Altered microbiota composition reflects enhanced communication in 15q11-13 CNV mice.

Autism spectrum disorder (ASD) is a complex and heterogeneous neurodevelopmental disorder. In addition to the core symptoms of ASD, many patients with ASD also show comorbid gut dysbiosis, which may lead to various gastrointestinal (GI) problems. Intriguingly, there is evidence that gut microbiota communicate with the central nervous system to modulate behavioral output through the gut-brain axis.

Distinct roles of BCNP1 in B-cell development and activation.

B-cell novel protein 1 (BCNP1) has recently been identified as a new B-cell receptor (BCR) signaling molecule but its physiological function remains unknown. Here, we demonstrate that mice deficient in BCNP1 exhibit impaired B-cell maturation and a reduction of B-1a cells. BCNP1-deficient spleen B cells show enhanced survival, proliferation and Ca2+ influx in response to BCR cross-linking as compared with wild-type spleen B cells.

The B cell novel protein 1 (BCNP1) regulates BCR signaling and B cell apoptosis.

The BCR plays a central role in B cell development, survival, activation, and differentiation. We have identified the B cell novel protein 1 (BCNP1) as a new regulator of BCR signaling. BCNP1 contains a pleckstrin homology domain, three proline-rich motifs, and a potential SH2 binding site, and is predominantly expressed by B cells.

FcμR interacts and cooperates with the B cell receptor To promote B cell survival.

The IgM FcR (FcμR) promotes B cell survival, but the molecular mechanism remains largely unknown. We show using FcμR(-/-) and wild-type mice that FcμR specifically enhanced B cell survival induced by BCR cross-linking with F(ab')2-anti-IgM Abs while having no effect on survival when the B cells were activated by CD40 ligation or LPS stimulation. FcμR expression was markedly upregulated by anti-IgM stimulation, which may promote enhanced FcμR signaling in these cells.

LAPTM5 promotes lysosomal degradation of intracellular CD3ζ but not of cell surface CD3ζ.

The lysosomal protein LAPTM5 has been shown to negatively regulate cell surface T cell receptor (TCR) expression and T-cell activation by promoting CD3ζ degradation in lysosomes, but the mechanism remains largely unknown. Here we show that LAPTM5 promotes lysosomal translocation of intracellular CD3ζ but not of the cell surface CD3ζ associated with the mature TCR complex. Kinetic analysis of the subcellular localization of the newly synthesized CD3ζ suggests that LAPTM5 targets CD3ζ in the Golgi apparatus and promotes its lysosomal translocation.

Complement-activating IgM enhances the humoral but not the T cell immune response in mice.

IgM antibodies specific for a certain antigen can enhance antibody responses when administered together with this antigen, a process believed to require complement activation by IgM. However, recent data show that a knock-in mouse strain, Cμ13, which only produces IgM unable to activate complement, has normal antibody responses. Moreover, the recently discovered murine IgM Fc receptor (FcµR or TOSO/FAIM3) was shown to affect antibody responses.

Critical role of the IgM Fc receptor in IgM homeostasis, B-cell survival, and humoral immune responses.

IgM antibodies have been known for decades to enhance humoral immune responses in an antigen-specific fashion. This enhancement has been thought to be dependent on complement activation by IgM-antigen complexes; however, recent genetic studies render this mechanism unlikely. Here, we describe a likely alternative explanation; mice lacking the recently identified Fc receptor for IgM (FcμR) on B cells produced significantly less antibody to protein antigen during both primary and memory responses.

A novel mechanism for the autonomous termination of pre-B cell receptor expression via induction of lysosome-associated protein transmembrane 5.

The expression of the pre-B cell receptor (BCR) is confined to the early stage of B cell development, and its dysregulation is associated with anomalies of B-lineage cells, including leukemogenesis. Previous studies suggested that the pre-BCR signal might trigger the autonomous termination of pre-BCR expression even before the silencing of pre-BCR gene expression to prevent sustained pre-BCR expression. However, the underlying mechanism remains ill defined.

LAPTM5 protein is a positive regulator of proinflammatory signaling pathways in macrophages.

LAPTM5 (lysosomal-associated protein transmembrane 5) is a protein that is preferentially expressed in immune cells, and it interacts with the Nedd4 family of ubiquitin ligases. Recent studies in T and B cells identified LAPTM5 as a negative regulator of T and B cell receptor levels at the plasma membrane. Here we investigated the function of LAPTM5 in macrophages.

Rapid cell division contributes to efficient induction of A/T mutations during Ig gene hypermutation.

Ig gene hypermutation is initiated by the activation-induced cytidine deaminase (AID), which converts cytosine to uracil and generates a U:G lesion. One of the unsolved mysteries is how AID-triggered U:G lesions result in efficient induction of mutations at non-damaged A/T bases in the V(H) genes of germinal center (GC) B cells. Genetic and biochemical evidence suggests that components of the mismatch repair pathway and the low fidelity DNA polymerase η are required for the induction of A/T mutations.

A role for lysosomal-associated protein transmembrane 5 in the negative regulation of surface B cell receptor levels and B cell activation.

Mechanisms by which cell surface levels of the BCR are regulated remain largely unknown. We found that B cells lacking the lysosomal-associated protein transmembrane 5 (LAPTM5) expressed higher levels of cell surface BCR than did wild-type (WT) B cells after Ag stimulation in vitro and in vivo. In addition, LAPTM5-deficient mice contained an increased frequency of Ag-specific B cells and produced greater amounts of Abs than did WT mice after immunization with a T-dependent Ag.

Deficiency of the oxidative damage-specific DNA glycosylase NEIL1 leads to reduced germinal center B cell expansion.

Mammalian cells possess multiple DNA glycosylases, including OGG1, NTH1, NEIL1, NEIL2 and NEIL3, for the repair of oxidative DNA damage. Among these, NEIL1 and NEIL2 are able to excise oxidized bases on single stranded or bubble-structured DNA and has been implicated in repair of oxidative damage associated with DNA replication or transcription. We found that Neil1 was highly constitutively expressed in the germinal center (GC) B cells, a rapidly dividing cell population that is undergoing immunoglobulin (Ig) gene hypermutation and isotype switching.

A critical role for REV1 in regulating the induction of C:G transitions and A:T mutations during Ig gene hypermutation.

REV1 is a deoxycytidyl transferase that catalyzes the incorporation of deoxycytidines opposite deoxyguanines and abasic sites. To explore the role of its catalytic activity in Ig gene hypermutation in mammalian cells, we have generated mice expressing a catalytically inactive REV1 (REV1AA). REV1AA mice developed normally and were fertile on a pure C57BL/6 genetic background.

Induction of a:T mutations is dependent on cellular environment but independent of mutation frequency and target gene location.

Based on its substrate specificity, activation-induced cytidine deaminase can directly induce C:G mutations in Ig genes. However the origin of A:T mutations, which occur in a similar proportion in germinal center (GC) B cells, is unclear. Genetic evidence suggests that the induction of A:T mutations requires the components of the mismatch repair system and DNA polymerase eta (POLH).

DNA polymerase eta is a limiting factor for A:T mutations in Ig genes and contributes to antibody affinity maturation.

DNA polymerase eta (POLH) is required for the generation of A:T mutations during the somatic hypermutation of Ig genes in germinal center B cells. It remains unclear, however, whether POLH is a limiting factor for A:T mutations and how the absence of POLH might affect antibody affinity maturation. We found that the heterozygous Polh+/- mice exhibited a significant reduction in the frequency of A:T mutations in Ig genes, with each type of base substitutions at a level intermediate between the Polh+/+ and Polh(-/-) mice.

A lysosomal protein negatively regulates surface T cell antigen receptor expression by promoting CD3zeta-chain degradation.

Modulation of surface T cell antigen receptor (TCR) expression is an important mechanism for the regulation of immune responses and the prevention of T cell hyperactivation and autoimmunity. The TCR is rapidly internalized after antigen stimulation and then degraded in lysosomes. However, few of the molecules involved in this process have been identified.

Genetic analysis reveals an intrinsic property of the germinal center B cells to generate A:T mutations.

The immunoglobulin genes undergo a high frequency of point mutations at both C:G and A:T pairs in the germinal center (GC) B cells. This hypermutation process is initiated by the activation-induced cytidine deaminase (AID), which converts cytosine to uracil and generates a U:G lesion. Replication of this lesion, or its repair intermediate the abasic site, could introduce C:G mutations but the mechanisms leading to mutations at non-damaged A:T pairs remain elusive.

DNA polymerases eta and theta function in the same genetic pathway to generate mutations at A/T during somatic hypermutation of Ig genes.

Somatic hypermutation of the Ig genes requires the activity of multiple DNA polymerases to ultimately introduce mutations at both A/T and C/G base pairs. Mice deficient for DNA polymerase eta (POLH) exhibited an approximately 80% reduction of the mutations at A/T, whereas absence of polymerase (POLQ) resulted in approximately 20% reduction of both A/T and C/G mutations. To investigate whether the residual A/T mutations observed in the absence of POLH are generated by POLQ and how these two polymerases might cooperate or compete with each other to generate A/T mutations, here we have established mice deficient for both POLH and POLQ.

Absence of DNA polymerase theta results in decreased somatic hypermutation frequency and altered mutation patterns in Ig genes.

Multiple DNA polymerases participate in somatic hypermutation of immunoglobulin (Ig) genes. Mutations at A/T are largely dependent on DNA polymerase eta (POLH) whereas mutations at C/G appear to be generated by several DNA polymerases. We have previously shown that mice expressing a catalytically inactive POLQ (Polq-inactive) have a reduction in C/G mutations.

Role of DNA polymerase theta in tolerance of endogenous and exogenous DNA damage in mouse B cells.

DNA polymerase theta (Poltheta) is a family A polymerase that contains an intrinsic helicase domain. To investigate the function of Poltheta in mammalian cells, we have inactivated its polymerase activity in CH12 mouse B lymphoma cells by targeted deletion of the polymerase core domain that contains the catalytic aspartic acid residue. Compared to parental CH12 cells, mutant cells devoid of Poltheta polymerase activity exhibited a slightly reduced growth rate, accompanied by increased spontaneous cell death.

DNA polymerase theta contributes to the generation of C/G mutations during somatic hypermutation of Ig genes.

Somatic hypermutation of Ig variable region genes is initiated by activation-induced cytidine deaminase; however, the activity of multiple DNA polymerases is required to ultimately introduce mutations. DNA polymerase eta (Poleta) has been implicated in mutations at A/T, but polymerases involved in C/G mutations have not been identified. We have generated mutant mice expressing DNA polymerase (Pol) specifically devoid of polymerase activity.

HEXIM1 forms a transcriptionally abortive complex with glucocorticoid receptor without involving 7SK RNA and positive transcription elongation factor b.

The HEXIM1 protein has been shown to form a protein-RNA complex composed of 7SK small nuclear RNA and positive transcription elongation factor b (P-TEFb), which is composed of cyclin-dependent kinase 9 (CDK9) and cyclin T1, and to inhibit the kinase activity of CDK9, thereby suppressing RNA polymerase II-dependent transcriptional elongation. Here, we biochemically demonstrate that HEXIM1 forms a distinct complex with glucocorticoid receptor (GR) without RNA, CDK9, or cyclin T1. HEXIM1, through its arginine-rich nuclear localization signal, directly associates with the ligand-binding domain of GR.

Bcl-2 prevents hypoxia/reoxygenation-induced cell death through suppressed generation of reactive oxygen species and upregulation of Bcl-2 proteins.

The function of bcl-2 in preventing cell death is well known, but the mechanisms whereby bcl-2 functions are not well characterized. One mechanism whereby bcl-2 is thought to function is by alleviating the effects of oxidative stress upon the cell. To examine whether Bcl-2 can protect cells against oxidative injury resulting from post-hypoxic reoxygenation (H/R), we subjected rat fibroblasts Rat-1 and their bcl-2 transfectants b5 to hypoxia (5% CO2, 95% N2) followed by reoxygenation (5% CO2, 95% air).

Role of the glucocorticoid receptor for regulation of hypoxia-dependent gene expression.

Glucocorticoids are secreted from the adrenal glands and act as a peripheral effector of the hypothalamic-pituitary-adrenal axis, playing an essential role in stress response and homeostatic regulation. In target cells, however, it remains unknown how glucocorticoids fine-tune the cellular pathways mediating tissue and systemic adaptation. Recently, considerable evidence indicates that adaptation to hypoxic environments is influenced by glucocorticoids and there is cross-talk between hypoxia-dependent signals and glucocorticoid-mediated regulation of gene expression.