Cdc7 kinase is required for postnatal brain development.

The evolutionally conserved Cdc7 kinase plays crucial roles in initiation of DNA replication as well as in other chromosomal events. To examine the roles of Cdc7 in brain development, we have generated mice carrying Cdc7 knockout in neural stem cells by using Nestin-Cre. The Cdc7Fl/Fl NestinCre mice were born, but exhibited severe growth retardation and impaired postnatal brain development. These mice exhibited motor dysfunction within 9 days after birth and did not survive for more than 19 days. The cerebral cortical layer formation was impaired, although the cortical cell numbers were not altered in the mutant. In the cerebellum undergoing hypoplasia, granule cells (CGC) decreased in number in Cdc7Fl/F l NestinCre mice compared to the control at E15-18, suggesting that Cdc7 is required for DNA replication and cell proliferation of CGC at mid embryonic stage (before embryonic day 15). On the other hand, the Purkinje cell numbers were not altered but its layer formation was impaired in the mutant. These results indicate differential roles of Cdc7 in DNA replication/cell proliferation in brain. Furthermore, the defects of layer formation suggest a possibility that Cdc7 may play an additional role in cell migration during neural development.

Loss of full-length DNA replication regulator Rif1 in two-cell embryos is associated with zygotic transcriptional activation.

Rif1 regulates DNA replication timing and double-strand break repair, and its depletion induces transcriptional bursting of two-cell (2C) zygote-specific genes in mouse ES cells. However, how Rif1 regulates zygotic transcription is unclear. We show here that Rif1 depletion promotes the formation of a unique Zscan4 enhancer structure harboring both histone H3 lysine 27 acetylation (H3K27ac) and moderate levels of silencing chromatin mark H3K9me3. Curiously, another enhancer mark H3K4me1 is missing, whereas DNA methylation is still maintained in the structure, which spreads across gene bodies and neighboring regions within the Zscan4 gene cluster. We also found by function analyses of Rif1 domains in ES cells that ectopic expression of Rif1 lacking N-terminal domain results in upregulation of 2C transcripts. This appears to be caused by dominant negative inhibition of endogenous Rif1 protein localization at the nuclear periphery through formation of hetero-oligomers between the N-terminally truncated and endogenous forms. Strikingly, in murine 2C embryos, most of Rif1-derived polypeptides are expressed as truncated forms in soluble nuclear or cytosolic fraction and are likely nonfunctional. Toward the morula stage, the full-length form of Rif1 gradually increased. Our results suggest that the absence of the functional full-length Rif1 due to its instability or alternative splicing and potential inactivation of Rif1 through dominant inhibition by N-terminally truncated Rif1 polypeptides may be involved in 2C-specific transcription program.

Mast Cell-Specific Deletion of Group III Secreted Phospholipase A2 Impairs Mast Cell Maturation and Functions.

Tissue-resident mast cells (MCs) have important roles in IgE-associated and -independent allergic reactions. Although microenvironmental alterations in MC phenotypes affect the susceptibility to allergy, understanding of the regulation of MC maturation is still incomplete. We previously reported that group III secreted phospholipase A2 (sPLA2-III) released from immature MCs is functionally coupled with lipocalin-type prostaglandin D2 (PGD2) synthase in neighboring fibroblasts to supply a microenvironmental pool of PGD2, which in turn acts on the PGD2 receptor DP1 on MCs to promote their proper maturation. In the present study, we reevaluated the role of sPLA2-III in MCs using a newly generated MC-specific Pla2g3-deficient mouse strain. Mice lacking sPLA2-III specifically in MCs, like those lacking the enzyme in all tissues, had immature MCs and displayed reduced local and systemic anaphylactic responses. Furthermore, MC-specific Pla2g3-deficient mice, as well as MC-deficient KitW-sh mice reconstituted with MCs prepared from global Pla2g3-null mice, displayed a significant reduction in irritant contact dermatitis (ICD) and an aggravation of contact hypersensitivity (CHS). The increased CHS response by Pla2g3 deficiency depended at least partly on the reduced expression of hematopoietic PGD2 synthase and thereby reduced production of PGD2 due to immaturity of MCs. Overall, our present study has confirmed that MC-secreted sPLA2-III promotes MC maturation, thereby facilitating acute anaphylactic and ICD reactions and limiting delayed CHS response.

PKCδ deficiency inhibits fetal development and is associated with heart elastic fiber hyperplasia and lung inflammation in adult PKCδ knockout mice.

Protein kinase C-delta (PKCδ) has a caspase-3 recognition sequence in its structure, suggesting its involvement in apoptosis. In addition, PKCδ was recently reported to function as an anti-cancer factor. The generation of a PKCδ knockout mouse model indicated that PKCδ plays a role in B cell homeostasis. However, the Pkcrd gene, which is regulated through complex transcription, produces multiple proteins via alternative splicing. Since gene mutations can result in the loss of function of molecular species required for each tissue, in the present study, conditional PKCδ knockout mice lacking PKCδI, II, IV, V, VI, and VII were generated to enable tissue-specific deletion of PKCδ using a suitable Cre mouse. We generated PKCδ-null mice that lacked whole-body expression of PKCδ. PKCδ+/- parental mice gave birth to only 3.4% PKCδ-/- offsprings that deviated significantly from the expected Mendelian ratio (χ2(2) = 101.7, P < 0.001). Examination of mice on embryonic day 11.5 (E11.5) showed the proportion of PKCδ-/- mice implanted in the uterus in accordance with Mendelian rules; however, approximately 70% of the fetuses did not survive at E11.5. PKCδ-/- mice that survived until adulthood showed enlarged spleens, with some having cardiac and pulmonary abnormalities. Our findings suggest that the lack of PKCδ may have harmful effects on fetal development, and heart and lung functions after birth. Furthermore, our study provides a reference for future studies on PKCδ deficient mice that would elucidate the effects of the multiple protein variants in mice and decipher the roles of PKCδ in various diseases.

Eukaryotic translation initiation factor 3 (eIF3) subunit e is essential for embryonic development and cell proliferation.

Mammalian eukaryotic translation initiation factor 3 (eIF3) is the largest complex of the translation initiation factors. The eIF3 complex is comprised of thirteen subunits, which are named eIF3a to eIF3 m in most multicellular organisms. The eIF3e gene locus is one of the most frequent integration sites of mouse mammary tumor virus (MMTV), which induces mammary tumors in mice. MMTV-integration events result in the expression of C-terminal-truncated eIF3e proteins, leading to mammary tumor formation. We have shown that tumor formation can be partly caused by activation of hypoxia-inducible factor 2α. To investigate the function of eIF3e in mammals, we generated eIF3e-deficient mice. These eIF3e-/- mice are embryonically lethal, while eIF3e+/- mice are much smaller than wild-type mice. In addition, eIF3e+/- mouse embryonic fibroblasts (MEFs) contained reduced levels of eIF3a and eIF3c subunits and exhibited reduced cellular proliferation. These results suggest that eIF3e is essential for embryonic development in mice and plays a role in maintaining eIF3 integrity.

PNPLA1 has a crucial role in skin barrier function by directing acylceramide biosynthesis.

Mutations in patatin-like phospholipase domain-containing 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, but the mechanism involved remains unclear. Here we show that PNPLA1, an enzyme expressed in differentiated keratinocytes, plays a crucial role in the biosynthesis of ω-O-acylceramide, a lipid component essential for skin barrier. Global or keratinocyte-specific Pnpla1-deficient neonates die due to epidermal permeability barrier defects with severe transepidermal water loss, decreased intercellular lipid lamellae in the stratum corneum, and aberrant keratinocyte differentiation. In Pnpla1-/- epidermis, unique linoleate-containing lipids including acylceramides, acylglucosylceramides and (O-acyl)-ω-hydroxy fatty acids are almost absent with reciprocal increases in their putative precursors, indicating that PNPLA1 catalyses the ω-O-esterification with linoleic acid to form acylceramides. Moreover, acylceramide supplementation partially rescues the altered differentiation of Pnpla1-/- keratinocytes. Our findings provide valuable insight into the skin barrier formation and ichthyosis development, and may contribute to novel therapeutic strategies for treatment of epidermal barrier defects.

Comprehensive application of an mtDsRed2-Tg mouse strain for mitochondrial imaging.

Mitochondria are essential for many cellular functions such as oxidative phosphorylation and calcium homeostasis; consequently, mitochondrial dysfunction could cause many diseases, including neurological disorders. Recently, mitochondrial dynamics, such as fusion, fission, and transportation, have been visualized in living cells by using time-lapse imaging systems. The changes in mitochondrial morphology could be an indicator for estimating the activity of mitochondrial biological function. Here, we report a transgenic mouse strain, mtDsRed2-Tg, which expresses a red fluorescent protein, DsRed2, exclusively in mitochondria. Mitochondrial morphology could be clearly observed in various tissues of this strain under confocal microscope. Recently, many transgenic mouse strains in which enhanced green fluorescent protein (EGFP)-tagged proteins of interest are expressed have been established for physiological analysis in vivo. After mating these strains with mtDsRed2-Tg mice, red-colored mitochondria and green-colored proteins were detected simultaneously using fluorescent imaging systems, and the interactions between mitochondria and those proteins could be morphologically analyzed in cells and tissues of the F(1) hybrids. Thus, mtDsRed2-Tg mice can be a powerful tool for bioimaging studies on mitochondrial functions.

Over-expression of Tfam improves the mitochondrial disease phenotypes in a mouse model system.

The phenotypes of mitochondrial diseases caused by mutations in mitochondrial DNA (mtDNA) have been proposed to be strictly regulated by the proportion of wild-type and pathogenically mutated mtDNAs. More specifically, it is thought that the onset of the disease phenotype occurs when cells cannot maintain the proper mitochondrial function because of an over-abundance of pathological mtDNA. Therapies that cause a decrease in the pathogenic mtDNA population have been proposed as a treatment for mitochondrial diseases, but these therapies are difficult to apply in practice. In this report, we present a novel concept: to improve mitochondrial disease phenotypes via an increase in the absolute copy number of the wild-type mtDNA population in pathogenic cells even when the relative proportion of mtDNA genotypes remains unchanged. We have succeeded in ameliorating the typical symptoms of mitochondrial disease in a model mouse line by the over-expression of the mitochondrial transcription factor A (Tfam) followed by an increase of the mtDNA copy number. This new concept should lead to the development of a novel therapeutic treatment for mitochondrial diseases.

Alivin 1, a novel neuronal activity-dependent gene, inhibits apoptosis and promotes survival of cerebellar granule neurons.

Neurons require Ca2+-dependent gene transcription for their activity-dependent survival, the mechanisms of which have not been fully elucidated yet. Here, we demonstrate that a novel primary response gene, alivin 1 (ali1), is an activity-dependent gene and promotes survival of neurons. Sequence analyses reveal that rat, mouse, and human Ali1 proteins contain seven leucine-rich repeats, one IgC2-like loop and a transmembrane domain, and display homology to Kek and Trk families. Expression of ali1 mRNA in cultured cerebellar granule neurons is rigidly regulated by KCl and/or NMDA concentrations in the culture medium and tightly correlated to depolarization-dependent survival and/or NMDA-dependent survival of the granule neuron. ali1 mRNA expression was regulated at the transcriptional step by the Ca2+ influx through voltage-dependent L-type Ca2+ channels when the cells were stimulated by 25 mm KCl. Expression of ali1 mRNA in cultured cortical neurons was inhibited when their spontaneous electrical activity was blocked by tetrodotoxin. Thus, the expression is neuronal activity dependent. Overexpression of Ali1 in cerebellar granule neurons inhibited apoptosis that was induced by the medium containing 5 mm KCl. The addition of anti-Ali1 antiserum or the soluble putative extracellular Ali1 domain to the 25 mm KCl-supported culture inhibited the survival of the granule neuron. These results suggest that expression of ali1 promotes depolarization-dependent survival of the granule neuron. Mouse ali1 was mapped to a locus approximately 55.3 cM from the centromere on chromosome 15 that is syntenic to positional candidate loci for familial Alzheimer's disease type 5 and Parkinson's disease 8 on human chromosome 12.