PubMed Health⌕ Search

Biomedical subjects

N Lu

Publications and source records attributed to N Lu.

At least 19 recordsLinked to original sources
PubMed1999

Genetic analysis of the mouse X inactivation center defines an 80-kb multifunction domain.

Dosage compensation in mammals occurs by X inactivation, a silencing mechanism regulated in cis by the X inactivation center (Xic). In response to developmental cues, the Xic orchestrates events of X inactivation, including chromosome counting and choice, initiation, spread, and establishment of silencing. It remains unclear what elements make up the Xic. We previously showed that the Xic is contained within a 450-kb sequence that includes Xist, an RNA-encoding gene required for X inactivation. To characterize the Xic further, we performed deletional analysis across the 450-kb region by yeast-artificial-chromosome fragmentation and phage P1 cloning. We tested Xic deletions for cis inactivation potential by using a transgene (Tg)-based approach and found that an 80-kb subregion also enacted somatic X inactivation on autosomes. Xist RNA coated the autosome but skipped the Xic Tg, raising the possibility that X chromosome domains escape inactivation by excluding Xist RNA binding. The autosomes became late-replicating and hypoacetylated on histone H4. A deletion of the Xist 5' sequence resulted in the loss of somatic X inactivation without abolishing Xist expression in undifferentiated cells. Thus, Xist expression in undifferentiated cells can be separated genetically from somatic silencing. Analysis of multiple Xic constructs and insertion sites indicated that long-range Xic effects can be generalized to different autosomes, thereby supporting the feasibility of a Tg-based approach for studying X inactivation.

Acetylation↗
PubMed1999

ELAV tumor antigen, Hel-N1, increases translation of neurofilament M mRNA and induces formation of neurites in human teratocarcinoma cells.

Human ELAV proteins are implicated in cell growth and differentiation via regulation of mRNA expression in the cytoplasm. In human embryonic teratocarcinoma (hNT2) cells transfected with the human neuronal ELAV-like protein, Hel-N1, neurites formed, yet cells were not terminally differentiated. Cells in which neurite formation was associated with Hel-N1 overexpression, also expressed increased levels of endogenous neurofilament M (NF-M) protein, which distributed along the neurites. However, steady-state levels of NF-M mRNA remained similar whether or not hNT2 cells were transfected with Hel-N1. These findings suggest that turnover of NF-M mRNA was not affected by Hel-N1 expression, despite the fact that Hel-N1 can bind to the 3' UTR of NF-M mRNA and was found directly associated with NF-M mRNA in transfected cells. Analysis of the association of NF-M mRNA with the translational apparatus in Hel-N1 transfectants showed nearly complete recruitment to heavy polysomes, indicating that Hel-N1 caused an increase in translational initiation. Our results suggest that the stability and/or translation of ARE-containing mRNAs can be regulated independently by the ELAV protein, Hel-N1, depending upon sequence elements in the 3' UTRs and upon the inherent turnover rates of the mRNAs that are bound to Hel-N1 in vivo.

3' Untranslated Regions↗
PubMed1998

The PACAP ligand/receptor system regulates cerebral cortical neurogenesis.

The PACAP ligand/type I receptor system is expressed throughout the embryonic nervous system, suggesting roles in regulating neural patterning and neurogenesis. In the forebrain, precursors of the six-layered cerebral cortex cease dividing in a highly reproducible spatiotemporal sequence. The time of cell cycle exit in fact determines neuron laminar fate. Our studies indicate that PACAP signaling may elicit cortical precursor withdrawal from the cell cycle, antagonizing mitogenic stimulators. PACAP inhibited embryonic day 13.5 rat cortical precursor [3H]thymidine incorporation, decreasing the proportion of mitotic cells. PACAP promoted morphological and biochemical differentiation, indicating that PACAP-induced cell cycle withdrawal was accompanied by neuronal differentiation. In vivo, embryonic cortex contains PACAP. In culture, 85% of cells expressed PACAP while 64% exhibited receptor. Co-localization studies indicated that PACAP ligand and receptor were expressed by the mitotic precursors that divided in response to bFGF, suggesting that precursors integrate mitogenic and anti-mitogenic signals to determine the timing of cell cycle exit. The expression of PACAP ligand and receptor in precursors raised the possibility of autocrine function. Indeed, peptide antagonists increased proliferation, suggesting that the PACAP system is expressed to elicit cell cycle exit. During ontogeny, an inhibitory signal, such as PACAP, may be required to counter the stimulatory activity of mitogenic bFGF and IGFI whose expression during cortical neurogenesis is sustained. The dynamic interplay of positive and negative regulators would regulate the timing of cell cycle withdrawal, and thus neuronal phenotype and laminar position.

Animals↗
PubMed1998

Tumor induction of VEGF promoter activity in stromal cells.

We have established a line of transgenic mice expressing the A. victoria green fluorescent protein (GFP) under the control of the promoter for vascular endothelial growth factor (VEGF). Mice bearing the transgene show green cellular fluorescence around the healing margins and throughout the granulation tissue of superficial ulcerative wounds. Implantation of solid tumors in the transgenic mice leads to an accumulation of green fluorescence resulting from tumor induction of host VEGF promoter activity. With time, the fluorescent cells invade the tumor and can be seen throughout the tumor mass. Spontaneous mammary tumors induced by oncogene expression in the VEGF-GFP mouse show strong stromal, but not tumor, expression of GFP. In both wound and tumor models the predominant GFP-positive cells are fibroblasts. The finding that the VEGF promoter of nontransformed cells is strongly activated by the tumor microenvironment points to a need to analyze and understand stromal cell collaboration in tumor angiogenesis.

Animals↗
PubMed1998

Opposing mitogenic regulation by PACAP in sympathetic and cerebral cortical precursors correlates with differential expression of PACAP receptor (PAC1-R) isoforms.

Neurogenesis in the peripheral and central nervous systems proceeds in region-specific fashion, although underlying mechanisms remain undefined. Emerging evidence indicates that the neuropeptide PACAP and its G-protein-coupled receptor are expressed widely in the embryonic brain, suggesting that the ligand/receptor system plays a role in development. We found previously that PAC1-R activation elicited opposing mitogenic effects in neurogenetic cultures, stimulating peripheral sympathetic neuroblasts while inhibiting cerebral cortical precursors. We have now defined the expression of PAC1-R mRNA isoforms and activation of second-messenger pathways in these model populations. Sympathetic neuroblasts express the "hop" receptor isoform, through which PACAP elicits increased levels of cAMP and activation of the PI signaling pathway. In contrast, cerebral cortical precursors express primarily the "short" (non-insert) receptor isoform and exhibit increased cAMP levels alone following PACAP treatment. Thus, opposing mitogenic regulation in sympathetic and cortical precursors correlates with differential receptor isoform expression and distinct second-messenger signaling. In addition to receptor, PACAP ligand mRNA was expressed by both populations, suggesting that the peptide is produced and acts locally to regulate precursor proliferation. These observations indicate that the PACAP ligand/receptor system is expressed in both the peripheral and central nervous system during development. More generally, these studies suggest that widely expressed extracellular factors mediate region-specific neurogenesis by activating lineage-restricted receptor isoforms and intracellular pathways.

Animals↗
PubMed1998

Mucosal iodine staining improves endoscopic visualization of squamous dysplasia and squamous cell carcinoma of the esophagus in Linxian, China.

BACKGROUND: In previous studies in the high risk population of Linxian, China, the majority of foci of high grade (moderate and severe) squamous dysplasia (HGD) and invasive squamous carcinoma (CA) of the esophagus were associated with endoscopically visible lesions that could be targeted for biopsy, but some foci of HGD were missed by routine endoscopic examination. This study examined whether spraying the mucosa with Lugol's iodine solution, which stains normal epithelium brown but leaves dysplasia and carcinoma unstained, could improve endoscopic detection and delineation of these lesions. METHODS: Two hundred twenty-five Linxian adults with balloon cytologic evidence of dysplasia or carcinoma underwent endoscopy. All visible lesions were described and photographed before and after staining with 1.2% Lugol's iodine solution. Biopsies were taken from all lesions visible before staining, from all unstained lesions (USLs) after applying the stain, and from representative control areas of stained mucosa. RESULTS: Two hundred fifty-three USLs and 255 control sites were biopsied. No complications occurred. Ninety-four biopsy sites contained HGD and 20 contained CA. Before staining, the sensitivity of visible lesions for identifying HGD or CA was 62%, and the specificity was 79%. After staining, the sensitivity of USLs for identifying HGD or CA was 96%, and the specificity was 63%. Eighty-eight percent of the HGD and CA lesions were larger or more clearly defined after staining. The diagnostic lesions in 17 of 31 patients with moderate dysplasia (55%), 8 of 35 patients with severe dysplasia (23%), and none of the 19 patients with invasive carcinoma (0%) were identified only after staining. CONCLUSIONS: Mucosal iodine staining improved endoscopic detection and delineation of HGD and CA in these patients. This simple technique is highly sensitive for identifying these precursor and invasive squamous lesions, and it should be used whenever optimal visualization of squamous mucosal abnormalities is required.

Adult↗
PubMed1997

Pituitary adenylate cyclase-activating polypeptide is an autocrine inhibitor of mitosis in cultured cortical precursor cells.

During brain development, an intricate array of signals is likely to control the transition from proliferation to differentiation, particularly in the complex cerebral cortex. Although factors regulating proliferation and differentiation have been identified, little is known about mechanisms governing the exit of precursors from the cell cycle. We now report that pituitary adenylate cyclase-activating polypeptide (PACAP), a new member of the vasoactive intestinal peptide family expressed in embryonic brain, promotes this transition. In virtually pure cultures of embryonic day 13.5 (E13.5) rat cortical precursors, PACAP inhibited [3H]thymidine incorporation by 43%, decreasing the proportion of mitotic cells. Moreover, the peptide promoted morphological and biochemical differentiation; PACAP elicited a 2-fold increase in cells bearing neurites and a 30% increase in neurotrophin trkB receptor expression, indicating that PACAP induced cell cycle withdrawal and promoted neuronal differentiation. The expression of PACAP ligand and receptor in precursors raised the possibility of autocrine function. Indeed, 85% of cells exhibited PACAP immunoreactivity while 64% expressed type I receptor, which, in turn, mediated cAMP activation and phosphorylated cAMP response element binding protein nuclear signaling. Furthermore, treatment with the PACAP antagonist or neutralizing antibody increased DNA synthesis and proliferation, which is consistent with interruption of ongoing mitotic inhibition mediated by endogenous PACAP. Our observations suggest that cortical precursors produce PACAP as an autocrine signal to elicit cell cycle withdrawal, inducing the transition from proliferation to neuronal differentiation.

Animals↗
PubMed1997

Follicle stimulating hormone is required for ovarian follicle maturation but not male fertility.

Follicle stimulating hormone (FSH) is a member of the glycoprotein hormone family that includes luteinzing hormone (LH), thyroid stimulating hormone, and chorionic gonadotropin. These heterodimeric hormones share a common alpha subunit and differ in their hormone-specific beta subunit. The biological activity is conferred only by the heterodimers. FSH and LH are synthesized in the same cells of the pituitary, the gonadotrophs. FSH receptors are localized to Sertoli cells of the testes and granulosa cells of the ovary. Minimal data has been accumulated so far involving human mutations in the FSH beta, LH beta, or the gonadotropin receptor genes. There are no known mouse strains with mutations in the FSH beta gene. To generate animal models for human diseases involving the gonadotropin signal transduction pathway, we produced mice deficient in the FSH beta subunit and therefore in FSH using ES cell technology. FSH-deficient females are infertile due to a block in folliculogenesis prior to antral follicle formation. Although FSH was predicted to be necessary for spermatogenesis and Sertoli cell growth in males, FSH-deficient males are fertile despite having small testes. Our findings have important implications for male contraceptive development in humans.

Animals↗
PubMed1996

Growth differentiation factor-9 is required during early ovarian folliculogenesis.

Growth factors synthesized by ovarian somatic cells directly affect oocyte growth and function, but it is unclear whether oocyte-secreted factors play a reciprocal role in modulating somatic cell functions in vivo. During the functional analysis of members of the transforming growth factor-beta superfamily in mouse development, we have uncovered a new family member, growth differentiation factor-9 (GDF-9), which is required for ovarian folliculogenesis. GDF-9 messenger RNA is synthesized only in the oocyte from the primary one-layer follicle stage until after ovulation. Here we analyse ovaries from GDF-9-deficient female mice and demonstrate that primordial and primary one-layer follicles can be formed, but there is a block in follicular development beyond the primary one-layer follicle stage which leads to complete infertility. Oocyte growth and zona pellucida formation proceed normally, but other aspects of oocyte differentiation are compromised. Thus, GDF-9 is the first oocyte-derived growth factor required for somatic cell function in vivo.

Animals↗
PubMed1996

Neurodegeneration, myocardial injury, and perinatal death in mitochondrial superoxide dismutase-deficient mice.

Manganese superoxide dismutase (SOD2) converts superoxide to oxygen plus hydrogen peroxide and serves as the primary defense against mitochondrial superoxide. Impaired SOD2 activity in humans has been associated with several chronic diseases, including ovarian cancer and type I diabetes, and SOD2 overexpression appears to suppress malignancy in cultured cells. We have produced a line of SOD2 knockout mice (SOD2m1BCM/SOD2m1BCM) that survive up to 3 weeks of age and exhibit several novel pathologic phenotypes including severe anemia, degeneration of neurons in the basal ganglia and brainstem, and progressive motor disturbances characterized by weakness, rapid fatigue, and circling behavior. In addition, SOD2m1BCM/SOD2m1BCM mice older than 7 days exhibit extensive mitochondrial injury within degenerating neurons and cardiac myocytes. Approximately 10% of SOD2m1BCM/SOD2m1BCM mice exhibit markedly enlarged and dilated hearts. These observations indicate that SOD2 deficiency causes increased susceptibility to oxidative mitochondrial injury in central nervous system neurons, cardiac myocytes, and other metabolically active tissues after postnatal exposure to ambient oxygen concentrations. Our SOD2-deficient mice differ from a recently described model in which homozygotes die within the first 5 days of life with severe cardiomyopathy and do not exhibit motor disturbances, central nervous system injury, or ultrastructural evidence of mitochondrial injury.

Animals↗
PubMed1996

A paradigm for distinguishing the roles of mitogenesis and trophism in neuronal precursor proliferation.

During nervous system development, the generation of neuronal populations is subject to regulation by extracellular growth factors. Traditional views suggest that growth factors promote proliferation by increasing the fraction of precursors that enter the mitotic cycle and subsequently divide (that is, enhance mitosis). However, recent evidence indicates that dividing precursors may undergo cell death. Consequently, a given molecule may also increase neuroblast proliferation by promoting survival of dividing precursors. In the present work, we developed a new approach to distinguish these two distinct effects of growth factors on dividing neuroblasts. By using a brief 6 h culture paradigm of embryonic day 15.5 sympathetic neuroblasts, we minimized cell death, thereby excluding the survival-promoting (trophic) activity of growth factors. In the absence of trophism, measured increases in [3H]thymidine incorporation reflected growth factor mitogenic activity only. Using a well-characterized sympathetic model, we found that insulin, EGF and vasoactive intestinal peptide (VIP) increased [3H]thymidine incorporation 30%, 20% and 46% respectively, consistent with their previously reported mitogenic activity. In contrast, neurotrophin-3 (NT3) and nerve growth factor (NGF), which serve as trophic signals for the neuroblasts, did not elicit any change in [3H]thymidine incorporation, indicating that the neurotrophins are not mitogenic for sympathetic precursors. This approach may be useful in distinguishing mitogenic and trophic regulation of proliferation in other brain precursor populations.

Animals↗
PubMed1995

Multiple defects and perinatal death in mice deficient in follistatin.

Follistatin, an activin-binding protein and activin antagonist in vitro, can bind to heparan sulphate proteoglycans and may function in vivo to present activins to their receptors. In the mouse, follistatin messenger RNA is first detected in the deciduum (on embryonic day 5.5), and later in the developing hindbrain, somites, vibrissae, teeth, epidermis and muscle. In Xenopus laevis, overexpression of follistatin leads to induction of neural tissue. Here we use loss-of-function mutant mice to investigate the function of follistatin in mammals. We find that follistatin-deficient mice are retarded in their growth, have decreased mass of the diaphragm and intercostal muscles, shiny taut skin, skeletal defects of the hard palate and the thirteenth pair of ribs, their whisker and tooth development is abnormal, they fail to breathe, and die within hours of birth. These defects are more widespread than those seen in activin-deficient mutant mice, indicating that follistatin may modulate the actions of several members of the transforming growth factor-beta family.

Animals↗
PubMed1995

Effects of gypenosides on mouse splenic lymphocyte transformation and DNA polymerase II activity in vitro.

AIM: To study the effects of gypenosides (Gyp) on lymphocyte transformation and DNA polymerase II activity. METHODS: Lymphocyte transformation response was induced by concanavalin A and lipopolysaccharides respectively. The activity of DNA polymerase II and DNA synthesis were assayed with TTP and [3H]TdR incorporation respectively in mixed lymphocyte culture test. RESULTS: Gyp 2.5-20 mg L-1 enhanced splenic T- and B- cell transformation, increased the DNA synthesis and potentiated the activity of DNA polymerase II. However, Gyp > 40 mg L-1 showed contrary effects. CONCLUSION: Gyp regulated lymphocyte transformation and DNA synthesis by regulating DNA polymerase II activity.

Animals↗