Tracing of cell lineage in embryonic development of Phallusia mammillata (ascidia) by vital staining of mitochondria

Vital staining of mitochondria with a fluorescent dye 3,3′-diethyloxacarbocyanine was used to follow cell lineage in embryos of Phallusia mammillata. The results agree in general with the plan established by Conklin in 1905. Strong fluorescence migrated after fertilization similarly to the pigment of the “yellow crescent” in Styela. Later, fluorescence segregated into muscle cell primordia, but not into mesenchyme cells. An animal hemisphere cell, b 8.17 also exhibited strong fluorescence and joined a group of muscle primordia, very likely becoming a muscle cell itself. In the tadpole, all the tail muscle cells were fluorescent. Fluorescence was also noticed in nerve cell primordia of the vegetal hemisphere, particularly in the cell A 8.16 whose descendants appeared to become part of the sensory vesicle which was strongly fluorescent in the tadpole. The usefulness of this type of vital staining in following cell lineage of colorless embryos is stressed.     

A membrane-associated form of C-reactive protein is the galactose-specific particle receptor on rat liver macrophages

Rat liver macrophages express a galactose-specific receptor which mediates endocytosis of particles or neuraminidase-treated blood cells. From rat serum we now have isolated and purified a galactose-specific lectin by affinity chromatography. Comparative analysis of this serum galactose-binding protein with the galactose-particle receptor protein purified from rat liver macrophages and with C-reactive protein (CRP) reveals close relation or identity of these proteins. An apparent m.w. of 30,000 was determined for all three proteins by SDS-PAGE under reducing conditions and m.w. of about 130,000 by native PAGE. All three proteins exhibit the same pentameric, ring-shaped structure in electron microscopy after negative staining. Antibodies raised against the serum galactose-binding protein or against the macrophage receptor cross-react. A mAb specific for rat neo-CRP labels liver macrophages but not hepatocytes and reacts with the isolated protein in a Western blot assay. Furthermore, the galactose-particle receptor can be functionally replaced by purified CRP: the binding capacity for neuraminidase-treated E of receptor-depleted liver macrophages can be restored by preincubation with purified rat CRP. We therefore conclude that CRP occurs as a membrane-associated protein constitutively expressed on liver macrophages functioning as a receptor mediating galactose-specific binding of particulate ligands.     

Transposable element-induced mutations of the viviparous-1 gene in maize

The viviparous-1 (vp1) locus in maize is a developmental gene that controls diverse aspects of the maturation phase of seed development. Mutations of vp1 alter embryo sensitivity to the hormone abscisic acid and block formation of anthocyanin pigment. Molecular cloning of a Robertson Mutator-induced mutant allele, vp1-mum-1, by transposable element tagging has allowed analysis of several transposon-induced vp1 mutants. In the vp1-Mc mutation, the gene is disrupted by 4.0 kbp insertion, which results in expression of a 3′ truncated mRNA. Phenotypically, this allele is at least partially functional in causing embryo dormancy, but is ineffective in controlling anthocyanin expression. This result suggests that disruption of the C-terminal domain of the Vp1 protein specifically affects regulation of the anthocyanin pathway. A second Mutator- derived allele, vp1-mum2, exhibits an unusual form of somatic mutability in which endosperm cells revert from wild-type vp1 expression to a mutant condition. The vp1-mum2 allele contains a 1.5 kbp Insertion that has no detectable homology to known Mu elements. This element is retained In wild-type germinal revertants derived from vp1-mum2 An apparent DNA modification affecting cleavage at an internal Sstl restriction site in the element correlates with vp1-mum2 states that exhibit wild-type Vp1 expression. A model involving mitotic assortment of modified and unmodified DNA strands during development is proposed for vp1-mum2 somatic mutation.     

Inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase by ribulose-1,5-bisphosphate epimerization and degradation products

Xylulose-1,5-bisphosphate in preparations of ribulose-1,5-bisphosphate (ribulose-P₂) arises from non-enzymic epimerization and inhibits the enzyme. Another inhibitor, a diketo degradation product from ribulose-P₂, is also present. Both compounds simulate the substrate inhibition of ribulose-P₂ carboxylase/oxygenase previously reported for ribulose-P₂. Freshly prepared ribulose-P₂ had little inhibitory activity. The instability of ribulose-P₂ may be one reason for a high level of ribulose-P₂ carboxylase in chloroplasts where the molarity of active sites exceeds that of ribulose-P₂. Because the K_D of the enzyme/substrate complex is ≤1 μM, all ribulose-P₂ generated in situ may be stored as this complex to prevent decomposition.     

Sarcomere length uniformity determined from three-dimensional reconstructions of resting isolated heart cell striation patterns.

A- and I-band striation positions have been obtained, three-dimensionally reconstructed, and statistically analyzed from the volumes of resting isolated heart cells. Striation patterns from optically discrete subvolumes are imaged along the length of these myocytes with a computer-interfaced optical microscope imaging system. Planar striation maps are reconstructed by the computer from sequentially obtained striation pattern images displaced across the width or depth of the cell in controlled steps. Multiple planar maps are combined to form full three-dimensional (3-D) reconstructions that illustrate the sarcomeric structure and ordering throughout the volume of the cell. These reconstructions demonstrate a high degree of striation registration throughout most regions of cardiac cells. The striation registration is often slightly (less than 10 degrees) skewed across the width or depth of nearly every cell and is occasionally disrupted between adjacent groups of sarcomeres. These disruptions in registration are always associated with the locations of the nuclei. Rigorous statistical analyses indicate small volumetric regions of the cell delineated by these disruptions can have significantly (0.014-0.113 micron) shorter or longer average sarcomere length periodicities. Unlike skeletal muscle "fibrillenstruktur," these data from cardiac cells exhibit no evidence of helical packing schemes for sarcomere order. These observations suggest that the relatively large nuclei displace and disrupt the normal registration of the sarcomeres, which is probably mediated by internal cytoskeletal structures.     

Melanin as a natural germ cell marker for intraspecific transplantation experiments in Ambystoma mexicanum (Urodela,Amphibia)

Summary In urodele amphibians, the lack of a reliable germ cell marker restricts the experimental study of the germ lineage. In the present work, we conducted genetic and histological analyses in order to demonstrate that melanin from oocytes constitutes a germ cell marker available for intraspecific experiments in Ambystoma mexicanum. Then, using this marker, we implanted germ cells from undifferentiated gonads (stage 48) into the blastocoel of host embryos and investigated their fate and determined state. Our results show that, from this stage on, the donor cells do not differentiate into other cell types; therefore, they are restricted in developmental capacity and irreversibly determined as germ cells. On the other hand, exogenous germ cells were found in an isotopic position until the young tail-bud stage, and then were found in an ectopic position; these results suggest that, from the middle tail-bud stage on, an active process contributes to migration of primordial germ cells to the gonadal territory.     

Effects of stormwater sewer discharges on the aquatic community in urban canals in Lelystad

In urban areas with a separate sewerage system, the stormwater runoff is discharged into surface waters. A study on the effects of stormwater sewer discharges on the composition of the aquatic community in urban waters was carried out in two areas with a primarily residential use in the new town of Lelystad. The aquatic organisms considered included hydrophytes, epiphytic diatoms, filamentous algae and macroinvertebrates.The results indicate that the stormwater sewer discharges cause a slight change in the composition of the aquatic community. The water in the urban surface waters can be characterized as eutrophic and - toa-mesosaprobic. Near stormwater sewer outfalls the water tends to the more polluteda-mesosaprobic state. The shifts in the composition of the aquatic community could be traced primarily on the basis of a number of epiphytic diatoms and macroinvertebrates (in particular some Diptera and Trichoptera). Most hydrophytes, filamentous algae and the remaining epiphytic diatoms and macroinvertebrates (in particular water beetles and water mites) turned out to be of little or no use in this respect.Because the investigation was carried out in an unusually dry summer, the results probably underestimate the effects of stormwater discharges on the aquatic community.