Fig. 5: Cellular polarization precedes chromatin orientation.
From: Biophysical ordering transitions underlie genome 3D re-organization during cricket spermiogenesis
A, B Round spermatids feature nascent flagella and acrosomes. A: Confocal microscopy images of testes stained for DNA (white) and αTubulin (green) show nascent flagellar microtubules in early spermatids. B Electron microscopy image of a round spermatid cyst showing multiple nuclei (left). The boxed region is zoomed in the right panel. Chromatin is homogeneously enriched at the nuclear periphery, flanked by nascent flagellar (arrow) and acrosomal (arrowhead) structures, indicating that cellular antero-posterior poles were defined before chromatin became oriented. C In polymer simulations, nuclear elongation drives the spontaneous reorientation of the chromatin spool axis perpendicular to the antero-posterior line, and leads to the distinct unidirectional alignment of the chromatin fiber coils. D Elongating spool organization observed in simulations and in vivo. Transversal sections of nuclei during elongation in polymer simulations (left) and in electron microscopy images of elongating spermatids (right) show a similar configuration whereby the vestigial spool axis perpendicular to the elongation axis is still apparent. E Alignment parameter \(\alpha\) computed through the bulk of the nuclear interior (see Methods), as a function of the applied stretching force \(F\). As in Fig. 3D, bars correspond to the standard error of the mean from experimental measurements from EM images at the elongating stage (gray box).
