Cellular and Molecular Nature of Fragmentation of Human Embryos.

Anna Cecchele,Greta Chiara Cermisoni,Monica Pinna,Paola Vigano,Elisa Giacomini

doi:10.3390/ijms23031349

Abstract

Embryo fragmentation represents a phenomenon generally characterized by the presence of membrane-bound extracellular cytoplasm into the perivitelline space. Recent evidence supports the cellular and molecular heterogeneity of embryo fragments. In this narrative review, we described the different embryo fragment-like cellular structures in their morphology, molecular content, and supposed function and have reported the proposed theories on their origin over the years. We identified articles related to characterization of embryo fragmentation with a specific literature search string. The occurrence of embryo fragmentation has been related to various mechanisms, of which the most studied are apoptotic cell death, membrane compartmentalization of altered DNA, cytoskeletal disorders, and vesicle formation. These phenomena are thought to result in the extrusion of entire blastomeres, release of apoptotic bodies and other vesicles, and micronuclei formation. Different patterns of fragmentation may have different etiologies and effects on embryo competence. Removal of fragments from the embryo before embryo transfer with the aim to improve implantation potential should be reconsidered on the basis of the present observations

Highlights

Embryo fragmentation represents a phenomenon generally characterized by the presence of membrane-bound extracellular cytoplasm into the perivitelline space
Embryo fragments are heterogeneous in size: they can vary from normal-size blastomeres to simple cellular debris
Fragmentation may occur from the first embryo division of pre-implantation development when the maternal genome drives the development; this phenomenon has been initially suggested to be less common after the embryonic genome activation [13]

Summary

Introduction

Embryo fragmentation represents a phenomenon generally characterized by the presence of membrane-bound extracellular cytoplasm into the perivitelline space. Highlights from the current literature support the cellular and molecular heterogeneity of embryo fragments: they can vary in size, kinetics, and organelle and molecular content [3]. During assisted reproduction technology (ART) procedures, fragmentation and cell debris are considered important prognostic factors in the static morphologic assessment of human embryo quality, along with cell number, size, and symmetry. In this context, the presence of cytoplasmic fragments is suggestive of a poor prognosis embryo development and poor ART outcomes. Time-lapse microscopy (TLM) documented that cellular fragments can be extruded or reabsorbed into blastomeres, highlighting a dynamism in the process [5]

Results

Discussion

Conclusion