Novel function of PIWIL1 in neuronal polarization and migration via regulation of microtubule-associated proteins.

BACKGROUND: Young neurons in the developing brain establish a polarized morphology for proper migration. The PIWI family of piRNA processing proteins are considered to be restrictively expressed in germline tissues and several types of cancer cells. They play important roles in spermatogenesis, stem cell maintenance, piRNA biogenesis, and transposon silencing. Interestingly a recent study showed that de novo mutations of PIWI family members are strongly associated with autism. RESULTS: Here, we report that PIWI-like 1 (PIWIL1), a PIWI family member known to be essential for the transition of round spermatid into elongated spermatid, plays a role in the polarization and radial migration of newborn neurons in the developing cerebral cortex. Knocking down PIWIL1 in newborn cortical neurons by in utero electroporation of specific siRNAs resulted in retardation of the transition of neurons from the multipolar stage to the bipolar stage followed by a defect in their radial migration to the proper destination. Domain analysis showed that both the RNA binding PAZ domain and the RNA processing PIWI domain in PIWIL1 were indispensable for its function in neuronal migration. Furthermore, we found that PIWIL1 unexpectedly regulates the expression of microtubule-associated proteins in cortical neurons. CONCLUSIONS: PIWIL1 regulates neuronal polarization and radial migration partly via modulating the expression of microtubule-associated proteins (MAPs). Our finding of PIWIL1's function in neuronal development implies conserved functions of molecules participating in morphogenesis of brain and germline tissue and provides a mechanism as to how mutations of PIWI may be associated with autism.

SIRT1 suppresses self-renewal of adult hippocampal neural stem cells.

The balance between self-renewal and differentiation of adult neural stem cells (aNSCs) is essential for the maintenance of the aNSC reservoir and the continuous supply of new neurons, but how this balance is fine-tuned in the adult brain is not fully understood. Here, we investigate the role of SIRT1, an important metabolic sensor and epigenetic repressor, in regulating adult hippocampal neurogenesis in mice. We found that there was an increase in SIRT1 expression during aNSC differentiation. In Sirt1 knockout (KO) mice, as well as in brain-specific and inducible stem cell-specific conditional KO mice, the proliferation and self-renewal rates of aNSCs in vivo were elevated. Proliferation and self-renewal rates of aNSCs and adult neural progenitor cells (aNPCs) were also elevated in neurospheres derived from Sirt1 KO mice and were suppressed by the SIRT1 agonist resveratrol in neurospheres from wild-type mice. In cultured neurospheres, 2-deoxy-D-glucose-induced metabolic stress suppressed aNSC/aNPC proliferation, and this effect was mediated in part by elevating SIRT1 activity. Microarray and biochemical analysis of neurospheres suggested an inhibitory effect of SIRT1 on Notch signaling in aNSCs/aNPCs. Inhibition of Notch signaling by a γ-secretase inhibitor also largely abolished the increased aNSC/aNPC proliferation caused by Sirt1 deletion. Together, these findings indicate that SIRT1 is an important regulator of aNSC/aNPC self-renewal and a potential mediator of the effect of metabolic changes.

Transcriptome analysis of microRNAs in developing cerebral cortex of rat.

BACKGROUND: The morphogenesis of the cerebral cortex depends on the precise control of gene expression during development. Small non-coding RNAs, including microRNAs and other groups of small RNAs, play profound roles in various physiological and pathological processes via their regulation of gene expression. A systematic analysis of the expression profile of small non-coding RNAs in developing cortical tissues is important for clarifying the gene regulation networks mediating key developmental events during cortical morphogenesis. RESULTS: Global profiling of the small RNA transcriptome was carried out in rat cerebral cortex from E10 till P28 using next-generation sequencing technique. We found an extraordinary degree of developmental stage-specific expression of a large group of microRNAs. A group of novel microRNAs with functional hints were identified, and brain-enriched expression and Dicer-dependent production of high-abundant novel microRNAs were validated. Profound editing of known microRNAs at "seed" sequence and flanking sequence was observed, with much higher editing events detected at late postnatal stages than embryonic stages, suggesting the necessity of microRNA editing for the fine tuning of gene expression during the formation of complicated synaptic connections at postnatal stages. CONCLUSION: Our analysis reveals extensive regulation of microRNAs during cortical development. The dataset described here will be a valuable resource for clarifying new regulatory mechanisms for cortical development and diseases and will greatly contribute to our understanding of the divergence, modification, and function of microRNAs.

[Sequence polymorphism of the promoter region of gene STK11 in patients with Peutz-Jeghers syndrome].

OBJECTIVE: To explore the relationship between the sequence variation of the promoter region (-1543 approximately -1160) of STK11 gene and the risk of developing Peutz-Jeghers syndrome (PJS). METHODS: The sequences of the promoter region of 14 PJS patients (7 patients are inherited and the other 7 patients are sporadic) and 42 normal individuals were PCR amplified and then sequenced. RESULTS: A new single nucleotide polymorphism (SNP) G/T (-1275) in STK11 promoter region was identified. The frequency of genotype GG, GT, and TT was 53.3%, 26.7%, and 20%, respectively among PJS patients and 33.3%, 64.3%, and 2.4%, respectively among the normal individuals. The frequency of genotype GG and TT among patients was significantly higher than that among the normal individuals, and the frequency of genotype GT among patients was significantly lower than that among the normal individuals (chi(2)=8.521, P<0.05). CONCLUSION: G/T(-1275) in STK11 promoter region is a new SNP. The genotype of this new SNP may relate to the risk of developing Peutz-Jeghers syndrome (PJS) deserve further research.

[Expression of Caspase-3 and Bcl-2 in bladder transitional carcinoma and their significance].

BACKGROUND & OBJECTIVE: Tumor growth was the result of cell excessive proliferation and lack of apoptosis. Apoptosis has been considered to be closely associated with Caspase-3 and Bcl-2. This study was designed to investigate the expression of Caspase-3 and Bcl-2 to evaluate their effects on the tumorigenesis and progression in bladder transitional carcinoma (BTCC). METHODS: The immunohistochemistry (SP method) was used to determine the expression of Caspase-3 and Bcl-2 in 52 cases of BTCC and 10 normal bladder mucosas. RESULTS: The protein expression level of Caspase-3 in BTCC (53.8%,28/52) was significantly lower than that in normal bladder samples (90.0%,9/10). Caspase-3 expression level was correlated with the grades of BTCC (P< 0.05), but had no significant correlation with clinical stages. The protein expression of Bcl-2 in BTCC (51.9%,27/52) was significantly higher than that of normal bladder samples (20.0%,2/10), while its expression level was not related to stage and grade of BTCC (P >0.05). The expression of Caspase-3 is negatively related to that of Bcl-2 (r(s)=-0.659,P< 0.01) in bladder tissues. CONCLUSION: Both over expression of Caspase-3 and descended expression of Bcl-2 may play an important role in the tumorigenesis and apoptotic regulation of bladder tissues.