Requirement of the transcription factor GATA4 for heart tube formation and ventral morphogenesis

The zinc finger transcription factor GATA4 has been implicated in heart development based on its early expression in precardiogenic splanchnic mesoderm and its ability to activate the expression of a number of cardiac-specific genes. To determine the role of GATA4 in embryogenesis, we generated mice homozygous for a GATA4 null allele. Homozygous GATA4 null mice arrested in development between E7.0 and E9.5 because of severe developmental abnormalities. Mutant embryos most notably lacked a primitive heart tube and foregut and developed partially outside the yolk sac. In the mutants, the two bilaterally symmetric promyocardial primordia failed to migrate ventrally but instead remained lateral and generated two independent heart tubes that contained differentiated cardiomyocytes. We show that these deformities resulted from a general loss in lateral to ventral folding throughout the embryo. GATA4 is most highly expressed within the precardiogenic splanchnic mesoderm at the posterior lip of the anterior intestinal portal, corresponding to the region of the embryo that undergoes ventral fusion. We propose that GATA4 is required for the migration or folding morphogenesis of the precardiogenic splanchnic mesodermal cells at the level of the AIP.

Control of mouse cardiac morphogenesis and myogenesis by transcription factor MEF2C

Members of the myocyte enhancer factor-2 (MEF2) family of MADS (MCM1, agamous, deficiens, serum response factor)-box transcription factors bind an A-T-rich DNA sequence associated with muscle-specific genes. The murine MEF2C gene is expressed in heart precursor cells before formation of the linear heart tube. In mice homozygous for a null mutation of MEF2C, the heart tube did not undergo looping morphogenesis, the future right ventricle did not form, and a subset of cardiac muscle genes was not expressed. The absence of the right ventricular region of the mutant heart correlated with down-regulation of the dHAND gene, which encodes a basic helix-loop-helix transcription factor required for cardiac morphogenesis. Thus, MEF2C is an essential regulator of cardiac myogenesis and right ventricular development.

Regulation of cardiac mesodermal and neural crest development by the bHLH transcription factor, dHAND

dHAND and eHAND are related basic helix-loop-helix (bHLH) transcription factors that are expressed in mesodermal and neural crest-derived structures of the developing heart. In contrast to their homogeneous expression during avian cardiogenesis, during mouse heart development we show that dHAND and eHAND are expressed in a complementary fashion and are restricted to segments of the heart tube fated to form the right and left ventricles, respectively. dHAND and eHAND represent the earliest cardiac chamber-specific transcription factors yet identified. Targeted gene deletion of dHAND in mouse embryos resulted in embryonic lethality at embryonic day 10.5 from heart failure. Our description of the cardiac phenotype of dHAND mutant embryos is the first demonstration of a single gene controlling the formation of the mesodermally derived right ventricle and the neural crest-derived aortic arches and reveals a novel cardiogenic subprogramme for right ventricular development.

Dopaminergic neurons protected from degeneration by GDNF gene therapy

Glial cell line-derived neurotrophic factor (GDNF) supports growth and survival of dopaminergic (DA) neurons. A replication-defective adenoviral (Ad) vector encoding human GDNF injected near the rat substantia nigra was found to protect DA neurons from the progressive degeneration induced by the neurotoxin 6-hydroxydopamine (6-OHDA) injected into the striatum. Ad GDNF gene therapy reduced loss of DA neurons approximately threefold 6 weeks after 6-OHDA lesion, as compared with no treatment or injection of Ad lacZ or Ad mGDNF (encoding a biologically inactive deletion mutant GDNF). These results suggest that Ad vector-mediated GDNF gene therapy may slow the DA neuronal cell loss in humans with Parkinson's disease.

Conjugation of arginine oligomers to cyclosporin A facilitates topical delivery and inhibition of inflammation

Many systemically effective drugs such as cyclosporin A are ineffective topically because of their poor penetration into skin. To surmount this problem, we conjugated a heptamer of arginine to cyclosporin A through a pH-sensitive linker to produce R7-CsA. In contrast to unmodified cyclosporin A, which fails to penetrate skin, topically applied R7-CsA was efficiently transported into cells in mouse and human skin. R7-CsA reached dermal T lymphocytes and inhibited cutaneous inflammation. These data establish a general strategy for enhancing delivery of poorly absorbed drugs across tissue barriers and provide a new topical approach to the treatment of inflammatory skin disorders.

Alterations in NF-kappaB function in transgenic epithelial tissue demonstrate a growth inhibitory role for NF-kappaB

Stratified epithelium contains a mitotically active basal layer of cells that cease proliferating, then migrate outwards and undergo terminal differentiation. The control of this process, which is abnormal in cutaneous neoplasia and inflammation, is not well understood. In normal epidermis, NF-kappaB proteins were found to exist in the cytoplasm of basal cells and then to localize in the nuclei of suprabasal cells, suggesting a role for NF-kappaB in the switch from proliferation to growth arrest and differentiation. Functional blockade of NF-kappaB by expressing dominant-negative NF-kappaB inhibitory proteins in transgenic murine and human epidermis produced hyperplastic epithelium in vivo. Consistent with this, application of a pharmacologic inhibitor of NF-kappaB to intact skin induced epidermal hyperplasia. In contrast, overexpression of active p50 and p65 NF-kappaB subunits in transgenic epithelium produced hypoplasia and growth inhibition. These data suggest that spatially restricted NF-kappaB activation occurs in stratified epithelium and indicate that NF-kappaB activation in this tissue, in contrast to its role in other settings, is important for cellular growth inhibition.

Heart and extra-embryonic mesodermal defects in mouse embryos lacking the bHLH transcription factor Hand1

The basic helix-loop-helix (bHLH) transcription factors, Hand1 and Hand2 (refs 1,2), also called eHand/Hxt/Thing1 and dHand/Hed/Thing2 (refs 3,4), respectively, are expressed in the heart and certain neural-crest derivatives during embryogenesis. In addition, Hand1 is expressed in extraembryonic membranes, whereas Hand2 is expressed in the deciduum. Previous studies have demonstrated that Hand2 is required for formation of the right ventricle of the heart and the aortic arch arteries. We have generated a germline mutation in the mouse Hand1 gene by replacing the first coding exon with a beta-galactosidase reporter gene. Embryos homozygous for the Hand1 null allele died between embryonic days 8.5 and 9.5 and exhibited yolk sac abnormalities due to a deficiency in extraembryonic mesoderm. Heart development was also perturbed and did not progress beyond the cardiac-looping stage. Our results demonstrate important roles for Hand1 in extraembryonic mesodermal and heart development.

Ubiquitous expression of the 43- and 44-kDa forms of transcription factor USF in mammalian cells

USF is a helix-loop-helix transcription factor that, like Myc, recognizes the DNA binding motif CACGTG. Two different forms of USF, characterized by apparent molecular weights of 43,000 and 44,000, were originally identified in HeLa cells by biochemical analysis. Clones for the 43-kDa USF were first characterized, but only partial clones for the human 44-kDa USF (USF2, or FIP) have been reported. Here we describe a complete cDNA for the 44-kDa USF from murine cells. Analysis of this clone has revealed that the various USF family members are quite divergent in their N-terminal amino acid sequences, while a high degree of conservation characterizes their dimerization and DNA-binding domains. Interestingly, the 3' noncoding region of the 44-kDa USF cDNAs displayed an unusual degree of conservation between human and mouse. In vitro transcription/translation experiments indicated a possible role for this region in translation regulation. Alternative splicing forms of the 44-kDa USF messages exist in both mouse and human. Examination of the tissue and cell-type distribution of USF by Northern blot and gel retardation assays revealed that while expression of both the 43- and 44-kDa USF species is ubiquitous, different ratios of USF homo- and heterodimers are found in different cells.

Requirement of the MADS-box transcription factor MEF2C for vascular development

The embryonic vasculature develops from endothelial cells that form a primitive vascular plexus which recruits smooth muscle cells to form the arterial and venous systems. The MADS-box transcription factor MEF2C is expressed in developing endothelial cells and smooth muscle cells (SMCs), as well as in surrounding mesenchyme, during embryogenesis. Targeted deletion of the mouse MEF2C gene resulted in severe vascular abnormalities and lethality in homozygous mutants by embryonic day 9.5. Endothelial cells were present and were able to differentiate, but failed to organize normally into a vascular plexus, and smooth muscle cells did not differentiate in MEF2C mutant embryos. These vascular defects resemble those in mice lacking the vascular-specific endothelial cell growth factor VEGF or its receptor Flt-1, both of which are expressed in MEF2C mutant embryos. These results reveal multiple roles for MEF2C in vascular development and suggest that MEF2-dependent target genes mediate endothelial cell organization and SMC differentiation.

Nonlinear optical phenomena in silicon waveguides: modeling and applications

<p> <a href="http://oe.osa.org/virtual_issue.cfm?vid=36">Focus Serial: Frontiers of Nonlinear Optics</a> </p>Several kinds of nonlinear optical effects have been observed in recent years using silicon waveguides, and their device applications are attracting considerable attention. In this review, we provide a unified theoretical platform that not only can be used for understanding the underlying physics but should also provide guidance toward new and useful applications. We begin with a description of the third-order nonlinearity of silicon and consider the tensorial nature of both the electronic and Raman contributions. The generation of free carriers through two-photon absorption and their impact on various nonlinear phenomena is included fully within the theory presented here. We derive a general propagation equation in the frequency domain and show how it leads to a generalized nonlinear Schrodinger equation when it is converted to the time domain. We use this equation to study propagation of ultrashort optical pulses in the presence of self-phase modulation and show the possibility of soliton formation and supercontinuum generation. The nonlinear phenomena of cross-phase modulation and stimulated Raman scattering are discussed next with emphasis on the impact of free carriers on Raman amplification and lasing. We also consider the four-wave mixing process for both continuous-wave and pulsed pumping and discuss the conditions under which parametric amplification and wavelength conversion can be realized with net gain in the telecommunication band.

Ligand selectivity of the peroxisome proliferator-activated receptor alpha

Peroxisome proliferator-activated receptors (PPAR alpha, beta, and gamma) are nuclear hormone receptors that play critical roles in regulating lipid metabolism. It is well established that PPARs are the targets for the hypolipidemic synthetic compounds known as peroxisome proliferators, and it has been proposed that various long-chain fatty acids and metabolites of arachidonic acid serve as the physiological ligands that activate these receptors in vivo. However, a persistent problem is that reported values of the equilibrium dissociation constants (Kds) of complexes of PPARs with these ligands are in the micromolar range, at least an order of magnitude higher than the physiological concentrations of the ligands. Thus, the identity of the endogenous ligands for PPAR remains unclear. Here we report on a fluorescence-based method for investigating the interactions of PPAR with ligands. It is shown that the synthetic fluorescent long-chain fatty acid trans-parinaric acid binds to PPARalpha with high affinity and can be used as a probe to monitor protein-ligand interactions by the receptor. Measurements of Kds characterizing the interactions of PPARalpha with various ligands revealed that PPARalpha interacts with unsaturated C:18 fatty acids, with arachidonic acid, and with the leukotriene LTB4 with affinities in the nanomolar range. These data demonstrate the utility of the optical method in examining the ligand-selectivity of PPARs, and resolve a long-standing uncertainty in understanding how the activities of these receptors are regulated in vivo.

Dark Matter Search Results from a One Ton-Year Exposure of XENON1T

We report on a search for weakly interacting massive particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of (1.30±0.01)  ton, resulting in a 1.0 ton yr exposure. The energy region of interest, [1.4,10.6]  keV_{ee} ([4.9,40.9] keV_{nr}), exhibits an ultralow electron recoil background rate of [82_{-3}^{+5}(syst)±3(stat)]  events/(ton yr keV_{ee}). No significant excess over background is found, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6  GeV/c^{2}, with a minimum of 4.1×10^{-47}  cm^{2} at 30  GeV/c^{2} and a 90% confidence level.

Structure, function and evolution of antifreeze proteins

Antifreeze proteins bind to ice crystals and modify their growth. These proteins show great diversity in structure, and they have been found in a variety of organisms. The ice-binding mechanisms of antifreeze proteins are not completely understood. Recent findings on the evolution of antifreeze proteins and on their structures and mechanisms of action have provided new understanding of these proteins in different contexts. The purpose of this review is to present the developments in contrasting research areas and unite them in order to gain further insight into the structure and function of the antifreeze proteins.

Low-temperature increases the yield of biologically active herring antifreeze protein in Pichia pastoris

Antifreeze proteins and antifreeze glycoproteins are structurally diverse molecules that share a common property in binding to ice crystals and inhibiting ice crystal growth. Type II fish antifreeze protein of Atlantic herring (Clupea harengus harengus) is unique in its requirement of Ca(2+) for antifreeze activity. In this study, we utilized the secretion vector pGAPZalpha A to express recombinant herring antifreeze protein (WT) and a fusion protein with a C-terminal six-histidine tag (WT-6H) in yeast Pichia pastoris wild-type strain X-33 or protease-deficient strain SMD1168H. Both recombinant proteins were secreted into the culture medium and properly folded and functioned as the native herring antifreeze protein. Furthermore, our studies demonstrated that expression at a lower temperature increased the yield of the recombinant protein dramatically, which might be due to the enhanced protein folding pathway, as well as increased cell viability at lower temperature. These data suggested that P. pastoris is a useful system for the production of soluble and biologically active herring antifreeze protein required for structural and functional studies.

Umifenovir treatment is not associated with improved outcomes in patients with coronavirus disease 2019: a retrospective study

Objectives

Coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Umifenovir (Arbidol®) is an antiviral drug being used to treat influenza in Russia and China. This study aimed to investigate the effectiveness and safety of umifenovir for COVID-19.

Methods

A retrospective study was performed in a non-intensive care unit (ICU) ward in Jinyintan Hospital from 2 February 2020 to 20 March 2020. COVID-19 was confirmed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) assay of pharyngeal swab specimens. The confirmed patients were divided into the umifenovir group and the control group according to the use of umifenovir. The main outcomes were the rate of negative pharyngeal swab tests for SARS-CoV-2 within 1 week after admission and the time for the virus to turn negative. The negativity time of SARS-CoV-2 was defined as the first day of a negative test if the nucleic acid of SARS-CoV-2 was negative for two consecutive tests.

Results

A total of 81 COVID-19 patients were included, with 45 in the umifenovir group and 36 in the control group. Baseline clinical and laboratory characteristics were comparable between the two groups. Thirty-three out of 45 (73%) patients in the umifenovir group tested negative for SARS-CoV-2 within 7 days after admission, the number was 28/36 (78%) in the control group (p 0.19). The median time from onset of symptoms to SARS-CoV-2 turning negative was 18 days (interquartile range (IQR) 12–21) in the umifenovir group and 16 days (IQR 11–21) in the control group (p 0.42). Patients in the umifenovir group had a longer hospital stay than patients in the control group (13 days (IQR 9–17) vs 11 days (IQR 9–14), p 0.04). No deaths or severe adverse reactions were found in both groups.

Discussion

Umifenovir might not improve the prognosis or accelerate SARS-CoV-2 clearance in non-ICU patients. A randomized control clinical trial is needed to assess the efficacy of umifenovir.

Immunization via hair follicles by topical application of naked DNA to normal skin

In order to test the immune response generated to small amounts of foreign protein in skin, we applied naked DNA in aqueous solution to untreated normal skin. Topical application of plasmid expression vectors for lacZ and the hepatitis B surface antigen (HBsAg) to intact skin induced antigen-specific immune responses that displayed TH2 features. For HBsAg, specific antibody and cellular responses were induced to the same order of magnitude as those produced by intramuscular injection of the commercially available recombinant HBsAg polypeptide vaccine. Finally, topical gene transfer was dependent on the presence of normal hair follicles.

Specificity and determinants of Sam68 RNA binding. Implications for the biological function of K homology domains

Sam68, a specific target of the Src tyrosine kinase in mitosis, possesses features common to RNA-binding proteins, including a K homology (KH) domain. To elucidate its biological function, we first set out to identify RNA species that bound to Sam68 with high affinity using in vitro selection. From a degenerate 40-mer pool, 15 RNA sequences were selected that bound to Sam68 with Kd values of 12-140 nM. The highest affinity RNA sequences (Kd approximately 12-40 nM) contained a UAAA motif; mutation to UACA abolished binding to Sam68. Binding of the highest affinity ligand, G8-5, was assessed to explore the role of different regions of Sam68 in RNA binding. The KH domain alone did not bind G8-5, but a fragment containing the KH domain and a region of homology within the Sam68 subgroup of KH-containing proteins was sufficient for G8-5 binding. Deletion of the KH domain or mutation of KH domain residues analogous to loss-of-function mutations in the human Fragile X syndrome gene product and the Caenorhabditis elegans tumor suppressor protein Gld-1 abolished G8-5 binding. Our results establish that a KH domain-containing protein can bind RNA with specificity and high affinity and suggest that specific RNA binding is integral to the functions of some regulatory proteins in growth and development.

Impairment of T and B cell development by treatment with a type I interferon

Type I interferons alpha and beta, naturally produced regulators of cell growth and differentiation, have been shown to inhibit IL-7-induced growth and survival of B cell precursors in vitro. After confirming an inhibitory effect on B lymphopoiesis in an ex vivo assay, we treated newborn mice with an active IFN-alpha2/alpha1 hybrid molecule to assess its potential for regulating B and T cell development in vivo. Bone marrow and splenic cellularity was greatly reduced in the IFN-alpha2/alpha1-treated mice, and B lineage cells were reduced by >80%. The bone marrow progenitor population of CD43+B220+HSA- cells was unaffected, but development of the CD19+ pro-B cells and their B lineage progeny was severely impaired. Correspondingly, IL-7-responsive cells in the bone marrow were virtually eliminated by the interferon treatment. Thymus cellularity was also reduced by >80% in the treated mice. Phenotypic analysis of the residual thymocytes indicated that the inhibitory effect was exerted during the pro-T cell stage in differentiation. In IFN-alpha/beta receptor-/- mice, T and B cell development were unaffected by the IFN-alpha2/alpha1 treatment. The data suggest that type I interferons can reversibly inhibit early T and B cell development by opposing the essential IL-7 response.

Behavioral and cellular protection of rat dopaminergic neurons by an adenoviral vector encoding glial cell line-derived neurotrophic factor

Previously, we observed that an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF), injected near the rat substantia nigra (SN), protects SN dopaminergic (DA) neuronal soma from 6-hydroxydopamine (6-OHDA)-induced degeneration. In the present study, the effects of Ad GDNF injected into the striatum, the site of DA nerve terminals, were assessed in the same lesion model. So that effects on cell survival could be assessed without relying on DA phenotypic markers, fluorogold (FG) was infused bilaterally into striatae to retrogradely label DA neurons. Ad GDNF or control treatment (Ad mGDNF, encoding a deletion mutant GDNF, Ad lacZ, vehicle, or no injection) was injected unilaterally into the striatum near one FG site. Progressive degeneration of DA neurons was initiated 7 days later by unilateral injection of 6-OHDA at this FG site. At 42 days after 6-OHDA, Ad GDNF prevented the death of 40% of susceptible DA neurons that projected to the lesion site. Ad GDNF prevented the development of behavioral asymmetries which depend on striatal dopamine, including limb use asymmetries during spontaneous movements along vertical surfaces and amphetamine-induced rotation. Both behavioral asymmetries were exhibited by control-treated, lesioned rats. Interestingly, these behavioral protections occurred in the absence of an increase in the density of DA nerve fibers in the striatum of Ad GDNF-treated rats. ELISA measurements of transgene proteins showed that nanogram quantities of GDNF and lacZ transgene were present in the striatum for 7 weeks, and picogram quantities of GDNF in the SN due to retrograde transport of vector and/or transgene protein. These studies demonstrate that Ad GDNF can sustain increased levels of biosynthesized GDNF in the terminal region of DA neurons for at least 7 weeks and that this GDNF slows the degeneration of DA neurons and prevents the appearance of dopamine dependent motor asymmetries in a rat model of Parkinson's disease (PD). GDNF gene therapy targeted to the striatum, a more surgically accessible site than the SN, may be clinically applicable to humans with PD.

Dorsal root reflexes and cutaneous neurogenic inflammation after intradermal injection of capsaicin in rats

The role of dorsal root reflexes (DRRs) in acute cutaneous neurogenic inflammation induced by intradermal injection of capsaicin (CAP) was examined in anesthetized rats. Changes in cutaneous blood flow (flare) on the plantar surface of the foot were measured using a laser Doppler flowmeter, and neurogenic edema was examined by measurements of paw thickness. To implicate DRRs in neurogenic inflammation after CAP injection, the ipsilateral sciatic and femoral nerves were sectioned, dorsal rhizotomies were performed at L(3-)-S(1), and antagonists of GABA or excitatory amino acid receptors were administered intrathecally. Intradermal injection of CAP evoked a flare response that was largest at 15-20 mm from the injection site and that spread >30 mm. Acute transection of the sciatic and femoral nerves or dorsal rhizotomies nearly completely abolished the blood flow changes 15-20 mm from the CAP injection site, although there was only a minimal effect on blood flow near the injection site. These procedures also significantly reduced neurogenic edema. Intrathecal bicuculline, 6-cyano-7-nitroquinoxaline-2,3-dione, (CNQX) or D(-)-2-amino-7-phosphonoheptanoic acid (AP7), but not phaclofen, also reduced dramatically the increases in blood flow 15-20 mm from the CAP injection site, but had only a minimal effect on blood flow near the injection site. Neurogenic edema was reduced by the same agents that reduced blood flow. Multiunit DRRs recorded from the central stumps of cut dorsal rootlets in the lumbar spinal cord were enhanced after CAP injection. This enhanced DRR activity could be reduced significantly by posttreatment of the spinal cord with bicuculline, CNQX or AP7, but not phaclofen. It is concluded that peripheral cutaneous inflammation induced by intradermal injection of CAP involves central nervous mechanisms. DRRs play a major role in the development of neurogenic cutaneous inflammation, although a direct action of CAP on peripheral nerve terminals or the generation of axon reflexes also may contribute to changes in the skin near the injection site.

Overlapping roles and asymmetrical cross-regulation of the USF proteins in mice

USF1 and USF2 are ubiquitously expressed transcription factors implicated as antagonists of the c-Myc protooncoprotein in the control of cellular proliferation. To determine the biological role of the USF proteins, mutant mice were generated by homologous recombination in embryonic stem cells. USF1-null mice were viable and fertile, with only slight behavioral abnormalities. However, these mice contained elevated levels of USF2, which may compensate for the absence of USF1. In contrast, USF2-null mice contained reduced levels of USF1 and displayed an obvious growth defect: they were 20-40% smaller at birth than their wild-type or heterozygous littermates and maintained a smaller size with proportionate features throughout postnatal development. Some of the USF-deficient mice, especially among the females, were prone to spontaneous epileptic seizures, suggesting that USF is important in normal brain function. Among the double mutants, an embryonic lethal phenotype was observed for mice that were homozygous for the Usf2 mutation and either heterozygous or homozygous for the Usf1 mutation, demonstrating that the USF proteins are essential in embryonic development.

Design of GFB-111, a platelet-derived growth factor binding molecule with antiangiogenic and anticancer activity against human tumors in mice

We have designed a molecule, GFB-111, that binds to platelet-derived growth factor (PDGF), prevents it from binding to its receptor tyrosine kinase, and blocks PDGF-induced receptor autophosphorylation, activation of Erk1 and Erk2 kinases, and DNA synthesis. GFB-111 is highly potent (IC50 = 250 nM) and selective for PDGF over EGF, IGF-1, aFGF, bFGF, and HRGbeta (IC50 values > 100 microM), but inhibits VEGF-induced Flk-1 tyrosine phosphorylation and Erk1/Erk2 activation with an IC50 of 10 microM. GFB-111 treatment of nude mice bearing human tumors resulted in significant inhibition of tumor growth and angiogenesis. The results demonstrate the feasibility of designing novel growth factor-binding molecules with potent anticancer and antiangiogenic activity.

Normal spermatogenesis in mice lacking the testis-specific linker histone H1t

H1 histones bind to linker DNA and nucleosome core particles and facilitate the folding of chromatin into a more compact structure. Mammals contain seven nonallelic subtypes of H1, including testis-specific subtype H1t, which varies considerably in primary sequence from the other H1 subtypes. H1t is found only in pachytene spermatocytes and early, haploid spermatids, constituting as much as 55% of the linker histone associated with chromatin in these cell types. To investigate the role of H1t in spermatogenesis, we disrupted the H1t gene by homologous recombination in mouse embryonic stem cells. Mice homozygous for the mutation and completely lacking H1t protein in their germ cells were fertile and showed no detectable defect in spermatogenesis. Chromatin from H1t-deficient germ cells had a normal ratio of H1 to nucleosomes, indicating that other H1 subtypes are deposited in chromatin in place of H1t and presumably compensate for most or all H1t functions. The results indicate that despite the unique primary structure and regulated synthesis of H1t, it is not essential for proper development of mature, functional sperm.

Astrocytes retrovirally transduced with BDNF elicit behavioral improvement in a rat model of Parkinson's disease

Neurotrophic factors that improve the survival of specific neuronal types during development and after exposure to various neuronal insults hold potential for treatment of neurodegenerative diseases. In particular, brain-derived neurotrophic factor (BDNF) has been shown to exert trophic and protective effects on dopaminergic neurons, the cell type known to degenerate in Parkinson's disease. To determine whether increased levels of biologically produced BDNF affect the function or regeneration of damaged dopaminergic neurons, the effects of grafting astrocytes transduced with the human BDNF gene into the striatum of the partially lesioned hemiparkinsonian rat were examined. Replication deficient retroviruses carrying either human prepro-BDNF or human alkaline phosphatase (AP) cDNA were used to transduce primary type 1 astrocytes purified from neonatal rat cortex. In vitro, BDNF mRNA was expressed by BDNF transduced astrocytes (BDNF astrocytes), but not control AP transduced astrocytes (AP astrocytes), as determined by reverse transcription polymerase chain reaction (RT-PCR). The modified astrocytes were injected into the right striatum 15 days after partial lesioning of the right substantia nigra with 6-hydroxydopamine. Transplantation of BDNF astrocytes, but not AP astrocytes, significantly attenuated amphetamine-induced rotation by 45% 32 days after grafting. Apomorphine-induced rotation increased over time in both groups, but was not significantly different in the BDNF-treated group. The modified BDNF astrocytes survived well with non-invasive growth in the brain for up to 42 days. Although BDNF mRNA positive cells were not detected within the graft site using in situ hybridization, alkaline phosphatase immunoreactive (IR) cells were present in control graft sites suggesting that the retroviral construct continued to be expressed at 42 days. Analysis of the density of tyrosine hydroxylase (TH)-IR fibers showed no effect of BDNF on TH-IR fiber density in the striatum on the lesioned side. These findings suggest that ex vivo gene therapy with BDNF ameliorates parkinsonian symptoms through a mechanism(s) other than one involving an effect of BDNF on regeneration or sprouting from dopaminergic neurons.