Analysis of hindbrain neural crest migration in the long-tailed monkey (Macaca fascicularis)

Neural crest cells make a substantial contribution to normal craniofacial development. Despite advances made in identifying migrating neural crest cells in avian embryos and, more recently, rodent embryos, knowledge of crest cell migration in primates has been limited to what was obtained by conventional morphological techniques. In order to determine the degree to which the nonhuman primate fits the mammalian pattern, we studied the features of putative neural crest cell migration in the hindbrain of the long-tailed monkey (Macaca fascicularis) embryo. Cranial crest cells were identified on the basis of reported distributional and morphological criteria as well as by immunocytochemical detection of the neural cell adhesion molecule (N-CAM) that labels a subpopulation of these cells. The persistent labeling of a sufficient number of crest cells with antibodies to N-CAM following their exit from the rostral, pre-otic and post-otic regions of the hindbrain facilitated tracking them along subectodermal pathways to their respective destinations in the first, second and third pharyngeal arches. Peroxidase immunocytochemistry was also employed to localize laminin and collagen-IV in neuroepithelial basement membranes. At stage 10 (8-11 somites), crest emigration occurred in areas of unfused neural folds through focal disruptions in the neuroepithelial basement membrane in both the rostral and pre-otic regions, although there was little evidence of crest migration in the post-otic hindbrain. By stage 11 (16-17 somites), the neural folds were fused (pre- and post-otic hindbrain) or in the process of fusing (rostral hindbrain), yet crest cell emigration was apparent in all three areas through discontinuities in the basement membrane. Emigration was essentially complete at stage 12 (21 somites) as indicated by nearly continuous cranial neural tube basement membranes. At this stage the pre-ganglia (trigeminal, facioacoustic and glossopharyngeal) were consistently stained with N-CAM. The current study has provided new information on mammalian neural crest in a well-established experimental model for normal and abnormal human development, including its use as a model for the retinoic acid syndrome. In this regard, the current results provide the basis for probing the mechanisms of retinoid embryopathy which may involve perturbation of hindbrain neural crest development.

The gene for transcription factor GATA-6 resides on mouse chromosome 18 and is expressed in myocardium and vascular smooth muscle

We report the mapping and developmental expression pattern of the gene encoding mouse GATA-6, a member of a family of transcription factors involved in tissue-specific gene expression. Using backcross analysis, the Gata6 gene was localized to mouse chromosome 18, linked to the gene encoding transthyretin. RNase protection analysis showed that Gata6 is abundantly expressed in the heart, stomach, intestine, and ovaries of the adult mouse. The developmental expression patterns of Gata6 and the closely related gene Gata4 were directly compared using in situ hybridization. Both genes were found to be highly expressed in the myocardium, stomach epithelium, and small intestinal epithelium throughout mouse development. Of the two genes, however, only Gata6 was expressed in vascular smooth muscle. The overlapping distributions of GATA-4 and GATA-6 transcripts in the heart support the possibility of functional redundancy or interplay between these two transcription factors in this tissue. The presence of GATA-6 mRNA in vascular smooth muscle suggests that this transcription factor may play a distinctive role in gene expression in this cell type.

Why are ruminal cellulolytic bacteria unable to digest cellulose at low pH?

Ruminant animals depend on cellulolytic ruminal bacteria to digest cellulose, but these bacteria cannot resist the low ruminal pH that modern feeding practices can create. Because the cellulolytic bacteria cannot grow on cellobiose at low pH, pH sensitivity is a general aspect of growth and not just a limitation of the cellulases per se. Acid-resistant ruminal bacteria have evolved the capacity to let their intracellular pH decrease, maintain a small pH gradient across the cell membrane, and prevent an intracellular accumulation of VFA anions. Cellulolytic bacteria cannot grow with a low intracellular pH, and an increase in pH gradient leads to anion toxicity. Prevotella ruminicola cannot digest native cellulose, but it grows at low pH and degrades the cellulose derivative, carboxymethylcellulose. The Prevotella ruminicola carboxymethylcellulase cannot bind to cellulose, but a recombinant enzyme having the Prevotella ruminicola catalytic domain and a binding domain from Thermomonspora fusca was able to bind and had cellulase activity that was at least 10-fold higher. Based on these results, gene reconstruction offers a means of converting Prevotella ruminicola into a ruminal bacterium that can digest cellulose at low pH.

Site-directed mutagenesis of monofunctional chorismate mutase engineered from the E. coli P-protein

Analysis of the active-site residues of a fully functional chorismate mutase representing the N-terminal 113 amino acids of the Escherichia coli P-protein suggests that Lys39 and Gln88 play critical roles in catalyzing the rearrangement of chorismate to prephenate. Five site-directed mutants at these positions have been constructed in which Lys39 was replaced with Arg, Asn, and Gln, and Gln88 was replaced with Arg and Glu. Although the Gln88Arg plasmid failed to produce detectable cross-reacting proteins in E. coli, the other four plasmids were expressed, and the mutant proteins purified to homogeneity. Their structures were similar to wild type enzyme, as indicated by circular dichroism spectra, with Lys39Gln showing a small deviation. In accordance with predictions, all mutations result in major loss of catalytic activity at pH 7.8. However, activity of the Gln88Glu mutant at pH 4.5 exceeded wild-type EcCM. Implications for the mechanism of mutase catalysis are discussed.

Transcription factors: regulators of gene expression in normal and pathological states

Initiation of transcription is the major control point for gene expression. The protein factors regulating transcription, the transcription factors, are modular proteins with distinct domains responsible for different functions including DNA binding, ligand binding, nuclear localization, and protein-protein interactions. Abnormal transcription has been associated with various human diseases from neoplasia to birth defects. These can result from chromosomal translocation or transcription factor genes (e.g. Burkitt's lymphoma) or by inappropriate activation of these factors due to synthesis of fusion genes (e.g. BCR-ABL fusion gene in Philadelphia positive leukaemia). More recently, abnormalities in transcription factor genes have been linked to such human birth defects as Waardenburg syndrome, vesicoureteral reflux and craniosynostosis.

Identification of two functionally different classes of exocellulases

There are two classes of synergism in cellulase mixtures: synergism between endocellulases and exocellulases, and synergism between certain exocellulases. Exocellulases have been defined traditionally as releasing cellobiose from the nonreducing ends of cellulose, but this definition is inadequate to explain exo/exo synergism. Several recent reports indicate that some exocellulases are capable of hydrolyzing cellulose from the reducing end. The existence of two exocellulase classes with different specificities could provide an explanation for exo/exo synergism. In this paper, we report the substrate specificity of three Thermomonospora fusca (E3, E4, and E6) and two Trichoderma reesei (CBH I and CBH II) exocellulases on labeled cellooligosaccharides. We describe a new nonradioactive technique for determining substrate specificity, in which ion-spray mass spectrometry was used to analyze the products of enzymatic digests of cellopentaose labeled with 18O at the reducing end. Exocellulase reactivity was also investigated on cellopentaose labeled at the nonreducing end with 14C, and cellooligosaccharides reduced with NaBH4. The distribution of label in the reaction products supports the existence of two functional classes of exocellulases. One class (containing CBH I, E4, and E6) preferentially cleaves cellooligosaccharides from the reducing end, while the other (containing E3 and CBH II) preferentially cleaves from the nonreducing end. This classification of exocellulases is consistent with exo/exo synergism experiments, and with published cellulase crystallographic data.

Use of a modified Bacteroides-Prevotella shuttle vector to transfer a reconstructed beta-1,4-D-endoglucanase gene into Bacteroides uniformis and Prevotella ruminicola B(1)4

A carboxymethyl cellulase (CMCase) gene from Prevotella ruminicola B(1)4 was reconstructed by adding a cellulose binding domain from a Thermomonospora fusca cellulase and was conjugally transferred from Escherichia coli to Bacteroides uniformis 0061 by using a chloramphenicol and tetracycline resistance shuttle vector (pTC-COW). pTC-COW was specifically constructed to facilitate conjugal transfer of vectors from B. uniformis donors to P. ruminicola recipients. B. uniformis transconjugants containing CMCase constructs cloned into pTC-COW expressed Cmr, but they did not produce the reconstructed CMCase until a xylanase promoter from P. ruminicola 23 was added upstream of the CMCase (pTC-XRCMC). The xylanase promoter allowed the B. uniformis transconjugants to produce large amounts of the reconstructed CMCase, which was present on the outside surface of the cells. Although the reconstructed CMCase alone did not allow B. uniformis to grow on acid-swollen cellulose, rapid growth was observed when two exocellulases were added to the culture supernatant. Under these conditions, the reconstructed CMCase permitted faster growth than the wild-type CMCase. The frequency of transfer of pTC-XRCMC from B. uniformis to P. ruminicola B(1)4 was increased 100-fold when strictly anaerobic conditions, nitrocelluose filters (cell immobilization), and more stringent selections were employed. Although the P. ruminicola B(1)4 (pTC-XRCMC) transconjugates expressed Tcr and had DNA that hybridized with a probe to the shuttle vector, these transconjugants did not produce detectable levels of the reconstructed CMCase even when xylan was the carbon source. On the basis of these results, it appears that not all of the promoters recognized by B. uniformis and P. ruminicola 23 are functional in P. ruminicola B(1)4. However, the results with B. uniformis suggest that the introduction of a P. ruminicola B(1)4 promoter should allow expression of the reconstructed CMCase in P. ruminicola B(1)4.

The effect of sugar on behavior or cognition in children. A meta-analysis

OBJECTIVE

To examine the effects of sugar on the behavior or cognition of children by using meta-analytic techniques on reported studies.

DATA SOURCES

Studies were identified through a literature search of the MEDLINE and PsychINFO databases and the authors' files using sugar, sucrose, and attention deficit disorder as the search terms.

STUDY SELECTION

Studies were required to (1) intervene by having the subjects consume a known quantity of sugar, (2) use a placebo (artificial sweetener) condition (3) blind the subjects, parents, and research staff to the conditions; and (4) report statistics that could be used to compute the dependent measures effect sizes.

DATA EXTRACTION

Variables included publication year, study setting, subject type and number, gender, age, sugar and placebo type and dose, prior dietary condition, measurement construct, means and SDs for the sugar and placebo conditions, and direction of effect.

DATA SYNTHESIS

Sixteen reports met the inclusion criteria for a total of 23 within-subject design studies. The weighted mean effect size and related statistics for each of the 14 measurement constructs revealed that although the range for these means was from -0.14 for direct observations and up to +0.30 for academic tests, the 95% confidence interval for all 14 mean effect sizes included 0.

CONCLUSION

The meta-analytic synthesis of the studies to date found that sugar does not affect the behavior or cognitive performance of children. The strong belief of parents may be due to expectancy and common association. However, a small effect of sugar or effects on subsets of children cannot be ruled out.

Conformational modeling of substrate binding to endocellulase E2 from Thermomonospora fusca

Molecular mechanics calculations have been used to place a cellotetraose substrate into the active site of the crystallographically determined structure of endocellulase E2 from Thermomonospora fusca. In the lowest energy model structure, the second residue of the substrate oligosaccharide is tilted away from the planar ribbon geometry of cellulose as it is in the X-ray structure of the E2cd-cellobiose co-crystal. This tilt is the result of the topology of the binding site, and results in several strong carbohydrate-protein hydrogen bonds. The tilting produces a twisting of the glycosidic linkage of the cleavage site between residues two and three. In the predicted enzyme-substrate complex both of the Asp residues believed to function in general acid and base roles in the previously proposed model for the mechanism are distant from the bond being cleaved. Molecular dynamics simulations of the complex were conducted, and while the putative catalytic Asp residues remained distant from the cleavage site, the proton of Tyr73 briefly came within van der Waals contact of the linkage oxygen.

Targeted mutagenesis of the transcription factor GATA-4 gene in mouse embryonic stem cells disrupts visceral endoderm differentiation in vitro

Transcription factor GATA-4 belongs to a family of zinc finger proteins involved in lineage determination. GATA-4 is first expressed in yolk sac endoderm of the developing mouse and later in cardiac tissue, gut epithelium and gonads. To delineate the role of this transcription factor in differentiation and early development, we studied embryoid bodies derived from mouse embryonic stem (ES) cells in which both copies of the Gata-4 gene were disrupted. Light and electron microscopy demonstrated that embryoid bodies formed from wild-type and heterozygous deficient ES cells were covered with a layer of visceral yolk sac endoderm, whereas no yolk sac endoderm was evident on the surface of the homozygous deficient embryoid bodies. Independently selected homozygous deficient cell lines displayed this distinctive phenotype, suggesting that it was not an artifact of clonal variation. Biochemical markers of visceral endoderm formation, such as alpha-feto-protein, hepatocyte nuclear factor-4 and binding sites for Dolichos biflorus agglutinin, were absent from the homozygous deficient embryoid bodies. Examination of other differentiation markers in the mutant embryoid bodies, studies of ES cell-derived teratocarcinomas and chimeric mouse analysis demonstrated that GATA-4-deficient ES cells have the capacity to differentiate along other lineages. We conclude that, under in vitro conditions, disruption of the Gata-4 gene results in a specific block in visceral endoderm formation. These homozygous deficient cells should yield insights into the regulation of yolk sac endoderm development and the factors expressed by visceral endoderm that influence differentiation of adjoining ectoderm/mesoderm.

Alterations in cranial morphogenesis in the Lp mutant mouse

The effects of exencephaly on cranial morphogenesis were studied at 10 to 12 days of gestation in the loop-tail (Lp) mutant mouse in which the hindbrain and spinal cord fail to close. At the level of the hindbrain, the otocysts became displaced ventrally in abnormal (Lp/Lp) embryos, and the everted neuroepithelium showed a diminished "luminal" reaction to the lectins WGA and Con A, as compared with normal embryos. Also, occasional clusters of rounded cells that resembled presumptive neural crest cells and that labeled with WGA, Con A, and anti-N-CAM were observed at the everted tips of the open neural folds. By 12 days' gestation, there was a loss of integrity in some areas of the neuroepithelium. However, despite the topographic and neuroepithelial distortions, normal differentiation of a roof plate-like neuroepithelium occurred at the ends of the everted neural folds. In addition, the mesenchyme showed normal condensations that labeled with WGA, Con A, and anti-N-CAM in the perinotochordal basicranium and periotic regions. Thus, in this mutant mouse model of neural dysraphism, some features of cranial morphogenesis and differentiation appear to be dependent on timely and proper closure of the cranial neural tube, whereas other aspects may proceed independently of neural closure.

Cloning, sequencing, and characterization of a membrane-associated Prevotella ruminicola B(1)4 beta-glucosidase with cellodextrinase and cyanoglycosidase activities

Prevotella ruminicola B(1)4 is a gram-negative, anaerobic gastrointestinal bacterium. A 2.4-kbp chromosomal fragment from P. ruminicola encoding an 87-kDa aryl-glucosidase (CdxA) with cellodextrinase activity was cloned into Escherichia coli DH5 alpha and sequenced. CdxA activity was found predominantly in the membrane fraction of both P. ruminicola and E. coli, but P. ruminicola localized the protein extracellularly while E. coli did not. The hydrolase had the highest activity on cellodextrins (3.43 to 4.13 mumol of glucose released min-1 mg of protein-1) and p-nitrophenyl-beta-D-glucoside (3.54 mumol min-1 mg of protein-1). Significant activity (70% of p-nitrophenyl-beta-D-glucoside activity) was also detected on arbutin and prunasin. Less activity was obtained with cellobiose, amygdalin, or gentiobiose. CdxA attacks cellodextrins from the nonreducing end, releasing glucose units, and appears to be an exo-1,4-beta-glucosidase (EC 3.2.1.74) which also is able to attack beta-1,6 linkages. Comparison of the deduced amino acid sequence with other glycosyl-hydrolases suggests that this enzyme belongs to family 3 (B. Henrissat, Biochem. J. 280:309-316, 1991). On the basis of this sequence alignment, the catalytic residues are believed to be Asp-275 and Glu-265. This is the first report of a cloned ruminal bacterial enzyme which can cleave cyanogenic plant compounds and which may therefore contribute to cyanide toxicity in ruminants.

The cellular location of Prevotella ruminicola beta-1,4-D-endoglucanase and its occurrence in other strains of ruminal bacteria

Prevotella ruminicola B(1)4, TC1-1, TF1-3, and TS1-5 all produced immunologically cross-reacting 88- and 82-kDa carboxymethyl cellulases (CMCases). P. ruminicola 23, 118B, 20-63, and 20-78 had much lower CMCase activities, and Western blots (immunoblots) showed no cross-reaction with the B(1)4 CMCase antiserum. Fibrobacter succinogenes S85 and Selenomonas ruminantium HD4 and D produced CMCase, but these enzymes were smaller and did not cross-react with the B(1)4 CMCase antiserum. The B(1)4 CMCase antiserum inhibited the B(1)4, TC1-1, TF1-3, and TS1-5 CMCase activities and agglutinated these cells, but it had no effect on the other strains or species. On the basis of these results, the B(1)4 CMCase is a strain-specific enzyme that is located on the outside surface of the cells. P. ruminicola B(1)4 cultures, grown on sucrose, did not have significant CMCase activity, but these cells could bind purified 88- and 82-kDa CMCase but not 40.5-kDa CMCase. Because the 40.5-kDa CMCase is a fully active, truncated form of the CMCase, it appears that the N-terminal domain of the 88-kDa B(1)4 CMCase anchors the CMCase to the cells. Cells grown on cellobiose produced at least 10-fold more CMCase than the sucrose-grown cells, and the cellobiose-grown cells could only bind 15% as much CMCase as sucrose-grown cells. Virtually all of the CMCase activity of exponentially growing cultures was cell associated, but CMCase activity was eventually detected in the culture supernatant. On the basis of the observation that the 88-kDa CMCase was gradually converted to the 82-kDa CMCase when cultures reached the stationary phase without a change in specific activity, it appears that the 82-kDa protein is probably a proteolytic degradation product of the 88-kDa CMCase.

Predicting coiled coils by use of pairwise residue correlations

A method is presented that predicts coiled-coil domains in protein sequences by using pairwise residue correlations obtained from a (two-stranded) coiled-coil database of 58,217 amino acid residues. A program called PAIRCOIL implements this method and is significantly better than existing methods at distinguishing coiled coils from alpha-helices that are not coiled coils. The database of pairwise residue correlations suggests structural features that stabilize or destabilize coiled coils.

Acute and subacute rehabilitation for stroke: a comparison

Subacute rehabilitation, a recent innovation, is a less intense form of traditional inpatient rehabilitation. This study is a retrospective comparison of stroke treatment in a comprehensive inpatient service (acute rehabilitation) and subacute rehabilitation in a skilled nursing facility. Consecutive records during 1990 and 1991 resulted in 331 patients at the acute level and 97 at the subacute. Analysis of patient characteristics found few major differences between the two populations. Scrutiny of billing records found that acute program patients had twice as much treatment during a stay, twice the daily treatment hours, and twice the average charge per day. Acute rehabilitation patients showed substantially greater gains in functional impairment measures (FIM), but the proportion of patients discharged to the community varied little. Cost-effectiveness analysis found that the charge per successful discharge was more than double for acute rehabilitation. The charge per one point of FIM gain also was substantially higher. Although subacute rehabilitation was found to be more cost-effective than acute, additional research is needed to establish policies regarding rehabilitation services.

Assignment of the transcription factor GATA4 gene to human chromosome 8 and mouse chromosome 14: Gata4 is a candidate gene for Ds (disorganization)

We report the mapping of the human and mouse genes for transcription factor GATA-4, a newly identified member of DNA-binding proteins involved in lineage determination. The human GATA4 gene was assigned to the short arm of human chromosome 8 using genomic DNAs from human-rodent somatic cell hybrid lines. Southern blot analyses indicated the presence of a human-specific 7.6-kb fragment that was observed only in DNA from the hybrid cells containing human chromosome 8 or the proximal region of its short arm. The mouse Gata4 gene was mapped to chromosome 14, closely linked to Clu (clusterin), using genomic DNAs from a (C57BL/6J x Mus spretus)F1 x M. spretus backcross. This mapping assignment places the Gata4 gene in the vicinity of the mouse Ds (disorganization) locus, a dominant gain-of-function mutation affecting embryonic development. We speculate that Ds is caused by a mutation in the Gata4 gene, ectopic expression of GATA-4, or a mutation in another lineage determination gene closely linked to Gata4.

Evaluating food fortification options: general principles revisited with folic acid

OBJECTIVES

This article uses folic acid as an example to illustrate some of the complex issues and general principles that emerge when evaluating fortification of the food supply as one possible means to address a public health recommendation.

METHODS

Distributions of current daily folate intakes from conventional foods and dietary supplements were estimated. Intakes that might result from fortification of cereal-grain products and ready-to-eat cereals at various levels for eight age-gender groups were also estimated by using the US Department of Agriculture's 1987-1988 Nationwide Food Consumption Survey.

RESULTS

The results illustrate that fortification of the US food supply tends to increase folate intakes of consumers at the high end of the intake distribution curves in the general population to a greater extent than it affects consumers at the low end of the intake distribution curves in the target population.

CONCLUSIONS

The effectiveness of food fortification options for a target population and the safety for the general population impose conflicting challenges that must be considered concurrently when making decisions about fortifying the US food supply.

Regulation of J6 gene expression by transcription factor GATA-4

Retinoic acid-induced differentiation of mouse F9 embryonal carcinoma cells into primitive endoderm is accompanied by increased transcription of the gene for J6, a heat shock protein implicated in collagen biosynthesis. In this paper we present evidence that transcription factor GATA-4, a retinoic acid-inducible GATA-binding protein, is involved in the regulation of J6 gene expression in F9 cells. Northern-blot analysis indicates that transcripts encoding GATA-4 and J6 increase in parallel during retinoic acid-induced differentiation of F9 cells. Gel-shift experiments and antibody binding studies demonstrate that: (1) GATA-4 is the major GATA-binding protein activity in differentiated F9 cells, and (2) GATA-4 binds to consensus GATA motifs in the retinoic acid-responsive portion of the J6 promoter. Co-transfection studies using NIH 3T3 cells show that GATA-4 is a potent trans-activator of the J6 promoter. These lines of evidence suggest that expression of J6 in F9 cells is regulated by GATA-4. We speculate that transcription factor GATA-4 may also control other genes involved in extracellular matrix formation in the yolk sac.

Characterization of a Thermomonospora fusca exocellulase

The exocellulase E3 gene was cloned on a 7.1 kb NotI fragment from Thermomonospora fusca genomic DNA into Escherichia coli and expressed in Streptomyces lividans. The E3 gene was sequenced and encoded a 596 residue peptide. The molecular masses of the native and cloned E3s were determined by mass spectrometry, and the value for E. coli E3, 59,797 Da, agreed well with that predicted from the DNA sequence, 59,646 Da. The value of 61,200 Da for T. fusca E3 is consistent with E3 being a glycoprotein. E3 is thermostable, retaining full activity after 16 h at 55 degrees C. It also has a broad pH optimum around 7-8, retaining 90% of its maximal activity between pH 6 and 10. The cloned E3s were identical to the native enzyme in their activity, cellulose binding, and thermostability. Papain digestion produced a 45.7 kDa catalytic domain with 77% of the native activity on amorphous cellulose and 33% on crystalline cellulose. E3 belongs to cellulase family B and retains the residues that have been identified to be crucial for catalytic activity in Trichoderma reesei cellobiohydrolase II and T. fusca E2. The E3 gene contains a 14 bp inverted repeat regulatory sequence 212 bp before the translational start codon instead of the 30-70 bp found for the other T. fusca cellulase genes. An additional copy of this sequence with one base changed is 314 bp before the translational start codon. The transcriptional start site of the E3 gene was shown to be between these two inverted repeats.

Localisation of glycoproteins and glycosaminoglycans during early eye development in the macaque

The composition of the extracellular matrix (ECM) was examined in the developing lens and optic cup (stages 11-16) of the long-tailed monkey (Macaca fascicularis) using peroxidase immunocytochemistry. The glycoproteins, fibronectin, laminin, and collagen types I and IV, were consistently associated with basement membranes (BM) of ocular epithelia at all stages examined. Discontinuity of the optic cup BM was observed during the early stages of evagination (stages 11 and 12); the even distribution of all 4 components was reestablished by stage 13 when the optic vesicle is closely apposed to the thickened lens placode. While fibronectin was most predominant in the mesenchymal matrix, all 4 glycoproteins were observed to variable degrees in the periocular mesenchyme. Particularly strong glycoprotein reactivity was observed in the interspace between the invaginating lens vesicle and optic cup whereas no significant reactivity occurred within the lens, developing retina or future corneal epithelium. Two glycosaminoglycans, hyaluronic acid and chondroitin sulphate, had virtually identical widespread staining patterns in all ocular BM and throughout the periocular mesenchyme and adjacent epithelial tissues, including the lens and retina. The observed temporal and regional staining patterns suggest that these ECM components are morphogenetic factors in the macaque eye, facilitating the complex series of integrated tissue interactions, movements and shape changes during the earliest stages of lens and optic vesicle morphogenesis. The macaque offers a valuable model to study these interactions due to the prolonged period of ocular development which is morphologically identical to humans.

Patterns of lectin binding during mammalian neurogenesis

Temporospatial changes in surface carbohydrates of neuroepithelial cells were analysed by means of lectin histochemistry in normal mouse embryos subsequent to closure of the neural tube. The lectins used were concanavalin A (con A), soybean (SBA), Maclura pomifera (MPA), peanut (PNA), wheatgerm (WGA), succinylated wheatgerm (sWGA) and Limax flavus (LFA). Although labelling was obtained with all of the lectins, the most striking temporospatial differences occurred with con A which in the early embryos (9-10 somites) labelled the basal and intercellular surfaces, but not the luminal surfaces of the neuroepithelial cells, whereas in the older embryos (26-30 somites), con A showed light luminal surface labelling. A midventral wedge of cells in the floor of the neural tube in the older embryos also exhibited more intense labelling with con A, WGA, and sWGA than with the other lectins. In addition, comparisons of lectin localisation were made between the closed neural tube in normal embryos and the open neural folds in the loop-tail (Lp) mutant mouse in which the neural tube fails to close. Although similar temporospatial patterns in lectin localisation occurred as in normal embryos, the retention of lectin labelling associated with rounded putative neural crest cells that remained sequestered in the apices of the open neural folds, along with an attenuation of the luminal reaction in the older abnormal embryos, suggest that during normal mammalian development closure of the spinal neural folds may be important for the timely exit of neural crest cells as well as for eliciting changes in the luminal surfaces of the neuroepithelial cells.

The effect of carbohydrates on the expression of the Prevotella ruminicola 1,4-beta-D-endoglucanase

The beta-1,4-endoglucanase of the ruminal bacterium, Prevotella ruminicola B14, hydrolysed carboxymethylcellulose and barley glucan but not xylan or mannan. Endoglucanase activity was present in 88- and 82-kDa proteins, and there was at least a 20-fold variation in endoglucanase activity when P. ruminicola B14 was grown on different sugars. The highest activities were observed with mannose, cellobiose or xylose and little activity was observed with sucrose, arabinose or rhamnose, P. ruminicola B14 also had significant xylanase and mannanase activities, but these activities were present in proteins that had lower molecular masses than the endoglucanase and these proteins did not cross-react with antibody made against the endoglucanase. Mannanase activity has a similar pattern of expression to the endoglucanase, while the xylanase was not induced or repressed by the same sugars or combinations of sugars. The xylanase activity was greatest when xylan was the energy source for growth, but xylose was a very poor inducer of xylanase activity.

Immunofluorescent analysis of the spinal cord in dysraphic mice

Development of the spinal cord was analyzed immunocytochemically at 10-12 days of gestation in normal and dysraphic embryos of the loop-tail mutant mouse, using an anti-neural cell adhesion molecule (NCAM) and the lectin concanavalin A (Con A) as histological markers for evaluating neural cell organization and distribution. The normal and abnormal embryos showed similar patterns of reactivity to anti-NCAM and Con A, even though the neural folds were open and everted in the abnormal embryos, with displacement of the dorsal root ganglia. In the abnormal embryos the floor plate was similar to that in normal embryos, as evidenced by its increased anti-NCAM and Con A labeling relative to that in the rest of the neuroepithelium. Moreover, each lateral end of the everted abnormal neuroepithelium developed an attenuated 'roof plate' that appeared to be structurally similar to the normal roof plate. However, some of these 'roof plates' exhibited prominent clusters of labeled and nonlabeled cells, especially in the 10-day embryos. In addition, whereas normal embryos showed strong luminal labeling of the neuroepithelial cells with Con A, comparable regions in the abnormals were spotty and poorly defined except for the 'roof plate' and floor plate. The results indicate that dorsoventral polarity in the spinal cord, as assessed structurally and histochemically, develops essentially normally in abnormal dysraphic embryos, even though the topographic relationships of the abnormal neural tube are disturbed.