RESUMEN
Heterochromatin-related epigenetic mechanisms, such as DNA methylation, facilitate pairing of homologous chromosomes during the meiotic prophase of mammalian spermatogenesis. In pro-spermatogonia, de novo DNA methylation plays a key role in completing meiotic prophase and initiating meiotic division. However, the role of maintenance DNA methylation in the regulation of meiosis, especially in the adult, is not well understood. Here, we reveal that NP95 (also known as UHRF1) and DNMT1 - two essential proteins for maintenance DNA methylation - are co-expressed in spermatogonia and are necessary for meiosis in male germ cells. We find that Np95- or Dnmt1-deficient spermatocytes exhibit spermatogenic defects characterized by synaptic failure during meiotic prophase. In addition, assembly of pericentric heterochromatin clusters in early meiotic prophase, a phenomenon that is required for subsequent pairing of homologous chromosomes, is disrupted in both mutants. Based on these observations, we propose that DNA methylation, established in pre-meiotic spermatogonia, regulates synapsis of homologous chromosomes and, in turn, quality control of male germ cells. Maintenance DNA methylation, therefore, plays a role in ensuring faithful transmission of both genetic and epigenetic information to offspring.
Asunto(s)
Proteínas Potenciadoras de Unión a CCAAT/genética , Emparejamiento Cromosómico/genética , ADN (Citosina-5-)-Metiltransferasa 1/genética , Metilación de ADN/genética , Espermatocitos/crecimiento & desarrollo , Espermatogénesis/genética , Ubiquitina-Proteína Ligasas/genética , Células Madre Germinales Adultas/citología , Animales , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , ADN (Citosina-5-)-Metiltransferasa 1/metabolismo , Epigénesis Genética/genética , Heterocromatina/metabolismo , Masculino , Ratones , Ratones Noqueados , Espermatocitos/fisiología , Espermatogénesis/fisiología , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
During meiosis, specific histone modifications at pericentric heterochromatin (PCH), especially histone H3 tri- and dimethylation at lysine 9 (H3K9me3 and H3K9me2, respectively), are required for proper chromosome interactions. However, the molecular mechanism by which H3K9 methylation mediates the synapsis is not yet understood. We have generated a Cbx3-deficient mouse line and performed comparative analysis on Suv39h1/h2-, G9a- and Cbx3-deficient spermatocytes. This study revealed that H3K9me2 at PCH depended on Suv39h1/h2-mediated H3K9me3 and its recognition by the Cbx3 gene product HP1γ. We further found that centromere clustering and synapsis were commonly affected in G9a- and Cbx3-deficient spermatocytes. These genetic observations suggest that HP1γ/G9a-dependent PCH-mediated centromere clustering is an axis for proper chromosome interactions during meiotic prophase. We propose that the role of the HP1γ/G9a axis is to retain centromeric regions of unpaired homologous chromosomes in close alignment and facilitate progression of their pairing in early meiotic prophase. This study also reveals considerable plasticity in the interplay between different histone modifications and suggests that such stepwise and dynamic epigenetic modifications may play a pivotal role in meiosis.
Asunto(s)
Proteínas Cromosómicas no Histona/genética , Emparejamiento Cromosómico , N-Metiltransferasa de Histona-Lisina/genética , Histonas/química , Meiosis , Animales , Centrómero/ultraestructura , Homólogo de la Proteína Chromobox 5 , Proteínas Cromosómicas no Histona/fisiología , Epigénesis Genética , Femenino , N-Metiltransferasa de Histona-Lisina/fisiología , Masculino , Metilación , Ratones , Ratones Noqueados , Microscopía Fluorescente/métodos , Modelos Genéticos , Espermatocitos/citologíaRESUMEN
The immune system encompasses acquired and innate immunity that matures through interaction with microenvironmental components. Cytokines serve as environmental factors that foster functional maturation of immune cells. Although NOD/SCID/IL2rgKO (NSG) humanized mice support investigation of human immunity in vivo, a species barrier between human immune cells and the mouse microenvironment limits human acquired as well as innate immune function. To study the roles of human cytokines in human acquired and innate immune cell development, we created NSG mice expressing hIL-7 and hIL-15. Although hIL-7 alone was not sufficient for supporting human NK cell development in vivo, increased frequencies of human NK cells were confirmed in multiple organs of hIL-7 and hIL-15 double knockin (hIL-7xhIL-15 KI) NSG mice engrafted with human hematopoietic stem cells. hIL-7xhIL-15 KI NSG humanized mice provide a valuable in vivo model to investigate development and function of human NK cells.