The Embryological Origin of Chimeras

Experimental and clinical research works

Lopata Alex

Abstract.
The author discusses the embryological aspects of such phenomenon as chimerism. The current literature contains the experimental works dealing with simulation of chimera formation conditions; however, research in this area and clinical data are sparse. Nevertheless, in the practice of infertility management by ART, at the embryological stage, it is possible to form embryos that carry foreign cell lines. The author proposes that the mechanism that leads to chimera development is the formation of two mature oocytes inside the same zona pellucida. This process is based on failed orientation of the meiotic spindle, therefore — instead of the first polar body a viable oocyte is formed.
The cytokinetics of this process has been demonstrated using time¬lapse technology. The experiment on mouse oocytes showed that such oocytes inside the same zona pellucida could be fertilized, produce two zygotes and following mixing the blastomeres at the stage of division form a single blasocyst – a chimera. The objective of further research is to determine, how the distinct cell lines are distributed in the individual development process.
In conclusion, the author highlights the existence of two major issues:
1. Can two secondary oocytes form inside the same zona and lead to the birth of a chimera in natural human reproduction?
2. Can two oocytes develop inside the same zona during assisted reproductive procedures and result in the birth of a human chimera?
A positive answer to the first question is reinforced by the increasing number of publications about the facts of spontaneous birth of chimeric individuals. Responding positively about the possibility of this phenomenon in ART, the author notes, however, that the literature in this area is still very sparse.

Key words:
chimera, meiotic spindle, abnormality of oocyte maturation.

Autor:
Lopata Alex
e-mail: alex.lopata15@gmail.com
Department of Obstetrics and Gynaecology University of Melbourne, Royal Women’s Hospital; MB BS PhD
132 Grattan St. Melbourne, Australia