Brain and ganglion development from two genotypic classes of cells in allophenic mice.

Several strain-specific markers were found to be histochemically visualizable in parts of the central nervous system in allophenic mice. These markers therefore provide a new basis for mapping the normal developmental lineages of major parts of the nervous system, and for identifying the focus of mutant gene action in some neurological mutations. Cell strains in mosaic animals were visualized on the basis of a quantitative difference in β-galactosidase activity (Bgs-locus), in the Purkinje zone of the cerebellum, and in the hippocampal pyramidal zone of the cerebrum. The differential between strains was increased if the beige ($\text{bg}{}^{\mathrm{J}}\text{bg}{}^{\mathrm{J}}$) mutation was included in the high-activity strain. (β-galactosidase is lysosomal, and enhanced visualization in beige results from its enlarged and aggregated lysosomes.) Purkinje cell-strain visualization was also obtained by an indirect fluorescent antibody technique, in sections treated with antisera containing antibodies against strain-type histocompatibility alloantigens, including H-2. The above markers reveal considerable interspersion of cells from separate lineages in short sequences of each genotype. Purkinje and pyramidal cells of the same brain sometimes differ appreciably in genotypic composition. The enzyme glucosephosphate isomerase was found histochemically to be localized in nerve fibers rather than cell bodies in the brain. However, it was prominent in the cell bodies of the spinal ganglia, so that biochemical determination of ganglion strain-types is possible by means of strain-specific isozymes (Gpi-1-locus). Individual ganglia contained both cell strains and thus are not individually derived as clones from the neural crest.     

Macrophages as effector cells of protective immunity in murine schistosomiasis: IV. Coincident induction of macrophage activation for extracellular killing of schistosomula and tumor cells

Peritoneal macrophages from Schistosoma mansoni-infected mice are activated both for nonspecific tumor cytotoxicity and for killing of skin-stage schistosomula in vitro. In the current study, mechanisms for induction of macrophage tumoricidal and schistosomulacidal activity have been compared. Examination of macrophages activated in vivo by BCG infection or C. parvum treatment, or in vitro by exposure to lymphokine prepared from antigen-stimulated BCG-immune spleen cells, showed that these effector functions were closely linked. Indeed, fractionation of lymphokine-rich supernatant fluids by Sephadex G-100 gel filtraction showed that activities responsible for induction of schistomula killing by inflammatory macrophages and for induction of tumoricidal activity cochromatographed as a single peak in the 50,000 MW region. Thus, development of macrophage-mediated cytotoxicity against these two extracellular (tumor cell or helminth) targets was coincident in several cell populations activated in vivo or in vitro. However, activation for tumoricidal and schistosomulacidal capacity appeared to be quantitatively dissociated in macrophages from mice with chronic schistosomiasis; those cells demonstrated low, yet significant, levels of larval killing ($\text{1}\text{3}$ to $\text{1}\text{5}$ those of BCG or lymphokine-activated cells) but maximal levels of tumor cell cytotoxicity. Furthermore, cytotoxicity by peritoneal cells from S. mansoni-infected mice was not increased in vitro by exposure to lymphokine. Identification of this functional alteration in S. mansoni-activated cells may help to clarify the role of macrophages in the partial immunity against challenge infection which is demonstrated by mice with chronic primary S. mansoni infection.     

Bacterial lipopolysaccharides and mycoplasmal lipoglycans: A comparison between their abilities to induce macrophage-mediated tumor cell killing and Limulus amebocyte lysate clotting

The ability of various bacterial lipopolysaccharides and mycoplasmal lipopolysaccharides (lipoglycans) to induce macrophage-mediated tumor cell killing and $\text{Limulus}$ amebocyte lysate clotting was determined. Lipoglycans from the mycoplasma $\text{Acholeplasma}\text{axantum}$ or $\text{Acholeplasma}\text{granularum}$ had no activity or 10⁴ to 10⁵ less activity than lipopolysaccharides from $\text{Escherichia}\text{coli}$ 0128:B12, $\text{Escherichia}\text{coli}$ K235, or $\text{Salmonella}\text{minnesota}$ R595 in causing $\text{Limulus}$ lysate clotting and tumor cell killing by peritoneal macrophages from normal or bacillus Calmette-Guérin-infected mice. Previous studies have shown that the lipid A portion of bacterial lipopolysaccharide is responsible for the effects on macrophage-mediated tumor cell killing and $\text{Limulus}$ lysate clotting. The known differences in the lipid structures of bacterial lipopolysaccharides and mycoplasmal lipopolysaccharides (lipoglycans) may account for the noted differences in the biologic potencies observed here.     

Plasmodium berghei: Thyroid hyperplasia and thyroid hyperactivity in mice

Statistically significant (P < 0.05) thyroid hyperactivity (¹³¹I% uptakes) occurs on certain days in Plasmodium berghei infected C3H mice. Male mice thyroid glands are made more hyperactive by the malaria than the female glands. Hyperactive thyroid glands may be at least one cause of hypocholesterolemia in plasmodium-infected rodents. Thyroid hyperplasia was found only in experimental mice ($\text{6}\text{20}$ males; $\text{8}\text{20}$ females). A hyperactive thyroid gland appears to be an unreported aspect of experimental acute P. berghei infections in mice. The hyperthyroidism may be due to possible toxic substances acting either directly on the thyroid gland, or indirectly on the hypothalamus affecting TSH production.     

Comparison of genetic and endocrine control of renin and kallikrein in mouse submandibular gland

The effects of strain, sex, hypophysectomy and hormone treatment on mouse submandibular gland renin, kallikrein, S2266 hydrolase, and BAEe esterase activities have been examined. Renin activity is determined by the $\text{Rnr}$ locus on mouse Chromosome 1. Female SWR/J mice ($\text{Rnr}$^$\text{s}$/$\text{Rnr}$^$\text{s}$) have 1000-fold higher submandibular gland renin activity than C57BL/6J mice ($\text{Rnr}$^$\text{b}$/$\text{Rnr}$^$\text{b}$). Both strains have similar kallikrein activity. Renin, BAEe esterase, and S2266 hydrolase are substantially higher in male mice compared to females of the same strain whereas kallikrein is not. Dihydrotestosterone and/or thyroxine treatment induces renin, BAEe esterase, and S2266 hydrolase in female mice with little effect on kallikrein. All four enzyme activities are profoundly reduced by hypophysectomy. Dihydrotestosterone and thyroxine are both required to restore renin, BAEe esterase, and S2266 hydrolase to induced levels. Dihydrotestosterone and.or thyroxine restores kallikrein to control levels. We conclude that renin and kallikrein in the mouse submandibular gland are under different genetic and endocrine control. In addition, the synthetic substrate S2266 is not a specific substrate for kallikrein activity in mouse submandibular gland cytosol.     

Increase of cyclic AMP-dependent protein kinase type II as an early event in hormone-dependent mammary tumor regression.

Primary, 7,12-dimethylbenz(α)anthracene (DMBA)-induced mammary carcinoma in the rat contains cyclic adenosine 3′,5′-monophosphate (cAMP)-dependent and -independent forms of protein kinase. When growth of DMBA-induced tumors was arrested by either ovariectomy or N⁶,O²′-dibutyryl cAMP treatment of the host, the activity of cAMP-dependent protein kinase type II markedly increased in the tumor cytosol, as shown by DEAE-cellulose chromatography and autophosphorylation. The increase in activity of cAMP-dependent protein kinase was also demonstrable in the tumor cytosol and nuclei following $\text{in}$$\text{vitro}$ incubation of tumor slices with cAMP. These results suggest that protein kinase type II is involved in the regression of hormone-dependent mammary tumors.     

Expression of subregion and haplotype preference for H-2Kk restricted cytotoxic T-cell responses in vivo and at the level of the precursor frequencies

Several strains of mice bearing the H-2K^k allele were found to generate in vivo strong CTL responses against TNP-haptenated syngeneic cells, while several other strains of mice were found to generate comparably weak or no responses. C3H × DBA/2)F1 mice (H-2^k × H-2^d) and A/J mice with the recombinant haplotype $\text{H-2}{}^{\mathrm{<mtext>k</mtext><mtext>d</mtext>}}$ generated CTL responses in vivo that were completely restricted toward the H-2^k haplotype or the K end of the $\text{H-2}{}^{\mathrm{<mtext>k</mtext><mtext>d</mtext>}}$ haplotype, respectively. The CTL activity of C3H × DBA/2)F1 and A/J mice against haptenated H-2^k targets was found to be more than 25-fold higher than the CTL activity on H-2^d targets. The CTL responses in vitro under macroculture conditions showed, on the other hand, only a 3- to 6-fold higher cytotoxic activity against the haptenated H-2^k targets as compared with haptenated allogeneic or H-2^d targets; and limiting dilution experiments in microcultures revealed that the CTL precursor frequencies were only 2- to 3-fold smaller for TNP-haptenated H-2^d or haptenated allogeneic targets than for haptenated H-2^k target cells. This indicated that sufficient numbers of H-2^d-restricted and allorestricted CTL precursors were actually present in these strains, but did not develop detectable cytotoxic activity in vivo. The exceptional property of the H-2^k haplotype is, therefore, only partly determined by a difference in the CTL precursor frequencies, and to the larger extent determined at the level of the activation of the CTL response.     

Lymphocyte and macrophage adenyl cyclase activity in animals with enhanced cell-mediated resistance to infection and tumors.

As cyclic AMP has been associated with the inhibition of lymphocyte cytotoxicity, studies were performed to investigate adenyl cyclase activity in lymphocytes and macrophages of Toxoplasma-infected mice in which the efferent limb of the cell-mediated immune response had previously been found to be activated. In peritoneal or splenic lymphocytes from $\text{Balb}\text{c}$ mice chronically infected with Toxoplasma in which growth of an isogeneic bladder tumor was found to be inhibited, adenyl cyclase activity was significantly less than in lymphocytes from uninfected control mice. Stimulation by prostaglandin E₁ or NaF in vitro led to higher levels of adenyl cyclase activity in lymphocytes from unifected animals than in cells from Toxoplasma-infected animals. Similar observations were made with peritoneal macrophages from Toxoplasma-infected and uninfected mice. Lower levels of adenyl cyclase activity were also found in lymphocytes from tumor-bearing mice than in lymphocytes from nontumor-bearing controls. These data suggest that production of cyclic AMP by lymphocytes is inhibited with activation of certain cell-mediated immune functions.     

Trichinella spiralis: genetic basis for differential expression of phase-specific intestinal immunity in inbred mice

Responsiveness of mouse strains after phase-specific immunization with Trichinella spiralis is compared. Two strains ($\text{NFR}\text{N, NFS/N}$) showed strong overall responsiveness. The response type could be characterized in phase-specific terms as: strongly anti-adult, weakly to moderately anti-preadult, and strongly antifecundity. By comparison, congenic mice of the C₅₇B1 $\text{10}\text{Sn}$ background (B10·A, B10·D₂, B10·S, B10·Q) displayed poor total responses that could be characterized as: weakly anti-adult, very weakly anti-preadult, weakly anti-fecundity after preadult immunization, and mixed (weak and strong) after adult immunization. The $\text{C}{}_3\text{H}\text{HeJ}$ mouse appeared to be intermediate between the B10·BR and the $\text{NFR}\text{N}$ strains in overall responsiveness. Genetic determinants of anti-preadult or anti-adult responses of $\text{NFR}\text{N}$ strain mice were dominant over their B10 congenic counterparts as shown in F₁, crosses of $\text{NFR}\text{N}$ × B1O·BR mice. Since the $\text{NFR}\text{N}$ (predominantly H-2^q) and the $\text{NFS}\text{N}$ (H-2^S) are both strong responders, while the B10·Q(H-2^q) and B10·S (H-2^S) are weak, it is suggested that the major genes controlling anti-preadult and anti-adult responses are not linked to the major histocompatibility complex. However, variations in anti-adult immunity and anti-fecundity in the B10 congenic mice (B10·Q and B10·S are the strongest responders) suggest that minor genes linked to the MHC exert some control over these responses. Some evidence was obtained for gene complementation as the F₁ cross of $\text{NFR}\text{N}$ and $\text{NFS}\text{N}$ mice responded more vigorously than the parental lines. We conclude that multiple genes determine anti-T. spiralis intestinal responses in mice. The major genes are unlinked to the major histocompatibility complex whereas several minor genes are linked.     

Separation of acetanilide and its hydroxylated metabolites and quantitative determination of "acetanilide 4-hydroxylase activity" by high-pressure liquid chromatography.

A simple and very sensitive method for the separation of 4-hydroxyacetanilide, 3-hydroxyacetanilide, 2-hydroxyacetanilide, and acetanilide was developed with the use of high-pressure liquid chromagraphy. Each of these phenolic derivatives can be separated completely from acetanilide and from one another. A simple assay for “acetanilide 4-hydroxylase activity” is thus described. The limit of sensitivity for cytochrome P-450-mediated acetanilide 4-hydroxylase activity is estimated to be 1.0 pmol/min/mg microsomal protein, thereby allowing this assay to be useful in detecting monooxygenase activity in “low level” nonhepatic tissues. Hepatic acetanilide 4-hydroxylase activity is induced about fourfold in $\text{C57BL}\text{6N}$ mice by 3-methylcholanthrene. Although acetanilide 2-hydroxylase activity is about seven times lower than the 4-hydroxylase activity, the 2-hydroxylase is also induced about three- or fourfold in $\text{C57BL}\text{6N}$ mice by 3-methylcholanthrene. The “2-hydroxylase activity” cannot, however, be strictly quantitated under the conditions described herein. The K_m values of both the 3-methylcholanthrene-induced and control 4-hydroxylase activity are about 0.55 mm; V_max values for 3-methylcholanthrene-treated and control mice, respectively, are 4.9 ± 1.1 and 1.1 ± 0.31 nmol/min/mg microsomal protein. The 4-hydroxylase in the liver of both 3-methylcholanthrene-treated and control mice appears to represent two or more catalytic activities, i.e., two or more forms of P-450 having widely differing affinities for the substrate acetanilide.     

Trichomonas vaginalis: Dependence of resistance among different mouse strains upon the non-H-2 gene haplotype,sex, and age of recipient hosts

The genetic control of resistance or susceptibility to Trichomonas vaginalis infection has been studied in mice of various strains infected by different routes. $\text{BALB}\text{c}$ and $\text{DBA}\text{2}$ female mice appear to be highly susceptible to intraperitoneal, subcutaneous, or intravaginal infection by T. vaginalis. By contrast, female mice on A background are resistant to T. vaginalis infection via any route. $\text{C}\text{57}\text{BL}\text{6}$ and C3H female mice display intermediate levels of resistance following intraperitoneal or subcutaneous inoculum, whereas they display high levels of resistance to intravaginal infection. On the other hand, susceptibility or resistance to T. vaginalis infection appears to be influenced by the host sex, since males inoculated subcutaneously display much higher levels of resistance than females of the same strain. Lastly, the age of the host seems to play an important role in determining the course of infection. Susceptibility to T. vaginalis decreases with age, being maximal at 3–4 weeks and minimal at 40–42 weeks. All together these results suggest that resistance or susceptibility to T. vaginalis infection is regulated by genes mapping outside the major histocompatibility complex (H-2 in the mouse), whose activity is modulated by the anatomic site first coming into contact with the protozoon, the sex, and the age of the recipient host.     

Compound 4880 is a selective and powerful inhibitor of calmodulin-regulated functions

Compound $\text{48}\text{80}$, a condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde, is composed of a family of cationic amphiphiles differing in the degree of polymerization. Compound $\text{48}\text{80}$ was found to be a potent inhibitor of the calmodulin-activated fraction of brain phosphodiesterase and red blood cell Ca²⁺-transport ATPase, with IC₅₀ values of 0.3 and 0.85 μg/ml, respectively. However, the basal activity of both enzymes is not at all suppressed by the drug at concentrations up to 300 μg/ml. Inhibition of Ca²⁺ transport into inside-out red blood cell vesicles by compound $\text{48}\text{80}$ follows a similar pattern in that basal, calmodulin-independent, transport is also not affected by the drug. Kinetic analysis revealed that the stimulation of Ca²⁺-transport ATPase induced by calmodulin is inhibited by compound $\text{48}\text{80}$ according to a competitive mechanism. It was demonstrated that the inhibitory constituents of compound $\text{48}\text{80}$ bind to calmodulin in a Ca²⁺-dependent fashion. Comparison of the specificity of several anti-calmodulin drugs showed that compound $\text{48}\text{80}$ is the most specific inhibitor of the calmodulin-dependent fraction of red blood cell Ca²⁺-transport ATPase that has been described hitherto. In addition, compound $\text{48}\text{80}$ was found to be a rather specific inhibitor of the calmodulin-induced activation of Ca²⁺-transport ATPase when compared with the stimulation induced by an anionic amphiphile or by limited proteolysis. Half-maximal inhibition of the activity stimulated by oleic acid or mild tryptic digestion required 8- and 32-times higher concentrations of compound $\text{48}\text{80}$, respectively, compared with the calmodulin-dependent fraction of the ATPase activity. Moreover, calmodulin-independent systems as rabbit skeletal muscle sarcoplasmic reticulum Ca²⁺-transport ATPase or calf cardiac sarcolemma (Na⁺ + K⁺)-transport ATPase are far less influenced by compound $\text{48}\text{80}$ as compared with trifluoperazine and calmidazolium. Because of its high specificity compound $\text{48}\text{80}$ is proposed to be a promising tool for studying calmodulin-dependent processes.     

Lymphocyte function in experimental African trypanosomiasis. IV. Immunosuppression and suppressor cells in the athymic nu/nu mouse

The role of T cells in the development and expression of antigen-nonspecific immunosuppression in experimental African trypanosomiasis was addressed. Nude ($\text{nu}\text{nu}$) C57BL/ 6 NIH mice and their thymus-bearing ($\text{nu}\text{+}$) littermates were infected with Trypanosoma rhodesiense and examined for suppression of splenic B-cell responses in vitro to the mitogen LPS. All animals developed splenic unresponsiveness to LPS. Further, both nu/nu and nu/ + infected mice displayed suppressor cell activity in their spleen cell populations upon transfer to normal uninfected mouse spleen cell cultures. On the basis of these findings we suggest that both the generalized immunosuppression and the development of suppressor cell activity in the spleens of mice infected with T. rhodesiense are T-independent processes.     

An analysis of the natural killer cell defect in beige mice

Although C57BL/6 bg^J/bg^J mice exhibit very low or undetectable levels of endogenous natural killer cell activity, such activity can be induced by the administration of BCG or tilorone hydrochloride to these animals. This cytotoxic activity has been shown to be due to NK cells by the criteria of nylon-wool nonadherence and of effector cell sensitivity to treatment with either anti-asialo GM₁ serum or high concentrations of anti-Thy 1.2 serum, in the presence of complement. Even after the administration of inducing agents, however, beige mice continue to display significantly less NK activity than do their heterozygous littermates. In an attempt to ascertain what cell might be defective in responding to induction, we utilized an in vitro system in which the induction of NK activity by poly I:C in a nylon-wool nonadherent population is dependent upon plastic-adherent cells. We found that adherent cells from either beige or heterozygous mice were indistinguishable in their ability to restore the NK response of nylon-wool-nonadherent spleen cells stimulated with poly I:C. This was true when either beige or heterozygous mice were used as the source of responder cells. Thus, it appears that the defect in responsiveness to inducing agents may reside in the beige NK cell itself.     

Cellular aspects of tolerance. IV. Strain variations of tolerance induceability

The antibody response to RGG of 8-wk old mice of various strains was assessed in terms of half-lives ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) of lightly iodinated rabbit gamma globulin (¹³¹I-RGG) elimination. $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ was increased if the small aggregate content in ¹³¹I-RGG was reduced. The effect of aggregates was least in AKR, largest in Balb/c and SJL and intermediate in the majority of strains, typified by A mice. Differences between various strains, in the degree of tolerance to aggregate freed RGG (centrifuged at 123,000 g), were observed. The level of residual responsiveness was greatest in SJL mice. More profound tolerance could be induced with biofiltered RGG. Resistance of SJL mice to tolerance induction was also observed when human gamma globulin (HGG) and bovine serum albumin served as tolerogen. Tolerance to RGG and sheep red cells was induced in cyclophosphamide-treated SJL animals.     

Procedure for measurement of amino acid transport from blood to brain in small animals

The exponential plasma specific activity curve 2.5 to 12.5 min after injection (sc) of [¹⁴C]tyrosine was integrated and divided by time to obtain the mathematical relationship between the average equivalent specific activity $\text{S}$ and the measured specific activity S in any individual animal. $\text{S}$ is the constant, average value of S that is equivalent to the curvllinearly varying quantity that the body tissues are actually exposed to. Dividing the total brain radioactivity by $\text{S}$ gave the tissue Tyr uptake U. The function $\text{dU}\text{dt}$ is linear from 2.5 to 12.5 min and represents the rate of uptake of the amino acid. Incorporation into protein was similarly measured. Brain uptake of Tyr averaged 7.06, and the apparent protein incorporation was 1.99 nmol/g of brain per min. The γ-glutamyl cycle inhibitor l-methionine-RS-sulfoximine reduced total brain uptake of tyrosine by 42.8% and the apparent rate of protein incorporation by 39.0%.     

Increased synthesis of L-glycerol 3-phosphate dehydrogenase during in vitro differentiation of reaggregating cerebellar cells

Reaggregating cell cultures of neonatal mouse cerebellar cells express many of the differentiated properties of normal developing cerebellum, including the transition for the embryonic and adult isozymes of l-glycerol 3-phosphate dehydrogenase (EC 1.1.1.8). In order to determine the mechanism leading to increased levels of adult isozyme, aggregates in culture from 2 to 17 days were labeled with radioactive leucine and the relative rate of enzyme synthesis was measured after purification of the enzyme by affinity chromatography on Blue Sepharose 6B. During the course of in vitro differentiation, the relative rate of synthesis increased 100-fold, such that it represented 0.5% of the total protein synthesized in the cytoplasmic fraction of the cell. In vivo, $\text{BALB}\text{cBy}$ mice have twice the level of enzyme activity in the cerebellum as do $\text{C57BL}\text{6J}$ mice. Reaggregating cell cultures of cerebellar cells from these strains of mice also express a difference in the activity level, but only when the cerebellar cells are taken from mice 4 days of age or less. When the relative rates of synthesis of l-glycerol 3-phosphate dehydrogenase were measured in cultures expressing the strain-dependent difference in activity, these rates were found to be approximately twofold greater in cultures of $\text{BALB}\text{cBy}$ cells. In contrast, estimates of the relative rate of enzyme degradation by the double-isotope labeling technique indicate that neither specific enzyme degradation nor degradation of total protein is different in aggregates from the two strains of mice. The results suggest that the genetic mechanisms controlling the levels of l-glycerol 3-phosphate dehydrogenase in the cerebellum during development are intrinsic to the cells and, with the exception of serum factors, are independent of systemic influences.     

Defect in 3'-phosphoadenosine 5'-phosphosulfate synthesis in brachymorphic mice. II. Tissue distribution of the defect

The tissue distribution of the defective PAPS synthetic pathway in homozygous brachymorphic mice ($\text{bm}\text{bm}$) has been investigated using four different criteria: (i) incorporation of ³⁵SO₄^2? into adenosine 5′-phosphosulfate (APS), 3′-phosphoadenosine 5′-phosphosulfate (PAPS), and endogenous macromolecular acceptors, (ii) APS kinase (adenylylsulfate kinase; ATP:adenylylsulfate 3′-phosphotransferase, EC 2.7.1.25) activity, (iii) ATP sulfurylase (sulfate adenylyltransferase; ATP:sulfate adenylyltransferase, EC 2.7.7.4) activity, (iv) thermostability of ATP sulfurylase. With respect to the first three criteria, the results indicate that liver is affected as profoundly as cartilage (K. Sugahara and N. B. Schwartz, Arch. Biochem. Biophys. (1982) 214, 589–601). In contrast, skin and brain show no differences between normal and mutant. Kidney is significantly, but only moderately, affected. The results from thermostability studies demonstrate that ATP sulfurylase activity is more labile in $\text{bm}\text{bm}$ cartilage, liver, and kidney, but not in skin or brain, supporting the above-observed distribution of the defect. Therefore, the present results indicate a multiple, but not universal, tissue distribution of the defective PAPS synthetic pathway in $\text{bm}\text{bm}$ mice. Furthermore, these findings support the suggestion that ATP sulfurylase as well as APS kinase is defective in brachymorphic mice.     

Met-tRNAfMet binding in murine dystrophy

Dystrophic mice of the C57B1 $\text{dy}{}^{\mathrm{2J}}\text{dy}{}^{\mathrm{2J}}$ strain and of the ReJ 129 $\text{dy}\text{dy}$ strain and littermate controls were used to prepare met-tRNA^fMet binding factors. The tissues were homogenized and fractions were obtained which contained ribosomes. The binding factors were assayed by the binding of [³⁵S]methionyl-tRNA to control liver ribosomes. The binding, i.e. eukaryotic initiation factor 2 (elF 2) activity, was measured in brain, liver and muscle and in all of these tissues there was a significant decrease in the dystrophic mice. This decrease in initiation factor activity of hindleg muscle resembled, in the direction of the effect, the decrease in elongation factor activity of hindleg muscle resembled, in the of $\text{dy}\text{dy}$ mice previously reported by our laboratory. Thus these two defects, taken together may help to explain the marked wasting of the muscles. The decrease in brain in both strains provides evidence for nervous tissue involvement in genetic dystrophy.