RESUMO
Mammalian DNA replication is a highly organized and regulated process. Large, Mb-sized regions are replicated at defined times along S-phase. Replication Timing (RT) is thought to play a role in shaping the mammalian genome by affecting mutation rates. Previous analyses relied on somatic RT profiles. However, only germline mutations are passed on to offspring and affect genomic composition. Therefore, germ cell RT information is necessary to evaluate the influences of RT on the mammalian genome. We adapted the RT mapping technique for limited amounts of cells, and measured RT from two stages in the mouse germline - primordial germ cells (PGCs) and spermatogonial stem cells (SSCs). RT in germline cells exhibited stronger correlations to both mutation rate and recombination hotspots density than those of RT in somatic tissues, emphasizing the importance of using correct tissues-of-origin for RT profiling. Germline RT maps exhibited stronger correlations to additional genetic features including GC-content, transposable elements (SINEs and LINEs), and gene density. GC content stratification and multiple regression analysis revealed independent contributions of RT to SINE, gene, mutation, and recombination hotspot densities. Together, our results establish a central role for RT in shaping multiple levels of mammalian genome composition.
Assuntos
Período de Replicação do DNA/genética , Replicação do DNA/genética , Genoma/genética , Células Germinativas/metabolismo , Células-Tronco/metabolismo , Animais , Composição de Bases/genética , Linhagem Celular Tumoral , Células Cultivadas , Elementos de DNA Transponíveis/genética , Feminino , Células Germinativas/citologia , Mutação em Linhagem Germinativa , Masculino , Mamíferos/genética , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos DBA , Camundongos Endogâmicos NOD , Camundongos SCID , Camundongos Transgênicos , Elementos Nucleotídeos Curtos e Dispersos/genética , Células-Tronco/citologiaRESUMO
Stem cells (SCs) play a key role in homeostasis and repair. While many studies have focused on SC self-renewal and differentiation, little is known regarding the molecular mechanism regulating SC elimination and compensation upon loss. Here, we report that Caspase-9 deletion in hair follicle SCs (HFSCs) attenuates the apoptotic cascade, resulting in significant temporal delays. Surprisingly, Casp9-deficient HFSCs accumulate high levels of cleaved caspase-3 and are improperly cleared due to an essential caspase-3/caspase-9 feedforward loop. These SCs are retained in an apoptotic-engaged state, serving as mitogenic signaling centers by continuously releasing Wnt3 and instructing proliferation. Investigating the underlying mechanism, we reveal a caspase-3/Dusp8/p38 module responsible for Wnt3 induction, which operates in both normal and Casp9-deleted HFSCs. Notably, Casp9-deleted mice display accelerated wound repair and de novo hair follicle regeneration. Taken together, we demonstrate that apoptotic cells represent a dynamic SC niche, from which emanating signals drive SC proliferation and tissue regeneration.