SCMH1 (Scm polycomb group protein homolog 1) is a mammalian homolog of the Drosophila Sex comb on midleg gene that functions as a component of Polycomb group (PcG) complexes involved in transcriptional repression 1. The protein contains characteristic domains including two 1(3)mbt domains and an SPM domain, sharing 41% identity with Drosophila Scm and 94% identity with its mouse counterpart 1. SCMH1 functions as an E3 ubiquitin ligase with dual substrate specificity, targeting both histone H2A for transcriptional silencing and geminin for stability regulation 2. As a substoichiometric component of PcG complex 1, SCMH1 provides an interaction domain for geminin and regulates the expression of direct PcG targets including Hoxb4 and Hoxa9 in hematopoietic cells 2. Interestingly, circular RNA derived from SCMH1 (circSCMH1) has emerged as therapeutically relevant in stroke recovery, promoting vascular repair through FTO-mediated m6A demethylation mechanisms 3 and enhancing neuroplasticity while inhibiting glial activation in stroke models 4. CircSCMH1 also regulates mitochondrial function by suppressing KMO expression through STAT5B binding 5. The regulation of circSCMH1 biogenesis itself is controlled by PTBP1, which inhibits back-splicing to reduce circSCMH1 production 6.