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L F Parada

Publications and source records attributed to L F Parada.

At least 37 records · Page 2Linked to original sources
PubMed2001

mKlf7, a potential transcriptional regulator of TrkA nerve growth factor receptor expression in sensory and sympathetic neurons.

Development of the nervous system relies on stringent regulation of genes that are crucial to this process. TrkA, the receptor for nerve growth factor (NGF), is tightly regulated during embryonic development and is essential for the survival and differentiation of neural crest-derived sensory and sympathetic neurons. We have previously identified a mouse TrkA enhancer and have characterized several cis regulatory elements that are important for appropriate TrkA expression in vivo. We now report the cloning of a novel gene encoding a Kruppel-like factor from a mouse dorsal root ganglion expression library. This Kruppel-like factor, named mKlf7, binds specifically to an Ikaros core binding element that is crucial for in vivo TrkA enhancer function. Using in situ hybridization, we demonstrate that mKlf7 is coexpressed with TrkA in sensory and sympathetic neurons during embryogenesis and in adulthood. These data are consistent with the idea that mKlf7 may directly regulate TrkA gene expression in the peripheral nervous system.

Amino Acid Sequence↗
PubMed2001

Leydig insulin-like hormone, gubernacular development and testicular descent.

PURPOSE: Testicular descent is controlled by 2 morphological and hormonal steps. Transabdominal testicular descent is mediated by gubernacular swelling and regression of the cranial suspensory ligament. Müllerian inhibiting substance (MIS) has been proposed to stimulate the swelling but this remains controversial. Recently, a mouse mutant for Leydig insulin-like hormone (Insl3) was found to have undescended testis and deficient gubernaculum. We examine the testicular position of Insl3 mutant mice and the development of gubernacula. MATERIALS AND METHODS: Mice with Insl3 homozygotes (-/-), heterozygotes (+/-) and wild-types (+/+) were examined at embryonic day 16.5 and birth. Macroscopic dissections and measurements of the testicular position, as well as microscopic analysis (hematoxylin and eosin, and Masson's trichrome) were performed. RESULTS: Of the mice 11 Insl3 homozygote males had significantly impaired testicular descent at embryonic day 16.5 and birth (p <0.01), and the cord was thin and elongated, while 14 heterozygotes and 7 wild-types had normal testicular descent. Microscopically, the gubernaculum of Insl3 homozygotes was small with some muscle development but no central core of mesenchyme at embryonic day 16.5. On the other hand, heterozygotes and wild-types had normal gubernacular development with a swelling reaction. CONCLUSIONS: Insl3 mutants show feminized gubernaculum with deficient mesenchymal core. Insl3 appears to have some role in the gubernacular swelling reaction in mice.

Animals↗
PubMed2000

Hormones in male sexual development.

Classical embryology has provided a clear view of the timing and hormonal cues that govern sexual differentiation. Molecular biology has added important details to this picture. The cloning of SRY, MIS, and INSL3 provide insight into the molecular signals that provide important cues at the cellular level. Continued understanding of these pathways may provide the necessary information to one day reverse defects of sexual differentiation.

Animals↗
PubMed2000

A molecular basis for estrogen-induced cryptorchidism.

Male sexual differentiation relies upon testicular secretion of the hormones testosterone, Mullerian inhibiting substance, and insulin-3 (Insl3). Insl3 is responsible for testicular descent through virilization and outgrowth of the embryonic gubernaculum. In mouse, prenatal exposure to 17beta-estradiol and the nonsteroidal synthetic estrogen diethylstilbestrol (DES) disturbs the endocrine balance, causing demasculinizing and feminizing effects in the male embryo, including impaired testicular descent (cryptorchidism). In the current study, we show that maternal exposure to estrogens, including 17alpha- and beta-estradiol, as well as DES, specifically down regulates Insl3 expression in embryonic Leydig cells, thereby providing a mechanism for cryptorchidism. These experiments may have implications for the widespread use of estrogenic substances in agriculture and the environment.

Animals↗
PubMed2000

Role of N-myc in the developing mouse kidney.

N-myc is a transcription factor expressed in the developing metanephric kidney and other organs. In mice, complete disruption of the N-myc gene results in fetal death on the first day of renal organogenesis. In addition to the null N-myc allele, others have generated a hypomorphic N-myc allele. In this study, combinations of these mutant genes were used to demonstrate that reduction in N-myc protein levels correlate with fewer developing glomeruli and collecting ducts in embryonic kidney explants. Histological sections revealed that the mutant kidneys were hypoplastic with normal developing structures. The data indicate that the hypoplasia is due to a reduction in proliferation rather than an increase in apoptosis. Thus, N-myc loss causes a decrease in numbers of ureteric bud tips and developing glomeruli in explants and hypoplastic kidneys in vivo, in a dose-dependent manner.

Animals↗
PubMed2000

BDNF regulates eating behavior and locomotor activity in mice.

Brain-derived neurotrophic factor (BDNF) was studied initially for its role in sensory neuron development. Ablation of this gene in mice leads to death shortly after birth, and abnormalities have been found in both the peripheral and central nervous systems. BDNF and its tyrosine kinase receptor, TrkB, are expressed in hypothalamic nuclei associated with satiety and locomotor activity. In heterozygous mice, BDNF gene expression is reduced and we find that all heterozygous mice exhibit abnormalities in eating behavior or locomotor activity. We also observe this phenotype in independently derived inbred and hybrid BDNF mutant strains. Infusion with BDNF or NT4/5 can transiently reverse the eating behavior and obesity. Thus, we identify a novel non-neurotrophic function for neurotrophins and indicate a role in behavior that is remarkably sensitive to alterations in BDNF activity.

Adipocytes↗
PubMed2000

Loss of brain-derived neurotrophic factor-dependent neural crest-derived sensory neurons in neurotrophin-4 mutant mice.

Peripheral ganglion neurons confer sensory information including touch, pain, temperature, and proprioception. Sensory modality is linked to specific neurotrophin (NTF) requirements. NT-3 supports survival of neurons that differentiate primarily into proprioceptors whereas nerve growth factor and brain-derived neurotrophic factor (BDNF) support subpopulations that transmit nociception and mechanoreception, respectively. We examined sensory neurons of gene-targeted mouse mutants at the NT-4, BDNF, NT-3, and TrkA loci. We show that NT-4 functions early in gangliogenesis, upstream of BDNF. In the absence of NT-4 function, BDNF-dependent, TrkB-expressing neurons fail to appear. The results are consistent with the model that precursor cells intended to become BDNF-dependent mechanoreceptors instead differentiate into NT-3-dependent proprioceptive neurons.

Animals↗
PubMed2000

Requirement for nitric oxide activation of p21(ras)/extracellular regulated kinase in neuronal ischemic preconditioning.

The mechanisms underlying neuronal ischemic preconditioning, a phenomenon in which brief episodes of ischemia protect against the lethal effects of subsequent periods of prolonged ischemia, are poorly understood. Ischemia can be modeled in vitro by oxygen-glucose deprivation (OGD). We report here that OGD preconditioning induces p21(ras) (Ras) activation in an N-methyl-D-aspartate receptor- and NO-dependent, but cGMP-independent, manner. We demonstrate that Ras activity is necessary and sufficient for OGD tolerance in neurons. Pharmacological inhibition of Ras, as well as a dominant negative mutant Ras, block OGD preconditioning whereas a constitutively active form of Ras promotes neuroprotection against lethal OGD insults. In contrast, the activity of phosphatidyl inositol 3-kinase is not required for OGD preconditioning because inhibition of phosphatidyl inositol 3-kinase with a chemical inhibitor or with a dominant negative mutant does not have any effect on the development of OGD tolerance. Furthermore, using recombinant adenoviruses and pharmacological inhibitors, we show that downstream of Ras the extracellular regulated kinase cascade is required for OGD preconditioning. Our observations indicate that activation of the Ras/extracellular regulated kinase cascade by NO is a critical mechanism for the development of OGD tolerance in cortical neurons, which may also play an important role in ischemic preconditioning in vivo.

Adenoviridae↗
PubMed2000

Neurofibromin negatively regulates neurotrophin signaling through p21ras in embryonic sensory neurons.

Embryonic sensory and sympathetic neurons that lack neurofibromin, the protein product of the neurofibromatosis type 1 (Nfl) gene, survive and extend neurites in the absence of neurotrophins. To determine whether neurofibromin negatively regulates neurotrophin signaling through its interaction with p21ras, we used Fab antibody fragments to block Ras function in DRG, trigeminal, nodose, and SCG neurons isolated from Nfl(-/-) and wild-type mouse embryos. We show that introduction of anti-Ras Fab fragments significantly reduces the ability of neurofibromin-deficient neurons to survive in the absence of neurotrophins. Moreover, addition of H-ras protein enhances the survival of Nfl(-/-), but not wild-type, DRG neurons. Our results are consistent with a major role for neurofibromin in modulating Trk signaling through p21ras during neuronal development.

Animals↗
PubMed2000

Molecular characterization of the TrkA/NGF receptor minimal enhancer reveals regulation by multiple cis elements to drive embryonic neuron expression.

Neural development relies on stringent regulation of key genes that mediate specialized function. TrkA is primarily expressed in neural crest-derived sensory and sympathetic neurons where it transmits critical survival information. We have identified a 457 base pair sequence upstream of the murine first TrkA coding exon that is conserved in human and in chick, and is sufficient for expression in the correct cells with appropriate timing. Mutation analysis of consensus transcription factor binding domains within the minimal enhancer reveals a complex positive regulation that includes sites required for global expression and sites that are specifically required for DRG, trigeminal or sympathetic expression. These results provide a foundation for identification of the transcriptional machinery that specifies neurotrophin receptor expression.

Animals↗
PubMed1999

Mouse tumor model for neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder characterized by increased incidence of benign and malignant tumors of neural crest origin. Mutations that activate the protooncogene ras, such as loss of Nf1, cooperate with inactivating mutations at the p53 tumor suppressor gene during malignant transformation. One hundred percent of mice harboring null Nf1 and p53 alleles in cis synergize to develop soft tissue sarcomas between 3 and 7 months of age. These sarcomas exhibit loss of heterozygosity at both gene loci and express phenotypic traits characteristic of neural crest derivatives and human NF1 malignancies.

Animals↗
PubMed1999

NT4/5 mutant mice have deficiency in gustatory papillae and taste bud formation.

Neurotrophins are key determinants for controlling the survival of peripheral neurons during development. Brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT4/5) exert their action through a common trkB receptor but independently support gustatory sensory neurons. To assess the role of NT4/5 during development, we examined the postnatal development and maintenance of fungiform taste buds in mice carrying a deletion of NT4/5. The absence of NT4/5 results in embryonic deficits in gustatory innervation and a reduced number of fungiform papillae at birth. No degenerative deficits of fungiform papillae were observed for the first 3 weeks of postnatal development. However, these remaining fungiform papillae were smaller in appearance and many did not contain taste pores. By postnatal day 60, there was 63% decrease in the number of fungiform papillae, and remaining papillae were smaller in size or modified into filiform-like spines. These papillae had either no taste bud or a taste bud with a reduced number of taste cells compared to controls. These findings demonstrate that the NT4/5 gene functions in the maintenance of fungiform gustatory papillae and raises the possibility for an earlier role in development.

Animals↗
PubMed1999

Nerve growth factor induces survival and differentiation through two distinct signaling cascades in PC12 cells.

Nerve growth factor induces differentiation and survival of rat PC12 pheochromocytoma cells. The activation of the erk cascade has been implicated in transducing the multitude of signals induced by NGF. In order to explore the role of this signaling cascade in NGF mediated survival, differentiation and proliferation, we generated recombinant adenoviruses which express the intermediates of the erk cascade in their wild type, dominant negative and constitutively activated forms. We show that differentiation of PC12 cells requires activity of the ras/erk pathway, whereas inhibition of this pathway had no effect on survival or proliferation. Constitutively active forms of ras, raf and mek induced PC12 cell differentiation, while dominant interfering forms inhibited differentiation. Survival of PC12 cells in serum-free medium did not require activity of the ras/erk pathway. Instead, PI3 Kinase signaling was necessary for PC12 cell survival. Interestingly, constitutively activated versions of raf and mek were able to promote survival, but again this was dependent on activation of PI3 Kinase. Therefore, at least two distinct signaling pathways are required in PC12 cells for mediation of NGF functions.

Animals↗
PubMed1999

Cryptorchidism in mice mutant for Insl3.

Impaired testicular descent (cryptorchidism) is one of the most frequent congenital abnormalities in humans, involving 2% of male births. Cryptorchidism can result in infertility and increases risk for development of germ-cell tumours. Testicular descent from abdomen to scrotum occurs in two distinct phases: the trans-abdominal phase and the inguino-scrotal phase. Currently, little is known about the factors that regulate the trans-abdominal phase of testicular descent. Leydig insulin-like hormone (Insl3) is a member of the insulin hormone superfamily expressed in the developing testis. We show here that mice mutant for Insl3 are viable, but exhibit bilateral cryptorchidism due to developmental abnormalities of the gubernaculum, resulting in abnormal spermatogenesis and infertility. Female homozygotes have impaired fertility associated with deregulation of the oestrus cycle. These findings reveal roles for Insl3 in the development of the urogenital tract and in female fertility. Insl3 may act as a hormone to regulate the growth and differentiation of the gubernaculum, thereby mediating intra-abdominal testicular descent.

Animals↗
PubMed1999

Mice lacking NT-3, and its receptor TrkC, exhibit profound deficiencies in CNS glial cells.

Neurotrophin-3 (NT-3) and its receptor TrkC are known to be important for neuronal survival. More recently, NT-3 has been implicated as playing a role in oligodendrocyte (OL) proliferation and survival in vitro. Examination of NT-3 and TrkC knockout mice revealed a reduction in NT-3-dependent neurons. To date, no study has examined alterations in glial cell populations in these knockout mice. In this report, we demonstrate a decline in OL progenitor cell numbers within the CNS of NT-3 and TrkC knockout mice. We also observed that immature and mature OL-specific markers were attenuated in the NT-3 and TrkC knockout animals. Deficiencies in other CNS glial cells, including astrocytes and ameboid microglia, were also observed. The subventricular zone (SVZ), a highly proliferative region for progenitor glial cells, was reduced in size. Furthermore, a nuclear-specific stain revealed a decline in the numbers of pyknotic nuclei in and around the SVZ of the knockout mice. These data will support an in vivo NT-3-dependent mechanism for the normal development of CNS glial cells.

Animals↗
PubMed1999

A TrkB/insulin receptor-related receptor chimeric receptor induces PC12 cell differentiation and exhibits prolonged activation of mitogen-activated protein kinase.

Insulin receptor-related receptor (IRR), an orphan receptor in the insulin receptor (IR) family of receptor tyrosine kinases, is primarily localized to neural crest-derived sensory neurons during embryonic development. Expression of IRR closely resembles that of the nerve growth factor receptor, TrkA. To analyze the signaling properties and function of IRR in PC12 cells, a TrkB/IRR hybrid receptor was used. In contrast to IR activation, brain-derived neurotrophic growth factor-mediated activation of the TrkB/IRR receptor resulted in differentiation rather than proliferation. Analysis of cytoplasmic substrates activated by the TrkB/IRR receptor indicates a signaling pathway similar to that of the IR. Mutagenesis studies further show that only TrkB/IRR receptors able to phosphorylate mitogen-activated protein kinase elicit a differentiation response. Our analysis indicates that prolonged kinetics of mitogen-activated protein kinase activation mediated by the TrkB/IRR chimeric receptor correlates with induction to differentiate.

Animals↗