PCNA-binding to DNA at the G1/S transition in proliferating cells of the developing cerebral wall

Single-Cell Atlas of Neonatal Mouse Hearts Reveals an Unexpected Cardiomyocyte

BACKGROUND

Single-cell RNA sequencing is widely used in cancer research and organ development because of its powerful ability to analyze cellular heterogeneity. However, its application in cardiomyocytes is dissatisfactory mainly because the cardiomyocytes are too large and fragile to withstand traditional single-cell approaches.

METHODS AND RESULTS

Through designing the isolation procedure of neonatal mouse cardiac cells, we provide detailed cellular atlases of the heart at single-cell resolution across 4 different stages after birth. We have obtained 10 000 cardiomyocytes; to our knowledge, this is the most extensive reference framework to date. Moreover, we have discovered unexpected erythrocyte-like cardiomyocyte-terminal cardiomyocytes, comprising more than a third of all cardiomyocytes. Only a few genes are highly expressed in these cardiomyocytes. They are highly differentiated cardiomyocytes that function as contraction pumps. In addition, we have identified 2 cardiomyocyte-like conducting cells, lending support to the theory that the sinoatrial node pacemaker cells are specialized cardiomyocytes. Notably, we provide an initial blueprint for comprehensive interactions between cardiomyocytes and other cardiac cells.

CONCLUSIONS

This mouse cardiac cell atlas improves our understanding of cardiomyocyte heterogeneity and provides a valuable reference in response to varying physiological conditions and diseases.

Maternal Dexamethasone Exposure Induces Sex-Specific Changes in Histomorphology and Redox Homeostasis of Rat Placenta

As the mediator between the mother and fetus, the placenta allows the most appropriate environment and optimal fetal growth. The placenta of one sex sometimes has a greater ability over the other to respond to and protect against possible maternal insults. Here, we characterized sex differences in the placenta’s morphological features and antioxidant status following dexamethasone (Dx) exposure. Pregnant rats were exposed to Dx or saline. The placenta was histologically and stereologically analyzed. The activity of the antioxidant enzymes, lipid peroxides (TBARS), superoxide anion and nitric oxide (NO) was measured. The decrease in placental zone volumes was more pronounced (p < 0.05) in female placentas. The volume density of PCNA-immunopositive nuclei was reduced (p < 0.05) in both sexes. The reduced (p < 0.05) antioxidant enzyme activities, enhanced TBARS and NO concentration indicate that Dx exposure triggered oxidative stress in the placenta of both fetal sexes, albeit stronger in the placenta of female fetuses. In conclusion, maternal Dx treatment reduced the size and volume of placental zones, altered placental histomorphology, decreased cell proliferation and triggered oxidative stress; however, the placentas of female fetuses exerted more significant responses to the treatment effects. The reduced placental size most probably reduced the transport of nutrients and oxygen, thus resulting in the reduced weight of fetuses, similar in both sexes. The lesser ability of the male placenta to detect and react to maternal exposure to environmental challenges may lead to long-standing health effects.

The subcommissural organ maintains features of neuroepithelial cells in the adult mouse

The subcommissural organ (SCO) is a part of the circumventricular organs located in the dorsocaudal region of the third ventricle at the entrance of the aqueduct of Sylvius. The SCO comprises epithelial cells and produces high molecular weight glycoproteins, which are secreted into the third ventricle and become part of Reissner's fibre in the cerebrospinal fluid. Abnormal development of the SCO has been linked with congenital hydrocephalus, a condition characterized by excessive accumulation of cerebrospinal fluid in the brain. In the present study, we characterized the SCO cells in the adult mouse brain to gain insights into the possible role of this brain region. Immunohistochemical analyses revealed that expression of Pax6, a transcription factor essential for SCO differentiation during embryogenesis, is maintained in the SCO at postnatal stages from P0 to P84. SCO cells in the adult brain expressed known neural stem/progenitor cell (NSPC) markers, Sox2 and vimentin. The adult SCO cells also expressed proliferating marker PCNA, although expression of another proliferation marker Ki67, indicating a G₂/M phase, was not detected. The SCO cells did not incorporate BrdU, a marker for DNA synthesis in the S phase. Therefore, the SCO cells have a potential for proliferation but are quiescent for cell division in the adult. The SCO cells also expressed GFAP, a marker for astrocytes or NSPCs, but not NeuN (for neurons). A few cells positive for Iba1 (microglia), Olig2 (for oligodendrocytes) and PDGFRα (oligodendrocyte progenitors) existed within or on the periphery of the SCO. These findings revealed that the SCO cells have a unique feature as secretory yet immature neuroepithelial cells in the adult mouse brain.

Photobiomodulation invigorating collagen deposition, proliferating cell nuclear antigen and Ki67 expression during dermal wound repair in mice

The present investigation focuses on understanding the role of photobiomodulation in enhancing tissue proliferation. Circular excision wounds of diameter 1.5 cm were created on Swiss albino mice and treated immediately with 2 J/cm² and 10 J/cm² single exposures of the Helium-Neon laser along with sham-irradiated controls. During different days of healing progression (day 5, day 10, and day 15), the tissue samples upon euthanization of the animals were taken for assessing collagen deposition by Picrosirius red staining and cell proliferation (day 10) by proliferating cell nuclear antigen (PCNA) and Ki67. The positive influence of red light on collagen synthesis was found to be statistically significant on day 10 (P < 0.01) and day 15 (P < 0.05) post-wounding when compared to sham irradiation, as evident from the image analysis of collagen birefringence. Furthermore, a significant rise in PCNA (P < 0.01) and Ki67 (P < 0.05) expression was also recorded in animals exposed to 2 J/cm² when compared to sham irradiation and (P < 0.01) compared to the 10 J/cm² treated group as evidenced by the microscopy study. The findings of the current investigation have distinctly exhibited the assenting influence of red laser light on excisional wound healing in Swiss albino mice by augmenting cell proliferation and collagen deposition.

Stable Regulation of Senescence-Related Genes in Galactose-alpha1,3-galactose Epitope Knockout and Human Membrane Cofactor Protein hCD46 Pig

BACKGROUND

Pigs are considered suitable animal donor models for xenotransplantation. For successful organ transplantation, immune rejection must be overcome. Xenotransplantation has recently been successfully performed using galactose-alpha1,3-galactose epitopes knockout (GalTKO) and a human membrane cofactor protein (hCD46) in a pig model. However, the growth and lifespan of the grafted organ have not been evaluated. Therefore, in the present study we evaluated aging and 84 senescence-related genes using the RT² Profiler PCR array and whole blood samples from GalTKO/hCD46 Massachusetts General Hospital (MGH) pigs.

METHODS

Experimental groups were double GalTKO/hCD46 (5-month-old), single GalTKO/hCD46 (2-year-old), and non-genetically modified (>3.5-year-old; control group within the same strain). Age-matched white hairless Yucatan (WHY) miniature pig groups were used as controls.

RESULTS

Among the 19 senescence-related genes selected from the 84 genes for further evaluation, 13 were upregulated in the double GalTKO/hCD46 MGH pigs compared to control MGH pigs; however, in WHY pigs, only 4 genes were up- or down-regulated among the 19 genes. Moreover, in double GalTKO/hCD46 MGH and WHY pigs, the expression of the 19 genes changed only 1- to 2-fold, suggesting that there were no significant differences in senescence signals between the 2 pig lines.

CONCLUSIONS

The present results indicate that the double GalTKO/hCD46 MGH pig might be a suitable model for human xenotransplantation studies. However, we used a limited number of experimental individuals, so further studies using larger experimental groups should be conducted to verify the present results.

Identification of runt family genes involved in planarian regeneration and tissue homeostasis

The runt family genes play important roles in physiological processes in eukaryotic organisms by regulation of protein transcription, such as hematopoietic system, proliferation of gastric epithelial cells and neural development. However, it remains unclear about the specific functions of these genes. In this study, the full-length cDNA sequences of two runt genes are first cloned from Dugesia japonica, and their roles are investigated by WISH and RNAi. The results show that: (1) the Djrunts are conserved during evolution; (2) the Djrunts mRNA are widely expressed in intact and regenerative worms, and their expression levels are up-regulated significantly on day 1 after amputation; (3) loss of Djrunts function lead to lysis or regeneration failure in the intact and regenerating worms. Overall, the data suggests that Djrunts play important roles in regeneration and homeostatic maintenance in planarians.

Responses of neurogenesis and neuroplasticity related genes to elevated CO2 levels in the brain of three teleost species

The continuous increase of anthropogenic CO₂ in the atmosphere resulting in ocean acidification has been reported to affect brain function in some fishes. During adulthood, cell proliferation is fundamental for fish brain growth and for it to adapt in response to external stimuli, such as environmental changes. Here we report the first expression study of genes regulating neurogenesis and neuroplasticity in brains of three-spined stickleback (Gasterosteus aculeatus), cinnamon anemonefish (Amphiprion melanopus) and spiny damselfish (Acanthochromis polyacanthus) exposed to elevated CO₂ The mRNA expression levels of the neurogenic differentiation factor (NeuroD) and doublecortin (DCX) were upregulated in three-spined stickleback exposed to high-CO₂ compared with controls, while no changes were detected in the other species. The mRNA expression levels of the proliferating cell nuclear antigen (PCNA) and the brain-derived neurotrophic factor (BDNF) remained unaffected in the high-CO₂ exposed groups compared to the control in all three species. These results indicate a species-specific regulation of genes involved in neurogenesis in response to elevated ambient CO₂ levels. The higher expression of NeuroD and DCX mRNA transcripts in the brain of high-CO₂-exposed three-spined stickleback, together with the lack of effects on mRNA levels in cinnamon anemonefish and spiny damselfish, indicate differences in coping mechanisms among fish in response to the predicted-future CO₂ level.

Determination of PCNA, cyclin D3, p27, p57 and apoptosis rate in normal and dexamethasone-induced intrauterine growth restricted rat placentas

Intrauterine growth restriction (IUGR) is a major clinical problem, which causes perinatal morbidity and mortality. One of the reasons for IUGR is abnormal placentation. In rats, fetal-placental exposure to maternally administered glucocorticoids decreases birth weight and placental weight. Proper placental development depends on the proliferation and differentiation of trophoblasts. Our knowledge about the mitotic regulators that play key roles in synchronizing these events is limited. Also the mechanisms underlying the placental growth inhibitory effects of glucocorticoids have not been elucidated. The aim of this study was to investigate the immunolocalization, mRNA and protein levels of proliferating cell nuclear antigen (PCNA), cyclin D3, p27 and p57 in normal and dexamethasone-induced IUGR Wistar rat placentas by reverse transcriptase polymerase chain reaction (RT-PCR), immunohistochemistry and Western blot. We also compared apoptotic cell numbers at the light microscopic level via terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) and transmission electron microscopy. Glucocorticoid levels were higher in IUGR rats than in control rats after 60 and 120min of injection. We showed reduced gene and protein expressions of PCNA and cyclin D3 and increased expressions of p27 and p57 in IUGR placentas compared to control placentas. Apoptotic cell number was higher in the placentas of the IUGR group. In brief we found that maternal dexamethasone treatment led to a shift from cell proliferation to apoptosis in IUGR placentas. Dexamethasone induced placental and embryonal abnormalities which could be associated with reduced expressions of PCNA and cyclin D3, increased expressions of p27 and p57 and increased rate of apoptosis in IUGR placentas.

Immunolocalization of cell cycle proteins (p57, p27, cyclin D3, PCNA and Ki67) in intrauterine growth retardation (IUGR) and normal human term placentas

Placental development involves a series of events that depend on the coordinated action of proliferation, differentiation and invasion of trophoblasts. Studies on cell cycle related proteins controlling these events are fairly limited. It is still not fully determined how placental tissue proliferation is affected by intrauterine growth retardation (IUGR). Information on cell cycle related proteins that control these events is limited and how they are affected in IUGR is not fully understood. The aim of this study was to understand the role of cell cycle regulators in IUGR placentas and to determine the spatio-temporal immunolocalization of these cell cycle regulators in human IUGR and normal term placentas. Placental samples were stained immunohistochemically with PCNA, Ki67, cyclin D3, p27 and p57 antibodies and were examined by light microscopy. In all regions of IUGR placentas, PCNA, Ki67 and cyclin D3 staining intensities were statistically significantly decreased compared to normal controls. p27 staining intensity of the IUGR group was statistically significantly increased in villous parts and chorionic plates in comparison with the normal term placentas. Moreover, p57 staining intensity was statistically significantly increased in all parts of the IUGR group compared to controls. The observed placental abnormalities in IUGR placentas may be associated with arrest mechanisms affecting cell proliferation and cell cycle alterations in IUGR.

Insulin-like growth factor binding protein 7 modulates estrogen-induced trophoblast proliferation and invasion in HTR-8 and JEG-3 cells

Previous research has reported that IGFBP7 functions as a tumor suppressor gene in different tumors, but its role in the trophoblast has not been elucidated. In this research, we studied the regulation mechanism of IGFBP7 in trophoblast proliferation and invasion in HTR-8 and JEG-3 cell lines. We found that IGFBP7 was abundantly expressed in normal human syncytiotrophoblast tissue samples but that this was lacking in hydatidiform moles. The proliferation and invasion capacities of HTR-8 and JEG-3 cells were significantly inhibited by recombinant IGFBP7. Estrogen (E2) stimulated the expression of IGFBP7 at a concentration of 5-10 ng/mL. This stimulation was inhibited by the estrogen receptor antagonist Fulvestrant (ICI182.780) and a TGFβ-neutralizing antibody. In conclusion, our data reveals that estrogen stimulates the expression of IGFBP7 through estrogen receptors and TGFβ. The expression of IGFBP7 could be stimulated by TGFβ in a dose-dependent manner and inhibited by IFNγ in HTR-8 and JEG-3 cells. IGFBP7 could also inhibit the phosphorylation of ERK and the expression of PCNA, MMP2 and MMP9 in HTR-8 and JEG-3 cells. These findings suggest that IGFBP7 is a key regulator of E2-induced trophoblast proliferation and invasion.

Signal transduction pathways mediating the effect of adrenomedullin on osteoblast survival

Adrenomedullin (ADM) plays an important role in the regulation of osteoblastic cells through both a proliferative and an anti-apoptotic effects. The present study investigated mechanisms involved in the effect of ADM on survival. We report that ADM can act in osteoblasts both through a non-transcriptional action, by phosphorylation of different kinases and components, and through a transcriptional effect by activation of CREB. So, we observed by Western blot analysis, modifications in the downstream targets of ERK, the pro-apoptotic protein Bad, which is inactivated by increase in Ser155 phosphorylation, and the transcription factor CREB, which is activated by phosphorylation at Ser133. CREB activation was confirmed by a CRE-dependent gene transcription assay and an immunocytochemical study. This increase in CREB phosphorylation could lead to its enhanced transcriptional activity, as indicated by the induced expression of the proliferation marker, PCNA. Moreover, ADM could also activate the tyrosine kinase Src and the PI3-Kinase, both of which are implicated in survival. The use of specific pharmacological inhibitors allowed to establish that ADM could activate a signaling cascade involving Src, MEK, ERK, p90RSK, and that the effect of ADM, in particular on the CREB protein, greatly depends on the regulatory control of interfering signaling pathways. Moreover, as Wnt signaling plays an important role in the control of osteoblast apoptosis, we explored a major component of this pathway, protein GSK3β. ADM-induced inactivation of GSK3β by phosphorylation at Ser9, highly suggests that ADM could also exert its survival effect in osteoblast via components of the Wnt pathway.

Neural plasticity is affected by stress and heritable variation in stress coping style

Here we use a comparative model to investigate how behavioral and physiological traits correlate with neural plasticity. Selection for divergent post-stress cortisol levels in rainbow trout (Oncorhynchus mykiss) has yielded low- (LR) and high responsive (HR) lines. Recent reports show low behavioral flexibility in LR compared to HR fish and we hypothesize that this divergence is caused by differences in neural plasticity. Genes involved in neural plasticity and neurogenesis were investigated by quantitative PCR in brains of LR and HR fish at baseline conditions and in response to two different stress paradigms: short-term confinement (STC) and long-term social (LTS) stress. Expression of proliferating cell nuclear antigen (PCNA), neurogenic differentiation factor (NeuroD) and doublecortin (DCX) was generally higher in HR compared to LR fish. STC stress led to increased expression of PCNA and brain-derived neurotrophic factor (BDNF) in both lines, whereas LTS stress generally suppressed PCNA and NeuroD expression while leaving BDNF expression unaltered. These results indicate that the transcription of neuroplasticity-related genes is associated with variation in coping style, while also being affected by STC - and LTS stress in a biphasic manner. A higher degree of neural plasticity in HR fish may provide the substrate for enhanced behavioral flexibility.

Immunolocalization of PCNA, Ki67, p27 and p57 in normal and dexamethasone-induced intrauterine growth restriction placental development in rat

Intrauterine growth restriction (IUGR) is a major clinical problem which causes perinatal morbidity and mortality. Although fetuses with IUGR form a heterogeneous group, a major etiological factor is abnormal placentation. Despite the fact that placental development requires the coordinated action of trophoblast proliferation and differentiation, there are few studies on cell cycle regulators, which play the main roles in the coordination of these events. Moreover it is still not determined how mechanisms of coordination of proliferation and differentiation are influenced by dexamethasone-induced IUGR in the placenta. The aim of the study was to investigate the spatial and temporal immunolocalization of proliferating cell nuclear antigen (PCNA), Ki67, p27 and p57 in normal and IUGR placental development in pregnant Wistar rats. The study demonstrated altered expressions of distinct cell cycle proteins and cyclin dependent kinase inhibitors (CKIs) in IUGR placental development compared to control placental development. We found reduced immunostaining of PCNA and Ki67 and increased immunostaining of p27 and p57 in the dexamethasone-induced IUGR placental development compared to control placental development. In conclusion, our data show that the cell populations in the placenta stain for a number of cell cycle related proteins and that these staining patterns change as a function of both gestational age and abnormal placentation.

Coordination of cell proliferation and anterior-posterior axis establishment in the mouse embryo

During development, the growth of the embryo must be coupled to its patterning to ensure correct and timely morphogenesis. In the mouse embryo, migration of the anterior visceral endoderm (AVE) to the prospective anterior establishes the anterior-posterior (A-P) axis. By analysing the distribution of cells in S phase, M phase and G2 from the time just prior to the migration of the AVE until 18 hours after its movement, we show that there is no evidence for differential proliferation along the A-P axis of the mouse embryo. Rather, we have identified that as AVE movements are being initiated, the epiblast proliferates at a much higher rate than the visceral endoderm. We show that these high levels of proliferation in the epiblast are dependent on Nodal signalling and are required for A-P establishment, as blocking cell division in the epiblast inhibits AVE migration. Interestingly, inhibition of migration by blocking proliferation can be rescued by Dkk1. This suggests that the high levels of epiblast proliferation function to move the prospective AVE away from signals that are inhibitory to its migration. The finding that initiation of AVE movements requires a certain level of proliferation in the epiblast provides a mechanism whereby A-P axis development is coordinated with embryonic growth.

Fangchinoline induced G1/S arrest by modulating expression of p27, PCNA, and cyclin D in human prostate carcinoma cancer PC3 cells and tumor xenograft

Prostate cancer (PCA) is the most common invasive malignancy and the second leading cause of cancer-related death in males. The present study investigated the effects of fangchinoline (Fan), an important compound in Stephania Tetradra S. Moore (Fenfangji) with pain-relieving, blood pressure-depressing, and antibiotic activities, on human PCA. It was found that Fan inhibited human prostate cancer cell lines (PC3) cell proliferation in a dose- and time-dependent manner. Studies of cell-cycle progression showed that the anti-proliferative effect of Fan was associated with an increase in the G1/S phase of PC3 cells. Western blot results indicated that Fan-induced G1/S phase arrest was mediated through inhibition of cyclin-regulated signaling pathways. Fan induced p27 expression and inhibited cyclin D and proliferating cell nuclear antigen (PCNA) expression in PC3 cells. Increased exposure time to Fan caused apoptosis of PC3 cells, which was associated with up-regulation of pro-apoptotic proteins Bax and caspase 3, and down-regulation of anti-apoptotic protein Bcl-2. Furthermore, Fan had anti-tumorigenic activity in vivo, including reduction of tumor volume and pro-apoptotic and anti-proliferative effects in a PC3 nude mouse xenograft. Taking all this together, it can be concluded that Fan is an effective anti-proliferative agent that modulates cell growth regulators in prostate cancer cells.

Effect of 14-3-3 tau protein on differentiation in BeWo choriocarcinoma cells

This study aimed to investigate the location and function of tau isoform of 14-3-3 proteins in human trophoblast. 14-3-3 tau was localized in human cytotrophoblast cells, but not in syncytiotrophoblast cells in both first trimester and term placenta by immunochemistry stain. Forskolin-induced cell fusion (BeWo cells) confirmed that 14-3-3 tau was decreased during trophoblast differentiation. Forskolin-induced differentiation was stimulated by small-interfering (si) RNA induced down-regulation of 14-3-3 tau, contrarily, it was suppressed by plasmid induced upregulation of 14-3-3 tau in BeWo cells. When BeWo cells were treated with 14-3-3 tau siRNA, an increase in protein concentration of cell cycle inhibitor p27kip1 and a decrease in protein concentration of proliferating cell nuclear antigen, as well as activation of the extracellular signal-regulated kinase (ERK) pathway, were also noticed. These findings suggest that 14-3-3 tau might be mediated trophoblast differentiation through cell cycle regulation.

Activation of cytosolic phospholipase A2-{alpha} as a novel mechanism regulating endothelial cell cycle progression and angiogenesis

Release of endothelial cells from contact-inhibition and cell cycle re-entry is required for the induction of new blood vessel formation by angiogenesis. Using a combination of chemical inhibition, loss of function, and gain of function approaches, we demonstrate that endothelial cell cycle re-entry, S phase progression, and subsequent angiogenic tubule formation are dependent upon the activity of cytosolic phospholipase A(2)-alpha (cPLA(2)alpha). Inhibition of cPLA(2)alpha activity and small interfering RNA (siRNA)-mediated knockdown of endogenous cPLA(2)alpha reduced endothelial cell proliferation. In the absence of cPLA(2)alpha activity, endothelial cells exhibited retarded progression from G(1) through S phase, displayed reduced cyclin A/cdk2 expression, and generated less arachidonic acid. In quiescent endothelial cells, cPLA(2)alpha is inactivated upon its sequestration at the Golgi apparatus. Upon the stimulation of endothelial cell proliferation, activation of cPLA(2)alpha by release from the Golgi apparatus was critical to the induction of cyclin A expression and efficient cell cycle progression. Consequently, inhibition of cPLA(2)alpha was sufficient to block angiogenic tubule formation in vitro. Furthermore, the siRNA-mediated retardation of endothelial cell cycle re-entry and proliferation was reversed upon overexpression of an siRNA-resistant form of cPLA(2)alpha. Thus, activation of cPLA(2)alpha acts as a novel mechanism for the regulation of endothelial cell cycle re-entry, cell cycle progression, and angiogenesis.

VEGF neutralizing antibody increases the therapeutic efficacy of vinorelbine for renal cell carcinoma

Renal cell carcinoma (RCC) is currently one of the most treatment-resistant malignancies and affects approximately three in 10,000 people. The impact of this disease produces about 31,000 new cases in the United States per year; and 12,000 people in the United States alone die from RCC annually. Although several treatment strategies have been investigated for RCC, this cancer continues to be a therapeutic challenge. For this reason, the aim of our study is to develop a more effective combinational therapy to treat advanced RCC. We examined the effect of vinorelbine on the signalling pathways of two human renal cancer cell lines (A498 and 786-O) and also examined the in vivo effect of vinorelbine treatment alone and vinorelbine in combination with the anti-VEGF antibody 2C3 on A498 and 786-O tumour growth in nude mice. Tumour angiogenesis was measured by vWF staining, and apoptosis was determined by the TUNEL assay. We observed a significant tumour growth inhibition when using a combinational therapy of anti-VEGF antibody 2C3 and vinorelbine in both A498 and 786-O tumour-bearing mice. The results suggest a breakthrough treatment for advanced RCC.

Is there a relationship between PCNA expression and diabetic placental development during pregnancy?

We aimed to investigate the distribution pattern of proliferating cell nuclear antigen (PCNA) by immunohistochemistry and Western blot in placentas of control and diabetic rats at different stages of pregnancy. It is still not clear how proliferation is coordinated and how this coordination is affected by diabetes in the placenta. Diabetes was induced by streptozocin on the first day of pregnancy. Animals were sacrificed on days 11, 13, 17 and 21 of pregnancy. In control placentas immunolabeling intensity of PCNA was the highest on days 11 and 13 of pregnancy and decreased with progression of pregnancy. In the diabetic groups immunolabeling was less intense on days 11 and 13 of pregnancy compared to controls. However, in parallel with placental weights, PCNA immunopositivity was more intense in diabetic groups than control groups on days 17 and 21 of pregnancy, and the difference was statistically significant on day 17. According to Western blot data, on days 11 and 13 of pregnancy the amount of PCNA was greater in control groups than in the diabetics, whereas it was greater in diabetic groups than the controls on days 17 and 21 of pregnancy. We conclude that PCNA may play a role in abnormal placenta formation resulting from diabetes.

Protocols for studying adult neurogenesis: insights and recent developments

The first evidence that neurogenesis occurs in the adult brain was reported in rodents in the early 1960s, using [(3)H]-thymidine autoradiography. In the 1980s and 90s, the advent of new techniques and protocols for studying cell proliferation in situ, and particularly bromodeoxyuridine labeling, helped to confirm that neurogenesis occurs in the adult brain and neural stem cells reside in the adult CNS, including in humans. Bromodeoxyuridine labeling is currently the method most commonly used for studying neurogenesis in the adult brain. However, this procedure is not without limitations, and controversies. In this article, I will review recent protocols for studying adult neurogenesis, particularly new protocols for studying cell kinetics and cell proliferative history, using halopyrimidines. I will review these techniques, and discuss their implications for the field of adult neurogenesis.

Determination of key aspects of precursor cell proliferation, cell cycle length and kinetics in the adult mouse subgranular zone

Neurogenesis studies on the adult mouse hippocampal subgranular zone (SGZ) typically report increases or decreases in proliferation. However, key information is lacking about these proliferating SGZ precursors, from the fundamental--what dose of bromodeoxyuridine (BrdU) is appropriate for labeling all S phase cells?--to the detailed--what are the kinetics of BrdU-labeled cells and their progeny? To address these questions, adult C57BL/6J mice were injected with BrdU and BrdU-immunoreactive (IR) cells were quantified. Initial experiments with a range of BrdU doses (25-500 mg/kg) suggested that 150 mg/kg labels all actively dividing precursors in the mouse SGZ. Experiments using a saturating dose of BrdU suggested BrdU bioavailability is less than 15 min, notably shorter than in the developing mouse brain. We next explored precursor division and maturation by tracking the number of BrdU-IR cells and colabeling of BrdU with other cell cycle proteins from 15 min to 30 days after BrdU. We found that BrdU and the Gap2 and mitosis (G2/M) phase protein pHisH3 maximally colocalized 8 h after BrdU, indicating that the mouse SGZ precursor cell cycle length is 14 h. In addition, triple labeling with BrdU and proliferating cell nuclear antigen (PCNA) and Ki-67 showed that BrdU-IR precursors and/or their progeny express these endogenous cell cycle proteins up to 4 days after BrdU injection. However, the proportion of BrdU/Ki-67-IR cells declined at a greater rate than the proportion of BrdU/PCNA-IR cells. This suggests that PCNA protein is detectable long after cell cycle exit, and that reliance on PCNA may overestimate the length of time a cell remains in the cell cycle. These findings will be critical for future studies examining the regulation of SGZ precursor kinetics in adult mice, and hopefully will encourage the field to move beyond counting BrdU-IR cells to a more mechanistic analysis of adult neurogenesis.

Molecular interaction between projection neuron precursors and invading interneurons via stromal-derived factor 1 (CXCL12)/CXCR4 signaling in the cortical subventricular zone/intermediate zone

Most cortical interneurons are generated in the subpallial ganglionic eminences and migrate tangentially to their final destinations in the neocortex. Within the cortex, interneurons follow mainly stereotype routes in the subventricular zone/intermediate zone (SVZ/IZ) and in the marginal zone. It has been suggested that interactions between invading interneurons and locally generated projection neurons are implicated in the temporal and spatial regulation of the invasion process. However, so far experimental evidence for such interactions is lacking. We show here that the chemokine stromal-derived factor 1 (SDF-1; CXCL12) is expressed in the main invasion route for cortical interneurons in the SVZ/IZ. Most SDF-1-positive cells are proliferating and express the homeodomain transcription factors Cux1 and Cux2. Using MASH-1 mutant mice in concert with the interneuron marker DLX, we exclude that interneurons themselves produce the chemokine in an autocrine manner. We conclude that the SDF-1-expressing cell population represents the precursors of projection neurons during their transition and amplification in the SVZ/IZ. Using mice lacking the SDF-1 receptor CXCR4 or Pax6, we demonstrate that SDF-1 expression in the cortical SVZ/IZ is essential for recognition of this pathway by interneurons. These results represent the first evidence for a molecular interaction between precursors of projection neurons and invading interneurons during corticogenesis.

Group VIA Calcium-independent Phospholipase A2 Mediates Endothelial Cell S Phase Progression

Arachidonic acid and its metabolites have been previously implicated in the regulation of endothelial cell proliferation. Arachidonic acid may be liberated from cellular phospholipids by the action of group VIA calcium-independent phospholipase A2 (iPLA2-VIA). Consequently, we tested the hypothesis that iPLA2-VIA activity is linked to the regulation of endothelial cell proliferation. Inhibition of iPLA2 activity by bromoenol lactone (BEL) was sufficient to entirely block endothelial cell growth. BEL dose-dependently inhibited endothelial cell DNA synthesis in a manner that was reversed upon the exogenous addition of arachidonic acid. DNA synthesis was inhibited by the S-isomer and not by the R-isomer of BEL, demonstrating that endothelial cell proliferation is mediated specifically by iPLA2-VIA. iPLA2-VIA activity was critical to the progression of endothelial cells through S phase and is required for the expression of the cyclin A/cdk2 complex. Thus, inhibition of iPLA2-VIA blocks S phase progression and results in exit from the cell cycle. Inhibition of iPLA2-VIA-mediated endothelial cell proliferation is sufficient to block angiogenic tubule formation in co-culture assays. Consequently, iPLA2-VIA is a novel regulator of endothelial cell S phase progression, cell cycle residence, and angiogenesis.

Location of cell cycle regulators cyclin B1, cyclin A, PCNA, Ki67 and cell cycle inhibitors p21, p27 and p57 in human first trimester placenta and deciduas

Although placental development and implantation depend on the coordination of trophoblast proliferation, differentiation and invasion, little is known about the cell cycle regulators that govern the control of these events. The hypothesis that the coordinated expression of cell cycle progression and inhibition factors will determine whether cytotrophoblasts proliferate or undergo cell cycle arrest or cell cycle exit allowing subsequent differentiation was tested. The cell cycle promotors cyclin A, cyclin B1, PCNA, Ki67 and the cell cycle inhibitors p21, p27 and p57 were immunolocalized in tissue sections of first trimester pregnancies (weeks 6 and 9-12). Double staining with cytokeratin 7 allowed unambiguous identification of extravillous cytotrophoblast (EVT) in the decidua. Villous cytotrophoblasts were immunolabelled for Ki67 and cyclin A but only few were stained with anti-cyclin B1. The syncytiotrophoblast was devoid of immunoreactivity for any of the cell cycle progression factors. It expressed especially p21, whereas p27 and p57 were predominantly found in villous cytotrophoblasts. PCNA, Ki67, cyclin A and cyclin B1 were immunolocalized in proximal and distal EVTs of anchoring villi and in EVT which had invaded the upper decidual segments. All EVTs strongly expressed p27 and p57, but not p21. These data clearly suggest different functions for p21, p27 and p57 in placental development with distinct roles for p21 and p57 in syncytiotrophoblast and EVT differentiation, respectively. p27 appears to be involved in both the processes. The results may also challenge the concept of differential mitotic activity in the proximal and distal parts of the first trimester cytotrophoblast cell column, but more functional studies are clearly needed. The presence of p27 and p57 in EVT cells, which invade the deciduas deeply, may account for the loss of mitogenic potential of these cells.

Expression of Zfhep/deltaEF1 protein in palate, neural progenitors, and differentiated neurons

Zfhep/deltaEF1 is essential for embryonic development. We have investigated the expression pattern of Zfhep protein during mouse embryogenesis. We show expression of Zfhep in the mesenchyme of the palatal shelves, establishing concordance of expression with the reported cleft palate of the deltaEF1-null mice. Zfhep protein is strongly expressed in proliferating progenitors of the nervous system. In most regions of the brain, post-mitotic cells stop expressing Zfhep when they migrate out of the ventricular zone (VZ) and differentiate. However, in the hindbrain, Zfhep protein is also highly expressed in post-mitotic migratory neuronal cells of the precerebellar extramural stream that arise from the neuroepithelium adjacent to the lower rhombic lip. Also, Zfhep is expressed as cells migrate from a narrow region of the pons VZ towards the trigeminal nucleus. Co-expression with Islet1 shows that Zfhep is expressed in motor neurons of the trigeminal nucleus of the pons, but not in the inferior olive motor neurons at E12.5. Therefore, Zfhep is strongly expressed in a tightly regulated pattern in proliferating neural stem cells and a subset of neurons. Zfhep protein is also strongly expressed in trigeminal ganglia, and is moderately expressed in other cranial ganglia. In vitro studies have implicated Zfhep as a repressor of myogenesis, however, we find that Zfhep protein expression increases during muscle differentiation.

Chronic morphine induces premature mitosis of proliferating cells in the adult mouse subgranular zone

The birth of cells with neurogenic potential in the adult brain is assessed commonly by detection of exogenous S phase markers, such as bromodeoxyuridine (BrdU). Analysis of other phases of the cell cycle, however, can provide insight into how external factors, such as opiates, influence the cycling of newly born cells. To this end, we examined the expression of two endogenous cell cycle markers in relation to BrdU: proliferating cell nuclear antigen (PCNA) and phosphorylated histone H3 (pHisH3). Two hours after one intraperitoneal BrdU injection, BrdU-, PCNA-, and pHisH3-immunoreactive (IR) cells exhibited similar distribution in the adult mouse subgranular zone (SGZ). Quantitative analysis within the SGZ revealed a relative abundance of cells labeled for PCNA > BrdU >> pHisH3. Similar to our reports in rat SGZ, chronic morphine treatment decreased BrdU- and PCNA-IR cells in mouse SGZ by 28 and 38%, respectively. We also show that pHisH3-IR cells are influenced by chronic morphine to a greater extent (58% decrease) than are BrdU- or PCNA-IR cells. Cell cycle phase analysis of SGZ BrdU-IR cells using triple labeling for BrdU, PCNA, and pHisH3 revealed premature mitosis in chronic morphine-treated mice. These results suggest that morphine-treated mice have a shorter Gap2/mitosis (G(2)/M) phase when compared to sham-treated mice. These findings demonstrate the power of using a combination of exogenous and endogenous cell cycle markers and nuclear morphology to track proliferating cells through different phases of the cell cycle and to reveal the regulation of cell cycle phase by chronic morphine.

Increased cell proliferation and neurogenesis in the adult human Huntington's disease brain

Neurogenesis has recently been observed in the adult human brain, suggesting the possibility of endogenous neural repair. However, the augmentation of neurogenesis in the adult human brain in response to neuronal cell loss has not been demonstrated. This study was undertaken to investigate whether neurogenesis occurs in the subependymal layer (SEL) adjacent to the caudate nucleus in the human brain in response to neurodegeneration of the caudate nucleus in Huntington's disease (HD). Postmortem control and HD human brain tissue were examined by using the cell cycle marker proliferating cell nuclear antigen (PCNA), the neuronal marker beta III-tubulin, and the glial cell marker glial fibrillary acidic protein (GFAP). We observed a significant increase in cell proliferation in the SEL in HD compared with control brains. Within the HD group, the degree of cell proliferation increased with pathological severity and increasing CAG repeats in the HD gene. Most importantly, PCNA+ cells were shown to coexpress beta III-tubulin or GFAP, demonstrating the generation of neurons and glial cells in the SEL of the diseased human brain. Our results provide evidence of increased progenitor cell proliferation and neurogenesis in the diseased adult human brain and further indicate the regenerative potential of the human brain.

Vitamin D growth inhibition of breast cancer cells: gene expression patterns assessed by cDNA microarray

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D, is a potent inhibitor of breast cancer cell growth. Although it is evident that 1,25(OH)2D3 inhibits growth of both estrogen receptor alpha-positive [ER alpha(+)] and -negative [ER alpha(-)] breast cancer cells, the cellular pathways contributing to these effects remain unclear. We studied the gene expression patterns in ER alpha(+) MCF-7 and ER alpha(-) MDA MB 231 human breast cancer cells following 1,25(OH)2D3 treatment, using cDNA expression arrays. Both cell lines showed a significant induction of the 1,25(OH)2D3-dependent 24-hydroxylase gene, a marker for the actions of 1,25(OH)2D3. In MCF-7 cells, 51 genes were up-regulated and 19 genes were down-regulated. The up-regulated genes encoded cell adhesion molecules, growth factors/modulators, steroid receptors/co-activators, cytokines, kinases and transcription factors. Of the up-regulated genes, 40% were implicated in cell cycle regulation and apoptosis and included cyclin G1 and cyclin I, p21-activated kinase-1 (PAK-1), p53, retinoblastoma like-2 [Rb2 (p130)], insulin-like growth factor binding protein-5 (IGFBP5) and caspases. Among the down-regulated genes were ER alpha, growth factors, cytokines and several kinases. Some of these results were confirmed by real-time PCR. In MDA MB 231 cells, 20 genes were up-regulated and 13 genes were down-regulated. Very few genes directly implicated in cell cycle regulation were up-regulated. The matrix metalloproteinases formed a major class of genes that were down-regulated in the MDA MB 231 cells. Seven genes were commonly up-regulated in both cell lines and these included transforming growth factor (TGFbeta2) and Rb2 (p130). In conclusion, the gene expression profiles of the two cell lines studied were different with a few overlapping genes suggesting that different cellular pathways might be regulated by 1,25(OH)2D3 to exert its growth inhibitory effects in ER alpha(+) and ER alpha(-) cells.

Active Src expression is induced after rat peripheral nerve injury

The non-receptor-type Src tyrosine kinases are key components of intracellular signal transduction that are expressed at high levels in the nervous system. To improve understanding of the cascades of molecular events underlying peripheral nerve regeneration, we analyzed active Src expression in the crushed or cut rat sciatic nerves using a monoclonal antibody (clone 28) that recognizes the active form of Src tyrosine kinases, including c-Src and c-Fyn. Western blots showed that active Src expressed in the normal sciatic nerve transiently increased up to threefolds after both types of injury. Immunohistochemistry using clone 28 showed that axonal components are the primary sites of active Src expression in the normal sciatic nerve. Soon after both types of injury, active Src was abundantly expressed in Schwann cells of the segments distal to the injury site. The expression of active Src in the cells decreased with restoration of the axon-Schwann cell relationship and eventually became depleted to very low levels after crushing, but was sustained at high levels in the cut model until the end of the experiment. Regenerated axons consistently expressed active Src throughout nerve regeneration and these eventually became the major sites of active Src expression in the crushed nerve. Among the Src tyrosine kinases, active c-Src selectively increased after crushing according to immunoprecipitation and immunoblotting analyses. Due to its potent biological activity, the increased amounts of the active form of Src probably enhance axonal regrowth, the Schwann cell response, and axon-Schwann cell contact for peripheral nerve regeneration.

In vivo cellular and molecular mechanisms of neuronal apoptosis in the mammalian CNS

Apoptosis has been recognized to be an essential process during neural development. It is generally assumed that about half of the neurons produced during neurogenesis die before completion of the central nervous system (CNS) maturation, and this process affects nearly all classes of neurons. In this review, we discuss the experimental data in vivo on naturally occurring neuronal death in normal, transgenic and mutant animals, with special attention to the cerebellum as a study model. The emerging picture is that of a dual wave of apoptotic cell death affecting central neurons at different stages of their life. The first wave consists of an early neuronal death of proliferating precursors and young postmitotic neuroblasts, and appears to be closely linked to cell cycle regulation. The second wave affects postmitotic neurons at later stages, and is much better understood in functional terms, mainly on the basis of the neurotrophic concept in its broader definition. The molecular machinery of late apoptotic death of postmitotic neurons more commonly follows the mitochondrial pathway of intracellular signal transduction, but the death receptor pathway may also be involved.Undoubtedly, analysis of naturally occurring neuronal death (NOND) in vivo will offer a basis for parallel and future studies aiming to elucidate the mechanisms of pathologic neuronal loss occurring as the result of conditions such as neurodegenerative disorders, trauma or ischemia.

Neurogenesis in explants from the walls of the lateral ventricle of adult bovine brain: role of endogenous IGF-1 as a survival factor

Previous studies have shown the existence of proliferating cells in explants from bovine (Bos Taurus) lateral ventricle walls that were maintained for several days in vitro in the absence of serum and growth factors. In this study we have characterized the nature of new cells and have assessed whether the insulin-like growth factor-1 (IGF-1) receptor regulates their survival and/or proliferation. The explants were composed of the ependymal layer and attached subependymal cells. Ependymal cells in culture were labelled with glial markers (S-100, vimentin, GFAP, BLBP, 3A7 and 3CB2) and did not incorporate bromodeoxiuridine when this molecule was added to the culture media. Most subependymal cells were immunoreactive for beta III-tubulin, a neuronal marker, and did incorporate bromodeoxiuridine. Subependymal neurons displayed immunoreactivity for IGF-1 and its receptor and expressed IGF-1 mRNA, indicating that IGF-1 is produced in the explants and may act on new neurons. Addition to the culture media of an IGF-1 receptor antagonist, the peptide JB1, did not affect the incorporation of bromodeoxiuridine to proliferating subependymal cells. However, JB1 significantly increased the number of TUNEL positive cells in the subependymal zone, suggesting that IGF-1 receptor is involved in the survival of subependymal neurons. In conclusion, these findings indicate that neurogenesis is maintained in explants from the lateral cerebral ventricle of adult bovine brains and that IGF-1 is locally produced in the explants and may regulate the survival of the proliferating neurons.

Subpial neuronal migration in the medulla oblongata of Pax-6-deficient rats

In rat fetuses, neurons generated in the lower rhombic lip on embryonic day 14 (E14) specifically express the transcription factor Pax-6 and migrate circumferentially in the subpial region along axons which are immunoreactive for TAG-1, a neural cell adhesion molecule. These neurons ultimately settle from E17 in the contralateral medulla oblongata to form the precerebellar nuclei, the lateral reticular and external cuneate nuclei. We have examined this migratory process in rat small eye (rSey2) which has a mutation in the Pax-6 gene. Both the migration and settlement of neurons labelled with 5-bromo-2'-deoxyuridine (BrdU) at E14 delayed in the mutant. Furthermore, in the ventrolateral part of the E16 mutant medulla oblongata, cells both expressing Pax-6 mRNA and prelabelled with BrdU at E14 were ectopically localized in the deep zone of the medullary parenchyma in addition to the normal subpial location. These ectopic neurons remained in close contact with ectopic TAG-1-immunoreactive axons. These results indicate that Pax-6 plays a role in the migration of medullary precerebellar neurons, although neurons generated in the lower rhombic lip can nevertheless migrate and settle to form the external cuneate nucleus in the absence of Pax-6.

Time course of proliferation and elimination of microglia/macrophages in different neurodegenerative conditions

Ablation of the hindlimb area of the sensorimotor cortex produces degeneration in the cortex (invasive traumatic injury) and leads to retrograde and/or anterograde degeneration in the thalamus (non-invasive injury, distal reaction). This provides an useful model to study the proliferation and elimination of microglia/macrophages in different neurodegenerative conditions. Changes in the morphology, distribution and numbers of microglia in the affected cortex and thalamus were analyzed at various time points (12 h to 30 days) after injury. In parallel, proliferation was determined by immunocytochemistry for the proliferating cell nuclear antigen and cell death by the TUNEL method. Proliferation was an early event in the microglia/macrophage response (from 12 h in the cortex and from 2 days post-lesion in the thalamus) and persisted up to 30 days. The different microglia/macrophage phenotypes proliferated in a specific temporospatial pattern. In the lesioned cortex, early activation and proliferation of intrinsic microglia was accompanied, from the second post-lesion day, by monocyte entrance and proliferation of monocyte-derived cells. In contrast, accumulation of cells in the thalamus resulted from proliferation of intrinsic microglia, without apparent/significant monocytic recruitment. During the subsequent microglia/macrophages removal the majority of the cells in the cortex transformed into ameboid cells devoid of cell processes that progressively accumulated as fully-developed macrophages tissue within the lesion (3-14 days) ultimately migrating out to the meningeal connective tissue (14-30 days). Only some process-bearing cells, remaining in the cortical tissue bordering the lesion, underwent degeneration by 14-21 days post-lesion. In contrast, in the distal affected thalamic nuclei, microglial cell death occurred by 14-30 days post-lesion. Altogether, this study shows that both the origin and fate of microglia/macrophages depend on the nature of the lesion.

Synapse-independent and synapse-dependent apoptosis of cerebellar granule cells in postnatal rabbits occur at two subsequent but partly overlapping developmental stages

It has long been known that cells in the external granular layer die during postnatal development of the cerebellum. More recent findings indicate that at certain developmental stages, cell death occurs upon activation of an apoptotic program. We show that cerebellar granule cells in rabbits undergo programmed cell death at two different stages of maturation. At postnatal day 5 (P5), granule cell precursors and pre-migratory granule cells in the external granular layer incorporate the S-phase markers 5-bromo-2'-deoxyuridine and 5-iodo-2'-deoxyuridine with a pattern that is dependent upon the interval between the administration of the two tracers. Within 12-24 h after proliferation a significant number of labeled cells show typical ultrastructural alterations of apoptosis. DNA electrophoresis and cleavage of poly-ADP-ribose polymerase confirm the activation of the apoptotic machinery. After Southern blotting and immunodetection, incorporated 5-bromo-2'-deoxyuridine is present at the level of low size DNA oligomers as soon as 12 h after cell division. Therefore, this apoptotic phase is intrinsic to external granular layer neurons and independent of synaptic interactions with targets.Apoptotic cells, although fewer in number, are detected also in the internal granular layer and tend to increase from P5 to P10. It seems unlikely that these cells undergo DNA fragmentation in the external granular layer and subsequently migrate to their final destination, considering the data on cell cycle kinetics and the rapid tissue clearance by the glia. Parallel fiber-Purkinje spine synapses are already present in the molecular layer at P5. Therefore, the post-migratory granule cells likely undergo apoptosis as a failure to make proper synaptic contacts in the forming molecular layer. We conclude that the massive apoptosis of pre-migratory cells likely has a role in regulating the size of this rapidly expanding population of pre-mitotic neurons. The less tumultuous cell death of post-mitotic granule cells in the internal granular layer appears to be linked to the formation of the mature synaptic circuitry of the developing cerebellar cortex.

Proliferation and apoptosis in the developing human neocortex

The cell kinetics of the developing central nervous system (CNS) is determined by both proliferation and apoptosis. In the human neocortex at week 6 of gestation, proliferation is confined to the ventricular zone, where mitotic figures and nuclear immunoreactivity for proliferating cell nuclear antigen (PCNA) are detectable. Cell division is symmetric, with both daughter cells reentering mitosis. At week 7, the subventricular zone, a secondary proliferative zone, appears. It mainly gives rise to local circuit neurons and glial cells. Around week 12, the ventricular and subventricular zones are thickest, and the nuclear PCNA label is strongest, indicating that proliferation peaks at this stage. Thereafter, asymmetric division becomes the predominant mode of proliferation, with one daughter cell reentering mitosis and the other one migrating out. Towards late gestation, the ventricular and subventricular zones almost completely disappear and proliferation shifts towards the intermediate and subplate zones, where mainly glial cells are generated. A remnant of the subventricular zone with proliferative activity persists into adulthood. In general, proliferation follows a latero-medial gradient in the neocortex lasting longer in its lateral parts. Apoptotic nuclei have been detected around week 5, occurring in low numbers in the ventricular zone at this stage. Apoptotic cell death increases around midgestation and then spreads throughout all cortical layers, with most dying cells located in the ventricular and subventricular zones. This spatial distribution of apoptosis extends into late gestation. During the early postnatal period, most apoptotic cells are still located in the subcortical layers. During early embryonic development, proliferation and apoptosis are closely related, and are probably regulated by common regulators. In the late fetal and early postnatal periods, when proliferation has considerably declined in all cortical layers, apoptosis may occur in neurons whose sprouting axons do not find their targets.

Suppressive effects of phosphodiesterase type IV inhibitors on rat cultured microglial cells: comparison with other types of cAMP-elevating agents

We investigated the effects of inhibitors of cAMP-specific phosphodiesterase type IV (PDE IV) on cultured rat microglial cells. Microglial cells expressed mRNA encoding PDE IV. Rolipram and RO-20-1724, specific inhibitors of PDE IV, elevated the intracellular cAMP level much higher than the other types of PDE inhibitors. cAMP in astrocytes but not in cerebrocortical neurons was similarly increased in response to treatment with PDE IV inhibitors examined. The PDE IV inhibitors, a beta-adrenergic agonist isoproterenol and an adenylyl cyclase stimulant forskolin suppressed the proliferation of microglial cells as revealed by PCNA-immunocytochemical staining. The PDE IV inhibitors suppressed release of TNF alpha and nitric oxide (NO) from lipopolysaccharide-activated microglial cells in pure culture, while they did not affect NO release from microglial cells in neuron-microglia coculture. The PDE IV inhibitors also suppressed superoxide anion production by phorbol ester-treated microglial cells. Isoproterenol and forskolin similarly suppressed the macrophage-like functions of activated microglial cells. However, the PDE IV inhibitors displayed novel effects distinct from those of isoproterenol, forskolin and 8Br-cAMP, regarding expression of mRNAs encoding PDE IV, metallothionein-1 and hemeoxigenase-1. The present data showed that the PDE IV inhibitors can be available to control microglial function and that their effects on glial cells should be taken into account when PDE IV inhibitors are used for treatment of brain diseases, such as multiple sclerosis.

Developmental and functional evidence of a role for Zfhep in neural cell development

The rat Zfhep gene encodes a member of the Zfh family of transcription factors having a homeodomain-like sequence and multiple zinc fingers. We examined expression of Zfhep in the rat forebrain during embryonic and postnatal development. Zfhep mRNA was strongly expressed in the progenitor cells of the ventricular zone around the lateral ventricles on E14 and E16, but showed little expression in cells that had migrated to form the developing cortex. Dual labeling with PCNA demonstrated expression of Zfhep mRNA in proliferating cells. Expression of Zfhep in the ventricular zone decreases during late development as the population of progenitor cells decreases. This pattern is distinctly different from other members of the Zfh family. We also examined the expression of Zfhep protein during retinoic acid-induced neurogenesis of P19 embryonal carcinoma cells. Zfhep is highly expressed in P19 neuroblasts, and expression decreases by the time of morphological neurogenesis. Hence, both P19 cells and embryonic brain demonstrate a loss of Zfhep expression during the transition from proliferating precursor to differentiated neural cells. We investigated a possible link between Zfhep and proliferation by treating human glial cell lines with Zfhep antisense phosphorothioate oligodeoxynucleotides. Two Zfhep antisense oligonucleotides repressed proliferation of either U-138 or U-343 glioblastoma cells more than control oligonucleotides. Based on the expression patterns of Zfhep in vivo and in the P19 cell model of neurogenesis, we suggest that Zfhep may play a role in proliferation or differentiation of neural cells.

The Phox2b transcription factor coordinately regulates neuronal cell cycle exit and identity

In the vertebrate neural tube, cell cycle exit of neuronal progenitors is accompanied by the expression of transcription factors that define their generic and sub-type specific properties, but how the regulation of cell cycle withdrawal intersects with that of cell fate determination is poorly understood. Here we show by both loss- and gain-of-function experiments that the neuronal-subtype-specific homeodomain transcription factor Phox2b drives progenitor cells to become post-mitotic. In the absence of Phox2b, post-mitotic neuronal precursors are not generated in proper numbers. Conversely, forced expression of Phox2b in the embryonic chick spinal cord drives ventricular zone progenitors to become post-mitotic neurons and to relocate to the mantle layer. In the neurons thus generated, ectopic expression of Phox2b is sufficient to initiate a programme of motor neuronal differentiation characterised by expression of Islet1 and of the cholinergic transmitter phenotype, in line with our previous results showing that Phox2b is an essential determinant of cranial motor neurons. These results suggest that Phox2b coordinates quantitative and qualitative aspects of neurogenesis, thus ensuring that neurons of the correct phenotype are generated in proper numbers at the appropriate times and locations.

Histogenesis of the cerebral cortex in rat fetuses with a mutation in the Pax-6 gene

The embryonic development of the cerebral cortex was histologically examined in rat homozygotes with a mutation of the Paired box (Pax)-6 gene, rat Small eye (rSey(2)/rSey(2)). Although the cerebral wall was thinner in rSey(2)/rSey(2) than in the wild type at embryonic day 16 (E16), cortical cells of mutants labeled with 5'-bromodeoxyuridine (BrdU) at E13 migrated as normal, settling in superficial layer at E16. Mitotic activity in the ventricular zone, estimated by immunoreactivity for proliferating cell nuclear antigen (PCNA), was also retained. On the other hand, after E20 cells were clustered in abnormally expanded ventricular and intermediate zones of the rSey(2)/rSey(2) cortex. Birthdating studies using BrdU revealed that most of these clustered cells were generated between E18 and E20. Most of clustered cells were immunoreactive for PCNA and highly polysialylated NCAM, while immunoreaction for neurofilament and microtubule-associated protein-2 (MAP-2) was hardly detected in the clusters. Furthermore, apoptosis detected with terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) was rarely seen, suggesting that the clustered cells remain in an undifferentiating state, but not degenerated by the end of the gestational period. Considering that Pax-6 immunoreactivity was exclusively localized in the ventricular zone of the normal rat cortex throughout the fetal period, the present results suggest that Pax-6 is crucial for differentiation and migration of late-generated cortical neurons.

Cell proliferation and death: morphological evidence during corticogenesis in the developing human brain

Cell proliferation and death account for the refinement of the cell number during corticogenesis. These processes have been investigated in the human developing telencephalon (12th-24th week of gestation) and cerebellum (16th-24th week). Only foetal brains, which had normal neuropathological examination, were utilised. Cell proliferation was analysed by classical histology and PCNA immunohistochemistry; cell death was investigated by the TUNEL method, which makes evident the different stages of apoptosis. High figures of mitotic nuclei were seen in the ventricular zone at the 12th-15th week of gestation, before sharply declining. The decrease of the proliferating cells occurs synchronously in both frontal and occipital germinal zones. Conversely, a slow increase of the number of the mitotic cells was observed in the more dorsal regions, probably due to the presence of proliferating glial elements. The amount of apoptotic nuclei was always remarkably low in the transient compartments of the wall of the telencephalon. The moderate number of apoptotic cells suggests that cellular mechanisms other than apoptosis are involved in the dissolution of the ventricular zone. Neither proliferating nor apoptotic cells were seen in the cortical plate. The topography of cell proliferation and death in the developing cerebellum did not account for a mutual relationship between the two events. The prolonged duration of the cell-cycle in the human developing CNS may explain its increased vulnerability to various DNA-damaging conditions, which can lead to either destructive lesions or malformations.

Heterotopic neurogenesis in a rat with cortical heterotopia

Early cellular development was studied in the neocortex of the tish rat. This neurological mutant is seizure-prone and displays cortical heterotopia similar to those observed in certain epileptic patients. The present study demonstrates that a single cortical preplate is formed in a typical superficial position of the developing tish neocortex. In contrast, two cortical plates are formed: one in a normotopic position and a second in a heterotopic position in the intermediate zone. As the normotopic cortical plate is formed, it characteristically separates the subplate cells from the superficial Cajal-Retzius cells. In contrast, the heterotopic cortical plate is not intercalated between the preplate cells because of its deeper position in the developing cortex. Cellular proliferation occurs in two zones of the developing tish cortex. One proliferative zone is located in a typical position in the ventricular/subventricular zone. A second proliferative zone is located in a heterotopic position in the superficial intermediate zone, i.e., between the two cortical plates. This misplaced proliferative zone may contribute cells to both the normotopic and heterotopic cortical plates. Taken together, these findings indicate that misplaced cortical plate cells, but not preplate cells, comprise the heterotopia of the tish cortex. Heterotopic neurogenesis is an early developmental event that is initiated before the migration of most cortical plate cells. It is concluded that misplaced cellular proliferation, in addition to disturbed neuronal migration, can play a key role in the formation of large cortical heterotopia.

Astrocytosis and proliferating cell nuclear antigen expression in brains of scrapie-infected hamsters

Scrapie is a neurodegenerative disease in sheep and goats. Neuropathological examination shows astrocytosis. One issue is whether the astrocytosis seen in scrapie is a function of an increase in reactivity of individual cells, or whether there is actual replication of astrocytes. We used double-label immunohistochemistry for proliferating cell nuclear antigen (PCNA) and for glial fibrillary acidic protein (GFAP) to determine the mitotic state of cells and to confirm their identity as astrocytes. Brain sections from hamsters (strain LVG/LAK) infected with 139H or 263K scrapie isolates were examined. GFAP immunostaining was increased in astrocytes in most regions of the brains of scrapie-infected hamsters. These qualitative observations were confirmed by computerized image analysis quantification. A proportion of the hypertrophic astrocytes (0.5-10.8%, depending on specific location) were PCNA immunoreactive. The PCNA-immunopositive astrocytes were most frequently found in cerebral cortex, corpus callosum, subependymal areas, fimbria, caudate, thalamus, hypothalamus, hippocampus, and dentate gyrus. Our results suggest that the astrocytosis seen in scrapie-infected animals is, at least in part, owing to actual replication of astrocytes in these animals. We hypothesize that the astrocytes may be an important locus for the disease process.