Production of recombinant human protein C in vitro and in vivo by muscle cells

Protein C plays a key role in a natural anticoagulation mechanism, and is also implicated in fibrinolytic and anti-inflammatory functions. Here we describe the production of biologically active human protein C by muscle-targeted gene transfer. Human protein C expression vectors were designed and constructed to produce human protein C in skeletal muscle cells. These vectors were tested in transient and stable transfections of SCID mice myoblasts. Stably transfected cells produced as high as 2.27 microg/10(6) cells/day. Human protein C produced had a relative activity of 92+/-8% compared to the plasma derived human protein C, and was composed of alpha and beta forms, 69% and 31%, respectively. After implantation of stably transfected myoblasts into the hind limb muscles of SCID mice, systemic stable production of human protein C in a range of 31-116 ng/ml serum was obtained up to at least 2.5 months.

Long-term administration of cyclosporin A to HCV-antibody-positive patients with dermatologic diseases

BACKGROUND

Cyclosporine A (CYA) is an immunosuppressive agent which is being used in the treatment of an increasingly wide range of dermatologic diseases, but its use has been avoided in carriers of hepatitis C virus (HCV).

METHODS

We administered small doses of CYA (maximum, 3 mg/kg/day) for a long time to treat dermatologic diseases in one HCV-antibody-positive patient with no HCV-RNA in the blood, one patient with a small amount of HCV-RNA in the blood, and two patients with large amounts of HCV-RNA in the blood.

RESULTS

Skin lesions improved in all patients, but recurred upon complete or partial withdrawal of CYA. In the absence of HCV-RNA in the blood, or when only a small quantity of HCV-RNA was present in the blood, HCV-RNA load showed no apparent change. In one patient with a large blood HCV-RNA load, CYA dosage reduction was followed by increases in alanine aminotransferase (ALT) levels and decreases in blood HCV-RNA. Aggravation of hepatitis due to immunologic reactivation was suspected in this patient.

CONCLUSIONS

The reduction of CYA dosage is a key element in the use of this agent for cutaneous diseases.

Advanced endocrine cell carcinoma of the gallbladder: a patient with 12-year survival

Gallbladder carcinoid is a rare disease. In previous reports, classical carcinoid, an entity with a good prognosis, has not been distinguished from endocrine cell carcinoma, a tumor associated with marked cell atypia and mitosis, and a poor prognosis. The patient was a 66 year old woman who presented to our hospital with a chief complaint of jaundice. Pre-operatively, she was diagnosed as having advanced gallbladder carcinoma invading the liver and the hepatic hilus. The patient underwent right hepatic trisegmentectomy with en bloc resection of the caudate lobe and extrahepatic bile ducts, extended lymph node clearance and left hepaticojejunostomy. Histopathological examination showed positive Grimelius staining, marked mitosis, and intense atypism, hence, the tumor was diagnosed as an endocrine cell carcinoma. Twelve years after surgery, the patient is healthy, without any sign of recurrence. We present this novel case of long-term survival and review the literature.

Targeted inactivation of the coagulation factor IX gene causes hemophilia B in mice

Hemophilia B is a leading target for gene therapy because current therapy is not optimal. Hence, a murine model of factor IX (F. IX) deficiency was generated to develop gene therapy strategies for hemophilia B. A targeting vector was created by replacing a 3.2-kb segment of the gene encompassing the catalytic domain with a phosphoglycerokinase promoter-driven neomycin resistant (neor) gene cassette. The transfected embryonic stem cell clones generated chimeric male mice, and germ line transmission of the inactivated F. IX gene was observed in their offsprings. Southern analysis confirmed the mutant genotype in hemizygous male and carrier female mice. F. IX transcripts were not detected in liver RNA isolated from hemizygous mice, and lower levels of F. IX mRNA were noted in carrier female mice when compared with those of normal litter mates. As expected, the mean F. IX coagulant titer of affected male mice was 2.8 U/dL (n = 10), while the mean F. IX titer of carrier female mice was 35 U/dL (n = 14), compared with 69 U/dL (n = 9) for the normal female mice and 92 U/dL (n = 22) for normal male and female litter mates. Further, the tail bleeding time of hemizygous mice was markedly prolonged (>3 hours) compared with those of normal and carrier female litter mates (15 to 20 minutes). Seven of 19 affected male mice died of exsanguination after tail snipping, and two affected mice died of umbilical cord bleeding. Currently, there are 10 affected mice surviving at 4 months of age. Aside from the factor IX defect, the carrier female and hemizygous male mice had no liver pathology by histologic examination, were fertile, and transmitted the F. IX gene mutation in the expected Mendelian frequency. Taken together, we have generated a F. IX knockout mouse for evaluation of novel gene therapy strategies for hemophilia B.

Sialic-acid-binding lectin from the slug Limax flavus--cloning, expression of the polypeptide, and tissue localization

A cDNA library of Limax flavus was constructed and screened for sialic-acid-specific lectins. Complementary DNA clones were categorized into seven groups corresponding to closely related but different sequences. Group 1 clones contained an ORF encoding 199 amino acids including a sequence identical to the partial amino acid sequence obtained from the lectin protein. Within its 1074-bp 3' untranslated region, ten closely related 60-bp sequence repeats were found. Group 2 clones contained an ORF encoding a polypeptide chain of the same number of amino acid residues, with 89.1% overall identity to that of the group 1 and eight 60-bp repeat sequences in the 3' untranslated region. The remaining groups of clones contained ORF with highly similar full or partial sequences, with or without 60 bp repeats in the 3' untranslated region. The large number of closely related but different cDNA clones obtained indicated that the slug sialic-acid-specific lectin gene is a member of a multigene family. The lectin amino acid sequence showed significant similarity with the fibrinogen domain of human tenascin-C, with a human C-type serum lectin, and with pig ficolin. Immunostaining analysis of slug tissue for the lectin indicated that it is present primarily on the epidermal surface and in mucous glands. Recombinant slug lectin protein lacking the 20-amino-acid N-terminal signal sequence produced in a bacterial expression system from a group-1 clone accumulated as aggregates in inclusion bodies, suggesting that large-scale production of the active agglutinin may be possible.

Persistent systemic production of human factor IX in mice by skeletal myoblast-mediated gene transfer: feasibility of repeat application to obtain therapeutic levels

Myoblast-mediated gene transfer and its repeated applications were tested for achieving a long-term stable systemic production of human factor IX (hFIX) at a therapeutic level in SCID mice. Primary skeletal myoblasts were stably transfected with a hFIX expression plasmid vector, pdLMe4 betaA-hIXm1, which contains a hFIX minigene under the control of a beta-actin promoter with muscle creatine kinase enhancers. Myotubes derived from the myoblasts produced 1,750 ng hFIX/10(6) cells/24 hours in culture. hFIX secretion by the myoblasts and thereof derived myotubes were equally efficient, and myotubes were shown to have a sufficient secretory capacity to handle a substantially elevated production of hFIX. After intramuscular injection of 5, 10, and 20 x 10(6) myoblasts, SCID mice stably produced hFIX into the systemic circulation proportional to the number of implanted cells, and the expression levels were maintained for at least up to 10 months (end of the experiment). Additional cell injections administered to animals that originally received 10 x 10(6) cells approximately 2 months later elevated the systemic hFIX levels to an average of 182 +/- 21 ng/mL, a therapeutic level, which persisted for at least 8 months (end of the experiment). These results indicate that long-term, stable systemic production of hFIX at therapeutic levels can be achieved by repeated application of myoblast-mediated gene transfer.

The carboxyl-terminal region of factor IX is essential for its secretion

The carboxyl-terminal region of factor IX (residues 403-415) contains several natural mutations which result in mild to severe forms of hemophilia B. A battery of factor IX minigene expression vectors carrying various mutations in the C-terminal region were constructed and studied by transient expression assay using HepG2 cells. Mutations included in this study are Y404P, I408N, T412N, T412S, T415G, T415S, T415L, and T415R as well as five selected naturally occurring mutations in the region, R403Q, R403W, Y404H, W407R, and T412K. In comparison to the normal factor IX, these mutations neither significantly affected the factor IX mRNA level nor affected the stability of the secreted factor IX in the culture medium but did decrease to various extents the intracellular and secreted factor IX protein levels as quantified by enzyme-linked immunosorbent assay. T415L, T415S, and T415R showed only minor reductions in the intracellular and minor to moderate reductions in the secreted factor IX levels. T415G showed only minor reduction in the intracellular factor IX level but substantial reduction in the secreted levels. R403Q, R403W, and T412S showed moderate reductions in both intracellular and secreted factor IX levels. Y404H, Y404P, W407R, I408N, T412K, and T412N also showed minor to moderate reductions in the intracellular factor IX levels but very severe reductions in the secreted factor IX level. In one stage clotting assays, secreted factor IX mutants showed specific activities very similar to that of the normal factor IX, suggesting that the carboxyl-terminal region is neither directly involved in the tenase complex formation required for factor X activation nor involved in the activation of factor IX itself. In comparison to the normal factor IX, secreted levels of factor IX mutants with mutations R403Q, Y404H, W407R, and T412K were also very similar to the plasma levels reported for the hemophilia B patients carrying the same mutations. Treatment of cells with proteasome inhibitors (ALLM and ALLN) added to the culture medium at 50 microM resulted in drastic increases of the intracellular mutant factor IX to the levels equivalent to that of the normal factor IX, while the secreted factor IX levels were little or only marginally affected. With a higher concentration of the inhibitors (100 microM), however, both the intracellular and secreted mutant factor IX were fully elevated to the normal factor IX levels. Intracellular and secreted levels of the normal factor IX were little affected by the low inhibitor concentration and only marginally, if at all, at the higher concentration (< or = 10%). Serine protease inhibitors did not significantly affect intracellular and secreted factor IX levels. These results indicate that the carboxyl-terminal region plays a critical role in the cellular secretion of factor IX and that the mutant factor IX proteins carrying specific mutations in this region are subjected to efficient elimination by the proteasome protein degradation mechanism. Furthermore, these results strongly support that HepG2 cells can be utilized as a robust in vitro assay system for studying factor IX biosynthesis, well mimicking the in vivo phenomenon.

Age and sex dependent regulation of the factor IX gene in mice

Plasma factor IX and liver factor IX mRNA levels in two normal mouse strains (B6D2F1 and BALB/CJNIA) were determined in relation to aging and sex of the animals. With male B6D2F1 mice, mean plasma factor IX activity levels for the 14 and 21 approximately 22 month-old animals were found to be 124% and 226%, respectively, of the 5 month-old group. Similarly, liver factor IX mRNA levels for the same age animal groups were 145% and 227%, respectively, of the reference group. Mean plasma factor IX levels for the same age female animals were 132% and 175%, respectively, and were accompanied by similarly elevated liver factor IX mRNA levels, 119 and 175%, respectively, of the 5 month-old female group. Factor IX activity and mRNA levels for the 5, 14 and 21 approximately 22 month-old female animal groups were lower than those of the corresponding male age groups by 25, 20 and 37%, and 20, 36 and 38%, respectively. With BALB/CJNIA mice, similar correlation was observed between the advancing age and substantial elevations in the factor IX mRNA level as well as on the unequal factor IX mRNA levels in females and males. These results indicate that the plasma factor IX level in both male and female mice is greatly elevated with aging, in general agreement with a similar phenomenon observed for human populations, and that this increase is due to a similar elevation in the factor IX mRNA level in the liver. In mice, both factor IX activity and mRNA levels are significantly higher in males than in females, which has not been described for humans.

Construction of human factor IX expression vectors in retroviral vector frames optimized for muscle cells

Development of a highly refined human factor IX (hFIX) expression vector system is critical for establishing a durable hemophilia B gene therapy. Here we report construction of a series of retroviral vectors and identification of an optimal basic structure and components for expressing hFIX in skeletal muscle cells. These vectors, which are derived from Moloney murine leukemia virus (MoMLV) with its enhancer sequence in the 3' long terminal repeat (LTR) deleted, contained internal hFIX expression units inserted in forward configuration without or with a viral vector intron sequence (pdL or pdLIn vector frame, respectively) or in inverted configuration without a viral vector intron sequence (pdLi frame). Internal expression units contained a hFIX cDNA or hFIX minigene (hIXm1 or hIXm2) derived from the hFIX cDNA by insertion of a shortened first intron sequence of the hFIX gene. Regardless of the promoter and vector frame used, both hIXm1 and hIXm2 gave 10- to 14-fold higher hFIX expression compared to those with hFIX cDNA. Internal hFIX transcriptional control units of these vectors were composed of various promoters linked with or without the muscle creatine kinase enhancer (Me) sequence. Promoters tested included those of alpha-actin (alpha A775), beta-actin (beta A280), cytochrome oxidase (CO1250 and CO650), myogenin (Mg1031 and Mg353), and Rous sarcoma virus (RSV). beta A200, which was derived from beta A280 by eliminating potential polyadenylation sites, was also tested. As extensively examined with the myogenin promoter, presence of one or multiple copies of Me in the vectors elevated the expression activity in myotubes by 4.5- to 19-fold over those without Me, but not significantly in myoblasts. Similar enhancements in expression activity with Me were also observed with other promoters, except those of RSV and CO. The latter two showed only modest enhancements in the presence of Me. As assayed with myotubes in culture, the general order of hFIX expression activity of various promoters with four copies of Me in the three different vector frames was beta A280 approximately beta A200 > Mg353 > Mg1031 approximately RSV approximately CO650 approximately alpha A775 > CO1250. One exception was that CO650 showed significantly less activity in pdLi-type vectors than in the pdLIn vectors. Based on the systematic analyses of various structural components, a group of pdLi vectors consisting of beta A200, two to four copies of Me, and hIXm2 was identified to have the optimal basic vector structure to be used in retrovirus for hFIX expression in differentiated skeletal muscle cells. The present studies provide the critical first step for establishing a highly refined hemophilia B gene therapy based on skeletal muscle-targeted hFIX gene transfer.

Loss of expression of a retrovirus-transduced gene in human keratinocytes

Retroviral-mediated transfer of new genetic information into keratinocytes is a key step in epidermal gene therapy. An obstacle to the use of retroviruses for gene therapy is that although high levels of expression of the transduced gene can be maintained in tissue culture, expression is often lost when the cells are transplanted to an animal host. To examine some of the factors involved in this instability of expression, we transduced keratinocytes with a retrovirus encoding the gene for human factor IX and monitored secretion of the transduced gene. We observed continued secretion of factor IX through five passages in culture. When, however, sheets of these cells were grafted to athymic mice, factor IX expression was reduced or lost within 6 wk. We show that the reduction of factor IX expression in grafted keratinocytes did not result from a loss of grafted cells, nor was there a block to systemic delivery of a secreted endogenous product.

Isolation and characterization of canine factor IX

Canine plasma factor IX was purified to homogeneity by a combination of barium citrate precipitation and three-step column chromatographies of DEAE sepharose, heparin agarose and a monoclonal antifactor IX antibody-linked agarose. Canine factor IX has an apparent molecular size of 61 kDa, which is slightly smaller than that of human factor IX, as determined by denatured polyacrylamide gel electrophoresis. Its amino acid composition, amino-terminal and carboxyterminal amino acid sequences agreed well with those predicted from the reported cDNA. Unlike purified human factor IX, canine factor IX preparation often showed a discrete smaller molecular species (approximately 50 kDa) which was generated by a specific proteolytic cleavage between Arg310 and Val311. When purified canine factor IX was utilized as a standard for enzyme linked immunosorbent assay, the concentration of canine factor IX in the pooled normal dog plasma was determined to be 5.3 micrograms/ml with 11.2% carbohydrate content (or 4.7 micrograms/ml for its polypeptide chain moiety). Concentration of plasma factor IX antigen was measured in six severely affected, unrelated hemophilia B dogs. Four had factor IX antigen of less than 1% of the normal, and two had undetectable levels. The latter two had gross molecular abnormalities in their factor IX genes. Three obligate carrier females had variable but proportionately reduced factor IX antigen and factor IX coagulant activity levels. These results provide a quantitative method for measuring canine factor IX antigen which is a prerequisite for studying hemostasis and development of gene transfer approaches in the canine model of hemophilia B.

Adenovirus-mediated transfer of human factor IX gene in immunodeficient and normal mice: evidence for prolonged stability and activity of the transgene in liver

Recombinant adenovirus has recently become a promising gene delivery vehicle that may be used therapeutically for various medical disorders. However, in vivo expression of transgenes delivered by E1 region-deleted adenoviral vectors is transient in immunocompetent animals. It has been proposed that destruction of adenovirally transduced cells by the host immune mechanisms, particularly cytotoxic T-lymphocytes, may play a major role in limiting the duration of transgene expression in vivo. In the present study, Southern blot analysis of genomic DNA prepared from transduced liver tissues showed the persistent presence of the viral genome in both immunocompetent and immunodeficient animals, indicating the survival of the adenovirally transduced liver cells. Furthermore, active expression of the surviving factor IX transgenes was shown by the presence of recombinant human factor IX as well as specific human factor IX mRNA and protein in the transduced liver tissues. The transient appearance of human factor IX in the circulation of normal as well as partially immunodeficient mice is primarily due to the generation of mouse antihuman factor IX antibodies in these mice rather than host immune destruction of transduced cells. These results suggest that liver cells transduced with recombinant adenoviral vectors can escape from being destroyed by the host immune mechanism in normal animals. The present study thus provides a new rationale for further engineering of adenoviral vectors into a durable expression system for gene therapy of various diseases including congenital disorders such as hemophilia B.

Resistance of highly branched (1-->3)-beta-D-glucans to formolysis

Small molecular weight (MW) glucan derivatives could be a useful tool for studying the mechanisms of beta-glucan mediated biological activity, especially as antagonists for a beta-glucan receptor. This paper described the stability of various (1-->6) branched (1-->3)-beta-D-glucans to formolysis in the preparation of small MW derivatives. The glucans used were curdlan (linear), pachyman (few branches), GRN (one branch in every third main chain unit; 2/6), SPG (2/6), SSG (3/6), and OL-2 (4/6). Curdlan and pachyman were easily degraded to oligosaccharides by degradation for 20 min at 100 degrees C by 90% formic acid. However, branched glucans, especially the highly branched glucans, SSG and OL-2, were significantly resistant to degradation, and the majority remained high MW. SSG required a longer period and/or a higher temperature (121 degrees C treatment) to produce small MW derivatives. Branched glucans were also resistant to zymolyase (an endo-(1-->3)-beta-D-glucan hydrolase) digestion. These facts suggest that the (1-->6)-beta-D-branched residues contribute to the glucans' resistance to formic acid degradation and zymolyase digestion.

Role of intron I in expression of the human factor IX gene

The first intron (intron I) of the human factor IX gene, which has been previously suggested of having an expression-augmenting activity, was systematically studied for its potential enhancer activity. When tested with the chloramphenicol acetyltransferase expression vector with a minimal factor IX promoter, subregions of intron I showed only marginal enhancing activities (1.7-1.9-fold enhancement at the highest). Smaller subregions encompassing nucleotides 5660-6350 of the intron sequence even showed some weak negative regulatory activities (approximately 50% suppression at the highest), while a cytomegalovirus enhancer sequence, which was used as the positive control, had a 7-fold enhancement. A set of three factor IX minigene expression vectors with the same factor IX promoter were then constructed: p-416FIXc which contained the factor IX cDNA, p-416FIXm1 which contained the factor IX cDNA with a largely truncated intron I, and p-416FIXm2 which contained the factor IX cDNA with the intron I sequence further truncated. The p-416FIXm1 and p-416FIXm2 constructs showed 7-9-fold higher expression activities than p-416FIXc. The elevated factor IX antigen levels agreed well with the grossly elevated factor IX clotting activity and mRNA levels. These results indicate that the expression enhancing activity of intron I is not due to specific enhancer elements present in the intron subsequences, but is due to functional splicing sequences present in the precursor mRNAs produced from the minigene constructs containing intron I. By being efficiently assembled into spliceosome complexes, transcripts with splicing sequences may be better protected in the nucleus from random degradations than those without such sequences.

Primary myoblast-mediated gene transfer: persistent expression of human factor IX in mice

Primary myoblast-mediated gene transfer was tested for its ability to mediate a persistent expression of recombinant human factor IX in SCID mice. Mouse primary myoblasts were transduced with factor IX retroviral vectors, LIXSN, which uses the retroviral long-terminal repeats as the promoter, or dLMMBAIX, which uses muscle creatine kinase enhancer and beta-actin promoter to drive factor IX transcription. In vitro, myoblasts transduced with either LIXSN or dLMMBAIX expressed recombinant human factor IX with full biological activity. Upon implantation of transduced myoblasts into skeletal muscles of SCID mice, a sustained systemic expression of factor IX at a level of 10-30 ng/ml plasma was achieved. This was further supported by the presence of recombinant factor IX protein and mRNA in muscle tissues after 5 months of myoblast implantation. Intramuscular implantation of the transduced myoblasts resulted in a gene transfer which was confined locally to the region of injection, with no dissemination to other organs and tissues including testis. Additionally, basic fibroblast growth factor co-injected with primary myoblasts significantly improved the expression level of recombinant factor IX in vivo. These results demonstrate that primary myoblast-mediated gene therapy for hemophilia B is feasible and safe, and can be optimized by using cytokines or other conditions which augment myoblast survival and fusion with myofibers.

Regulatory mechanism of human factor IX gene: protein binding at the Leyden-specific region

Hemophilia B-Leyden is characterized by the gradual amelioration of bleeding after the onset of puberty. All Leyden phenotype mutations found to date lie within the Leyden-specific region, which spans roughly nt-40 to +20 in the 5' end of the human factor IX gene. With HepG2 cell nuclear extracts, the Leyden-specific region and its immediate neighboring region of the normal factor IX gene showed five DNase I footprints: FP-I (nt +4 to +19), FP-II (nt -16 to -3), FP-III (nt -27 to -19), FP-IV (nt -67 to -49), and FP-V (nt -99 to -77). Protein binding affinities of short oligonucleotides containing sequences of FP-I, FP-II, or FP-III were substantially reduced in the presence of Leyden phenotype mutations in these areas, correlating well with the negative effects of these mutations on factor IX gene expression. A Leyden phenotype mutation at nt -20 (T to A) caused a loss of both footprints FP-III and FP-II but generated a new footprint, FP-III' (nt -34 to -23), partially overlapping with FP-III, indicating mutation-dependent competitive protein binding at these sites. Although the FP-III' area contains an androgen responsive element-like sequence, the nuclear protein that binds at FP-III' is not androgen receptor. The protein was not recognized by anti-androgen receptor antibody and, furthermore, was present not only in liver but also in both androgen receptor-positive and androgen receptor-negative cells in electrophoretic mobility shift assays. The nuclear concentration of this protein increased significantly upon treatment of the HepG2 cells with testosterone. Its binding affinity to an oligonucleotide (-32sub) containing the FP-III' sequence was greatly reduced in the presence of exogenous androgen receptor, suggesting a possible interaction of this protein with androgen receptor. The affinities of both this protein and a protein which binds to FP-III (presumably HNF-4) to -32sub with a mutation at nt -26 were grossly lowered. These findings suggest that the amelioration of hemophilia B-Leyden with a mutation at nt -20 after puberty involves binding of a specific non-androgen receptor nuclear protein at FP-III' and it is able to substitute for the function of a protein bound at FP-III in the normal gene optimally through its elevated interaction with androgen receptor upon a surge of testosterone.(ABSTRACT TRUNCATED AT 400 WORDS)

Biology of factor IX

Within the past 20 years or so, factor IX has been at the centre of particularly intensive studies of its physiology, pathology and biochemistry as well as its molecular genetics and biology. With the complete nucleotide sequence of its human gene determined in 1985 and the molecular defects of over 600 abnormal human factor IX genes analysed to date, factor IX is among the few mammalian proteins which have been exhaustively studied in almost every aspect. The enormous amount of information we now have on this medium-sized plasma protein sheds light on how a gene and its protein evolve, how the protein carries out a highly regulated, specific and pivotal role in the delicately balanced blood coagulation reaction, and the correlation between clinical presentations and its highly diverse molecular mechanism of defects. This wealth of knowledge makes factor IX an excellent model for deeper study, such as truly quantitative analysis of its structure-function relationship and in vivo function and regulation. It will also provide a sound foundation which may lead to improved treatment of haemophilia B and perhaps to its cure. This paper attempts to review the recent progress in research on factor IX.

Hepsin, a putative cell-surface serine protease, is required for mammalian cell growth

Hepsin was previously identified as a putative cell-surface serine protease. When hepatoma cells were treated with anti-hepsin antibodies, their growth was substantially arrested, suggesting the requirement of hepsin molecules present at the cell surface for normal cell growth. This was further supported by a gross inhibition of cell growth with hepsin-specific antisense oligonucleotides. Upon treatment of cells with antisense oligonucleotides, rapid reduction in cellular hepsin was observed. This reduction in cellular hepsin levels was accompanied by drastic morphological changes. Various tissues in the developing mouse embryo showed greatly elevated hepsin levels in regions of active proliferation. These results indicate that hepsin plays an essential role in cell growth and maintenance of cell morphology.

Implanted myoblasts not only fuse with myofibers but also survive as muscle precursor cells

Intramuscular implanted myoblasts can fuse with existing myofibers. Here we report that implanted primary myoblasts marked with retroviral transgenes can also persist as muscle precursor cells. These cells can be recovered as viable myoblasts from muscles of recipient mice even months after myoblast implantation, and they can fully resume expression of the transgenes in culture. Upon re-implantation into muscles, they again not only fuse with existing myofibers, but also survive as muscle precursor cells in the tissue. These reserve myogenic cells should be able to contribute to host myofibers in muscle regeneration when the recombinant myofibers are damaged, providing an additional mechanism to maintain a persistent expression of transgenes delivered by myoblast-mediated gene transfer.

Biology of factor IX

Hemophilia B, one of two common hereditary bleeding disorders, is caused by a deficiency of factor IX in the circulation. Molecular mechanisms of hemophilia B are highly heterogeneous including gene deletions, insertions, complex rearrangements, and a large number of point mutations. Currently, hemophilia B is treated by plasma protein replacement therapy. This therapy is effective but exposes patients to possible side effects and complications such as infection of blood-borne pathogens including hepatitis viruses and HIV-1. Intensive efforts to develop alternative, safer therapies for hemophilia B, including somatic gene therapy, are now under way.