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The cuticle of the American horseshoe crab, Limulus polyphemus, is largely free of the macroscopic epibionts that rapidly colonize most solid surfaces exposed to sea water. Here, we describe a viscous surface secretion that coats the carapace of the horseshoe crab. We report methods for stimulating production of the substance, identify hemolytic and liposome-permeabilizing activities and provide a partial biochemical characterization. We propose that this secretion functions as an anti-fouling agent protecting the chitinized epithelium of the cuticle from colonization by deleterious epibionts.

Transforming growth factor-beta 1 is a pleiotropic peptide mediator of growth, differentiation, and extracellular matrix synthesis. In the embryonic chick heart prior to the formation of the endocardial cushions, evidence from in vitro experiments suggests that transforming growth factor-beta 1 may be an inducer of the differentiation of atrioventricular endothelial cells into endocardial cushion mesenchyme. Further in vitro evidence suggests that the factor stimulates mesenchymal cell proliferation, and, thus, growth of the cushions. Using an antibody made against a peptide duplicating the aminoterminal 30 amino acid sequence of transforming growth factor-beta 1, we stained sections of stage 11, 18, 23, 26, and 36 chick hearts by an in situ immunofluorescence technique. Transforming growth factor-beta 1 staining localized to the endocardial surface and epicardial surface of the stage 11 heart, but it decreased from these locations in later stages. The cardiac jelly (stage 11), endocardial cushions (stage 18, 23, and 26), and, subsequently, the heart valve leaflets (stage 36) stained intensely for the growth factor.

A sensitive method for assaying aggregation of dissociated cells has been developed which allows the determination of the mean number of cells per aggregate of a cell population. We have demonstrated that exposure of dissociated 6- or 7-day chick embryo neural retinal cells to trypsin in calcium-free solution renders them unable to aggregate for a half hour in stirred cell suspensions. Aggregation was noticeable first at 30 to 40 minutes and, progressed to the formation of massive compact aggregates. Because the half-hour aggregation lag occurred both in the absence of serum and in medium reclaimed from aggregated preparations, the possibilities were excluded that it was due either to an inhibitor of aggregation in the serum, or was the time required for release into the medium of soluble aggregation-promoting materials emanating from the cells themselves. Cells dissociated by divalent cation withdrawal (Ca++, Mg++-free saline with EDTA) aggregated without a lag. The trypsin-induced lag does not appear to be the result of trypsin adsorbed to the, surfaces of dissociated cells, as the lag is not abolished by addition of trypsin inhibitors to the aggregation medium. Microelectrophoresis of dissociated cells did not reveal changes in surface charge density during recovery from trypsinization. A variety of proteins and calcium ion, if present during trypsinization, protect the cells against the trypsin-induced aggregation lag. If the temperature was reduced from 37 to 6°C, aggregation of fully adhesive cell populations came to a complete halt within 2 to 3 minutes. Aggregation resumed with a 5 to 10 minute delay when the temperature was returned to 37°C. The rapidity of onset and reversal of inhibition of aggregation by low temperature treatment militates against the hypothesis that the low-temperature inhibition of aggregation acts by suppressing the synthesis of cell surface components necessary for adhesion. The abolition of the aggregation lag in trypsinized cells was also shown to be temperature-dependent; a 20-minute cold, pulse administered in the middle of the lag period extended the length of the lag by exactly 20 minutes.

Concentrations of copper, zinc, chromium, lead, cadmium, and phosphorus were obtained from 81 samples of unconsolidated estuarine sediment from Great Bay, New Hampshire. Dispersal of aqueous chromium from localized industrial effluent is believed responsible for an increase in sediment chromium throughout the entire estuary. High phosphorus concentrations exist in sediment near the outfalls from several waste-water treatment plants. There is no evidence for any increase of copper, zinc, lead, or cadmium in this estuary, except for localized high concentrations close to industrial outfalls.

A recent hypothesis, proposed by A. S. G. Curtis, asserts that the formation of homogeneous tissues within heterotypic aggregates occurs during the initial phases of cellular aggregation rather than by a process of cell sorting in mixed aggregates. The present studies of the early stages of aggregation of mixed suspensions of dissociated chick embryo pigmented retinal epithelial and neural retinal cells do not support Curtis' hypothesis. The early aggregates formed from these mixed cell suspensions are disordered mixtures of the two cell types. Establishment of homogeneous neural retinal and pigmented retinal epithelial tissues occurs much later in the aggregates. The hypothesis of Moscona that the process of formation of type-specific tissues in mixed aggregates requires a specificity of cell adhesion was examined by attempting to demonstrate cell contact specificity at the electron microscope level in heterotypic aggregates undergoing cell sorting. Specificity of cell contact was not observed. Instead, fine structural studies of cell contact interactions demonstrate that pigmented retinal epithelial cells have broad areas of cell contact and specialized contact junctions with neural retinal cells within the aggregates.

Three heretofore undescribed types of yolk platelets are described from embryos of Xenopus laevis. The first (designated the multiple main-body platelet) is characterized by the occurrence of numerous randomly oriented small main-body crystals embedded in the noncrystalline superficial layer material. The second is characterized by the occurrence of a main-body crystal with an extremely irregular profile. The main-body element of the third platelet type (designated the cavitated main-body platelet) invariably shows little or no evidence of crystalline substructure and contains numerous internal cavities.

The role of dissolved organic matter (DOM) in the speciation of trace metals in natural waters is poorly understood1–3. Although dissolved organic matter–iron associations have been observed in freshwater systems4–6, it has been thought that DOM–iron species are not significant in saline waters7. Yet recent studies have suggested that iron–DOM interactions in the pore waters of anoxic marine sediments may be important8,9. The possibility of organically associated trace metals in anoxic water has been used to explain why metal concentrations are higher than those predicted by sulphide-mineral equilibria10,11. We present here data that indicate that strong iron–DOM associations do occur in the anoxic pore waters of nearshore marine sediments and that both the total dissolved iron and organically associated iron change seasonally.

The formaldoxime colorimetric method for manganese, previously utilized for freshwater and seawater samples of large volume, has been modified for the analysis of small volume, iron-rich sediment pore water samples. Using as little as 3 ml of sample and the addition of EDTA to destroy the Fe-formaldoxime interference (at concentrations of 9 μM Mnl−1), a precision of 3% is obtained.