Impaired B-lymphopoiesis, myelopoiesis, and derailed cerebellar neuron migration in CXCR4- and SDF-1-deficient mice

The chemokine stromal cell-derived factor 1, SDF-1, is an important regulator of leukocyte and hematopoietic precursor migration and pre-B cell proliferation. The receptor for SDF-1, CXCR4, also functions as a coreceptor for T-tropic HIV-1 entry. We find that mice deficient for CXCR4 die perinatally and display profound defects in the hematopoietic and nervous systems. CXCR4-deficient mice have severely reduced B-lymphopoiesis, reduced myelopoiesis in fetal liver, and a virtual absence of myelopoiesis in bone marrow. However, T-lymphopoiesis is unaffected. Furthermore, the cerebellum develops abnormally with an irregular external granule cell layer, ectopically located Purkinje cells, and numerous chromophilic cell clumps of abnormally migrated granule cells within the cerebellar anlage. Identical defects are observed in mice lacking SDF-1, suggesting a monogamous relationship between CXCR4 and SDF-1. This receptor-ligand selectivity is unusual among chemokines and their receptors, as is the function in migration of nonhematopoietic cells.

[Cloning of DNA sequences involved in exopolysaccharide synthesis of Xanthomonas campestris pv. campestris]

By using a cloned DNA segment containing the mutated sequences from the exopolysaccharide-deficient mutant T117 of Xanthomonas campestris pv. campestris as a probe, a 9.4 kb HindIII fragment harbouring DNA sequences corresponding to the mutated site was identified and cloned from the wild-type strain. The fragment could complement the mutant strain T117 in trans and restore the synthesis of exopolysaccharide. This indicates that the fragment contains at least an intact gene which is involved in the exopolysaccharide synthesis of Xanthomonas campestris pv. campestris.

Lidocaine prolongs the safe duration of circulatory arrest during deep hypothermia in dogs

PURPOSE

To test the hypothesis that lidocaine prolongs the safe period of circulatory arrest during deep hypothermia.

METHODS

Sixteen dogs were subjected to cooling, first surface cooling to 30 degrees C and then core cooling to 20 degrees C rectal temperature). The circulation was then stopped for 90 min. In the lidocaine group, 4 mg.kg-1 lidocaine was injected into the oxygenator two minutes before circulatory arrest and 2 mg.kg-1 at the beginning of reperfusion and rewarming. The control group received equivalent volumes of normal saline. Post-operatively, using a neurological deficit scoring system (maximum deficit score-100; minimum-zero indicating that no scored deficit could be detected). Neurological function was evaluated hourly for six hours and then daily for one week, the pharmacokinetic parameters were calculated using one compartment model.

RESULTS

On the seventh day, the neurological deficit score and overall performance were better in the lidocaine (0.83 +/- 2.04) than in the control group (8.33 +/- 4.08 P < 0.05). During the experiment, the base excess values were also better in the lidocaine than in the control group (at 30 min reperfusion: -4.24 +/- 1.30 vs -8.20 +/- 2.82 P < 0.01, at 60 min reperfusion was -3.34 +/- 1.87 vs -7.52 +/- 2.40 (P < 0.01). On the eighth day the extent of pathological changes were milder in the lidocaine group than that in the control group. The elimination half life of lidocaine was 40.44 +/- 7.99 during hypothermia and 2.01 +/- 4.56 during rewarming.

CONCLUSIONS

In dogs lidocaine prolongs the safe duration of circulatory arrest during hypothermia.

[Long-term results of combined splenorenal shunt and porta-azygos devascularization in patients with portal hypertension]

OBJECTIVE

To investigate the long-term effects of combined splenorenal shunt and porta-azygos devascularization in patients with portal hypertension.

METHOD

We analysed retrospectively the follow-up results of 140 portal hypertensive patients undergoing the combined therapy in our hospital from April 1978 to April 1997. Changes of portal hemodynamics were studied by Doppler Flowmeter and DSA pre- and-postoperatively and direct FPP measurement intraoperatively.

RESULT

The operative mortality was 3.6%. No rebleeding was noted in a short period and rebleeding rate was 8.3% in a long term follow-up. The rate of postoperative hepatic encephalopathy was 5.0%. The long-term survival rate of 5-, 10- and 15-years was 83.6%, 64.5% and 54.5%, respectively. After operation FPP and PVP decreased significantly (P < 0.01) and FPP maintained at the level of 3.2 +/- 0.4 kPa.

CONCLUSION

The combined procedure is a rational and practical procedure for the treatment of patients with portal hypertension.

Cell lineage determination and the control of neuronal identity in the neural crest

The molecular mechanisms underlying the determination of neuronal identity in the vertebrate peripheral nervous system are only just beginning to come into focus. Many of these mechanisms, such as the involvement of cascades of bHLH transcription factors and lateral inhibition via the Notch-Delta system, appear to have been conserved from Drosophila (Ghysen et al. 1993; Jan and Jan 1993). The way in which these genetic circuits are controlled by instructive growth factors, and the manner in which they lead to expression of a particular neuronal identity, is far from clear. This process is being elucidated by studies of neurogenesis in the peripheral autonomic lineage, which is arguably the best-understood neurogenic lineage in vertebrates. Emerging evidence is beginning to suggest that neuronal diversity within the autonomic and sensory lineages may be generated by related, but distinct, mechanisms. All autonomic progenitors express a common bHLH protein, MASH1, which appears to be induced by members of the BMP2 subfamily secreted by the tissues to which these progenitors migrate. Additional signals may then act on these progenitors in different locations to induce the expression of other transcription factors, which act in conjunction with MASH1 to specify the final phenotypes of the different autonomic neuron subtypes (sympathetic, parasympathetic, and enteric). Although different classes of autonomic neurons develop in very different locations within the body, different classes of sensory neurons are located together in dorsal root ganglia. The finding that distinct but related subtypes of bHLH proteins, the neurogenins, are expressed by different classes of sensory neuron precursors early in development suggests that sensory neuron diversity, in contrast to autonomic neuron diversity, may be pre-specified at or before the time neural crest cells begin their emigration from the neural tube.

Simultaneous up-regulation of viral receptor expression and DNA synthesis is required for increasing efficiency of retroviral hepatic gene transfer

To understand the relative contribution of viral receptor expression and cell proliferation in retroviral gene transfer, we created human hepatocyte-derived HuH-7.MCAT-1 cell lines. These cells constitutively express the murine ecotropic retroviral receptor MCAT-1 without changes in morphology or proliferation states. The MCAT-1 receptor is also a cationic amino acid transporter, and the HuH-7.MCAT-1.7 cells showed increased Vmax of uptake and steady-state accumulation of the cationic amino acids L-arginine and L-lysine. In HuH-7.MCAT-1 cells, L-arginine uptake was significantly up-regulated by norepinephrine and dexamethasone, and hepatocyte growth factor also increased L-arginine uptake along with cellular DNA synthesis. Gene transfer was also markedly increased in HuH-7. MCAT-1.7 cells incubated with an ecotropic LacZ retrovirus, and this further increased with hormones and hepatocyte growth factor. To define whether viral receptor up-regulation by itself increased gene transfer, cell cycling was inhibited by a recombinant adenovirus expressing the Mad transcription factor (AdMad), which is a dominant-negative c-Myc regulator. This restricted cells in G0/G1, without attenuating MCAT-1 activity, as shown by flow cytometry and L-arginine uptake analysis, respectively. When asynchronously cycling HuH-7.MCAT-1.7 cells were first infected with the AdMad virus and then exposed to the ecotropic LacZ virus, gene transfer was virtually abolished. The data indicate that while up-regulation of viral receptors can greatly enhance retrovirally mediated gene transfer, DNA synthesis remains an absolute requirement for hepatic gene therapy with this approach.

[Study on the health of cotton mill workers]

A group of 110 workers in a cotton mill was investigated by questionnaire, skin testing, and the measurement of airway responsiveness through forced expiratory volume for one second(FEV1) by spirometry. The workers were examined before starting work, 10 weeks and one year after exposure. Decreases in FEV1 over shifts were small at 10 weeks and one year, and were slightly higher among people with positive skin reactions to cotton dust extracts. Airway responsiveness, defined as the average decrease in FEV1 after 1.25 mg methacholin, was increased at 10 weeks. It remained about the same after one year, except in the workers with positive skin test. Subjective symptoms of chest tightness and cough with phlegm increased progressively at 10 weeks and one year. Nasal irritation remained unchanged and dry cough decreased in one year. The results suggest that the airway inflammation caused by cotton dust increases with the exposure time and that the changes are more notable in workers with reactivity to cotton dust extract.

[Human bone morphogenetic protein-2: recombinant expression in E. coli]

OBJECTIVE

To explore the way of producing human bone morphogenetic protein-2(hBMP-2) for bone healing by using the gene engeneering techniques.

METHODS

hBMP-2 cDNA fragment, which consists of 3' end partial propeptide and mature peptide sequence, was inserted into the multiple cloning site of expression vector pkpL-3a via ligation. The recombinant plasmid pkpL-3a/hBMP-2 was transformed into E. coli pOp2136. By the method of restriction map, the positive expression clone was selected. SDS-PAGE analysis showed a new foreign protein band near 27,000 after induction. The yield of induced hBMP-2 accouned for 10% of the total bacterial proteins.

RESULTS

The partial purified recombinant hBMP-2 was implanted into Wistar rat thigh. After 4 weeks, histological analysis showed that it induced the proliferation of mesenchymal type cells and formation of new cartilage and bone in the implantation area.

CONCLUSION

The hBMP-2 produced by gene engeneering techniques has the biologic capacity of ectopic bone formation.

[Reconstruction of transcriptional regulatory elements of human alpha-fetoprotein gene]

OBJECTIVE

To construct vectors that express therapeutic genes specifically in hepatocellular carcinoma, the TREs (Tissue-specific transcriptional regulatory elements) of natural human alpha-fetoprotein (AFP) was reconstructed.

METHODS

Using subcloning techniques, the -870 bp(-)-3.06 kb fragment of the natural human AFP TREs was deleted to construct an artificial AFP(e/p) TREs which contains the "core" promoter and the -3.06 kb(-)-5.1 kb fragment of natural human AFP TREs that contains enhancer activity.

RESULTS

By using chloramphenicol acetyltransferase (CAT) assay, the artificial AFP(e/p) TREs showed an activity 1.8 fold as high as that of the natural AFP TREs in an AFP positive human hepatocarcinoma cell line HepG2, and it also remained to be tissue-specific since there was no activity was detected in an AFP negative human larynxcarcinoma cell line Hep2.

CONCLUSIONS

These results indicate that the artificial AFP(e/p) TREs we have constructed has higher activity than the natural AFP TREs and it also remains its hepatocarcinoma specificity. The reconstructed AFP(e/p) TREs is suitable for constructing of gene therapy vector with hepatocarcinoma expression specificity.

[Studies on microbiological factor in colour change of mogao graffito's mural. II. Effect of microorganism on the pigment of imitative mural]

Throung the assay and analysis of the imitative mural after cultivated with microorganisms, it has been shown that microorganisms had a pronounced effect on the pigments of the mural: the pigments secreted by microorganisms changed the colour of the mural, and produced much oxalic acid salt, which damaged the formation of crystals of the pigment, moreover, the chemical combination valence of Pb3O4 had been changed due to the metabolic products of microorganisms, that may play an important role in the chemical change of Pb3O4.

[The timing and mode of surgery in patients with severe acute pancreatitis]

OBJECTIVE

To investigate the timing and mode of surgical management in patients with severe acute pancreatitis (SAP).

METHOD

The timing, mode of operation and mortality were reviewed retrospectively in 50 SAP cases undergoing laparotomy in our hospital from 1985 to 1994.

RESULT

The overall mortality was 14% and 85.7% of the mortality falls on the age between 40 to 60 years, with no difference in etiology and sex. The operative mortality reduced gradually in patients with longer duration of illness (P > 0.05). The operative mortality of 31.8% in patients undergoing laparotomy within 12 h after hospitalization was significantly higher (P < 0.05) than in these operated on later. When the number of injured extra-pancreatic organs increased, the mortality also increased significantly (chi(2) = 5.99, P < 0.05). The related mortality with shock, pancreatic necrosis and multiorgan failure (MOF) was 31.8%, 31.6% and 28%, respectively (P < 0.05). The main procedures of surgical management were pancreatic debridement and/or drainage, and combined surgical measures.

CONCLUSION

The laparotomy timing is an important factor influencing mortality as well as the severity of pancreatic necrosis, sepsis, and MOF. Delayed laparotomy and 24 h preoperative management is recommended. Surgery adopted should be simple, efficient in drainage and debridement.

neurogenin1 is essential for the determination of neuronal precursors for proximal cranial sensory ganglia

The NEUROGENINS (NGNs) are neural-specific basic helix-loop-helix (bHLH) transcription factors. Mouse embryos lacking ngn1 fail to generate the proximal subset of cranial sensory neurons. ngn1 is required for the activation of a cascade of downstream bHLH factors, including NeuroD, MATH3, and NSCL1. ngn1 is expressed by placodal ectodermal cells and acts prior to neuroblast delamination. Moreover, NGN1 positively regulates the Delta homolog DLL1 and can be negatively regulated by Notch signaling. Thus, ngn1 functions similarly to the proneural genes in Drosophila. However, the initial pattern of ngn1 expression appears to be Notch independent. Taken together with the fact that ectopic ngn1 expression can convert ectodermal cells to neurons in Xenopus (Ma et al., 1996), these data and those of Fode et al. (1998 [this issue of Neuron]) identify ngns as vertebrate neuronal determination genes, analogous to myoD and myf5 in myogenesis.

Mathematical considerations for modeling cerebral blood flow autoregulation to systemic arterial pressure

The shape of the autoregulation curve for cerebral blood flow (CBF) vs. pressure is depicted in a variety of ways to fit experimentally derived data. However, there is no general empirical description to reproduce CBF changes resulting from systemic arterial pressure variations that is consistent with the reported data. We analyzed previously reported experimental data used to construct autoregulation curves. To improve on existing portrayals of the fitting of the observed data, a compartmental model was developed for synthesis of the autoregulation curve. The resistive arterial and arteriolar network was simplified as an autoregulation device (ARD), which consists of four compartments in series controlling CBF. Each compartment consists of a group of identical vessels in parallel. The response of each vessel category to changes in perfusion pressure was simulated using reported experimental data. The CBF-pressure curve was calculated from the resistance of the ARD. The predicted autoregulation curve was consistent with reported experimental data. The lower and upper limits of autoregulation (LLA and ULA) were predicted as 69 and 153 mmHg, respectively. The average value of the slope of the CBF-pressure curve below LLA and beyond ULA was predicted as 1.3 and 3.3% change in CBF per mmHg, respectively. Our four-compartment ARD model, which simulated small arteries and arterioles, predicted an autoregulation function similar to experimental data with respect to the LLA, ULA, and average slopes of the autoregulation curve below LLA and above ULA.

[Semiquantitative measurement of progesterone receptors in luteal-phase-defect endometrial cells during secretory phase]

To investigate the changes of endometrial progesterone receptor (PR) of luteal-phase-defect (LPD) patients during the secretory phase, thirteen patients with complaints of infertility or habitual abortion were studied. During the early-mid secretory phase, endometrial tissue was obtained by dilatation and curettage (D & C) for histological and receptor study: meanwhile serum E2, P, FSH, LH and PRL were measured. Based on histologic diagnosis, the patients were divided into two groups: the LPD group (n = 7) and the normal control group(n = 6). PR content was determined by immunohisto-chemical (IHC) assay. The results showed that during the early-mid luteal phase a significantly low PR content on endometrial glandular nucleus was observed in LPD group, compared with normal control(6.75 +/- 2.57 vs 9.50 +/- 1.64 P < 0.05), but no difference in serum progesterone was noted between the two groups. These findings suggest that during early-mid secretory phase, PR content on endometrial glandular nucleus decreases in LPD cases, which results in deficient response of endometrium to proper stimulus of progesterone. This change may cause endometrial secretory deficiency and blockade of embreyo implantation. That is why infertility or habitual abortion happened.

Use of murine CXCR-4 as a second receptor by some T-cell-tropic human immunodeficiency viruses

The human CXCR-4 molecule serves as a second receptor for primary, T-cell-tropic, and laboratory-adapted human immunodeficiency virus type 1 (HIV-1) isolates. Here we show that murine CXCR-4 can support the entry of some of these HIV-1 isolates. Differences between mouse and human CXCR-4 in the ability to function as an HIV-1 receptor are determined by sequences in the second extracellular loop of the CXCR-4 protein.

[The experimental research of transforming growth factor-beta 1 expression during fracture healing]

OBJECTIVE

To observe the effect of TGF-beta 1 in the regulation of fracture healing.

METHOD

The expression of transforming growth factor-beta 1 (TGF-beta 1) in different period of fracture healing was investigated by immunohistochemistry.

RESULTS

It was found that the expression of TGF-beta 1 changed in different period. The cells in the cambial layer of the periostlum showed low or negative signal in the immediate injury response period. The osteoblasts differentiated from the periosteum cells stained strongly in the intramembranous ossification period, and the differentiated chondrocytes stained most strongly in the chondrogenesis period. The hypertrophic chondrocytes showed negative signal and the osteoblasts stained strongly in the endochondral ossification period. These results suggested that the expression of TGF-beta 1 was closely related to the proliferation and differentiation state of repair cells.

CONCLUSION

TGF-beta 1 is intimately involved in the control of fracture healing.

Cerebral arteriovenous malformation feeding artery aneurysms: a theoretical model of intravascular pressure changes after treatment

OBJECTIVE

A quantitative model may be used to estimate the magnitude of expected pressure changes along the vascular tree with shunt ablation and may provide information to assess the hemodynamic risk of arteriovenous malformation (AVM) treatment.

METHODS

A computer model of the cerebral circulation was applied to estimate the changes in intravascular pressure, velocity, biomechanical stress, and shear stress that might be expected from either endovascular or surgical ablation of AVMs. Two AVM sizes and two feeding artery constellations were simulated. The effect of different shunt flows on vascular pressure was modeled. In each simulation, AVMs were occluded in a stepwise fashion. The effects of systemic hypertension and hypotension in various vascular zones were also simulated.

RESULTS

As large (1000 ml/min) AVMs were occluded, the mean feeding arterial pressure increased from 18 to 68 mm Hg; the percent-occlusion at half-maximal pressure increase was 92%. For medium (500 ml/min) AVMs, feeding arterial pressure increased from 37 to 66 mm Hg; the percent-occlusion at half-maximal pressure increase was 71%. During manipulation of systemic pressure, hemodynamic changes in the circulation close to the nidus were proportionally less than changes in systemic pressure; the degree of proportionality depended on the magnitude of AVM shunt flow.

CONCLUSION

In this simulation, shunt obliteration increased pressure in the nidus and feeding arteries with little effect on the proximal circulation. The shunt provided a "buffering" effect, i.e., higher flow fistulas were exposed to smaller variations in intravascular pressure in feeding artery and nidal pressures during manipulation of systemic pressure.

Down-regulation of major histocompatibility complex Q1b gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin

We analyzed mouse hepatoma cells using differential display to discover new genes that respond to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We identified a class I major histocompatibility complex (MHC) gene, which we designated as MHC Q1b, whose expression decreases in the presence of TCDD. TCDD-induced down-regulation of MHC Q1b requires both the aromatic hydrocarbon receptor and the aromatic hydrocarbon receptor nuclear translocator, transcription factors that up-regulate other genes in response to TCDD. Down-regulation of MHC Q1b by TCDD appears to involve both transcriptional and post-transcriptional regulatory events; the post-transcriptional destabilization of MHC Q1b mRNA is probably a secondary response to TCDD. Our findings reveal new mechanistic aspects of gene regulation by TCDD. In addition, our observations suggest a mechanism that might account for some of TCDD's immunotoxic effects.

[A prospective study on respiratory symptoms and functions in new employees exposed to cotton dust]

Sixty new employees in a cotton textile mill were followed up for five years to study their occurrence of byssinosis and its natural history. Results showed that the workers complained more cough, expectoration and other respiratory irritation symptoms at their early exposure to cotton dust, and the frequency of chest tightness in them reached the peak one year after exposure and remained at higher level later. Stratified analysis showed that all the respiratory symptoms did not correlate with their smoking habits, specific body constitution, etc. Forced expiratory volume at one second (FEV1) after shift declined with length of exposure and appeared a tendency to exacerbate gradually, especially in workers with a positive skin test of cotton antigen. Smoking had no influence on it. It suggests that exposure to cotton dust and idiosyncracy of the workers play important roles in damage to lung function.

Direct evidence for a soluble methane monooxygenase from type I methanotrophic bacteria: purification and properties of a soluble methane monooxygenase from Methylomonas sp. GYJ3

The hydroxylase and reductase components of a soluble methane monooxygenase from type I methanotrophs--Methylomonas sp. GYJ3--were purified by a multiple-step LC procedure. The hydroxylase (approximately 240 kDa, determined by an HPLC-size exclusion chromatography method) has three subunits with molecular masses of 56, 43, and 27 kDa, suggesting that the enzyme has an (alphabeta gamma)2 subunit structure. The HPLC method was developed to purify the hydroxylase component, and the purified protein has a specific activity of 541 nmol propene oxide x mg(-1) protein x min(-1), which is two times the specific activity of the protein purified by the two-step LC procedure. The iron content in the hydroxylase purified by the two-step LC procedure is 2.1 mol of Fe per mole of protein, but the iron content in the protein by the HPLC procedure is 3.78 mol of Fe per mole of protein. The diversity of iron contents in this protein is due mainly to the use of different purification methods. The reductase has a molecular mass of 42 kDa. The UV-VIS spectrum of the protein is similar to that of proteins from other methanotrophs, suggesting that the protein contains a FAD cofactor and a [2Fe-2S] center. The partially purified component B stimulated the MMO activity of the hydroxylase and reductase system by 40-fold.

A theoretical model of cerebral hemodynamics: application to the study of arteriovenous malformations

A comprehensive computer model of the cerebral circulation, based on both hydrodynamics and electrical network analysis, was used to investigate the influences of arteriovenous malformations (AVM) on regional cerebral hemodynamics. The basic model contained 114 normal compartments: 55 arteries, 37 veins, 20 microvessel groups (MVG), one compartment representing systemic and extracranial vascular resistance, and one representing the heart. Each microvessel group, which represented the arteriolar bed, consisted of 5000 microvessels. Cerebral blood flow autoregulation was simulated by a formula that determined the resistance and therefore the flow rate of the microvessel groups (arterioles) as a function of perfusion pressure. Elasticity was introduced to describe the compliance of each vessel. Flow rate was made a controlling factor for the positive regulation of the diameters of conductance vessels by calculation of shear stress on the vessel wall (vessel dilation). Models containing an AVM were constructed by adding an AVM compartment and its feeding arteries and draining veins. In addition to the basic model, AVM models were simulated with and without autoregulation and flow-induced conductance vessel dilation to evaluate the contributions of these factors on cerebral hemodynamics. Results for the model with vessel dilation were more similar to clinical observations than those without vessel dilation. Even in the presence of total vasoparalysis of the arteriolar bed equivalent, obliteration of a large (1000 mL/min) shunt flow AVM resulted in a near-field CBF increase from a baseline of 21 to a post-occlusion value of no more than 74 mL/100 g/min, casting doubt on a purely hemodynamic basis for severe hyperemia after treatment. The results of the simulations suggest that our model may be a useful tool to study hemodynamic problems of the cerebral circulation.

[Relation of Lac promotor and the expression of cholera toxin subunit B gene in recombinant Escherichia coli MM2]

Effects of different carbon sources including glucose, lactate and acetate and IPTG induction on the expression of ctb gene, which is on the downstream of lac promotor, in recombinant Escherichia coli MM2 were studied. In medium YC were added 0.048mol/L glucose, 0.102mol/L lactate or 0.167mol/L acetate which separately produce the same energy in the condition of complete oxidization. Addition of glucose largely decreased the expression level of ctb gene because of decrease of pH during culture process. Addition of lactate increased the expression level of ctb gene by 1.15 fold and did not inhibit the growth of MM2 strain. Addition of acetate increasd the expression level of ctb gene by 0.97 fold and inhibited the growth of MM2 strain. Induction by IPTG at different time and different concentration did not increase the expression level of ctb gene, so the lac promotor had no or a little influence upon the expression of ctb gene in recombinant MM2 strain.

Transactivation domains facilitate promoter occupancy for the dioxin-inducible CYP1A1 gene in vivo

We have studied the transcriptional regulation of the dioxin-inducible mouse CYP1A1 gene in its native chromosomal setting. We analyzed the ability of aromatic hydrocarbon receptor (AhR) mutants and AhR chimeras to restore dioxin responsiveness to the CYP1A1 gene in AhR-defective mouse hepatoma cells. Our data reveal that transactivation domains in AhR's C-terminal half mediate occupancy of the nuclear factor 1 site and TATA box for the CYP1A1 promoter in vivo. Transactivation domains of VP16 and AhR nuclear translocator, but not Sp1, can substitute for AhR's C-terminal half in facilitating protein binding at the promoter. Our data also reveal an apparent linear relationship between promoter occupancy and CYP1A1 gene expression in chromatin. These findings provide new insights into the in vivo mechanism of transcriptional activation for an interesting mammalian gene.