Zinc finger protein ZFP57 requires its co-factor to recruit DNA methyltransferases and maintains DNA methylation imprint in embryonic stem cells via its transcriptional repression domain.

Previously, we discovered that ZFP57 is a maternal-zygotic effect gene, and it maintains DNA methylation genomic imprint at multiple imprinted regions in mouse embryos. Despite these findings, it remains elusive how DNA methyltransferases are targeted to the imprinting control regions to initiate and maintain DNA methylation imprint. To gain insights into these essential processes in genomic imprinting, we examined how ZFP57 maintains genomic DNA methylation imprint in mouse embryonic stem (ES) cells. Here we demonstrate that the loss of ZFP57 in mouse ES cells led to a complete loss of genomic DNA methylation imprint at multiple imprinted regions, similar to its role in mouse embryos. However, reintroduction of ZFP57 into Zfp57-null ES cells did not result in reacquisition of DNA methylation imprint, suggesting that the memory for genomic imprinting had been lost or altered in Zfp57-null ES cells in culture. Interestingly, ZFP57 and DNA methyltransferases could form complexes in the presence of KAP1/TRIM28/TIF1ß when co-expressed in COS cells. We also found that the wild-type exogenous ZFP57 but not the mutant ZFP57 lacking the KRAB box that interacts with its co-factor KAP1/TRIM28/TIF1ß could substitute for the endogenous ZFP57 in maintaining the DNA methylation imprint in ES cells. These results suggest that ZFP57 may recruit DNA methyltransferases to its target regions to maintain DNA methylation imprint, and this interaction is likely facilitated by KAP1/TRIM28/TIF1ß.

A maternal-zygotic effect gene, Zfp57, maintains both maternal and paternal imprints.

The mechanisms responsible for maintaining genomic methylation imprints in mouse embryos are not understood. We generated a knockout mouse in the Zfp57 locus encoding a KRAB zinc finger protein. Loss of just the zygotic function of Zfp57 causes partial neonatal lethality, whereas eliminating both the maternal and zygotic functions of Zfp57 results in a highly penetrant embryonic lethality. In oocytes, absence of Zfp57 results in failure to establish maternal methylation imprints at the Snrpn imprinted region. Intriguingly, methylation imprints are reacquired specifically at the maternally derived Snrpn imprinted region when the zygotic Zfp57 is present in embryos. This suggests that there may be DNA methylation-independent memory for genomic imprints. Zfp57 is also required for the postfertilization maintenance of maternal and paternal methylation imprints at multiple imprinted domains. The effects on genomic imprinting are consistent with the maternal-zygotic lethality of Zfp57 mutants.

Dendritic cell-expanded, islet-specific CD4+ CD25+ CD62L+ regulatory T cells restore normoglycemia in diabetic NOD mice.

Most treatments that prevent autoimmune diabetes in nonobese diabetic (NOD) mice require intervention at early pathogenic stages, when insulitis is first developing. We tested whether dendritic cell (DC)-expanded, islet antigen-specific CD4+ CD25+ suppressor T cells could treat diabetes at later stages of disease, when most of the insulin-producing islet beta cells had been destroyed by infiltrating lymphocytes. CD4+ CD25+ CD62L+ regulatory T cells (T reg cells) from BDC2.5 T cell receptor transgenic mice were expanded with antigen-pulsed DCs and IL-2, and were then injected into NOD mice. A single dose of as few as 5x10(4) of these islet-specific T reg cells blocked diabetes development in prediabetic 13-wk-old NOD mice. The T reg cells also induced long-lasting reversal of hyperglycemia in 50% of mice in which overt diabetes had developed. Successfully treated diabetic mice had similar responses to glucose challenge compared with nondiabetic NOD mice. The successfully treated mice retained diabetogenic T cells, but also had substantially increased Foxp3+ cells in draining pancreatic lymph nodes. However, these Foxp3+ cells were derived from the recipient mice and not the injected T reg cells, suggesting a role for endogenous T reg cells in maintaining tolerance after treatment. Therefore, inoculation of DC-expanded, antigen-specific suppressor T cells has considerable efficacy in ameliorating ongoing diabetes in NOD mice.

Comparative pharmacology and cloning of two novel arachnid sodium channels: Exploring the adaptive insensitivity of scorpion to its toxins.

Scorpion toxins have been found lacking effect on Na(+) current of its own sodium channel, whereas the molecular mechanism remains mystery. In this study, the binding affinity of pharmacologically distinct scorpion toxins was found much weaker to scorpion (Buthus martensii) nerve synaptosomes than to spider (Ornithoctonus huwena) ones. The sodium channel cDNA from these two species were further cloned. The deduced proteins contain 1871 and 1987 amino acids respectively. Several key amino acid substitutions, i.e., A1610V, I1611L and S1617K, are found in IVS3-S4 constituting receptor site-3, and for receptor site-4, two residues (Leu-Pro) are inserted near IIS4 of scorpion sodium channel.

The cDNA and genomic DNA organization of a novel toxin SHT-I from spider Ornithoctonus huwena.

In present study the full-length cDNA of a novel toxin from the venom gland of spider Ornithoctonus huwena, named as SHT-I, has been cloned using the strategy of rapid amplification of cDNA ends, and then the whole genomic sequence of SHT-I (Selenocosmia huwena toxin-I) was determined using sequence-specific primers synthesized based on the acquired 3' and 5' ends of SHT-I cDNA sequence. It is unexpectedly found that intron was lacking in the genomic sequence of SHT-I. The result might evoke an interesting question whether the gene code of inhibitor cystine-knot peptides from spider venom is distinct from that of those known toxic peptides of scorpion and cone snail.

Molecular mechanism of scorpion neurotoxins acting on sodium channels: insight into their diverse selectivity.

Scorpion toxins that affect sodium channel gating traditionally are divided into alpha- and beta-classes. They show vast diversity in their selectivity for phyletic- or isoform-specific sodium channels. This article discusses the molecular mechanism of the selectivity. Moreover, a phylogenetic tree of scorpion toxins has been constructed, which, together with the worldwide distribution of toxins and the zoogeographic dispersion of the studied genera, offers an insight into the evolution of diverse scorpion toxins.