SEARCH · PubMed Health

Results for “knockout”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources

PubMed2002

Targeted proteomic profiling of renal Na(+) transporter and channel abundances in angiotensin II type 1a receptor knockout mice.

The renal tubule transporters responsible for Na(+) and water transport along the nephron have been identified and cloned, permitting comprehensive analysis of transporter protein abundance changes in complex physiological models by using a "targeted proteomics" approach. Here, we apply this approach to screen renal homogenates from mice in which the gene for the angiotensin II type 1a (AT(1a)) receptor has been deleted (versus wild-type mice) to determine which sodium transporters and channels are regulated by the AT(1a) receptor at the protein abundance level. In mice maintained on a low NaCl diet (<0.02% NaCl), (1) the abundances of 2 aldosterone-regulated transporters were markedly decreased in knockout versus wild-type mice, namely, the thiazide-sensitive cotransporter and the alpha-subunit of the amiloride-sensitive Na(+) channel (alpha-ENaC); (2) the abundances of beta-ENaC and gamma-ENaC were markedly increased; and (3) there were no significant changes in the abundances of the proximal tubule Na+-H(+) exchanger or the Na(+)-K(+)-2Cl(-) cotransporter of the thick ascending limb. When the experiment was repeated on higher NaCl diets (0.4% or 6% NaCl), the decrease in alpha-ENaC abundance persisted, whereas the other changes were abolished. Analysis of serum aldosterone concentration in AT(1a) knockout mice and wild-type mice on the low NaCl diet revealed the absence of a decrease with AT(1a) gene deletion (11.8 +/- 2.3 nmol/L for knockout mice and 5.7 +/- 0.8 nmol/L for wild-type mice [significantly increased]). These results reveal that the AT(1a) receptor plays an important role in regulation of Na(+) transporter and channel proteins in the "post-macula densa" region of the renal tubule via a mechanism that is not dependent on altered circulating aldosterone concentrations.

Angiotensin II↗

PubMed1999

Cholinergic contraction is altered in nNOS knockouts. Cooperative modulation of neural bronchoconstriction by nNOS and COX.

Endogenous nitric oxide (NO) is a bronchodilator but its physiologic role in small airways is not clear. In this study, we investigated the role of endogenous NO in the regulation of bronchiolar tone in the small airways of wild type and NO synthase (NOS) isoform (eNOS and nNOS)-knockout mice. Pretreatment with the cyclooxygenase inhibitor indomethacin significantly enhanced electrical field stimulation (EFS)-induced contraction in the airways from all types of mice by approximately 60 to 170% (n = 8 in each case), whereas pretreatment with the NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) did not (n = 8). Combined pretreatment with L-NAME and indomethacin enhanced airway contraction of wild-type and eNOS-knockout mice to a significantly greater extent (i.e., by 140 to 290%) than did indomethacin alone (n = 8 for each). This potentiation by L-NAME was not seen in nNOS knockout mice (n = 8). Neither indomethacin nor L-NAME alone affected carbachol (CCh) potency or maximal efficacy in the airways of wild-type mice, whereas the combined pretreatment slightly enhanced the maximal response without altering the potency of CCh (n = 6). Our results show that both NO and prostaglandins modulate neuronal contraction of murine small airways. NO is produced by nNOS, which may be located in nerves, and its overall effects are tonically inhibited by cyclooxygenase products.

Animals↗

PubMed2007

Relative axial myopia in Egr-1 (ZENK) knockout mice.

PURPOSE: Experiments in chickens have implicated the transcription factor ZENK (also known as Egr-1, NGFI-A, zif268, tis8, cef5, and Krox24) in the feedback mechanisms for visual control of axial eye growth and myopia development. ZENK is upregulated in retinal glucagon amacrine cells when axial eye growth is inhibited by positive spectacle lens wear and is downregulated when it is enhanced by negative spectacle lens wear, suggesting that ZENK may be linked to an inhibitory signal for axial eye growth. This study was undertaken to determine whether a Egr-1(-/-) knockout mouse mutant, lacking ZENK completely, has longer eyes and more myopic refraction, than do Egr-1(+/)(-) heterozygous and Egr-1(+/+) wild-type mice with near-identical genetic backgrounds. METHODS: Eye growth and refractive development were tracked from day P28 to P98. Corneal radius of curvature was measured with infrared photokeratometry, refractive state with infrared photoretinoscopy, and ocular dimensions with low-coherence interferometry. As a functional vision test, grating acuity was determined in an automated optomotor task. The abundance of ZENK protein in the retina was quantified by immunohistochemistry. RESULTS: Egr-1 knockout mice had longer eyes and a relative myopic shift in refraction, with additional minor effects on anterior chamber depth and corneal radius of curvature. Paraxial schematic eye modeling suggested changes in the optics of the crystalline lens as well. With increasing age, the differences between mutant and wild-type mice declined, although the differences in refraction persisted over the observation period. Grating acuity was not affected by the lack of the Egr-1 protein during development. CONCLUSIONS: Although it has been shown that different mouse strains may have differently large eyes, the present study shows that a specific gene knockout can produce relative myopia, compared with the wild-type with near-identical genetic background. Further experiments are needed to determine whether the observed effects of Egr-1 deletion are due to changes in function within the retina or other ocular tissues or to changes of function in other systems that may affect ocular growth from outside the eye.

Animals↗

PubMed2003

Uroguanylin knockout mice have increased blood pressure and impaired natriuretic response to enteral NaCl load.

Guanylin and uroguanylin, peptides synthesized in the intestine and kidney, have been postulated to have both paracrine and endocrine functions, forming a potential enteric-renal link to coordinate salt ingestion with natriuresis. To explore the in vivo role of uroguanylin in the regulation of sodium excretion, we created gene-targeted mice in which uroguanylin gene expression had been ablated. Northern and Western analysis confirmed the absence of uroguanylin message and protein in knockout mice, and cGMP levels were decreased in the mucosa of the small intestine. Ussing chamber analysis of jejunum revealed that Na+/H+ exchanger-mediated Na+ absorption and tissue conductance was not altered in the knockout animals, but short-circuit current, an index of electrogenic anion secretion, was reduced. Renal clearance measurements showed that uroguanylin deficiency results in impaired ability to excrete an enteral load of NaCl, primarily due to an inappropriate increase in renal Na+ reabsorption. Finally, telemetric recordings of blood pressure demonstrated increased mean arterial pressure in uroguanylin knockout animals that was independent of the level of dietary salt intake. Together, these findings establish a role for uroguanylin in an enteric-renal communication axis as well as a fundamental principle of this axis in the maintenance of salt homeostasis in vivo.

Animals↗

PubMedDate not supplied

Carcinogenic responses of transgenic heterozygous p53 knockout mice to inhaled 239PuO2 or metallic beryllium.

The transgenic heterozygous p53+/- knockout mouse has been a model for assessing the tumorigenicity of selected carcinogens administered by noninhalation routes of exposure. The sensitivity of the model for predicting cancer by inhaled chemicals has not been examined. This study addresses this issue by acutely exposing p53+/- mice of both sexes by nose-only inhalation to either air (controls), or to 1 of 2 levels of 239PuO2 (500 or 100 Bq 239Pu) or beryllium (Be) metal (60 or 15 micrograms). Additional wild-type p53+/+ mice were exposed by inhalation to either 500 Bq of 239PuO2 or 60 micrograms of Be metal. These carcinogens were selected because they operate by differing mechanisms and because of their use in other pulmonary carcinogenesis studies in our laboratory. Four or 5 of the 15 mice per sex from each group were sacrificed 6 mo after exposure, and only 2 pulmonary neoplasms were observed. The remainder of the mice were held for life-span observation and euthanasia as they became moribund. Survival of the p53+/- knockout mice was reduced compared to the p53+/+ wild-type mice. No lung neoplasms were observed in p53+/- mice exposed to air alone. Eleven of the p53+/- mice inhaling 239PuO2 developed pulmonary neoplasms. Seven p53+/+ mice exposed to 239PuO2 also developed pulmonary neoplasms, but the latency period for pulmonary neoplasia was significantly shorter in the p53+/ mice. Four pulmonary neoplasms were observed in p53+/- mice exposed to the higher dose of Be, whereas none were observed in the wild-type mice or in the heterozygous mice exposed to the lower dose of Be. Thus, both p53+/- and p53+/+ mice were susceptible to 239Pu-induced carcinogenesis, whereas the p53+/- but not the p53+/+ mice were susceptible to Be-induced carcinogenesis. However, only 2 pulmonary neoplasms (1 in each of the 239PuO2 exposure groups) were observed in the 59 p53+/ mice that were sacrificed or euthanatized within 9 mo after exposure, indicating that the p53+/- knockout mouse might not be appropriate for a 6-mo model of carcinogenesis for these inhaled carcinogens.

Adenocarcinoma↗

PubMed2006

Impact of Cu, Zn-superoxide dismutase and Se-dependent glutathione peroxidase-1 knockouts on acetaminophen-induced cell death and related signaling in murine liver.

There is increasing evidence showing dual functions of antioxidant enzymes in coping with reactive oxygen species (ROS) versus reactive nitrogen species (RNS). The objective of this study was to compare the impacts of knockout of Cu, Zn-superoxide dismutase (SOD1) and Se-dependent glutathione peroxidase-1 (GPX1) on cell death and related signaling mediated by acetaminophen (APAP), a RNS inducer in liver. Two groups of young adult knockout mice (SOD1(-/-) and GPX1(-/-)), along with their wild types (WT), were killed 5 hrs after an ip injection of saline or APAP (300 mg/kg body wt). While the WT mice showed more hepatic necrosis and DNA breakage than the GPX1(-/-) mice, the SOD1(-/-) mice had essentially no positive response compared with their saline-injected controls. The APAP treatment activated liver c-jun N-terminal kinase (JNK) in the WT and GPX1(-/-) mice, but not in the SOD1(-/-) mice. The APAP-induced changes in other cell death-related signal proteins such as p21, caspase-3, and poly(ADP-ribose) polymerase (PARP) also were obviated in the SOD1(-/-) mice. In conclusion, knockout of GPX1 did not potentiate APAP-induced cell death and related signaling, whereas the SOD1 null blocked APAP-induced hepatic JNK phosphorylation and cell death.

Acetaminophen↗

PubMed2003

An imbalance in antioxidant defense affects cellular function: the pathophysiological consequences of a reduction in antioxidant defense in the glutathione peroxidase-1 (Gpx1) knockout mouse.

Aerobic cells are subjected to damaging reactive oxygen species (ROS) as a consequence of oxidative metabolism and/or exposure to environmental toxins. Antioxidants limit this damage, yet peroxidative events occur when oxidant stress increases. This arises due to increased radical formation or decreased antioxidative defenses. The two-step enzymatic antioxidant pathway limits damage to important biomolecules by neutralising superoxides to water. However, an imbalance in this pathway (increased first-step antioxidants relative to second-step antioxidants) has been proposed as etiological in numerous pathologies. This review presents evidence that a shift in favor of hydrogen peroxide and/or lipid peroxides has pathophysiological consequences. The involvement of antioxidant genes in the regulation of redox status, and ultimately cellular homeostasis, is explored in murine transgenic and knockout models. The investigations of Sod1 transgenic cell-lines and mice, as well as Gpx1 knockout mice (both models favor H(2)O(2) accumulation), are presented. Although in most instances accumulation of H(2)O(2) affects cellular function and leads to exacerbated pathology, this is not always the case. This review highlights those instances where, for example, increased Sod1 levels are beneficial, and indicates a role for superoxide radicals in pathogenesis. Studies of Gpx1 knockout mice (an important second-step antioxidant) lead us to conclude that Gpx1 functions as the primary protection against acute oxidative stress, particularly in neuropathological situations such as stroke and cold-induced head trauma, where high levels of ROS occur during reperfusion or in response to injury. In summary, these studies clearly highlight the importance of limiting ROS-induced cellular damage by maintaining a balanced enzymatic antioxidant pathway.

Animals↗

PubMed2001

Second generation knockout sickle mice: the effect of HbF.

Sickle transgenic mice expressing exclusively human globins are desirable for studying pathophysiology and testing gene therapy strategies, but they must have significant pathology and show evidence of amelioration by antisickling hemoglobins. Mice were generated that expressed exclusively human sickle hemoglobin with 3 levels of HbF using their previously described sickle constructs (cointegrated human miniLCRalpha2 and miniLCRbeta(S) [PNAS 89:12150, 1992]), mouse alpha- and beta-globin-knockouts, and 3 different human gamma-transgenes. It was found that, at all 3 levels of HbF expression, these mice have balanced chain synthesis, nearly normal mean corpuscular hemoglobin, and, in some cases, F cells. Mice with the least adult HbF expression were the most severe. Progressive increase in HbF from less than 3% to 20% to 40% correlated with progressive increase in hematocrit (22% to 34% to 40%) and progressive decrease in reticulocyte count (from 60% to 30% to 13%). Urine concentrating ability was normalized at high HbF, and tissue damage detected by histopathology and organ weight were ameliorated by increased HbF. The gamma-transgene that produces intermediate levels of HbF was introduced into knockout sickle mice described by Pàszty and coworkers that express the miniLCRalpha1(G)gamma(A)gammadeltabeta(S) transgene and have fetal but not adult expression of HbF. It was found that the level of HbF required to ameliorate low hematocrit and normalize urine concentrating defect was different for the miniLCRalpha2beta(S) and miniLCRalpha1(G)gamma(A)gammadeltabeta(S) mice. We conclude that knockout mice with the miniLCRalpha2beta(S) transgene and postnatal expression of HbF have sufficiently faithful sickle pathology to serve as a platform for testing antisickling interventions.

2,3-Diphosphoglycerate↗

PubMed2006

Neural stem cells from protein tyrosine phosphatase sigma knockout mice generate an altered neuronal phenotype in culture.

BACKGROUND: The LAR family Protein Tyrosine Phosphatase sigma (PTPsigma) has been implicated in neuroendocrine and neuronal development, and shows strong expression in specific regions within the CNS, including the subventricular zone (SVZ). We established neural stem cell cultures, grown as neurospheres, from the SVZ of PTPsigma knockout mice and sibling controls to determine if PTPsigma influences the generation and the phenotype of the neuronal, astrocyte and oligodendrocyte cell lineages. RESULTS: The neurospheres from the knockout mice acquired heterogeneous developmental characteristics and they showed similar morphological characteristics to the age matched siblings. Although Ptprs expression decreases as a function of developmental age in vivo, it remains high with the continual renewal and passage of the neurospheres. Stem cells, progenitors and differentiated neurons, astrocytes and oligodendrocytes all express the gene. While no apparent differences were observed in developing neurospheres or in the astrocytes and oligodendrocytes from the PTPsigma knockout mice, the neuronal migration patterns and neurites were altered when studied in culture. In particular, neurons migrated farther from the neurosphere centers and the neurite outgrowth exceeded the length of the neuronal processes from age matched sibling controls. CONCLUSION: Our results imply a specific role for PTPsigma in the neuronal lineage, particularly in the form of inhibitory influences on neurite outgrowth, and demonstrate a role for tyrosine phosphatases in neuronal stem cell differentiation.

Animals↗

PubMed2002

Knockout and transgenic mice of Trp53: what have we learned about p53 in breast cancer?

The human p53 tumor suppressor gene TP53 is mutated at a high frequency in sporadic breast cancer, and Li-Fraumeni syndrome patients who carry germline mutations in one TP53 allele have a high incidence of breast cancer. In the 10 years since the first knockout of the mouse p53 tumor suppressor gene (designated Trp53) was published, much has been learned about the contribution of p53 to biology and tumor suppression in the breast through the use of p53 transgenic and knockout mice. The original mice deficient in p53 showed no mammary gland phenotype. However, studies using BALB/c-Trp53-deficient mice have demonstrated a delayed involution phenotype and a mammary tumor phenotype. Together with other studies of mutant p53 transgenes and p53 bitransgenics, a greater understanding has been gained of the role of p53 in involution, of the regulation of p53 activity by hormones, of the effect of mouse strain and modifier genes on tumor phenotype, and of the cooperation between p53 and other oncogenic pathways, chemical carcinogens and hormonal stimulation in mammary tumorigenesis. Both p53 transgenic and knockout mice are important in vivo tools for understanding breast cancer, and are yet to be exploited for developing therapeutic strategies in breast cancer.

Animals↗

PubMed2003

Establishing insulin 1 and insulin 2 knockout congenic strains on NOD genetic background.

As insulin is a major autoantigen in autoimmune diabetes and because the insulin gene region locus in humans has been linked to diabetes risk, we have bred insulin gene knockouts onto the NOD mouse. Mice differ from humans in terms that they express two nonallelic genes of insulin. Insulin 2 is the murine homologue of the human insulin gene and is located on mouse chromosome 7. Insulin 1 is thought to have evolved by a gene duplication event, lacks the second intron of the insulin 2 gene, and is located on mouse chromosome 19. The differential thymic expression of the insulin gene may be important for central tolerance induction. Here, we present the initial establishment of congenic knockouts and characterization of the congenic intervals corresponding to insulin 1 and insulin 2 knockout genes on mouse chromosome 19 and 7, respectively.

Animals↗

PubMed2000

Disposition of acetaminophen and indocyanine green in cystic fibrosis-knockout mice.

Drug treatment poses a therapeutic challenge in cystic fibrosis (CF) because the disposition of a number of drugs is altered in CF. Enhanced clearance of acetaminophen (APAP) and indocyanine green (ICG) have previously been reported in CF patients. The objective of the current study was to investigate if the CF-knockout mouse model (cftr(m1UNC)) shows altered pharmacokinetics similar to those seen in CF patients using the 2 model compounds APAP and ICG. Clearance (CL/F) of APAP and renal (CLR) and formation (CLf) clearance of acetaminophen glucuronide (AG) and acetaminophen sulfate (AS) were determined in CF-knockout mice following administration of APAP (50 mg/kg, intraperitoneal). CLR of AS was 19.5 and 12.9 (mL/min per kg) and CLf of AS was 10.4 and 6.7 mL/min per kg for homozygous and heterozygous males, respectively, which was significantly different between groups. CLR of AG was 6.3 and 4.8 mL/min per kg and CLf of AG was 9.6 and 8.9 mL/min per kg for homozygous and heterozygous males, respectively, although not reaching statistical significance. No significant differences were noted in either ClR or CLf of AG and AS in female CF mice. Plasma concentrations of ICG (10 mg/kg, intravenous) were determined over 0 to 15 minutes. Homozygous females showed a higher apparent volume of distribution (96 mL/kg) relative to heterozygous females (72 mL/kg). Similar to CF patients, a trend toward a lower Cmax was noted in homozygous male and female mice. However, contrary to human data, no significant differences in CL of ICG were noted. These results suggest that the CF-knockout mice have potential as a model for studying altered drug disposition in CF patients.

Acetaminophen↗

PubMed2001

Ovarian pathology and high incidence of sex cord tumors in follitropin receptor knockout (FORKO) mice.

In this investigation we describe our observations of the status of the aging ovary in mice with disruption of the receptor for FSH. Knockout mice at 3-5 months of age are acyclic and sterile, with very small, underdeveloped ovaries. Thus, they exhibit hypergonadotropic-hypogonadism with high levels of circulating FSH similar to the postmenopausal state in women. By 12 months more than 92% of these animals developed various kinds of ovarian pathology, including neoplasms of sex cord-stromal type as well as cysts. Interestingly, the majority of tumors were located in the right ovary, with the contralateral ovary remaining unaffected but atrophic. The ovary from heterozygotes also showed pathology after 15 months. None of the age-matched wild-type mice that remained fertile developed any sign of ovarian tumors. Circulating LH and FSH levels were increased in follitropin receptor knockout mice and remained severalfold higher in tumor-bearing animals. The histological appearances of ovarian tumors were similar to the pathology observed in some types of sex cord-stromal neoplasms in women. The tumor burden caused weight loss and cachexia in follitropin receptor knockout mice. Based on these characteristics as well as the high incidence of ovarian pathology in the aging mutant, we propose that the loss of the FSH receptor signaling mechanisms predispose the ovary to molecular and structural changes leading to tumor formation. Hence, in the intact and fertile animal, FSH receptor signaling offers a protective mechanism that is lost upon reproductive senescence (menopause in women). Further studies are warranted in this genetic model to explore the molecular changes underlying the development of ovarian neoplasia.

Animals↗

PubMed2004

Tissue-specific differences in activation of atypical protein kinase C and protein kinase B in muscle, liver, and adipocytes of insulin receptor substrate-1 knockout mice.

Insulin receptor substrates (IRSs) 1 and 2 are postulated to control the activation of phosphatidylinositol 3-kinase (PI3K)-dependent signaling factors, namely, atypical protein kinase C (aPKC) and protein kinase B (PKB)/Akt, which mediate metabolic effects of insulin. However, it is uncertain whether aPKC and PKB are activated together or differentially in response to IRS-1 and IRS-2 activation in insulin-sensitive tissues. Presently, we examined insulin activation of aPKC and PKB in vastus lateralis muscle, adipocytes, and liver in wild-type and IRS-1 knockout mice, and observed striking tissue-specific differences. In muscle of IRS-1 knockout mice, the activation of both aPKC and PKB was markedly diminished. In marked contrast, only aPKC activation was diminished in adipocytes, and only PKB activation was diminished in liver. These results suggest that IRS-1 is required for: 1) activation of both aPKC and PKB in muscle; 2) aPKC, but not PKB, activation in adipocytes; and 3) PKB, but not aPKC, activation in liver. Presumably, IRS-2 or other PI3K activators account for the normal activation of aPKC in liver and PKB in adipocytes of IRS-1 knockout mice. These complexities in aPKC and PKB activation may be relevant to metabolic abnormalities seen in tissues in which IRS-1 or IRS-2 is specifically or predominantly down-regulated.

Adipocytes↗

PubMed2006

Premature luteinization and cumulus cell defects in ovarian-specific Smad4 knockout mice.

SMAD4 is a central component of the TGFbeta superfamily signaling pathway. Within the ovary, TGFbeta-related proteins play crucial roles in controlling granulosa cell growth, differentiation, and steroidogenesis. To study the in vivo roles of SMAD4 during follicle development, we generated an ovarian conditional knockout of Smad4 using the cre/loxP recombination system. Smad4 ovarian-specific knockout mice are subfertile with decreasing fertility over time and multiple defects in folliculogenesis. Regulation of steroidogenesis is disrupted in the Smad4 conditional knockout, leading to increased levels of serum progesterone. In addition, severe cumulus cell defects are present both in vivo and when assayed in vitro. These findings demonstrate that disrupting signaling through SMAD4 in the ovarian granulosa cells leads to premature luteinization of granulosa cells and eventually premature ovarian failure, thereby demonstrating key in vivo roles of TGFbeta superfamily signaling in the timing of granulosa cell differentiation.

Animals↗

PubMed2002

Acute disruption of select steroid receptor coactivators prevents reproductive behavior in rats and unmasks genetic adaptation in knockout mice.

Estrogen (E) and progesterone exert profound influence on development and reproduction. In vitro, steroid receptor coactivators (SRCs) are nuclear proteins that interact with DNA-bound steroid receptors to potentiate their transcriptional efficiency. We examined the effects of antisense oligonucleotides to SRC-1, SRC-2, and SRC-3 on female sexual behavior and steroid receptor-mediated transcription. Rat (r) SRC-1, rSRC-2, and rSRC-3 genes were cloned. Our results reveal a significant inhibitory effect by antisense (AS) to SRC-1 and SRC-2, but not SRC-3, on hormone-induced reproductive behavior. Importantly, sexual behavior was attenuated through estrogen receptor alpha (ERalpha)-dependent, rather than progesterone receptor (PR)-dependent, transcription, as E failed to induce the synthesis of PR content in the medial basal hypothalamus, and immunoreactive PR in the ventromedial nucleus were depleted in tissue from rSRC-1-AS- and rSRC-2-AS-treated, but not rSRC-3-AS-treated, rats primed with E. Consistent with interruption of ERalpha-induced transcription, high dose of E and epidermal growth factor alone failed to induce sexual behavior in females treated with either rSRC-1-AS or SRC-2-AS. Immunoreactive SRC-1 and SRC-2, but not SRC-3, proteins were abundant in the ventromedial nucleus, thus demonstrating that the biological activities of hypothalamic steroid receptors are selectively regulated by regional distribution of specific SRCs. As SRC-1 knockout mice have only a slight loss in reproductive function, the possibility that genetic adaptation occurs during development was tested. Mouse (m) SRC-1-AS suppressed lordosis in wild-type, but not SRC-1, knockout mice, whereas mSRC-2-AS suppressed behavior in both genotypes. mSRC-3-AS had no effect in either genotype, and SRC-3 knockout mice exhibited full receptivity. Collectively, the findings clearly implicate dual regulation of ERalpha-dependent function by SRC-1 and SRC-2 in the intact female brain. In the genetic, but not acute, absence of SRC-1, up-regulation of SRC-2 serves as a critical adaptive mechanism during female development.

Adaptation, Physiological↗

PubMed1999

Smad5 knockout mice die at mid-gestation due to multiple embryonic and extraembryonic defects.

Smad5 has been implicated as a downstream signal mediator for several bone morphogenetic proteins (BMPs). To understand the in vivo function of Smad5, we generated mice deficient in Smad5 using embryonic stem (ES) cell technology. Homozygous mutant embryos die between E9.5 and E11.5, and display variable phenotypes. Morphological defects are first detected at E8.0 in the developing amnion, gut and heart (the latter defect being similar to BMP-2 knockout mice). At later stages, mutant embryos fail to undergo proper turning, have craniofacial and neural tube abnormalities, and are edematous. In addition, several extraembryonic lesions are observed. After E9.0, the yolk sacs of the mutants contain red blood cells but lack a well-organized vasculature, which is reminiscent of BMP-4, TGF-beta1 and TGF-beta type II receptor knockout mice. In addition, the allantois of many Smad5 mutants is fused to the chorion, but is not well-elongated. A unique feature of the Smad5 mutant embryos is that ectopic vasculogenesis and hematopoiesis is observed in the amnion, likely due to mislocation of allantois tissue. Despite the expression of Smad5 from gastrulation onwards, and in contrast to knockouts of Smad2 and Smad4, Smad5 only becomes essential later in extraembryonic and embryonic development.

Animals↗

PubMed2002

Brn3b/Brn3c double knockout mice reveal an unsuspected role for Brn3c in retinal ganglion cell axon outgrowth.

In mice, Brn3 POU domain transcription factors play essential roles in the differentiation and survival of projection neurons within the retina, inner ear, dorsal root and trigeminal ganglia. During retinal ganglion cell differentiation, Brn3b is expressed first, followed by Brn3a and Brn3c. Targeted deletion of Brn3b, but not Brn3a or Brn3c, leads to a loss of most retinal ganglion cells before birth. However, as a few retinal ganglion cells are still present in Brn3b(-/-) mice, Brn3a and Brn3c may partially compensate for the loss of Brn3b. To examine the role of Brn3c in retinal ganglion cell development, we generated Brn3b/Brn3c double knockout mice and analyzed their retinas and optic chiasms. Retinal ganglion cell axons from double knockout mice were more severely affected than were those from Brn3b-deficient mice, indicating that Brn3c was required for retinal ganglion cell differentiation and could partially compensate for the loss of Brn3b. Moreover, Brn3c had functions in retinal ganglion cell differentiation separate from those of Brn3b. Ipsilateral and misrouted projections at the optic chiasm were overproduced in Brn3b(-/-) mice but missing were entirely in optic chiasms of Brn3b/Brn3c double knockout mice, suggesting that Brn3c controlled ipsilateral axon production. Forced expression of Brn3c in Brn3b(-/-) retinal explants restored neurite outgrowth, demonstrating that Brn3c could promote axon outgrowth in the absence of Brn3b. Our results reveal a complex genetic relationship between Brn3b and Brn3c in regulating the retinal ganglion cell axon outgrowth.

Animals↗