] OCB cultures contain small, middle, large and very large cells. Cell size depends on the age of the culture. There are no definitive small or large cell classes: secondary MAS cells are smaller than tertiary MAT cells and cycling SRS cells are smaller than self renewing SRT cells. Similarly, young MAT cells are smaller than old MAT cells or MAS cells, and endopolyploid MAS/EP 8C cells are in certain circumstances smaller than hyperpolyploid 8-16 C cells [5,6]. Thus, cell size alone is not a good marker for cell typing and the magna/minuta classification must be considered today obsolet. More suitable cell markers are the ploidy range, the number of genome copies and the capacity of cells for ATD or ITD encystment. Antigenic surface proteins are also good markers for typing protist cells [7].
Finally, we found that terminal differentiation is a general capacity of cells outside the mitotic cycle. It concerns MAS and MAT cells and similarely, early G1 cells not yet committed for self renewing and mitotic cycle [4, 8].
REFERENCES
1. Luis Menchaca Arredondo J, Barron Gonzalez MP, Leon Coria A, Ortega JE, Vargas Villareal J, Hernandez Pinero JL, MoralesVallarta MR. Entamoeba histolytica: trophozoite, precyst and cyst studied by atomic force microscopy. In Microscopy: Advances in Scientific Research and Education, 2014; Mendez Vilas (ed). Formatex Research Center, Mexico.
2. Said-Fernández S, Mata-Cardenas BD, González-Garza MT; Navarro-Marmolejo L, Rodriguez-Pérez E. Entamoeba histolytica cysts with a defective wall formed under axenic conditions. Parasitology Research 1992; 79:200-203 doi:10.1007/BF00931893
3. Niculescu VF. Growth of Entamoeba invadens in sediments with
metabolically repressed bacteria leads to multicellularity and
redefinition of the amoebic cell system. Roum Arch Microbiol Immunol.
2013; 72:25-48. PMID: 23947012 doi: 01460749/87/020272-13$02.00/0
4. Niculescu VF. The stem cell biology of the protist pathogen Entamoeba invadens in the context of eukaryotic stem cell evolution. Stem Cell Biol Res. 2015; 2:2 (in press)
5. Lee HO, Davidson JM, Duronio RJ. Endoreplication: polyploidy with purpose. Genes Dev. 2009; 23(21): 2461–2477. doi: 10.1101/gad.1829209
PMCID: PMC2779750 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2779750/pdf/2461.pdf
6. Byers J, Eichinger D. Entamoeba invadens: restriction of ploidy by colonic short chain fatty acids. Experimental Parasitology 2005; 110: 203-206 doi:10.1016/j.exppara.2005.02.019 PMID: 15955313 http://www.ncbi.nlm.nih.gov/pubmed/15955313
7. Niculescu VF. The cell system of Giardia lamblia in the light of the protist stem cell biology. Stem Cell Biol Res. 2014; 1:3.
http://dx.doi.org/10.7243/2054-717X-1-3 http://www.hoajonline.com/journals/pdf/2054-717X-1-3.pdf
8. Niculescu VF. Mitotic and endopolyploid cell cycles following asymmetric division of Entamoeba invadens’ ancient stem cells. 2015