Biomedical subjects

Ulla Aapola

Publications and source records attributed to Ulla Aapola.

3 recordsLinked to original sources

PubMed2005

Meiotic and epigenetic defects in Dnmt3L-knockout mouse spermatogenesis.

The production of mature germ cells capable of generating totipotent zygotes is a highly specialized and sexually dimorphic process. The transition from diploid primordial germ cell to haploid spermatozoa requires genome-wide reprogramming of DNA methylation, stage- and testis-specific gene expression, mitotic and meiotic division, and the histone-protamine transition, all requiring unique epigenetic control. Dnmt3L, a DNA methyltransferase regulator, is expressed during gametogenesis, and its deletion results in sterility. We found that during spermatogenesis, Dnmt3L contributes to the acquisition of DNA methylation at paternally imprinted regions, unique nonpericentric heterochromatic sequences, and interspersed repeats, including autonomous transposable elements. We observed retrotransposition of an LTR-ERV1 element in the DNA from Dnmt3L-/- germ cells, presumably as a result of hypomethylation. Later in development, in Dnmt3L-/- meiotic spermatocytes, we detected abnormalities in the status of biochemical markers of heterochromatin, implying aberrant chromatin packaging. Coincidentally, homologous chromosomes fail to align and form synaptonemal complexes, spermatogenesis arrests, and spermatocytes are lost by apoptosis and sloughing. Because Dnmt3L expression is restricted to gonocytes, the presence of defects in later stages reveals a mechanism whereby early genome reprogramming is linked inextricably to changes in chromatin structure required for completion of spermatogenesis.

Animals↗

PubMed2004

Epigenetic modifications affect Dnmt3L expression.

Imprinted genes are expressed from a single allele due to differential methylation of maternal or paternal alleles during gametogenesis. Dnmt3L (DNA cytosine-5-methyltransferase 3 like), a member of de novo methyltransferase Dnmt3 protein family, is a regulator of maternal imprinting. In the present study, we have characterized the promoter region of the mouse Dnmt3L gene. Transient transfection assays performed with 5'-deletion promoter constructs indicated a minimal promoter area within 440 bp upstream from the translational start site. Longer promoter constructs showed decreased activity, suggesting the presence of repressor elements within the upstream sequences. According to electrophoretic mobility-shift assays and mutation analysis, the minimal promoter region contained four functional binding sites for the Sp1 (specificity protein 1) family of transcription factors, Sp1 and Sp3. In vitro methylation of Dnmt3L promoter constructs decreased the transcriptional activity significantly, demonstrating down-regulation by cytosine methylation. This was supported by the results from bisulphite sequencing and real-time quantitative reverse transcriptase-PCR analysis of different mouse cell lines and tissues. In testis and embryonic stem cells showing strong Dnmt3L expression, all CpG sites studied were fully unmethylated, whereas non-expressive cell lines and tissues with lesser Dnmt3L expression showed complete or diverse CpG methylation levels. Treatment of Dnmt3L non-expressive cell lines with deacetylase inhibitor trichostatin A and methyltransferase inhibitor 5-aza-2'-deoxycytidine induced the expression of Dnmt3L mRNA. Furthermore, we show that the repressional effect of longer promoter fragments was also relieved by these inhibitors, altogether indicating an epigenetic control for Dnmt3L gene regulation.

Animals↗

PubMed2002

Imprinting regulator DNMT3L is a transcriptional repressor associated with histone deacetylase activity.

DNMT3L is a regulator of imprint establishment of normally methylated maternal genomic sequences. DNMT3L shows high similarity to the de novo DNA methyltransferases, DNMT3A and DNMT3B, however, the amino acid residues needed for DNA cytosine methyltransferase activity have been lost from the DNMT3L protein sequence. Apart from methyltransferase activity, Dnmt3a and Dnmt3b serve as transcriptional repressors associating with histone deacetylase (HDAC) activity. Here we show that DNMT3L can also repress transcription by binding directly to HDAC1 protein. We have identified the PHD-like zinc finger of the ATRX domain as a main repression motif of DNMT3L, through which DNMT3L recruits the HDAC activity needed for transcriptional silencing. Furthermore, we show that DNMT3L protein contains an active nuclear localisation signal at amino acids 156-159. These results describe DNMT3L as a co-repressor protein and suggest that a transcriptionally repressed chromatin organisation through HDAC activity is needed for establishment of genomic imprints.

Acetylation↗