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. 2020 Sep 30;3:542. doi: 10.1038/s42003-020-01265-w

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 1 — Images show steps for isolation of meiotic (a) and mitotic (b) chromosomes. a A large spermatocyte containing chromosomes (subpanel 1) was identified, and lysed with Triton X-100 in a pipette to release the prophase nucleus (2). Another pipette then was used to grab and hold the nucleus (3). A chromosome end at the edge of the nucleus then was grabbed with a soft force-measuring pipette (4); the other chromosome end was captured with a stiff pulling pipette (5), and the rest of the nucleus was removed, leaving only the prophase chromosomes on the pipettes (6). b A rounded mitotic cell with visible dark chromosomes in prometaphase was identified (1), lysed with Triton X-100 sprayed from a pipette to release the prometaphase mitotic bundle (2), and another pipette then grabbed and held the bundle (3). A chromosome end at the edge of the bundle was grabbed with a thin, force pipette and moved away from the bundle (4), where the other end of the chromosome was grabbed by a stiff, pulling pipette (5), and the bundle was removed, leaving one chromosome isolated between two pipettes (6). Scale bars are 5 μm. c Distinguishing mitotic MEF from meiotic prophase spermatocyte chromosomes using fluorescence microscopy. MEF chromosomes appear as rod-like structures in the phase-contrast channel that stain for DNA, but do not immunostain for SYCP1 or SYCP3. Wildtype spermatocyte chromosomes appear as rod-like structures that stain for DNA, SYCP1, and SYCP3. Sycp1^−/− spermatocyte chromosomes stain for DNA and SYCP3, but not SYCP1. Scale bar is 5 μm. d Stiffness (Young’s Modulus) of mitotic and meiotic chromosomes. MEF chromosomes have a stiffness of 370 ± 70 Pascals (Pa, N = 10), ten-fold weaker than wildtype spermatocyte chromosomes (3700 ± 800 Pa, N = 17, p = 0.006 relative to MEF). Wildtype and Sycp1^−/− spermatocyte chromosomes (Sycp1^−/− modulus 3600 ± 700 Pa, N = 8, p = 0.0001 relative to MEF) do not have a statistically significant difference in stiffness (p = 0.93). All averages are reported as mean value ± SEM. All p values calculated via t-test.