Inactivation of the murine pyruvate dehydrogenase (Pdha1) gene and its effect on early embryonic development

A deficiency of pyruvate dehydrogenase complex (PDC) in humans results in lactic acidosis and neurological dysfunction that frequently results in death during infancy. Using gene targeting technology, a silent mutation was introduced into the murine X-linked Pdha1 gene that encodes the alpha subunit of the pyruvate dehydrogenase or E1 component of the complex. Two loxP sequences were introduced into intronic sequences flanking exon 8 to generate the Pdha1(flox8) allele. In vitro studies in embryonic stem cells demonstrated that deletion of exon 8 ablated PDC activity. Homozygous Pdha1(flox8) females were bred with male mice carrying a wild-type Pdha1 allele and a transgene that ubiquitously expresses the Cre recombinase to produce progeny with a deletion in exon 8, Pdha1(Deltaex8). The majority of progeny were found to be mosaic with the presence of both the flox and deleted alleles, and there were no apparent phenotypic effects associated with the null allele. The mosaic mice were interbred to increase the degree of mosaicism for the Pdha1(Deltaex8) allele in the subsequent generation, resulting in a significantly smaller litter size (54% reduction). Embryos carrying predominantly the Pdha1(Deltaex8) allele were found to be globally delayed in development by 9.5 days postcoitus, with resorption occurring over the following several days. These findings demonstrate an essential role for oxidative metabolism of glucose during the early postimplantation period of prenatal development.

Randomized trial of progressive resistance training to counteract the myopathy of chronic heart failure

Chronic heart failure (CHF) is characterized by a skeletal muscle myopathy not optimally addressed by current treatment paradigms or aerobic exercise. Sixteen older women with CHF were compared with 80 age-matched peers without CHF and randomized to progressive resistance training or control stretching exercises for 10 wk. Women with CHF had significantly lower muscle strength (P < 0.0001) but comparable aerobic capacity to women without CHF. Exercise training was well tolerated and resulted in no changes in resting cardiac indexes in CHF patients. Strength improved by an average of 43.4 +/- 8.8% in resistance trainers vs. -1.7 +/- 2.8% in controls (P = 0.001), muscle endurance by 299 +/- 66% vs. 1 +/- 3% (P = 0.001), and 6-min walk distance by 49 +/- 14 m (13%) vs. -3 +/- 19 m (-3%) (P = 0.03). Increases in type I fiber area (9.5 +/- 16%) and citrate synthase activity (35 +/- 21%) in skeletal muscle were independently predictive of improved 6-min walk distance (r2 = 0.78; P = 0.0024). High-intensity progressive resistance training improves impaired skeletal muscle characteristics and overall exercise performance in older women with CHF. These gains are largely explained by skeletal muscle and not resting cardiac adaptations.

Actinide interactions with microbial chelators: the dioxobis[pyridine-2,6-bis(monothiocarboxylato)]uranium(VI) ion

The title complex, bis(tetraphenylphosphonium) dioxobis(pyridine-2,6-dicarbothioato-O,N,O')uranium(VI), (C(24)H(20)P)(2)[UO(2)(C(7)H(3)NO(2)S(2))(2)], was prepared by reacting two equivalents of pyridine-2,6-bis(monothiocarboxylate) (pdtc) with uranyl nitrate. The geometry of the eight-coordinate U atom is hexagonal bipyramidal, with the uranyl O atoms in apical positions. This is the first reported complex in which this ligand binds a metal through the O and not the S atoms. Principal bond lengths include uranyl lengths of 1.774 (2) A, U--O distances of 2.434 (2) and 2.447 (3) A, and two U--N distances of 2.647 (3) A. The anion lies on an inversion centre.

Electromagnetic field effects: changes in protein phosphorylation in the Jurkat E6.1 cell line

This study is aimed at expanding the role of electromagnetic field (EMF) therapy for treatment of inflammatory diseases and obtaining new information on the biophysical mechanism of action of weak EMFs. The mechanism of action of EMFs on biological systems is a question that has yet to be answered. Several models have been proposed to explain the coupling of low frequency fields to biological systems, although no consensus has been reached as to which most adequately portrays the true mechanism. Protein phosphorylation is a major cellular metabolic regulator. As such, it has the potential to be a valuable indicator of the impact of EMFs on cellular metabolism. Using a well-controlled EMF exposure system, we examined the regulatory role of EMFs on low molecular weight protein phosphorylation in Jurkat E6.1 cells, a transformed human leukemic T cell line. Jurkat cells were grown to mid-log phase, preloaded with 32P and exposed to EMF (0.1 mT, 60 Hz) or sham for 30 minutes. Cell proteins were separated by SDS-polyacrylamide gel electrophoresis and incorporated radioactivity of low molecular weight proteins (18-23 kDa) was quantified by AMBIS data analysis. Three of five experiments showed no difference in protein phosphorylation in EMF exposed samples compared to controls, while two experiments revealed an EMF effect. We identified stathmin, an important T cell signaling phosphoprotein, as one of the low molecular weight proteins present in our Jurkat cell system. Stathmin expression as well as its phosphorylation was decreased in samples that were exposed to EMFs compared to controls. These data indicate that phosphorylation of individual proteins might be masked by the presence of numerous other proteins in whole cell lysate experiments. Further studies testing other low molecular weight T cell signaling molecules may validate this hypothesis.

Electromagnetic fields used clinically to improve bone healing also impact lymphocyte proliferation in vitro

An important aspect of medical device development is the need to understand how a device produces a specific biological effect. The focus can then be on optimizing that effect by device modification and repeated testing. Several reports from this lab have targeted programmed cell death, or apoptosis, as a cellular pathway that is induced by exposure of transformed leukemic T-cells in culture to specific frequency and intensity electromagnetic fields (EMFs). An EMF delivery device capable of selectively inducing T-cell apoptosis in human tissues could be used to enhance healing by limiting the production of molecules that promote inflammatory disorders such as psoriasis and tendonitis. In the present study, we examined the normal T-cell response to EMF exposure in vitro. In the peripheral blood, 70-80% of the lymphocytes are T-cells, and thus is a rich source of normal cells that match the transformed T-cells used in other experiments (Jurkat cells). We isolated lymphocytes from the peripheral blood of humans and rats, cultured them in nutritive medium and exposed them to either a complex 1.8 mT pulsed EMF (Electrobiology, Inc.), a 0.1 mT, 60 Hz power frequency EMF or a 0.2 mT, 100 Hz sinusoidal EMF. Control lymphocytes were cultured similarly, without field exposure. Lymphocytes were then treated with T-cell mitogens and evaluated for proliferative capacity after an additional 72 hours culture. Results indicate that T-cell proliferation is modulated by in vitro exposure to defined EMFs. The potential use of an EMF delivery device capable of selectively inducing such T-cell effects is discussed.

Effect of a wound healing electromagnetic field on inflammatory cytokine gene expression in rats

In earlier studies, we have shown that pulsed electromagnetic fields (PEMFs) induce programmed cell death in cultured T cells and that rats exposed in vivo to PEMFs have decreased T-cell proliferative capacity. These data led us to hypothesize that PEMFs might be used to control proliferation of inflammatory lymphocytes and therefore beneficially affect inflammatory diseases. Tendinitis is characterized by painful inflammation of the tendon. Inflammation is characterized by massive infiltration of T lymphocytes, neutrophils and macrophages into the damaged tissue. These inflammatory cells produce a variety of cytokines, which are the cellular regulators of inflammation. The current study tests whether in vivo PEMF effects are mediated via systemic cytokine production in rat tendinitis. Inflammation was chemically induced in female Harlan Sprague Dawley rats Achilles' tendons and a wound healing PEMF (Electrobiology, Inc.) was applied for 4 hours immediately following injury. Spleens from control and experimental animals were harvested 24 hours later and total RNA was extracted from the tissues. Gene expression was analyzed by reverse transcription of mRNA, and polymerase chain reaction amplification (RT-PCR) using primers specific for the cytokines IFN-gamma, IL-1 beta, IL-6, TNF-alpha, and TGF-beta, as well as for the control beta-actin. RT-PCR products were separated on 1.5% agarose gels and band intensities were normalized to beta-actin gene expression of the same sample. TGF-beta was the only cytokine produced at high levels in rats with tendinitis in comparison to the other cytokines. PEMFs did not show an effect on any cytokine expression in the spleens, 24 hours after induction of tendinitis. Further studies need to test if cumulative exposures of PEMFs are able to regulate inflammatory cytokine expression either at the site of inflammation or at the local lymph nodes.

A system for simultaneous ultraviolet light and electromagnetic field exposure in in vitro experiments

Ultraviolet light (UV) is a common treatment for skin diseases such as psoriasis, but bears the risk of carcinogenic side effects. We have biological evidence that electromagnetic fields (EMFs) can act additively with UV so that new therapeutic protocols combining UV and EMF might be developed to improve psoriasis phototherapy. In this study we report on a system that allows in vitro experiments testing this hypothesis. For simultaneous exposure of cell cultures to UVB and EMF, we built Merritt coils with an integrated UV exposure system. The coils can be operated in a sham or experimental mode (up to 1.5 mT and 20,000 Hz). Two UV bulbs were fitted inside the coils for UVB doses between 100-1000 J/m2/nm. In the exposure area the EMF is uniform within 0.0038%. For exposure, the cells are cultured in standard culture plates and placed in a specifically designed box. The box holds two plates in a top chamber covered with a Saran Wrap lid (91% UV transmission) so that cells are exposed to UVB and EMFs. The bottom chamber holds two plates, where cells are screened from UVB and only exposed to EMFs. Temperature control is maintained (+/- 1 degree C) by airflow vents on the side of the box and a fan placed 25 cm away from the cell culture box. To maintain sterility within the box the vents are covered with a bacterial filter. The box lid has additional ventilation through two air direction changes to create an additional bacterial barrier similar to that in culture plate lids.

Population code for tracking velocity based on cerebellar Purkinje cell simple spike firing in monkeys

Velocity is an important determinant of the simple spike discharge of cerebellar Purkinje cells. In a previous study, Purkinje cells in the intermediate and lateral cerebellum recorded during manual tracking were found to be tuned to a combination of direction and speed, (i.e. preferred velocity). In this study a population analysis of this simple spike discharge was used to determine whether the velocity of tracking could be predicted. For the majority (30/32) of direction-speed combinations, the population response accurately specified the target velocity. A temporal analysis showed how the population response gradually converged to the required velocity 200 ms prior to the onset of tracking. Therefore, the simple spike discharge of a Purkinje cell ensemble contains sufficient information to reconstruct target velocity, providing support for the hypothesis that the cerebellum controls or signals movement velocity.

Processing of multiple kinematic signals in the cerebellum and motor cortices

The cerebellum and motor cortices are hypothesized to make fundamentally different but synergistic contributions to the control of movement. Richly interconnected, these structures must communicate and translate salient parameters of movement. This review examines the similarities and differences in the encoding of multiple limb movement parameters in the cerebellum and motor cortices. Also presented are recent data on direction and speed coding by cerebellar Purkinje cells and primary motor and dorsal premotor cortical neurons during a visually-instructed, manual tracking task. Both similarities and differences have been found in the way that these two motor areas process movement parameters. For example, the two motor control structures encode direction with almost identical depths of modulation, which may simplify the exchange of directional signals. Two major differences between the cerebellum and motor cortices consist of the distribution of the preferred directions and the manner in which direction and speed are jointly signaled within the discharge of individual neurons. First, an anterior-posterior distribution of preferred directions has been shown for both reaching and manual tracking, consistent with an intrinsic reference frame and/or the structure of afferent input. In contrast, neurons in the motor cortices have uniformly distributed preferred directions, consistent with general purpose directional calculations. Secondly, Purkinje cells in the cerebellum and motor cortices combine movement direction and speed information differently. For example, Purkinje cell discharge encodes combinations of direction and speed, a 'preferred velocity', while the motor cortical neurons use a temporal parcellation scheme to encode multiple parameters of movement. These results demonstrate that the cerebellum and motor cortices process and use kinematic information in fundamentally different ways that may underlie the functional uniqueness of the two motor control structures.

Synthesis and reactivity of the Tl1 salts of

Synthons Tl1[TCNE]*- (1) and Tl12[TCNE]2- (2), for [TCNE]*- and [TCNE]2-, respectively, in metathesis reactions have been quantitatively prepared and characterized. The structure of 1 was solved and refined in a monoclinic unit cell at 27 degrees C [C2/c, a = 12.6966 (12) angstroms, b=7.7599 (7) angstroms, c=15.5041 (15) angstroms, beta = 96.610 (5) degrees , V= 1517.4 (2) angstroms3, Dcalcd = 2.911 gcm-3, Z=8, R1 = 0.0575, omegaR2=0.0701] and exhibits nuCN absorptions at 2,191 (s) and 2,162 (s) cm-1 consistent with metal-bound [TCNE]*-. The structure of 1 consists of a distorted square antiprismatic octacoordinate Tl1 bound to six monodentate [TCNE]*-s with TlN separations ranging from 2.901 to 3.171 angstroms averaging 3.020 angstroms, and one bidentate [TCNE]*- with TlN separations averaging 3.279 angstroms. The TlN bonding is attributed to electrostatic bonding. The [TCNE]*-s form dimerized zigzag chains with intra- and interdimer separations of 2.87 and 3.29 angstroms, respectively. The tight pi-[TCNE](2)2- dimer is diamagnetic and has the shortest intradimer [TCNE]*- distance reported. These synthons for [TCNE]*- and [TCNE]2- in metathesis reactions lead to the precipitation of, for example, TlIX (X = Cl, Br, OAc). Reaction of 1 with MnIII(porphyrin)X (X = Cl, OAc) forms the molecule-based magnets of [MnIII(porphyrin)][TCNE] composition, while the reaction of [CrI(C6H6)2]Br and (Me2N)2CC(NMe2)2Cl2, [TDAE]Cl2, with 1 forms [CrI(C6H6)2] [TCNE] and [TDAE][TCNE]2, respectively. The structure of [TDAE][TCNE]2.MeCN was solved and refined in an orthorhombic unit cell at 21 degrees C [I222, a = 10.2332(15), b = 13.341(6), c = 19.907(8) angstroms, V= 2717.7 angstroms3, Z = 4; Dcalcd = 1.216 gcm-3, R=0.083, Romega = 0.104] and exhibits upsilonCN absorptions at 2,193 (m), 2,174 (s), and 2,163 (s) cm-1 consistent with isolated [TCNE](2)2- , in contrast to the aforementioned TlI bound [TCNE](2)2-. The reaction of 2 with [TDAE]Cl2 forms [TDAE]2+[TCNE]2-.

A single-visit cervical carcinoma prevention program offered at an inner city church: A pilot project

BACKGROUND

A single-visit cervical carcinoma prevention program was implemented, integrating screening, diagnosis, treatment, and health education in the familiar environment of the community church.

METHODS

Nonpregnant women age 18 years or older, who had not received cervical carcinoma screening in the preceding year were eligible. Subjects provided information on personal demographics, health, and knowledge regarding cervical carcinoma prevention. Thereafter, cervical cytology was collected, processed, and interpreted on site. Participants attended small-group instruction on cervical carcinoma prevention. Screening results were given to each subject individually. Patients with abnormal cytology underwent immediate colposcopy with biopsies or loop electrosurgical excision procedure as indicated. Participant satisfaction and educational impact were evaluated.

RESULTS

Ninety of the 98 participants reported that Spanish was their native language; 59 did not speak English. Fifty-four had had fewer than 6 years of education and 55 were unemployed. Seventy-eight did not have a regular physician or health insurance. Twenty-four either had never undergone cervical carcinoma screening or had let more than 5 years elapse since their previous examination. None of nine potential barriers assessed correlated with past compliance with cervical carcinoma screening. The mean time for processing and on-site interpretation of cervical cytology smears was 22.6 +/- 5.3 minutes. The median time patients spent in the program was 75 minutes. There was a significant improvement in the subjects' knowledge regarding cervical carcinoma prevention. All participants were highly satisfied.

CONCLUSIONS

This parish-based, integrated, single-visit program for the prevention of cervical carcinoma was easily implemented and provided care to a substantial proportion of underserved patients.

Encoding of target direction and speed during visual instruction and arm tracking in dorsal premotor and primary motor cortical neurons

The encoding of direction and speed in the discharge of dorsal premotor (PMd) and primary motor (MI) neurons was studied during two-dimensional visually-instructed pursuit arm movements in which eight directions and four constant speeds were independently manipulated. Each trial consisted of equal durations of visual observation of target movement without hand movement (cue) and visual pursuit-tracking of the target with the hand (track). A total of 240 neurons was recorded from PMd and MI in two Macaca mulatta monkeys. Two classes of regression analyses were used to relate neuronal firing during the cue and track periods to direction and speed. First, the average firing from each period was fitted to target direction or speed. Period-averaged firing significantly correlated with direction more frequently in the track than in the cue period. Conversely, correlations with speed (with or without direction) were more common in the cue than in the track period. Secondly, a binwise regression evaluated the temporal evolution of firing correlations with direction and speed. Supporting the period-based results, significant binwise correlations of the discharge with speed occurred preferentially during the cue period when there was no hand movement. Prior to movement, correlations of the firing with direction became significant and continued through the movement. Both analyses demonstrated a distinct tendency for neurons to be modulated by speed information early and by direction information later. This temporal parcellation reflects both the sequential demands of the task and constraints placed on the neural computations. The early representation of target speed is hypothesized to reflect the need to calculate a 'go signal' for the initiation of movement.

Familiarity and pronounceability of nouns and names

Ratings of familiarity and pronounceability were obtained from a random sample of 199 surnames (selected from over 80,000 entries in the Purdue University phone book) and 199 nouns (from the Kucera-Francis, 1967, word database). The distributions of ratings for nouns versus names are substantially different: Nouns were rated as more familiar and easier to pronounce than surnames. Frequency and familiarity were more closely related in the proper name pool than the word pool, although both correlations were modest. Ratings of familiarity and pronounceability were highly related for both groups. A production experiment showed that rated pronounceability was highly related to the time taken to produce a name. These data confirm the common belief that there are differences in the statistical and distributional properties of words as compared to proper names. The value of using frequency and the ratings of familiarity and pronounceability for predicting variations in actual pronunciations of words and names are discussed.

Cerebellar Purkinje cell simple spike discharge encodes movement velocity in primates during visuomotor arm tracking

Pathophysiological, lesion, and electrophysiological studies suggest that the cerebellar cortex is important for controlling the direction and speed of movement. The relationship of cerebellar Purkinje cell discharge to the control of arm movement parameters, however, remains unclear. The goal of this study was to examine how movement direction and speed and their interaction-velocity-modulate Purkinje cell simple spike discharge in an arm movement task in which direction and speed were independently controlled. The simple spike discharge of 154 Purkinje cells was recorded in two monkeys during the performance of two visuomotor tasks that required the animals to track targets that moved in one of eight directions and at one of four speeds. Single-parameter regression analyses revealed that a large proportion of cells had discharge modulation related to movement direction and speed. Most cells with significant directional tuning, however, were modulated at one speed, and most cells with speed-related discharge were modulated along one direction; this suggested that the patterns of simple spike discharge were not adequately described by single-parameter models. Therefore, a regression surface was fitted to the data, which showed that the discharge could be tuned to specific direction-speed combinations (preferred velocities). The overall variability in simple spike discharge was well described by the surface model, and the velocities corresponding to maximal and minimal discharge rates were distributed uniformly throughout the workspace. Simple spike discharge therefore appears to integrate information about both the direction and speed of arm movements, thereby encoding movement velocity.

Visuomotor processing as reflected in the directional discharge of premotor and primary motor cortex neurons

Premotor and primary motor cortical neuronal firing was studied in two monkeys during an instructed delay, pursuit tracking task. The task included a premovement "cue period," during which the target was presented at the periphery of the workspace and moved to the center of the workspace along one of eight directions at one of four constant speeds. The "track period" consisted of a visually guided, error-constrained arm movement during which the animal tracked the target as it moved from the central start box along a line to the opposite periphery of the workspace. Behaviorally, the animals tracked the required directions and speeds with highly constrained trajectories. The eye movements consisted of saccades to the target at the onset of the cue period, followed by smooth pursuit intermingled with saccades throughout the cue and track periods. Initially, an analysis of variance (ANOVA) was used to test for direction and period effects in the firing. Subsequently, a linear regression analysis was used to fit the average firing from the cue and track periods to a cosine model. Directional tuning as determined by a significant fit to the cosine model was a prominent feature of the discharge during both the cue and track periods. However, the directional tuning of the firing of a single cell was not always constant across the cue and track periods. Approximately one-half of the neurons had differences in their preferred directions (PDs) of >45 degrees between cue and track periods. The PD in the cue or track period was not dependent on the target speed. A second linear regression analysis based on calculation of the preferred direction in 20-ms bins (i.e., the PD trajectory) was used to examine on a finer time scale the temporal evolution of this change in directional tuning. The PD trajectories in the cue period were not straight but instead rotated over the workspace to align with the track period PD. Both clockwise and counterclockwise rotations occurred. The PD trajectories were relatively straight during most of the track period. The rotation and eventual convergence of the PD trajectories in the cue period to the preferred direction of the track period may reflect the transformation of visual information into motor commands. The widely dispersed PD trajectories in the cue period would allow targets to be detected over a wide spatial aperture. The convergence of the PD trajectories occurring at the cue-track transition may serve as a "Go" signal to move that was not explicitly supplied by the paradigm. Furthermore, the rotation and convergence of the PD trajectories may provide a mechanism for nonstandard mapping. Standard mapping refers to a sensorimotor transformation in which the stimulus is the object of the reach. Nonstandard mapping is the mapping of an arbitrary stimulus into an arbitrary movement. The shifts in the PD may allow relevant visual information from any direction to be transformed into an appropriate movement direction, providing a neural substrate for nonstandard stimulus-response mappings.

A contractile activity that closes phagosomes in macrophages

Studies of Fc-mediated phagocytosis by mouse macrophages identified a contractile activity at the distal margins of forming phagosomes. Time-lapse video microscopic analysis of macrophages containing rhodamine-labeled actin and fluorescein dextran showed that actin was concentrated at the distal margins of closing phagosomes. Phagocytosis-related contractile activities were observed when one IgG-opsonized erythrocyte was engaged by two macrophages. Both cells extended pseudopodia until they met midway around the erythrocyte. It was then constricted and pulled into two phagosomes, which remained interconnected by a string of erythrocyte membrane. Butanedione monoxime, an uncompetitive inhibitor of class II and perhaps other myosins, and wortmannin and LY294002, inhibitors of phosphoinositide 3-kinase, prevented the constrictions without inhibiting the initial pseudopod extension. Immunofluorescence microscopy showed the presence of myosins IC, II, V and IXb in phagosomes. Of these, only myosin IC was concentrated around the strings connecting shared erythrocytes, suggesting that myosin IC mediates the purse-string-like contraction that closes phagosomes. The sequential processes of pseudopod extension and contraction can explain how macropinosomes and spacious phagosomes form without guidance from a particle surface.

Temporal profile of the directional tuning of the discharge of dorsal premotor cortical cells

This study examined the directional modulation of dorsal premotor (PMd) cells as a function of time in an instructed delay, reaching task that systematically varied direction and accuracy constraints. In two monkeys, the activity of 150 PMd cells was recorded and the preferred direction (PD) of the firing as a function of time, the PD trajectory, was calculated. Forty-one cells had nearly continuous significant directional tuning of at least 1 s duration (mean duration 1694 +/- 754 ms) that began in the instructed delay period and continued into the movement period. The PD gradually changed in time (mean change of 47.7 +/- 40.8 degrees), a change best described as a rotation. The change in the directional tuning as a function of time is consistent with the hypothesis that the PMd plays a role in the non-standard mapping of sensory stimuli into motor commands.

Thin-Film Reaction between [alpha]-Fe2O3 and (001) MgO

The kinetics of a thin-film, solid-state reaction were investigated in the spinel-forming oxide system Fe2O3/MgO. In this study, epitactic thin films of Fe2O3 (α, or corundum, structure) were deposited on (001)-oriented MgO using pulsed-laser deposition (PLD). The resulting diffusion couples were then reacted at elevated temperatures in air to induce the reaction between the thin-film and bulk substrate to form the spinel, MgFe2O4. Both the as-deposited and reacted diffusion couples were characterized using low-voltage scanning and transmission electron microscopy. These techniques allow the kinetics of the reaction and the structural properties of the spinel to be investigated.

Targeted disruption of the murine dihydrolipoamide dehydrogenase gene (Dld) results in perigastrulation lethality

The Dld gene product, known as dihydrolipoamide dehydrogenase or the E3 component, catalyzes the oxidation of dihydrolipoyl moieties of four mitochondrial multienzyme complexes: pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain alpha-ketoacid dehydrogenase, and the glycine cleavage system. Deficiency of E3 activity in humans results in various degrees of neurological dysfunction and organic acidosis caused by accumulation of branched-chain amino acids and lactic acid. In this study, we have introduced a null mutation into the murine Dld gene (Dldtm1mjp). The heterozygous animals are shown to have approximately half of wild-type activity levels for E3 and all affected multienzyme complexes but are phenotypically normal. In contrast, the Dld-/- class dies prenatally with apparent developmental delay at 7.5 days postcoitum followed by resorption by 9.5 days postcoitum. The Dld-/- embryos cease to develop at a time shortly after implantation into the uterine wall when most of the embryos have begun to gastrulate. This null phenotype provides in vivo evidence for the requirement of a mitochondrial oxidative pathway during the perigastrulation period. Furthermore, the early prenatal lethal condition of the complete deficiency state may explain the low incidence of detectable cases of E3 deficiency in humans.