Cadmium-induced osteomalacic and osteopetrotic lesions in ovariectomized rats

The effects of long-term administration of cadmium (Cd) chloride on the bone were studied using ovariectomized rats. The rats were injected iv with the compound at doses of 1.0 and 2.0 mg/kg, 5 days a week, for 13 weeks. The serum concentrations of calcium and inorganic phosphorus were significantly increased from 8 weeks in the 2.0 mg/kg group. The bone Cd content was gradually increased for 13 weeks in a dose-dependent manner. Calcium and phosphorus contents in the bone, and serum levels of parathyroid hormone and osteocalcin, were not significantly different between Cd-treated and control rats. Histopathologically, chronic Cd nephropathy such as tubular atrophy and interstitial fibrosis was observed with clinical polyuria and increased enzymuria. The skeletal changes were detected mainly in the femur and tibia. In the metaphysis of Cd-treated rats, cancellous bone mass increased with time. This change was detected as an increased opacity by a roentgenogram. In the cortical bone of the midshaft haversian canals were dilated with clearly bordered osteoid seams and showed a motheaten pattern in rats in the 2.0 mg/kg group at 13 weeks. In the present study, we report Cd nephropathy and osteomalacic changes in ovariectomized rats with iv injection of CdCl2 for 13 weeks. Although an involvement of the indirect action of Cd through renal failure could not be ruled out in this experiment, our biochemical and pathological data suggested that osteomalacia was induced by a direct action of Cd on the bone through abnormal calcium homeostasis.

[Pharmacokinetics of isosorbide dinitrate studied by the extrapolation model]

To make a pharmacokinetic model of isosorbide dinitrate (ISDN), we infused ISDN at 1, 10 or 30 micrograms.kg-1.min-1 into anesthetized rabbits and measured concentrations of ISDN and its metabolites (2-ISMN and 5-ISMN) in plasma, urine and bile. We found the concentration gradient of ISDN between arteries and veins and between the ascending aorta and femoral artery. These concentration gradients may occur due to metabolism and accumulation of ISDN in many organs and tissues, let alone the vascular endothelium. There was no significant difference in plasma concentrations of ISDN or its metabolites between the hepatic vein and femoral vein. It seems that ISDN is metabolized in various organs and tissues. By ISDN infusion of more than 10 micrograms.kg-1.min-1, the plasma concentration of ISDN showed a pronounced increase. It appears that there is metabolic saturation of ISDN. Using these informations, we extrapolated the model to human and the estimated values were compared with observed values to determine the validity of the extrapolation model. There was no remarkable differences between the estimated values and observed values. This suggests the validity of the model. The plasma concentrations of ISDN, estimated by this extrapolated model, showed a linear increase (Y = 30X) with the flow rate range of 0.2-5.0 micrograms.kg-1.min-1, when the metabolic rate was normal. With ISDN infusion of more than 5.0 micrograms.kg-1.min-1, the plasma concentrations of ISDN showed a pronounced increase. In the conditions of impaired metabolism, the plasma concentrations of ISDN increase exponentially.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of the biological pharmacology of IFO, a new selective and reversible monoamine oxidase-B inhibitor

3-[4-[3-(1H-Imidazol-1-yl)propoxy]phenyl]-5-trifluoromethyl-1,2,4- oxadiazole (IFO), designed to be a novel selective inhibitor of monoamine oxidase (MAO), showed highly selective inhibition for type-B (MAO-B); its IC50 was approximately > 200 microM and 30 nM for type-A (MAO-A) and MAO-B, respectively, in the standard assay using mitochondrial preparations from rat brain or liver. The in vitro MAO-B inhibition by IFO was time-independent, non-competitive and tight-binding; and furthermore, in the presence of sodium cholate its inhibition was not tight-binding and was reversible. Oral administration of IFO (0.5-100 mg/kg) produced a dose-dependent MAO-B inhibition in mouse brain; its ED50 (p.o., 1 hr) was 1.6 mg/kg, while L-deprenyl inhibited the enzyme with the ED50 of approximately 8.0 mg/kg. The ED50 for MAO-A was > 100 mg/kg for either IFO and L-deprenyl. The MAO inhibitive effect of IFO in mouse liver was the same as that in the brain, but that of L-deprenyl in mouse liver was different from that in the brain as shown by the ED50 values of 35 mg/kg and 0.6 mg/kg for MAO-A and MAO-B, respectively. In mice, IFO increased the striatal concentrations of 2-phenylethylamine (2-PEA) and showed almost the same protective efficacy as L-deprenyl against the lethality and striatal dopamine (DA) depletion induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). These results indicate that IFO appears to be a potent inhibitor of MAO-B in mouse brain.

Involvement of the BCL3 gene in two patients with chronic lymphocytic leukemia

The t(14;19)(q32;q13) is a recurring translocation found in some patients with chronic lymphocytic leukemia (CLL), and the t(14;19) juxtaposes the BCL3 gene on chromosome 19 with the immunoglobulin heavy chain gene (IGH) locus on chromosome 14. Genomic DNAs from 49 patients with chronic B-cell leukemia and the related lymphomas were examined by Southern blot hybridization using 2 separate probes, named p alpha 1.4P and p alpha .5B, from the BCL3 gene locus. None of the 18 patients with leukemic manifestations of non-Hodgkin's lymphomas had detectable BCL3 rearrangements. Of 31 patients with CLL, 2 had the BCL3 rearrangements. A comigration study using the C alpha and C epsilon constant gene probe from IGH indicated that the t(14;19) translocation occurred in these 2 patients, and they were diagnosed with CLL/prolymphocytic (PL) according to the French-American-British (FAB) classification. Probes for the IGH locus revealed that leukemia cells of the 2 patients each were clonal, indicating that both small lymphocytes and prolymphocytoid cells found in the peripheral blood of one patient had the t(14;19), as well as a major population of the small lymphocytes in the peripheral blood of a second patient. It thus appears that tumor cells carrying the t(14;19) constitute a distinct disease entity in a group of chronic B-cell leukemia, that has a converting potential to more aggressive forms.

Synthesis and biological activities of the optical isomers of (+/-)-4-amino-5-chloro-2-ethoxy-N-[[4-(4-fluorobenzyl)-2- morpholinyl]methyl]benzamide (mosapride)

The enantiomers, (S)-(-)-1 and (R)-(+)-1, of (+/-)-4-amino-5-chloro-2-ethoxy- N-[[4-(4-fluorobenzyl)-2-morpholinyl]methyl]benzamide (mosapride) [(+/-)-1], a new and selective gastroprokinetic agent, were prepared from optically active [4-(4-fluorobenzyl)-2-morpholinyl]methylamines (S)-(-)-4 and (R)-(+)-4, respectively. The requisite (S)-(-)-4 and (R)-(+)-4 were prepared by optical resolution of [4-(4-fluorobenzyl)-2-morpholinyl]methyl p-toluenesulfonate [(+/-)-5] using (-)- and (+)-N-(p-toluenesulfonyl)glutamic acids, followed by amination of the tosyloxy groups of (R)-(-)-5 and (S)-(+)-5, respectively. The absolute configurations of (R)-(-)-5 and (S)-(+)-5 were determined on the basis of an asymmetric synthesis of (R)-(-)-5 from (S)-(+)-benzyl glycidyl ether [(S)-(+)-11]. Mosapride and its enantiomers, (S)-(-)-1 and (R)-(+)-1, were essentially equipotent in serotonin 5-HT4 receptor agonistic activity on the electrically evoked contractions in isolated guinea pig ileum.

Acute ischemia of the lower legs from blunt abdominal trauma: an unusual cause of atheroembolism--case report

A 79-year-old man sustained blunt abdominal trauma in an automobile crash, resulting in intra-abdominal bleeding and acute ischemia of the lower extremities. Angiography demonstrated occlusion of the popliteal arteries bilaterally. He died of multiple organ failure despite immediate surgical intervention. Pathologic examination revealed diffuse atheroembolism of the lower legs.

[Validity of the values of maximal oxygen intake for women recommended in the 'Quantity of exercise for developing health' by Ministry of Health and Welfare]

The purpose of this study was to examine the value of maximal oxygen intake per kilogram body weight (VO2max/wt) recommended for women between 20 and 29 years of age by the Ministry of Public Welfare. The subjects were 199 female college students, who were not in the habit of drinking and smoking. Results obtained were as follows: After controlling the effects of age and percent body fat (%fat), VO2max/wt showed a significant correlations with %fat, high-density lipoprotein cholesterol and systolic blood pressure. The values of VO2max/wt corresponding to borderline values of these CHD risk factors ranged from 27.6 to 29.5ml/kg.min. The highest value of VO2max/wt was very close to the value recommended for women older than 60 years of age by the Ministry of Public Welfare. The subjects were then divided into 4 groups; at above and below the value of VO2max/wt (35ml/kg.min) recommended for women between 20 and 29 years of age, and at above and below the value of VO2max/wt (31ml/kg.min) recommended for women older than 60 years of age by the Ministry of Public Welfare. There were no significant differences among 4 groups in occurrence of abnormal values in CHD risk factors. The results of this study support the validity of the value of VO2max/wt (31ml/kg.min) recommended for women older than 60 years of age by the Ministry of Public Welfare. However, it seems that it is not necessary to recommend the value of VO2max/wt (35ml/kg.min) for women between 20 and 29 years of age, who were not in the habit of drinking and smoking.

[Nonspecific anaphylactoid reaction in low IgE patients]

We reported two cases of anaphylactoid reaction caused by ranitidine and alprostadil. We suggest that these anaphylactoid reactions are nonspecific reactions which are observed in low IgE patients, because plasma IgE was still low 6 weeks after allergic reaction and these drugs have not been given to them before and eosinophilic and basophilic cells showed no change at all. We have to consider that there is a high risk of allergic reaction during general anesthesia, because many drugs are injected intravenously during general anesthesia.

Regulation of gastroduodenal bicarbonate secretion by capsaicin-sensitive sensory neurons in rats

We investigated the role of capsaicin-sensitive sensory neurons in regulation of gastroduodenal HCO3- secretion in anesthetized rats. The stomach (under acid inhibition by omeprazole 60 mg/kg i.p.) or the duodenum was perfused with saline (pH 4.5) and HCO3- output was determined by pH change in the perfusate. Both the duodenum and stomach responded to prostaglandin E2 (PGE2; 300 micrograms/kg i.v.) or luminal acid by a significant increase in pH and HCO3- output. These tissues also responded to luminal application of capsaicin (0.3-6 mg/ml for 30 min), resulting in a significant increase of pH and HCO3- output in a concentration-related manner. The HCO3- stimulatory action of capsaicin was markedly attenuated by functional ablation of capsaicin-sensitive sensory neurons, significantly mitigated by indomethacin, and exhibited tachyphylaxis after repeated application at a high concentration. The acid-induced pH and HCO3- responses were also significantly mitigated by sensory deafferentation and by indomethacin, whereas those induced by PGE2 remained unaffected. In addition, defunctionalization of these sensory nerves resulted in macroscopically visible damage in the duodenum when acid secretion was concomitantly stimulated by histamine. We conclude that capsaicin-sensitive sensory neurons may be involved in the regulatory mechanism of gastroduodenal HCO3- secretion and contribute to protection of the mucosa against acid. Endogenous PGs may be involved in the HCO3- stimulatory action mediated by capsaicin-sensitive sensory neurons.

Dual appearances of pigment cells from in vitro cultured embryonic cells of Japanese flounder: an implication for a differentiation-associated clock

The cells dissociated from developing embryos of Japanese flounder (Paralichthys olivaceus) are cultured in vitro to examine the developmental fate of their pigment cells in relation to establishment of bilaterally asymmetric integumental coloration in vivo. When neurula embryos are dissociated using trypsin-EDTA in Dulbecco's modified Ca(2+)-, Mg(2+)-free phosphate buffered saline and then cultured in vitro using L-15-based fetal calf serum-supplemented growth medium at 20 degrees C, numerous pigment cells appear twice in the same culture with an interval of approximately 1 month even under similar culture conditions. The first group of pigment cells, which is relatively larger in cell size (about 70 microns wide) and lower in cell density, emerges within 12 hr after plating, whereas the second, which is far smaller in cell size (about 30 microns) and overwhelmingly higher in cell density than the first, does so about 1 month after plating. The timing of their appearances in vitro is in good accordance, respectively, with that observed for the larvae under normal development in vivo; the first group appears at the period corresponding to hatching, whereas the second at the period corresponding to the completion of metamorphosis. Light microscopic examinations disclose that each group of pigment cells is composed of black melanophores and reflecting leucophores, and that the population density of melanophores and leucophores in the first group at the climax of appearance is approximated as 1:4. Typical xanthophores that are distributed in the skin of the larvae of this species are scarcely observed in culture in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

[Postoperative disturbance of consciousness due to tumor emboli of the orifice of pulmonary artery]

We reported a case of an abrupt hypotension and hypoxemia which lasted more than 60 min due to emboli of tumor at the orifice of the pulmonary artery during operation. Although the emboli were removed under the cardiopulmonary bypass (CPB) and later the patient regained good respiratory and hemodynamic conditions, he had a disturbance of consciousness after the operation. We began oxygen hyperbaric therapy (OHP) from the 6th postoperative day under spontaneous ventilation. His consciousness improved quickly after the beginning of OHP. We conclude that OHP and CPB might be useful to treat the postoperative disturbance of consciousness due to hypotension and hypoxemia during operation.

Speculations on the roles of ADP-ribosyl transferase based on analogies between RecA and poly(ADP-ribose) polymerase

A model for eukaryotic DNA damage repair is proposed in which poly(ADP-ribose) polymerase(NAD+ ADP-ribosyl transferase, EC 2,4,2,30) plays an important role. In this model, poly(ADP-ribose) polymerase regulates transcription of genes that are induced by DNA-damaging agents. This transcriptional regulation results from poly(ADP-ribosyl)ation and inactivation of DNA sequence-specific regulatory proteins such as silencer element-binding proteins, thereby inducing transcription of DNA polymerase beta, which is a DNA repair enzyme in higher eukaryotes. Poly(ADP-ribose) polymerase has a number of similarities to RecA in Escherichia coli. Therefore, the genes related to DNA damage repair in higher eukaryotes are proposed to form a "poly(ADP-ribose) polymerase regulatory network" similar to the "SOS regulatory network" in E. coli.

[Effects of DbcAMP on tumor necrosis factor and interleukin-1 production in human monocytes]

Recent reports have shown that dibutyryl cAMP (DbcAMP) blocks endotoxin-induced lung injury. To determine whether DbcAMP suppresses the production of tumor necrosis factor (TNF) and interleukin-1 (IL-1) in human monocytes, we measured the levels of TNF and IL-1 in response to E. Coli lipopolysaccharide (40 micrograms.ml-1) in vitro. We now show that DbcAMP suppressed dose-dependently the production of TNF in human monocytes, and DbcAMP totally suppressed it at the dose above 5 x 10(-4) M. However, DbcAMP did not suppress the production of IL-1 even at the dose of 5 x 10(-3) M in human monocytes. These data suggest that the productive mechanism of IL-1 may be different from that of TNF. Further, suppression of TNF by DbcAMP may contribute to the beneficial effects in animal models of septic shock or lung injury and this may have clinical implications.

Acute toxicity of cadmium in rats with or without cadmium pretreatment

The acute toxicity of cadmium (Cd) in male rats was examined with or without Cd pretreatment. Firstly, the metallothionein (MT) contents in the liver and kidney after Cd exposure (2.0 mg/kg, i.v.) were determined. The MT contents in the liver increased immediately to a peak (36.0 +/- 5.5 n mol/g wet tissue) 2 days after Cd exposure and were 55-fold higher than that at 0 day (0.64 +/- 0.25 n mol/g wet tissue). On the other hand, the MT contents in the kidney increased slightly but steadily for 14 days after Cd exposure. In the study for comparison of Cd-induced toxicity, the LD50 value of the Cd-pretreatment group (Group II) was approximately 2-fold higher than that of the non-pretreatment group (Group I). In microscopic findings, differences between rats in Group I and Group II were recognized in the kidney. Cytoplasmic vacuolation of the proximal tubular epithelium in the kidney was observed in Group I, while degeneration or coagulative necrosis in the proximal tubular epithelium was observed in some rats in Group II in addition to the cytoplasmic vacuolation. Because the toxic changes other than in the kidney in Group II were almost equal to or less than that in Group I, in spite of the doubled dosage of Cd, the toxic effects of Cd, except on the kidneys, were considered to be reduced by the pretreatment with Cd.

[Hepatic arterial infusion chemotherapy combined with calcium antagonist for liver metastases]

We noticed inactivation of calcium antagonists in liver and investigated treatment with combined intraarterial chemotherapy. Both verapamil (VER) and adriamycin were infused into the hepatic artery of patients with liver metastases. The serum concentration of VER in the hepatic vein was 0.325 +/- 0.203 g/ml at maximum in 11 cases receiving bolus infusion. Blood pressures, heart rates and electrocardiograms were stable. The concentration in the peripheral vein was lower (0.089 +/- 0.027 g/ml) in 4 cases receiving 3-hour continuous infusion. Five patients received more than 10 infusions, and a partial response was observed in 2 cases. A more appropriate dose and the corresponding prognosis should be studied in the future.

[Anesthetic management for cesarean section and clipping of aneurysm in a pregnant woman with ruptured cerebral aneurysm]

We report an anesthetic management for Cesarean section and clipping of aneurysm in a pregnant woman with a subarachnoidal hemorrhage secondary to a ruptured cerebral aneurysm. Anesthesia was induced with thiopental, vecuronium and sevoflurane, and maintained with sevoflurane (0.5-1%) before the delivery. Apgar score at 1 min was 1, but after 30 min her activity became almost normal. After the delivery, anesthesia was maintained with fentanyl for clipping surgery, because sevoflurane may inhibit uterine contraction and increase bleeding from the uterus after the delivery. We also infused prostaglandin E1 continuously at a rate of 50-70 ng.kg-1.min-1 to control arterial blood pressure and to maintain good contraction of the uterus during clipping surgery. We conclude that prostaglandin E1 is useful as a vasodilator after delivery because prostaglandin E1 contracts the uterus.

Ovariectomy enhances cadmium-induced nephrotoxicity and hepatotoxicity in rats

The toxicity of cadmium (Cd) chloride was studied in ovariectomized (OX) female rats and non-OX female rats after intravenous administration of the compound at doses of 2.0 and 3.0 mg/kg for 14 days. Mild hypochromic microcytic anemia developed in all rats treated with Cd, but growth retardation in the OX rats was more prominent than that in the non-OX rats. There was an increase of AST and ALT and a decrease of total cholesterol and the A/G ratio in both OX and non-OX rats treated with Cd. The hepatic and renal Cd concentrations increased in a dose-dependent manner, and the concentrations in both organs on Day 14 were comparable in the 3.0 mg/kg OX group (liver, 270.0 +/- 39.6 micrograms/g; kidney, 121.3 +/- 10.1 micrograms/g) and non-OX group (liver, 277.0 +/- 29.9 micrograms/g; kidney, 100.8 +/- 1.3 micrograms/g). Hepatocyte necrosis developed only in OX rats treated with Cd, and the nephrotoxicity of Cd was also notably enhanced by ovariectomy, since Cd nephropathy affected the proximal convoluted epithelium more severely and more frequently in OX rats than in non-OX rats. BrdU-labeled cells in the renal cortex were increased by approximately 2.7-fold in OX rat (7.4 cells/mm2) over those in the renal cortex in non-OX rat (2.7 cells/mm2). In conclusion, the present study demonstrated that ovariectomy enhanced Cd-induced nephrotoxicity and hepatotoxicity in rats.

Source analysis of scalp-recorded movement-related electrical potentials

We used brain electric source analysis to study the sources generating the movement-related cortical potentials during the interval from 200 msec before to 200 msec after the movement onset. Dipole solutions were obtained for the peak of the negative slope (pNS') and the frontal peak of the motor potential (fpMP) on scalp-recorded movement-related electrical potentials elicited by self-paced, repetitive unilateral finger movements in 10 normal volunteers. Two sources in homologous areas on each side of a spherical head model provided a satisfactory solution for the activity occurring at the instant of the pNS' in all subjects. The fpMP was modeled by a contralateral source and a midline source in 6 subjects and by a single contralateral source in the remaining 4 subjects. The percentage of the residual variance, or goodness-of-fit, over the interval from -200 to 200 msec, using the derived at pNS' and fpMP, was low. The results support the hypothesis that the NS' originates from the activity of bilateral generators in the sensorimotor cortex, and the motor potential arises from the combined activity of sources in the contralateral postcentral regions and the supplementary motor area.

Deficiency of the gene B impairs differentiation of melanophores in the medaka fish, Oryzias latipes: fine structure studies

In an orange-colored variant of the medaka fish, Oryzias latipes, which is homozygous for b allele, the melanophores represent a tissue-specific differentiation, manifesting an amelanotic appearance in the skin, an incomplete melanogenesis in the choroid and the peritoneum, and mosaic phenotype-like melano-iridophores in the peritoneum. In a wild-type strain of this species carrying the B gene, all melanophores are terminally differentiated irrespective of the tissues in which they are located. This indicates that the deficiency of B gene impairs the differentiation of melanophores in the medaka. Electron microscopy disclosed that the deficiency of B gene causes deterioration of melanogenesis to occur inside the melanosomes and that the manner of deterioration in the melanophores in the skin, the choroid and the peritoneum is different. The ubiquitous occurrence of reflecting platelet-laden melanophores in the peritoneum of this variant and the total absence of a mosaicism in pigment cells of the wild-type strain indicate that the deficiency of B gene predestines melanoblasts distributed in this tissue to an ambiguous state with regard to their differentiation. Little difference is observed between melanosomes maturation in pigment epithelial cells of the orange-colored variant and the wild-type strain, indicating an innocent role of the B gene in their differentiation.

Appearance of tumorous phenotypes in goldfish erythrophores transfected with ras, src, and myc oncogenes and spontaneous differentiation of the transformants in vitro

When goldfish erythrophores isolated from the skin by tissue digestion and centrifugation in a Percoll density gradient were transfected in a monolayer-culture with v-Ha-ras or v-src oncogene either singly or in combination with v-myc by means of calcium phosphate-DNA co-precipitation, there appeared a certain number of transformants manifesting a chromatoblast-like profile and tumorous phenotypes as seen in the capability for unlimited growth, and piling-up in a monolayer-culture or colony formation in semi-solid soft agar. After successive growth in vitro for longer than one month which was scarcely observed with the erythrophores, the vast majority of such transformants began to differentiate into erythrophores and ceased proliferation spontaneously. The onset of their differentiation was ascertained by the deposition of marker pteridine pigments. None of the transformants differentiated into melanophores or iridophores or other neural crest derivatives as seen in goldfish erythrophoroma cells. Little difference was observed in their transforming efficiency (0.2-0.3 transformants/micrograms DNA) between the combinations of oncogenes applied but a tendency was noted that cells transfected with ras or src in combination with myc developed the capacity to grow for a longer period and differentiated at a later stage than those transfected solely with ras or src. One cell line (ESM-1) derived from the erythrophores transfected with src/myc grew successively over nine months, indicating its acquisition of immortality. The expression of the transfected oncogenes in this cell line was examined in comparison with the erythrophoroma cells by Western and Northern blot analyses.

Expression and transmission of wild-type pigmentation in the skin of transgenic orange-colored variants of medaka (Oryzias latipes) bearing the gene for mouse tyrosinase

Transgenic fish carrying a reconstructed mouse tyrosinase gene, mg-Tyrs-J, were produced by microinjecting the gene into the oocyte nucleus of an orange-colored variant of medaka (Oryzias latipes). Of 64 oocytes microinjected and subsequently inseminated, 13 embryos developed normally beyond hatching and three of them exhibited brown skin pigmentation in the adult as was commonly observed in the wild type of this species. Light and electron microscopic examination disclosed a ubiquitous distribution of typical melanophores in the skin of these transgenic fish. Judging from their population density and distribution pattern, it was presumed that melanogenesis in these fish was elicited in amelanotic melanophores that resided in the skin of the orange-colored fish of this variant. Immunofluorescence with use of the anti-mouse tyrosinase antiserum lacking reactivity to medaka tyrosinase clearly disclosed that the gene introduced was expressed in the melanophores of transgenic fish. Crosses of female transgenic fish and males from an orange-colored variant yielded offspring exhibiting wild-type or orange-colored pigmentation in a ratio of 1:1, thus implying that mg-Tyrs-J integrated into the medaka genome behaves like a dominant gene. Little melanogenesis was observed in xanthophores, leucophores and iridophores in transgenic fish, suggesting possible specificity in recognition of teleostean cell types (i.e., melanophores) by the regulatory region of the mouse tyrosinase gene.