Mammalian DNA replication initiates at multiple sites along chromosomes at different times, following a temporal replication program. Homologous alleles typically replicate synchronously; however, mono-allelically expressed genes such as imprinted genes, allelically excluded genes and genes on the female X chromosome replicate asynchronously. We have used a chromosome engineering strategy to identify a human autosomal locus that controls this replication timing program in cis. We show that Cre/loxP-mediated rearrangements at a discrete locus at 6q16.1 result in delayed replication of the entire chromosome. This locus displays asynchronous replication timing that is coordinated with other mono-allelically expressed genes on chromosome 6. Characterization of this locus revealed mono-allelic expression of a large intergenic non-coding RNA, which we have named asynchronous replication and autosomal RNA on chromosome 6, ASAR6. Finally, disruption of this locus results in the activation of the previously silent alleles of linked mono-allelically expressed genes. We previously found that chromosome rearrangements involving eight different autosomes display delayed replication timing, and that cells containing chromosomes with delayed replication timing have a 30-80-fold increase in the rate at which new gross chromosomal rearrangements occurred. Taken together, these observations indicate that human autosomes contain discrete cis-acting loci that control chromosome-wide replication timing, mono-allelic expression and the stability of entire chromosomes.

Purpose:To assess the potential of whole-genome sequencing (WGS) to replicate and augment results from conventional blood-based newborn screening (NBS). Methods:Research-generated WGS data from an ancestrally diverse cohort of 1,696 infants and both parents of each infant were analyzed for variants in 163 genes involved in disorders included or under discussion for inclusion in US NBS programs. WGS results were compared with results from state NBS and related follow-up testing.Results: NBS genes are generally well covered by WGS. There is a median of one (range: 0-6) database-annotated pathogenic variant in the NBS genes per infant. Results of WGS and NBS in detecting 28 state-screened disorders and four hemoglobin traits were concordant for 88.6% of true positives (n = 35) and 98.9% of true negatives (n = 45,757). Of the five infants affected with a state-screened disorder, WGS identified two whereas NBS detected four. WGS yielded fewer false positives than NBS (0.037 vs. 0.17%) but more results of uncertain significance (0.90 vs. 0.013%). Conclusion:WGS may help rule in and rule out NBS disorders, pinpoint molecular diagnoses, and detect conditions not amenable to current NBS assays.

The transcriptional co-activator p300 has been reported to regulate the tumor suppressor p53 and its ortholog p73. Here we describe a study showing that this coactivator also regulates the transcriptional function of p63. p300 bound to the N-terminal domain of p63␥, and p63␥ bound to the N terminus of p300 in vitro and in cells. p300, but not its acetylase-defective mutant AT2, stimulated p63␥-dependent transcription and induction of p21 in cells, consequently leading to G 1 arrest. Inversely, the ⌬N-p63␥ isoform as well as p300AT2 inhibited the induction of p21 by p63␥. These results suggest that p300 regulates p63-dependent transcription of p21.

The highly related acetyltransferases, p300 and CREB-binding protein (CBP) are coactivators of signal-responsive transcriptional activation. In addition, recent evidence suggests that p300/CBP also interacts directly with complexes that mediate DNA replication and repair. In this report, we show that loss of p300/CBP in mammalian cells results in a defect in the cell cycle arrest induced by stalled DNA replication. We demonstrate that complexes containing p300/CBP and ATR can be detected in mammalian cells, and that the downstream kinase CHK1 fails to be phosphorylated in response to stalled DNA replication in cells that lack p300/CBP. These observations broaden the roles for the p300/CBP acetyltransferases to include the modulation of chromatin structure and function during DNA metabolic events as well as for transcription.

Muscle cell differentiation is controlled by a complex set of interactions between tissue restricted transcription factors, ubiquitously expressed transcription factors, and cell cycle regulatory proteins. We previously found that amplification of MDM2 in rhabdomyosarcoma cells interferes with MyoD activity and consequently inhibits overt muscle cell differentiation (1). Recently, we found that MDM2 interacts with Sp1 and inhibits Sp1-dependent transcription and that pRb can restore Sp1 activity by displacing MDM2 from Sp1 (2). In this report, we show that forced expression of Sp1 can restore MyoD activity and restore overt muscle cell differentiation in cells with amplified MDM2. Furthermore, we show that pRb can also restore MyoD activity and muscle cell differentiation in cells with amplified MDM2. Surprisingly, we found that the MyoD-interacting domain of pRb is dispensable for this activity. We show that the C-terminal, MDM2-interacting domain of pRb is both necessary and sufficient to restore muscle cell differentiation in cells with amplified MDM2. We also show that the C-terminal MDM2-interacting domain of pRb can promote premature differentiation of proliferating myoblast cells. Our data support a model in which the pRb-MDM2 interaction modulates Sp1 activity during normal muscle cell differentiation.We previously found that amplification of MDM2 1 in rhabdomyosarcoma cells inhibits MyoD function and inhibits muscle cell differentiation (1). The oncogenic properties of MDM2 are thought to result from interactions with several cell cycle regulatory proteins. MDM2 interacts directly with the tumor suppressor protein p53 (3) and blocks p53-mediated transactivation (4 -9). In addition, MDM2 has been shown to target p53 for rapid degradation (10, 11). MDM2 also interacts with a second tumor suppressor protein, the retinoblastoma-associated protein, pRb. This MDM2-pRb interaction results in inhibition of pRb growth regulatory function (12, 13). Furthermore, MDM2 interacts with the activation domains of the S-phasepromoting transcription factors E2F1 and DP1, resulting in stimulation of E2F1/DP1 transcriptional activity (14). Taken together, these observations suggest that MDM2 not only relieves the proliferative block mediated by either p53 or pRb but also promotes the G 1 -to-S-phase transition by stimulating E2F1/DP1 activity. The results presented here show that MDM2 can also modulate cellular differentiation through pRb and Sp1.Differentiating muscle cells fuse to form multinucleated myotubes, thereby withdrawing permanently from the cell cycle. This process is controlled by the MyoD family (MyoD, Myf-5, myogenin, and MRF4/Myf-6) of muscle-specific transcription factors (15). The MyoD family of basic helix-loop-helix transcription factors acts at multiple points in the myogenic lineage to establish muscle cell identity and control terminal differentiation. MyoD is found in a multiprotein complex that contains tissue-restricted (SRF or MEF2C) and ubiquitously expressed (E12/E47 and Sp1) transcription facto...