Figure: pericentric heterochromatin formation (GO:0031508)¶
This figure illustrates pericentric heterochromatin formation in fission yeast (S. pombe) through both direct and siRNA-mediated pathways. In the direct pathway, FACT complex cooperates with CLRC complex (containing the H3K9 methyltransferase Clr4) to establish H3K9 methylation marks. The SHREC complex (including Clr3 deacetylase) facilitates this process by removing H3K14 acetylation, while Sir2 removes H3K9 acetylation. Swi6 and Chp2 (HP1 homologs) bind to methylated H3K9 and recruit additional factors to stabilize heterochromatin.
In the siRNA-mediated pathway, the RITS complex (containing Ago1, Chp1, and Tas3) targets nascent transcripts and recruits the RDRC complex (Rdp1, Hrr1, Cid12) for RNA-dependent RNA synthesis. Dcr1 (Dicer) processes double-stranded RNA into siRNAs that feed back into the RITS complex. The adaptor protein Stc1 bridges the siRNA machinery with the CLRC methyltransferase complex, reinforcing H3K9 methylation.
Histone demethylases (Lsd1/Lsd2) provide regulatory control, while scaffolding proteins (Ers1/Rad25) help organize the assembly of these complexes. Together, these pathways establish and maintain pericentric heterochromatin, which is essential for genomic stability and proper chromosome segregation in fission yeast.
Feedback from AI on figure:
{"feedback":"The diagram effectively illustrates the pericentric heterochromatin formation pathway in fission yeast. Key strengths include:\n\n1. Clear organization of the complexes (SHREC, CLRC, RITS, ARC, RDRC) with distinctive color-coding makes the diagram visually intuitive\n2. Different arrow styles with accompanying labels clearly distinguish between types of interactions (direct, enzymatic, binding, etc.)\n3. The well-designed legend provides a comprehensive reference for understanding all elements\n4. The siRNA feedback loop is distinctly highlighted, emphasizing this important regulatory mechanism\n5. Text sizes are consistent and appropriately sized for readability\n\nThe diagram successfully captures both the siRNA-mediated and direct heterochromatin formation mechanisms, effectively showing how these pathways interconnect to establish heterochromatin at pericentric regions in S. pombe. The addition of a brief contextual description at the top helps orient viewers unfamiliar with the subject matter.","necessary_changes":null,"optional_changes":null}