Recent computer simulation of selleck chemical chromatin dynamics suggests that these depletion attraction forces are sufficient to explain the position of chromocenters and nucleoli in interphasic Arabidopsis nuclei. Structural features of the centromeres/pericentromeres in post zygotic embryonic stages Because of the highly decondensed state of pericentro meric heterochromatin in zygotes, we were not able to segment the FISH signals in these embryos with suffi cient precision to perform further computational ana lysis. On the other hand, as reorganization of the centromeric and pericentromeric heterochromatin into chromocenters occurs post zygotically, in subsequent stages we were able to more precisely analyze hetero chromatin reorganization as well as various nuclear parameters using the 3D FISH images.
Unique image analysis tools developed for large objects such as individ ual embryos in toto were specifically adapted to analyze nuclear elements of highly different and complex sizes and shapes, especially the pericentromeric Inhibitors,Modulators,Libraries signals. Fi nally, as all the segmented signals/objects bore labels, we were able to analyze their relationships and measure interaction volumes. Inhibitors,Modulators,Libraries Thanks to these computational tools, we were able to analyze, for the first time, a large number of embryos Inhibitors,Modulators,Libraries covering the whole preimplantation period. These methods also allowed us to statistically document development dependent modifications of embryonic gen ome organization. In particular, we show here that nuclear polarity is conserved up to the 32 cell stage but decreases in blastocysts, as previously suggested by 2D FISH on centromeric repeats.
Unexpectedly, we also found that the Inhibitors,Modulators,Libraries 4 cell stage represents a major step in preimplantation develop ment. When we classified the pericentromeres as either compact or elongated, we observed that the propor tion of elongated pericentromeres with a strong NPB/ Inhibitors,Modulators,Libraries nucleolus interaction was higher in the early 2 cell than in the late 2 cell stage. This proportion then decreased dramatically between the 2 and 4 cell stages, while the percentage of compact pericentromeres increased drastically to reach 90%. Altogether, this suggests that dissociation of pericentromeric heterochromatin from NBPs/nucleoli begins at the 2 cell stage but finishes at the 4 cell stage. The factors or mechanisms that first favor pericentromeric/centromeric association to NPBs and then initiate the formation of chromocenters re main largely unknown.
However, one such factor could be the HP1B protein. In somatic cells, the presence of HP1B in fibrillarin rich regions of nucleoli has already been reported. inhibitor Erlotinib In mouse 1 and 2 cell embryos, we previously showed that fibrillarin is located at the NPB surface and could therefore represent an anchoring protein for HP1B and pericentromeric heterochromatin.