The Impact of Entropy on the Spatial Organization of Synaptonemal Complexes within the Cell Nucleus

• Published in: PloS one Vol. 7; no. 5; p. e36282
• Main Authors: Fritsche, Miriam, Reinholdt, Laura G., Lessard, Mark, Handel, Mary Ann, Bewersdorf, Jörg, Heermann, Dieter W.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 04.05.2012; Public Library of Science (PLoS)
• Subjects: Actin; Animals; Biology; Biopolymers; Cables; Cell division; Chromosomes; Chromosomes - metabolism; Confining; Deoxyribonucleic acid; DNA; Entanglement; Entropy; Imaging, Three-Dimensional; Laboratories; Male; Mathematical models; Meiosis; Mice; Microscopy; Nuclei; Nuclei (cytology); Numerical models; Pachytene; Physics; Polymers; Proteins; Rigidity; Spatial distribution; Spermatocytes - cytology; Studies; Synaptonemal Complex - metabolism; Tethering; Theoretical physics; Three dimensional models; United States > US; Maine; Germany
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0036282

We employ 4Pi-microscopy to study SC organization in mouse spermatocyte nuclei allowing for the three-dimensional reconstruction of the SC's backbone arrangement. Additionally, we model the SCs in the cell nucleus by confined, self-avoiding polymers, whose chain ends are attached to the envelope of the confining cavity and diffuse along it. This work helps to elucidate the role of entropy in shaping pachytene SC organization. The framework provided by the complex interplay between SC polymer rigidity, tethering and confinement is able to qualitatively explain features of SC organization, such as mean squared end-to-end distances, mean squared center-of-mass distances, or SC density distributions. However, it fails in correctly assessing SC entanglement within the nucleus. In fact, our analysis of the 4Pi-microscopy images reveals a higher ordering of SCs within the nuclear volume than what is expected by our numerical model. This suggests that while effects of entropy impact SC organization, the dedicated action of proteins or actin cables is required to fine-tune the spatial ordering of SCs within the cell nucleus.