Abstract
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.
Highlights
Reproducing organisms employ a specialized cell division cycle, meiosis, to produce haploid gametes from diploid nuclei [1]
Since the resolution of synaptonemal complex (SC) entanglement plays an important role during meiosis, we study the impact that tethering and semiflexibility can have on the intrachain-entanglement as well as on interchain-entanglement between SC polymers in confinement
Analysing intra- and interchain entanglement from data experimentally obtained by 4Pi microscopy of mouse spermatocytes, we find a low amount of both types of chain overcrossings, mACNintra,exp~0:1+0:075 and mACNinter,exp~0:13+0:08, which cannot be explained within our SC polymer model
Summary
Reproducing organisms employ a specialized cell division cycle, meiosis, to produce haploid gametes from diploid nuclei [1] This process is accomplished by first pairing homologous chromosomes, and recombining and subsequently segregating them from each other [2,3]. Optical sectioning and fluorescence deconvolution light microscopy have shown that SCs undergo dramatic rearrangements during meiotic prophase leading to the resolution of interlocks [6,8,9]. During this phase SCs appear well separated and uniformly distributed throughout the nucleus
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