Better early outcome with enteral rather than parenteral nutrition in children undergoing MAC allo-SCT

There is no consensus on the type of nutritional support to introduce in children undergoing allogeneic stem cell transplantation (allo-SCT) after myeloablative conditioning (MAC). This retrospective, multicenter, observational study compared the early administration of enteral nutrition (EN group, n = 97) versus parenteral nutrition (PN group, n = 97) in such patients with matching for important covariates. The primary endpoint was the study of day 100 overall mortality. The early outcome at day 100 was better in EN group regarding mortality rate (1% vs. 13%; p = 0.0127), non relapse mortality (1% vs. 7%; p = 0.066), acute GVHD grades II-IV (37% vs. 54%; p = 0.0127), III-IV (18% vs. 34%; p = 0.0333) and its gut localization (16% vs. 32%; p = 0.0136). Platelet engraftment was better in EN group than in PN group for the threshold of 20 G/L (97% vs. 80% p < 0.0001) and 50 G/L (92% vs. 78%, p < 0.0001). The length of stay was shorter in EN group (28 vs. 52 days, p < 0.0001). There were no differences between the two groups regarding the polynuclear neutrophil engraftment, infection rate or mucositis occurrence. These results suggest that, in children undergoing MAC allo-SCT, PN should be reserved to the only cases when up-front EN is insufficient or impossible to perform.

[Superior vena cava thrombosis in patients with mediastinal large B-cell lymphoma: two pediatric cases]

We report two pediatric cases of superior vena cava thrombosis (VTE) in patients treated for primary mediastinal large B-cell lymphoma (PMBCL). PMBCL is a rare entity in children and adolescents and no thrombosis has been described in this population. Thrombosis in lymphoma is frequently asymptomatic, detected as an incidental finding in the first months following diagnosis. The thrombosis mechanisms are often multifactorial based on veinous compression by the mass, elevated risk of thrombosis in neoplasia, and/or presence of a central catheter. The risk factors of venous thromboembolism (VTE) in lymphoma are high-grade lymphoma, comorbidities, central nervous system lymphoma, and mediastinal mass. Because thrombosis has an impact on prognosis and treatment, it seems important to improve knowledge in order to improve the diagnosis and prevention of thrombosis in lymphoma.

[Cutaneous polymorph manifestations of familial Mediterranean fever in a child]

We describe the case of a 4-year-old child with Mediterranean fever characterized by cutaneous features. Familial Mediterranean fever is an autosomal recessive disorder characterized by recurrent attacks of fever and polyserositis including peritonitis, pleuritis, and arthritis. Skin involvement is less common. In our case, the successively patient presented erysipelas-like erythema, edemas of the palmar and plantar regions, and purpuric lesions. From these clinical observations, several diagnoses were raised: infectious erysipelas, Kawasaki disease, Henoch-Schönlein purpura, and familial Mediterranean fever. Only the latter diagnosis was confirmed after exploration and then confirmed with genetic analysis, which found a M694V homozygous mutation. Erysipelas-like erythema is the most frequent cutaneous sign reported in the literature and the only one to be associated with the M694V homozygous mutation. The originality of this case is the dominancy and polymorphism of the skin lesions.

Transcriptional recapitulation and subversion of embryonic colon development by mouse colon tumor models and human colon cancer

Colon tumors from four independent mouse models and 100 human colorectal cancers all exhibited striking recapitulation of embryonic colon gene expression from embryonic days 13.5-18.5.

Background

The expression of carcino-embryonic antigen by colorectal cancer is an example of oncogenic activation of embryonic gene expression. Hypothesizing that oncogenesis-recapitulating-ontogenesis may represent a broad programmatic commitment, we compared gene expression patterns of human colorectal cancers (CRCs) and mouse colon tumor models to those of mouse colon development embryonic days 13.5-18.5.

Results

We report here that 39 colon tumors from four independent mouse models and 100 human CRCs encompassing all clinical stages shared a striking recapitulation of embryonic colon gene expression. Compared to normal adult colon, all mouse and human tumors over-expressed a large cluster of genes highly enriched for functional association to the control of cell cycle progression, proliferation, and migration, including those encoding MYC, AKT2, PLK1 and SPARC. Mouse tumors positive for nuclear β-catenin shifted the shared embryonic pattern to that of early development. Human and mouse tumors differed from normal embryonic colon by their loss of expression modules enriched for tumor suppressors (EDNRB, HSPE, KIT and LSP1). Human CRC adenocarcinomas lost an additional suppressor module (IGFBP4, MAP4K1, PDGFRA, STAB1 and WNT4). Many human tumor samples also gained expression of a coordinately regulated module associated with advanced malignancy (ABCC1, FOXO3A, LIF, PIK3R1, PRNP, TNC, TIMP3 and VEGF).

Conclusion

Cross-species, developmental, and multi-model gene expression patterning comparisons provide an integrated and versatile framework for definition of transcriptional programs associated with oncogenesis. This approach also provides a general method for identifying pattern-specific biomarkers and therapeutic targets. This delineation and categorization of developmental and non-developmental activator and suppressor gene modules can thus facilitate the formulation of sophisticated hypotheses to evaluate potential synergistic effects of targeting within- and between-modules for next-generation combinatorial therapeutics and improved mouse models.

Enumeration of waterborne Escherichia coli with petrifilm plates: comparison to standard methods

Escherichia coli is often monitored in environmental waters as an indicator of the possible presence of human pathogens associated with feces. Petrifilm E. coli/coliform count plates (3M, Minneapolis, MN), previously validated for enumerating E. coli in food, were tested for monitoring E. coli in environmental water. Escherichia coli counts in environmental water samples enumerated with Petrifilm were significantly correlated (R > 0.9; slope = 0.9-1.0; p < 0.001) with counts obtained with three commonly used methods, mTEC (Becton Dickinson, Sparks, MD), m-ColiBlue (Hach, Loveland, CO), and Colilert-18/IDEXX Quanti-Tray 2000 (IDEXX, Westbrook, ME). Blue colonies on Petrifilm plates were most reliably identified as E. coli when accompanied by gas formation, as determined by characterization of the colonies on MacConkey agar plates (PML Microbiologicals, Mississauga, ON, Canada) and by polymerase chair reaction (PCR) with E. coli-specific primers. The main disadvantage of Petrifilm plates for environmental water testing is the small volume (1 mL per sample) that can be tested; however, the plates appear to be suitable for screening and locating sites that exceed criteria for total body and partial body contact. Simplicity of use and storage, reliability, and relatively low cost make Petrifilm plates suitable for volunteer-based and educational water quality monitoring applications, particularly when used as a preliminary screening method to identify problem sites.

PPAR alpha is necessary for the lipopenic action of hyperleptinemia on white adipose and liver tissue

Adenovirus-induced hyperleptinemia causes rapid disappearance of body fat in normal rats, presumably by up-regulating fatty acid oxidation within white adipocytes. To determine the role of peroxisomal proliferation-activated receptor (PPAR)alpha expression, which was increased during the rapid loss of fat, we infused adenovirus-leptin into PPAR alpha(-/-) and PPAR alpha(+/+) mice. Despite similar degrees of hyperleptinemia and reduction in food intake, epididymal fat pad weight declined 55% in wild-type but only 6% in PPAR alpha(-/-) mice; liver triacylglycerol fell 39% in the wild-type group but was unchanged in PPAR(-/-) mice. Carnitine palmitoyl transferase-1 mRNA rose 52% in the wild-type mice but did not increase in PPAR alpha(-/-) mice. PPAR gamma coactivator-1 alpha rose 3-fold in the fat and 46% in the liver of wild-type mice but was unchanged in PPAR alpha(-/-) mice. Although AMP-activated protein kinase could not be implicated in the lipopenic actions of hyperleptinemia, acetyl CoA carboxylase protein was reduced in the liver of wild-type but not in PPAR alpha(-/-) mice. Thus, in PPAR alpha(-/-) mice, up-regulation of carnitine palmitoyl transferase-1 mRNA in fat, down-regulation of acetyl CoA carboxylase in liver, and up-regulation of PPAR gamma coactivator-1 alpha mRNA in both tissues are abolished, as is the reduction in their triacylglycerol content.

Do multi-sectoral development programmes affect health? A Bolivian case study

This cross-sectional study, carried out in Inquisivi, Bolivia, a rural area where Save the Children/US works, tests the hypothesis that participation in multisectoral development programmes results in improved health behaviours and better health outcomes. To test this hypothesis, four groups of households were compared: those participating in Save the Children's health-only programmes; those with access to health and micro-enterprise credit or health and literacy programmes; those participating in all three programmes (health, credit and literacy); and households from comparison communities (no access to any of Save the Children's programmes). Data come from a stratified sample of 499 households in the altiplano, foothills and valleys of the Andes. Findings reported here suggest that there is no clear association between participation in one or more of Save the Children's programmes and parents' actions to prevent and treat diarrhoea. Additionally, the point prevalence of diarrhoea was similar for all four groups. However, children of individuals participating in health, credit and literacy were significantly less likely than children from comparison communities to be malnourished or at risk of becoming malnourished, even after controlling for such potentially confounding factors as social class, source of drinking water, and the availability of health facilities.

Quantitative detection of hepatitis B virus by transcription-mediated amplification and hybridization protection assay

We have developed a sensitive and quantitative assay using transcription-mediated amplification and hybridization protection assay for the detection of hepatitis B virus (HBV) DNA in serum. The transcription-mediated amplification was carried out in a single tube. The hybridization protection assay was carried out in a microtiter plate with two probes with different specific activities to obtain a broad detection range. As a result, the assay had a detection range of 5 x 10(3) to 5 x 10(8) genome equivalents (GE)/ml and good quantitative accuracy on a logarithmic scale. A moderately sized manual assay run can be completed within 5 h. Measurements of the amounts of HBV DNA in clinical samples by the assay showed the amounts under various disease conditions to be widely distributed (more than 5 logs, from approximately 5 x 10(3) to 5 x 10(8) GE/ml). It was also shown that the amount of HBV DNA in one chronic hepatitis patient varied widely, with a range of more than 5 logs during long-term monitoring. Our assay has the potential to be used to monitor and determine the prognosis of HBV patients and carriers, especially during interferon treatment.

Blood platelet function in healthy individuals of different ages. Effects of exercise and exercise conditioning

The influence of age, physical conditioning and physical exercise on platelet function on human being is still controversial. The aim of our study were to evaluate the effect of physical exercise on platelet activation measured by beta-thromboglobulin (beta-TG) levels and the number of platelets in sedentary and athlete subjects of different ages, and also to investigate the response of these parameters during the period of recover immediately after a bicycle exercise test. Our results show differences in platelet count and beta-TG levels among the experimental groups studied, in basal conditions, in response to the exercise test and during postexercise period. These results seem to indicate that regardless age, regular physical exercise diminish age negative effects on platelet aggregation.

Predilection of brain metastasis in gray and white matter junction and vascular border zones

BACKGROUND

The purpose of this study was to asses the importance of the vascular border zone and the gray and white matter junction on the distribution of brain metastases.

METHODS

We reviewed the medical records, computed tomography (CT) of magnetic resonance imaging (MRI) of 105 patients with secondary brain tumors. The metastatic lesions noted on CT scans of MRI ere matched with a predetermined standard sheet containing axial images with shading on the border zones. To be included in the border zones, the center on more than 50% of the lesion had to be situated within these zones.

RESULTS

Among 100 evaluable patients, there were 302 metastatic brain lesions. Of the 302 lesions, 210 lesions were 2 cm or smaller in greatest dimension and located in the cerebral and cerebellar hemispheres. The major vascular border zones were the site of predilection for 103 lesions (62%) although the border zones constitute only 29% of the area. Gray and white matter junction was the preferred site for 135 lesions (64%).

CONCLUSION

The results demonstrated that brain metastasis occurs in the vascular border zone regions and the gray and white matter junction more frequently than previously recognized, and also supported the notion that metastatic emboli tend to lodge in an area of sudden reduction of vascular caliber (gray/white matter junction) and in the area most distal vascular field (border zone).

Arthrodiastasis for stiff hips in young patients

Joint distraction (arthrodiastasis) with a unilateral fixator was used to treat 9 patients with stiffness of the hip which had followed Perthes' disease (3), epiphysiolysis (2), congenital dysplasia (2), tuberculosis (1) and idiopathic chondrolysis (1). Their average age was 14 years, and they all had pain, limp and shortening of the leg. Distraction of 0.5 to 1 cm was maintained for an average of 94 days. The average range of movement subsequently was 65 degrees compared with 20 degrees before. The articular space was widened by an average of 2.8 mm, and only 3 patients had pain on follow up.

Progressive stages of "transdifferentiation" from epidermal to mesenchymal phenotype induced by MyoD1 transfection, 5-aza-2'-deoxycytidine treatment, and selection for reduced cell attachment in the human keratinocyte line HaCaT

The ability of the myogenic determination gene (MyoD1) to convert differentiating human keratinocytes (HaCaT cell-line) to the myogenic pathway and the effect of MyoD1 on the epidermal phenotype was studied in culture and in surface transplants on nude mice. MyoD1 transfection induced the synthesis of myosin, desmin, and vimentin without substantially altering the epidermal differentiation properties (morphology, keratin profile) in vitro nor epidermal morphogenesis (formation of a complex stratified squamous epithelium) in surface transplants, demonstrating the stability of the keratinocyte phenotype. 5-Aza-CdR treatment of these MyoD1-transfected cells had little effect on the cultured cells but a morphologically unstructured epithelium was formed with no indications of typical cell layers including cornification. Since prevention of epidermal strata in transplants was not accompanied by blocked epidermal differentiation markers (keratins K1 and K10, involucrin, and filaggrin), the dissociation of morphogenesis and expression of these markers argues for independently controlled processes. A subpopulation of less adhesive cells, isolated from the 5-aza-CdR treated MyoD1-transfectants, had lost most epithelial characteristics in culture (epidermal keratins, desmosomal proteins, and surface-glycoprotein Gp90) and had shifted to a mesenchymal/myogenic phenotype (fibroblastic morphology, transactivation of Myf3 and myogenin, expression of myosin, desmin, vimentin, and Gp130). Moreover, the cells had lost the ability to stratify and remained as a monolayer of flat elongated cells in transplants. These subsequent changes from a fully differentiated keratinocyte to a mesenchymal/myogenic phenotype strongly argue for a complex "transdifferentiation" process which occurred in the original monoclonal human epidermal HaCaT cells.

Changes in the allelic methylation patterns of c-H-ras-1, insulin and retinoblastoma genes in human development

The methylation status of the c-H-ras-1, insulin and retinoblastoma genes was determined in human sperm, hydatidiform mole, fetal tissues, adult lymphocytes and adult kidney. Individual alleles of c-H-ras-1 and insulin were distinguishable due to presence of endogenous variable number of tandem repeat (VNTR) polymorphisms. Both alleles of the latter two genes were extensively methylated in sperm compared to the other tissues. Several sites within these genes were less methylated in fetal tissues and the two alleles were differentially methylated in some cases. The retinoblastoma gene was highly methylated in all tissues examined, with the exception of a single site that was under-methylated in sperm only. The sperm-specific methylation patterns in all three genes could represent imprinting of the parental chromosomes. Since 5-methylcytosine is inherently mutagenic, it is possible that methylation imprinting could alter the susceptibilities of human genes to point mutations.

Methylation and expression of the Myo D1 determination gene

Mouse embryo cells induced to differentiate with the demethylating agent 5-azacytidine represent an excellent model system to investigate the molecular control of development. Clonal derivatives of 10T1/2 cells that have become determined to the myogenic or adipogenic lineages can be isolated from the multipotential parental line after drug treatment. These determined derivatives can be cultured indefinitely and will differentiate into end-stage phenotypes on appropriate stimulation. A gene called Myo D1, recently isolated from such a myoblast line, will confer myogenesis when expressed in 10T1/2 or other cell types (Davis et al. 1987). The cDNA for Myo D1 contains a large number of CpG sequences and the gene is relatively methylated in 10T1/2 cells and an adipocyte derivative, but is demethylated in myogenic derivatives. Myo D1 may therefore be subject to methylation control in vitro. On the other hand, preliminary observations suggest that Myo D1 is not methylated at CCGG sites in vivo so that a de novo methylation event may have occurred in vitro. These observations may have significance in the establishment of immortal cell lines and tumours.

Expression of the MyoD1 muscle determination gene defines differentiation capability but not tumorigenicity of human rhabdomyosarcomas

Several human rhabdomyosarcoma cell lines, cultured primary tumor explants, and biopsies of tumor and normal skeletal muscle tissue expressed a 2.0-kilobase transcript that hybridized to the mouse muscle determination gene MyoD1. This transcript was found in tumor cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines derived from other mesenchymal tumor cell types. Expression of the human homolog of MyoD1 therefore can define a tumor as a rhabdomyosarcoma. Transfection of the mouse MyoD1 gene into the human rhabdomyosarcoma cell line RD increased the ability of the tumor cells to differentiate into multinucleated myotubes and enhanced myosin heavy-chain gene expression but did not decrease tumorigenicity in nude mice.

The effect of cyclic AMP on neuritic outgrowth in explant cultures of developing chick olfactory epithelium

The effect of cyclic AMP (cAMP) analogs and phosphodiesterase (PDE) inhibitors on neurite outgrowth was studied in explant cultures of olfactory neurons. Nasal pits from 5- or 6-day-old chick embryos were minced, explanted into culture dishes, and grown in a serum-free medium. One of the cyclic AMP analogs, dibutyryl cyclic AMP (dbcAMP) or 8-bromo-cyclic AMP (8-Br-cAMP), or one of the PDE inhibitors, theophylline or isobutylmethylxanthine (IBMX), was added to the culture medium. The explants were examined for neurite outgrowth after 2 days in vitro. Db-cAMP increased the number of explants expressing neurites by 25-35% over control cultures, whereas 8-Br-cAMP had essentially no effect at the same concentrations. Addition of dibutyryl cyclic GMP (dbcGMP) gave no increase in neurite outgrowth, thus indicating that the effect of enhancing neuritic growth is specific to cAMP and not cyclic nucleotides in general. The resulting increase in neurite outgrowth is due to the cyclic nucleotide component of dbcAMP, since both IBMX and theophylline, which elevate intracellular cAMP, also increased neurite outgrowth significantly. When forskolin was added to the culture medium, there was a trend to increased neurite outgrowth; this was significantly enhanced when a subthreshold concentration of theophylline was added in addition to the forskolin.

Effect of cellular determination on oncogenic transformation by chemicals and oncogenes

Three developmentally determined myogenic cell lines derived from C3H 10T1/2 C18 (10T1/2) mouse embryo cells treated with 5-azacytidine were compared with the parental 10T1/2 line for their susceptibility to oncogenic transformation by 3-methylcholanthrene or the activated human c-Ha-ras oncogene. Neither the 10T1/2 cells nor the myogenic derivatives grew in soft agar or formed tumors in nude mice. In contrast to 10T1/2 cells, the three myogenic derivatives were not susceptible to transformation by 3-methylcholanthrene, so that cellular determination altered the response of 10T1/2 cells to chemical carcinogen. On the other hand, all cell types were transformed to a tumorigenic phenotype following transfection with the activated c-Ha-ras gene. The transfected myogenic cells expressed both the c-Ha-ras gene and the muscle determination gene MyoD1. In contrast to other reports, the presence of as many as six copies of the c-Ha-ras gene per genome did not prevent the formation of striated muscle cells which expressed immunologically detectable muscle-specific myosin. The expression of the c-Ha-ras gene does not therefore necessarily preclude the expression of the determination gene for myogenesis or prevent end-stage myogenic differentiation.

The effect of amitriptyline on growth of olfactory and cerebral neurons in vitro

The tricyclic antidepressant drug amitriptyline has a detrimental effect on neurite outgrowth in primary explant cultures containing either olfactory receptor neurons or cerebral neurons, from both rat and chick embryos. When the drug is added to the culture medium in doses similar to the plasma concentrations known to be therapeutic in humans, the number of explant cultures expressing neurites is significantly reduced. In higher doses, amitriptyline reduces the amount of olfactory marker protein synthesized by organ cultures of olfactory mucosa.

Osteomyelitis associated with pressure ulcers

Bone biopsies were performed in spinal cord injured patients with pressure ulcers in whom osteomyelitis was suspected. Roentogenograms and bone and gallium scans were also evaluated to determine their usefulness in diagnosing osteomyelitis. Infected bone underlying pressure ulcers revealed only mild focal inflammatory changes which did not correlate well with x-ray and nuclear scan abnormalities. Negative scans, however, essentially ruled out osteomyelitis. There was no clear association of delayed healing or recurrence of pressure sore with osteomyelitis. Antibiotic therapy of greater than three weeks' duration did not significantly affect the outcome of the disease.

Cell and explant culture of olfactory chemoreceptor cells

An in vitro system for the study of maturation of rat and chick embryonic olfactory receptor cells is presented. A variety of dissociating agents, culture media and substrata were tried in attempts to obtain a preparation of mature living olfactory receptor cells readily visible in the microscope. Maturation was judged by the development of axons greater than 1 mm long, by the presence of cilia at the end of the dendrites and, in the rat, by the presence of immunohistochemically demonstrable olfactory marker protein, a protein present only in olfactory receptor cells. By these criteria, dissociated cells did not mature in vitro, though occasional bipolar cells with relatively short axons were seen. In explant culture, small fragments of rat tissue were positive for all 3 criteria after 6 days. In 9-day cultures, the axons had grown up to 3 mm long in both rat and chick cultures. Olfactory bulb fragments co-cultured close to the olfactory epithelium had no influence on the direction of outgrowth of axons from the olfactory receptor cells. Preliminary experiments with intracellular electrodes on the fragment cultures suggest that there are two cell types in the epithelium; one with a potential of -25 to -30 mV and, the other, -12 to -15 mV.

Fetal hiccups: an associated fetal heart rate pattern

Fetal hiccups are commonly diagnosed during the antepartum period, and they have a tendency to recur. The reflex of hiccuping is similar to that of gasping, except hiccuping efforts are made against a closed airway. An episode of intrapartum hiccups was confirmed via real-time ultrasound scanning during monitoring with a direct fetal scalp electrode. A neonatal heart rate pattern during hiccuping is also included. Distinctive fetal and neonatal heart rate patterns were observed during the hiccuping episode. It is speculated that the fetal heart rate pattern seen with hiccups may resemble that of fetal gasping.

Invasion of an artificial blood vessel wall by human fibrosarcoma cells

Artificial blood vessel walls constructed by the addition of bovine arterial endothelial cells to multilayers of rat smooth muscle cells were used as substrates for the human fibrosarcoma cell line HT1080. The extracellular matrix proteins elaborated by the smooth muscle cells were prelabeled with [3H]-proline; therefore, their subsequent digestion could be followed by the appearance of radioactivity in the culture medium. The fibrosarcoma cells rapidly hydrolyzed smooth muscle multilayers in the absence of endothelial cells, but an endothelial layer markedly retarded the destructive ability of the tumor cells. The protective effect of the endothelium was not due to a lack of penetration of this cell layer, since HT1080 cells were observed by light and electron microscopy to be in the subendothelial area 24 hr after plating. Subsequently, the tumor cells multiplied in the region between the endothelial and smooth muscle layers and, although their degradative ability was retarded, they were ultimately capable of destroying the structure. Endothelial cells also inhibited hydrolysis of the smooth muscle layers if added simultaneously or up to 1 week after HT1080 cells, but the degree of inhibition was not as great as that seen with a preestablished endothelial layer. Measurable inhibition of tumor cell degradative activity was observed at fibrosarcoma:endothelial cell ratios of 25:1, demonstrating the potency of endothelial cells in modulating this aspect of the invasive phenotype. Although the HT1080 cells only slowly degraded the preexisting matrix proteins in artificial vessel wall cultures, they interfered with the production of new connective tissue proteins which occurred in control cultures. These experiments therefore suggest that endothelial cells have profound effects on tumor cell proteolytic activity, and the significance of these observations to tumor cell extravasation in vivo is discussed.

The relationship of ribosomal RNA synthesis to the formation of segregated nucleoli and nucleolus-like bodies

The relationship of ribosomal RNA (rRNA) synthesis to nucleolar ultrastructure was studied in partial nucleolar mutants of Xenopus laevis. These mutations are the result of a partial deletion of rRNA genes and therefore alow studies on nucleolar structure and function without using drugs that inhibit rRNA synthesis. Ultrastructural studies demonstrated that normal embryos have reticulated nucleoli that are composed of a loose meshwork of granules and fibrils and a typical nucleolonema. In contrast, partial nucleolar mutants in which rRNA synthesis is reduced to less than 50% of the normal rate have compact nucleoli and nucleolus-like bodies. The compace nucleoli contain granules and fibrils, but they are segregated into distinct regions, and a nucleolonema is never seen. Since other species of RNA are synthesized normally by partial nucleolar mutants, these results demonstrate that nucleolar segragation is related specifically to a reduction in rRNA synthesis. The nucleolus-like bodies are composed mainly of fibrils,and the number of such bodies are composed mainly of fibrils, and the number of such bodies present in the different nucleolar mutants is inversely related to the relative rate of rRNA synthesis. Although the partial nucleolar organizers produce segregated nucleoli in these mutants, they organize morphologically normal, but smaller, nucleoli in heterozygous embryos. Alternative explanations to account for these results are discussed.