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PubMed2023

EMPIAR: the Electron Microscopy Public Image Archive.

Public archiving in structural biology is well established with the Protein Data Bank (PDB; wwPDB.org) catering for atomic models and the Electron Microscopy Data Bank (EMDB; emdb-empiar.org) for 3D reconstructions from cryo-EM experiments. Even before the recent rapid growth in cryo-EM, there was an expressed community need for a public archive of image data from cryo-EM experiments for validation, software development, testing and training. Concomitantly, the proliferation of 3D imaging techniques for cells, tissues and organisms using volume EM (vEM) and X-ray tomography (XT) led to calls from these communities to publicly archive such data as well. EMPIAR (empiar.org) was developed as a public archive for raw cryo-EM image data and for 3D reconstructions from vEM and XT experiments and now comprises over a thousand entries totalling over 2 petabytes of data. EMPIAR resources include a deposition system, entry pages, facilities to search, visualize and download datasets, and a REST API for programmatic access to entry metadata. The success of EMPIAR also poses significant challenges for the future in dealing with the very fast growth in the volume of data and in enhancing its reusability.

Imaging, Three-Dimensional↗

PubMed2026

Fused Deposition Modeling (FDM) of polyether-ether-ketone (PEEK) dental implants: A systematic review of the effect of printing parameters on mechanical behaviour and surface quality.

PURPOSE: This systematic review evaluated how FDM printing parameters influence mechanical behaviour and surface characteristics of 3D-printed PEEK and identified parameter combinations linked to the most favourable mechanical performance and surface quality. MATERIALS AND METHODS: An electronic search was conducted in: MEDLINE (Ovid), PubMed, Embase, Web of Science, Scopus, and Compendex (last update: January 2025). Studies that evaluated the effect of FDM printing parameters on mechanical and surface properties of PEEK were included. Outcomes comprised compressive, tensile, and flexural strengths, elastic modulus, fracture toughness, surface hardness, roughness, and wettability. RESULTS: Of 4005 reports screened, 54 manuscripts were included. 92.6% (n = 50) of articles showed low risk-of-bias, while 7.4% (n = 4) showed medium risk-of-bias. Tensile strength was the most investigated mechanical parameter (78%), followed by elastic modulus (41%), flexural strength (30%), compressive strength (20%), and fracture toughness (6%). Surface roughness was the most evaluated surface property (30%), followed by hardness (17%) and wettability (6%). Across studies, higher printing temperatures, lower printing speed, thinner layer thickness, and maximum infill ratio in a horizontal printing orientation were associated with higher strengths, less warpage, increased accuracy, and improved surface quality. CONCLUSION: Specific combinations of FDM printing parameters can significantly improve the mechanical and surface properties of PEEK. However, it is difficult to meet all the optimal conditions simultaneously. Thus, balancing between different parameters must be considered in practical production.

Benzophenones↗

PubMed1977

Structure of bovine trypsinogen at 1.9 A resolution.

The three-dimensional crystal structure of bovine trypsinogen at approximately pH 7.5 was initially solved at 2.6 A resolution using the multiple isomorphous replacement method. Preliminary refinement cycles of the atomic coordinates trypsinogen have been carried out first to a resolution of 2.1 A, and later to 1.9 A, using constrained difference Fourier refinement; During the process, structure factors Fc and phi c were calculated from the trypsinogen structure and final interpretation was based on an electron-density map computed with terms (2 Fo - Fc) and phases phic at a resolution of 1.9 A. Crystals of trypsinogen grown from ethanol-water mixtures are trigonal with space group P3121, and cell dimension a = 55.17 A and c = 109.25 A. The structure is compared with the bovine diisopropylphosphoryltrypsin structure at approximately pH 7.2, oirginally determined from orthohombic crystals by Stroud et al. (Stroud, R.M., Kay L.M., and Dickerson, R.E. (1971), Cold Spring Harbor Symp. Quant. Biol. 36, 125-140; Stroud, R.M., Kay, L.M., and Dickerson, R.E. (1974), J. Mol. Biol. 83, 185-208), and later refined at 1.5 A resolution by Chambers and Stroud (Chambers, J.L., and Stroud, R.M. (1976), Acta Crystallogr. (in press)). At lower pH, 4.0-5.5 diogen, with cell dimensions a = 55.05 A and c = 109.45 A. This finding was used in the solution of the six trypsinogen heavy-atom derivatives prior to isomorphous phase analysis, and as a further basis of comparison between trypsinogen and the low pH trypsin structure. There are small differences between the two diisopropylphosphoryltrypsin structures. Bovine trypsinogen has a large and accessible cavity at the site where the native enzyme binds specific side chains of a substrate. The conformation and stability of the binding site differ from that found in trypsin at approximately pH 7.5, and from that in the low pH form of diisopropylphosphoryltrypsin. The catalytic site containing Asp-102, His-57, and Ser-195 is similar to that found in trypsin and contains a similar hydrogen-bounded network. The carboxyl group of Asp-194, which is salt bridged to the amino terminal of Ile-16 in native trypsin or other serine proteases, is apparently hydrogen bonded to internal solvent molecules in a loosely organized part of the zymogen structure. The unusually charged N-terminal hexapeptide of trypsinogen, whose removal leads to activation of the zymogen, lies on the outside surface of the molecule. There are significant structural changes which accompany activation in neighboring regions, which include residues 142-152, 215-550, 188A-195. The NH group of Gly-193, normally involved in stabilization of reaction intermediates (Steitz, T.A., Henderson, R., and Blow, D.M. (1969), J. Mol. Biol. 46, 337-348; Henderson, R. (1970), J. Mol. Biol. 54, 341-354; robertus, J.D., Kraut, J., Alden, R.A., and Birkoft, J.J. (1972), Biochemistry 11, 4293-4303) in the enzyme, is moved 1.9 A away from its position in trypsin...

Animals↗

PubMed1979

Staphylococcal nuclease reviewed: a prototypic study in contemporary enzymology. III. Correlation of the three-dimensional structure with the mechanisms of enzymatic action.

This is the third in a series of four articles in which the chemical, enzymological and crystallographic work on Ribonucleate (deoxribonucleate)-3'-nucleotidohydrolase, EC 3.1.4.4 (staphylococcal nuclease, micrococcal nuclease) will be reviewed and correlated. This article describes the structure of the nuclease and of a nuclease-inhibitor complex as determined by x-ray crystallography. The crystal structures are correlated with some of the known chemical and enzymological properties of the enzyme, and the three areas combined to propose a mechanism of action.

Amino Acid Sequence↗

PubMed1977

Proton magnetic resonance studies of histidines in human, rhesus monkey, and bovine carbonic anhydrases.

Histidine C-2 proton resonances in rhesus monkey carbonic anhydrase B (carbonate hydro-lyase, EC 4.2.1.1) and bovine carbonic anhydrase were investigated using 270-MHz proton magnetic resonance. The results suggest that there are extensive three-dimensional homologies between the human B and rhesus B enzymes and between the human C and bovine enzymes. Resonances from solvent exchangeable protons have been observed in the 11-16 ppm range in the NMR spectra of human carbonic anhydrases B and C and bovine carbonic anhydrase. Up to five of these are sensitive to changes of pH and the presence of inhibitors. Three of these resonances are assigned to NH protons of the metal coordinated imidazole groups. These results are discussed in relation to various models for the catalytic mechanism of carbonic anhydrase.

Animals↗

PubMed1979

An analytical investigation into possible mechanical causes of bone remodelling.

Three-dimensional finite element analyses were carried out on idealisations of two situations where bone remodelling has been reported clinically viz. the malaligned femur and a maxillary central incisor under orthodontic loading. The mechanical responses, i.e. stress, strain and change of curvature, in various directions, are presented. They are compared with the biological response, either bone resorption or bone deposition. The results are discussed in relation to three current theories of bone remodelling.

Alveolar Process↗

PubMed2026

Four-dimensional molecular mapping from a spatial snapshot reveals the dynamics of hair follicle organogenesis.

Understanding organ formation requires capturing molecular information simultaneously in three-dimensional (3D) space and across developmental time. To this end, we developed 3D DNase-Enhanced Expression Profiling (3DEEP), a tissue-clearing approach that removes genomic DNA to extend spatial transcriptomic profiling hundreds of microns into intact tissues. We applied 3DEEP to neonatal mouse skin, capturing hundreds of developing hair follicles across their organogenesis trajectory. Ordering follicles by molecularly inferred developmental age transformed this single spatial snapshot into a four-dimensional (3D + time) molecular map of organogenesis. This map revealed developmental dynamics spanning stem cell compartment stratification, emergence of new cell subtypes within the follicle, and cascading structural transformations leading to hair canal formation. Comparative analysis of Foxn1-deficient nude mice, a hairlessness model, revealed organ-wide changes in developmental dynamics, including delayed molecular progression, reduced coordination, and increased developmental instability, preceding overt structural defects. This work demonstrates how deep-tissue spatial transcriptomics can uncover hidden dynamics of organ formation.

Animals↗

PubMed1979

Lifetimes and NADH quenching of tryptophan fluorescence in pig heart lactate dehydrogenase.

The decay of tryptophan emission from pig heart lactate dehydrogenase following pulsed excitation has been recorded in Tris buffer solution at pH 7.4. All tryptophan residues emit. A good least-squares two-component fit is obtained with I(t)-0.53e-t/1.2 + 0.47e-t/68. A longer lived emitter (r=7.4--8.1 ns) is also observed. Bound NADH strongly quenches most of the 6.8-ns emission, but the 1.2-ns component is relatively unaffected. The fluorescence is moderately quenched by acrylamide and only slighty quenched by I- and Cs+. The pulsed and steady-state fluorescence is discussed in terms of a model with three lifetime classes of tryptophan, viz., 1, 4, and 8 ns. The three-dimensional structure of the enzyme--NADH complex is used to develop a description of the individual residues in terms of their lifetimes and sensitivity to NADH and I- quenching. The nonlinear NADH quenching is due to intersubunit energy transfer from Trp-248 to NADH.

Animals↗

PubMed1979

Information used in judging impending collision.

Many subhuman species and human infants, children, and adults can use two-dimensional information of relative rate of angular-size change to anticipate collisions between the self and approaching objects or surfaces. But extant studies have not determined what information is used when subjects view simulated approach events providing two-dimensional information and three-dimensional information (distance and distance change), as well as lower-order visual information contained in real approach events. Three experiments suggest that, given these several possibilities, adults' judgments of collision time are best predicted by two-dimensional spatiotemporal values which are invariant over object sizes, distances traversed, approach velocities, and several lower-order variables such as absolute angular size. However, collision time is substantially underestimated, with absolute amount of underestimation increasing as a function of actual time-to-collision. Large constant errors and loss of judgment linearity beyond about 10 s to contact time suggest that current models of human performances based on use of time-to-collision information require modified assumptions of operator efficiency.

Depth Perception↗

PubMed2022

Morphological instability and roughening of growing 3D bacterial colonies.

How do growing bacterial colonies get their shapes? While colony morphogenesis is well studied in two dimensions, many bacteria grow as large colonies in three-dimensional (3D) environments, such as gels and tissues in the body or subsurface soils and sediments. Here, we describe the morphodynamics of large colonies of bacteria growing in three dimensions. Using experiments in transparent 3D granular hydrogel matrices, we show that dense colonies of four different species of bacteria generically become morphologically unstable and roughen as they consume nutrients and grow beyond a critical size-eventually adopting a characteristic branched, broccoli-like morphology independent of variations in the cell type and environmental conditions. This behavior reflects a key difference between two-dimensional (2D) and 3D colonies; while a 2D colony may access the nutrients needed for growth from the third dimension, a 3D colony inevitably becomes nutrient limited in its interior, driving a transition to unstable growth at its surface. We elucidate the onset of the instability using linear stability analysis and numerical simulations of a continuum model that treats the colony as an "active fluid" whose dynamics are driven by nutrient-dependent cellular growth. We find that when all dimensions of the colony substantially exceed the nutrient penetration length, nutrient-limited growth drives a 3D morphological instability that recapitulates essential features of the experimental observations. Our work thus provides a framework to predict and control the organization of growing colonies-as well as other forms of growing active matter, such as tumors and engineered living materials-in 3D environments.

Models, Biological↗

PubMed1977

Membrane-controlled depletion of complement activity by spin-label-specific IgM.

Complement depletion mediated by high molecular weight (IgM) rabbit antibodies specifically bound to spin-label lipid haptens dispersed in model membranes is controlled by various physical attributes of those membranes other than the total number of exposed determinants that they provide. Carrier lipids used at 32 degrees were (i) a "fluid" phosphatidylcholine (PC), (ii) a "solid" PC, and (iii) a cholesterol/PC mixture. The concentration of hapten in the plane of the membranes (two-dimensional concentration) was varied while the overall hapten molarity (three-dimensional concentration) was kept constant. Both specific binding and the efficiency of depletion by IgM are markedly enhanced by systematically decreasing the average distance between haptens (infinity --> 26 A). Heterogeneous distribution was found to be more favorable than a random homogeneous distribution of the same number of haptens in the same total quantity of lipids. IgM efficiency is also markedly increased by the inclusion of cholesterol in PC membranes, an effect thought to result from enhanced projection of the determinant from the surface of the membrane and hence increased accessibility to the antibody-binding site. Furthermore, the efficiency of IgM was increased by using haptens dispersed in fluid rather than in solid PC membranes. The results are consistent with the hypothesis that IgM molecules must be bound to a critical multiple of antigenic determinants at a membrane surface in order to induce complement-mediated attack and that subtle variation of the physical state of membrane antigens can be the crucial factor in determining the outcome of this type of efferent immune response.

Animals↗

PubMed2025

Knowledge-enhanced protein subcellular localization prediction from 3D fluorescence microscope images.

MOTIVATION: Pinpointing the subcellular location of proteins is essential for studying protein function and related diseases. Advances in spatial proteomics have shown that automatic recognition of protein subcellular localization from images could highly facilitate protein translocation analysis and biomarker discovery, but existing machine-learning works have been mostly limited to processing 2D images. By contrast, 3D images have higher spatial resolution and allow researchers to observe cellular structures in their natural context, but currently, there are only a few studies of 3D image processing for protein distribution analysis due to the lack of data and complexity of modeling. RESULTS: We developed a knowledge-enhanced protein subcellular localization model, KE3DLoc, which could recognize distribution patterns in 3D fluorescence microscope images using deep learning methods. The model designs an image feature extraction module that incorporates information from 3D and 2D projected cells and implements asymmetric loss and confidence weights to address data imbalance and weak cell annotation issues. Besides, considering that the biological knowledge in the Gene Ontology (GO) database can provide valuable support for protein location understanding, the KE3DLoc model incorporates a novel knowledge enhancement module that optimizes the protein representation by related knowledge graphs derived from the GO. Since the image module and the knowledge module calculate features from different levels, KE3DLoc designs protein ID aggregation to enhance the consistency of protein features across different cells. Experimental results on three public datasets have demonstrated that the KE3DLoc significantly outperforms existing methods and provides valuable insights for spatial proteomics research. AVAILABILITY AND IMPLEMENTATION: All datasets and codes used in this study are available at GitHub: https://github.com/PRBioimages/KE3DLoc.

Microscopy, Fluorescence↗

PubMed2025

TRB proteins in moss reveal their evolutionarily conserved roles in plant development and telomere maintenance.

Telomere repeat binding (TRB) proteins are plant-specific proteins with a unique domain structure distinct from telomerebinding proteins in animals and yeast. While extensively studied in seed plants, their role in early-diverging plant lineages remains largely unexplored. Here, we investigate TRB proteins in a model moss, Physcomitrium patens, to assess their evolutionary conservation and functional significance. Functional analysis using single knockout mutants revealed that individual PpTRB genes are essential for normal development, with mutants exhibiting defects in the two-dimensional (protonemal) stage, and more prominently, in the formation of three-dimensional (gametophore) structures. Some double mutants displayed telomere shortening, a phenotype also observed in TRB-deficient seed plants, indicating a conserved role for TRBs in telomere maintenance. Transcriptome profiling of TRB mutants revealed altered expression of genes associated with transcriptional regulation and stimulus response in protonema. Subcellular localization studies across various plant cell types confirmed that PpTRBs, like their seed plant counterparts, localize prevalently to the plant nucleus and mutually interact. In bryophytes, TRBs form a monophyletic group that mirrors the species phylogeny, whereas in seed plants, TRBs have diversified into two distinct monophyletic groups. Our findings provide the first comprehensive characterization of TRB proteins in non-vascular plants and demonstrate their conserved roles in telomere maintenance, with additional implications for plant development and gene regulation across land plant lineages.

Bryopsida↗

PubMed1978

Study of pole assembly in Bacillus subtilis by computer reconstruction of septal growth zones seen in central, longitudinal thin sections of cells.

The septal growth of Bacillus subtilis 168/s has been studied by making a number of observations from thin sections of cells from exponentially growing cultures. The process was initiated by the formation of a new cross wall under a preexisting layer of cylindrical wall. An annular notch appeared to cut through the overlying wall and presumably allowed the cross wall to split into two layers of peripheral wall. During this initial notching process, two raised bands of wall material were produced which resembled those previously observed in morphological studies of Streptococcus faecalis. Through an improved fixation technique, it was possible to preserve the bands seen in B. subtilis to the extent that they were used as markers to study the subsequent stages of septal growth. These stages included (i) the continued displacement of the two bands from the cross wall (as the two nascent polar surfaces enlarged and as the diameter of the cross wall decreased), (ii) the closure of the cross wall, and (iii) the final severance of the common cross wall connection between two completed poles. To study this process in a more quantitative manner, three-dimensional reconstructions of the envelope observed between pairs of the raised bands were made from axial thin sections of cells. The process of reconstruction was based on a technique by which x, y coordinates were taken from thin sections and were rotated around the cell's central axis. These reconstructions were used to estimate the surface area or volume of the reconstructed zones or their parts. A round of septal growth was then simulated by arranging 118 reconstructions in order of increasing surface area or volume. The topology of the process was studied by noting how various measurements of septal thickness, length, surface area, and volume varied as a function of increasing septal zone size. This analysis was based on several assumptions, of which three of the most important are: (i) the bands produced by the initial notching process are markers which separate septal from cylindrical wall growth; (ii) a septal zone observed between pairs of bands is made up of two nascent poles and a single cross wall; and (iii) as septal zones develop in terms of relative age they increase in size (volume or surface area) or amount of wall. The data suggested that the S. faecalis model of surface growth (in which polar growth occurs through a regulated constrictive separation and expansion of a cross wall) also seems applicable to the pattern of septal growth observed here for B. subtilis. This was indicated from measurements which showed that increases in the size of nascent polar surfaces were correlated with decreases in cross wall diameter. An explanation of these observations may be that decreases in cross wall diameter were due to a progressive splitting of the cross wall that removed surface from the outer circumference of the cross wall and converted it into new polar surface. Calculations further suggested that if the poles of B. subtilis were made by this model a sizeable and variable increase in surface area of the cross wall would also be required to convert these separating cross wall layers into two curved polar structures. Measurements of wall thickness taken from various locations within septal zones indicated that while the thickness of the polar wall of B. subtilis was constant over its surface, the width of the cross wall varied considerably during a round of synthesis. Again, one of the simplest explanations compatible with these observations and those previously made in S. faecalis is that the B. subtilis cross wall is brought to a constant thickness (possibly by remodeling or precursor addition) before or during separation. Although most observations made from the reconstruction of the septal zones of B. subtilis may fit the S. faecalis model of surface growth, differences in the pattern of septal growth were seen when the two organisms were compared. These have been discussed in terms of differences in the regulation of their respective septal growth sites and basic mechanisms of wall assembly and modification.

Bacillus subtilis↗

PubMed1976

The biological origin of antibody diversity.

Antibody diversity has a compelling fascination for many scientists and over the years speculations have sometimes seemed more numerous than facts. Now the structural basis of antibody specificity is well defined. Amino acid sequences and recently three-dimensional structures of various immunoglobulins provide the most solid basis for discussing the origin of diversity. The novel pattern of variable (V) and Constant (C) regions of amino acid sequence has been resolved further to show the functional pattern of variability. Inheritance of separate V and C genes is accepted, but attempts to define more than one gene coding for each V region are considered here to be unnecessary. The pattern of variability is still best understood in terms of mutation and the presence or absence of various selective pressures. The major area of debate still hinges around the extent to which mutation and selection operate during evolution or somatically. Sequence data have now been generally interpreted to require multiple V genes carried in the germ line. A few individual VH genes have been mapped in close linkage to CH genes in the mouse. The apparent existence of three VH alleles in rabbits was a strong argument against multiple V genes. Now the three phenotypes have been shown to be due to alleles controlling the expression of three sets of VH genes all present on the same chromosome. That V-gene expression requires rejoining of V and C genes at the DNA level is now almost certain. Models for the joining process can draw on the precedents of transposable genetic elements, which are widespread in Nature. The total extent of antibody diversity remains a philosophical point. Estimates of the number of antibody molecules required for observed diversity are reduced by two recently documented proposals. Each antibody combining site apparently has many (estimated at 100) different specificities and most combinations of VH and VL regions probably form a viable site. A given combining site can be defined by its pattern of shared specificities. Several specific antibody repertoires have been measured and the size in each case is consistent with the stringency with which the specificity is selected. Repertoire size appears to be under genetic control, but there are problems in viewing the genotype through the veil of clonal selection. Molecular hybridization has been used recently in an attempt to count V and C genes directly. C genes are seen in DNA having nonreiterated sequences, as formal genetics predicts. Each V-region probe hybridizes at a similar rate to C-region probes. Interpretation of this result depends on the extent to which one V-region probe will reveal nonhomologous V genes. Previous estimates that many cross-hybridizing genes should have been seen if present are possibly exaggerated. It is argued here that the data are compatible with a germ-line gene for each probe studied. Maximum estimates for the number of germ-line genes are sufficient to account for antibody diversity...

Amino Acid Sequence↗

PubMed1979

Changing concepts in psychosomatic theory. I. Historical analysis.

Psychosomatic medicine has utilized static, linear, two-dimensional models in attempting to identify a causative relationship between psychosocially conceptualized events and biologically conceptualized ones. This has led to inherent difficulties that are logistically unresolvable. For example, the different language systems lend themselves to overlap with the possibility of addressing themselves to describing manifestations of the same phenomenon from dissimilar conceptual orientations. The problem is further complicated by attempting to link these together in a temporal sequence suggesting a causal relationship. We have ignored both feedback processes in terms of a sequential process modifying a preceding one and the possibility that a reverse order of relationships might explain some processes. In our quest for specificity, we have ignored that disease states are not static ones any more than is life but change over time, suggesting that alterations will occur in the original relationships proposed among our different systems of conceptualization. Among the remedies suggested for a reordering of our thinking are: (a) a revision of linear unidirectional causative models to cyclical bidirectional models; (b) a reformulation of two-dimensional temporal linear relationships toward three-dimensional spherical ones which overlap in time; (c) the relating of these aspects not to each other but to a third factor, common to the three which remains to be identified; (d) the development of a language that bridges the psychological, social and biological.

History, 19th Century↗

PubMed1977

Stereology, a new quantitative morphological approach to study prostatic function and disease.

Although a considerable amount of quantitative biochemical data of the prostatic gland is available the current morphological information is restricted up to now to descriptive findings. Stereology is the application of mathematical axioms and allows one to quantitate three-dimensional structures from the measurement of two-dimensional cross sections thereof. The stereological techniques provide values for volumes, surfaces and number of tissue and glandular cellular components found within the prostatic gland. Four examples are presented to illustrate how quantitative morphology can be applied to study prostatic function and disease. A stereological model, which provides information on the structure of the prostatic gland is shown for the rat prostate (ventral lobe). The model consists of morphologically defined space and membrane components of the prostatic gland and the glandular cell. The alteration, induced in the glandular cells of the ventral lobe of the rat prostate by administration of a synthetic progestine (ethinyl-norgestrienone) were studied by stereological methods. An attempt was made to quantify the morphological aspects of both, the epithelial and stromal components of the normal human prostate (3rd decade of life) and of benign prostatic hyperplasia. In comparing the stereological data of the glandular prostatic cell in the normal human prostate with that in benign prostatic hyperplasia, a diminished secretory activity of the glandular cell in benign prostatic hyperplasia is indicated. A high volume density of the fibromuscular tissue, as well as an activation of the smooth muscle cell in the fibromuscular tissue is observed in benign prostatic hyperplasia.

Adult↗

PubMed1979

Three-dimensional reconstruction of the chromatin bodies in the nuclei of mature erythrocytes from the newt Triturus cristatus: the number of nuclear envelope-attachment sites.

The arrangement of the chromatin bodies in the interphase nuclei of 6 erythrocytes has been investigated by means of 3-dimensional reconstruction from electron micrographs of serial sections. When the borders of chromatin bodies are marked on the surface of each model, discrete areas of chromatin in contact with the nuclear envelope are revealed. The number of these areas in approximately equal to the number of chromosomes in the diploid set. The data suggest that each chromatin body corresponds to a condensed interphase chromosome and that each chromosome is attached to one discrete site on the nuclear envelope. The data are insufficient to show whether or not the condensed chromosomes are arranged in any orderly pattern in these nuclei.

Animals↗