The benefit to some minnows of spawning in the nests of other species

Synopsis Fishes that act as nest associates spawn simultaneously with nest-building hosts and then abandon their eggs. The proposed benefit for this behavior is increased brood survivorship, arising from the physical environment provided by the nest or the parental care provided by the host. Field and enclosure experiments indicated that associates benefit from the parental care provided by the host, and not from the physical environment provided by the nests of hosts. This information, along with the effect of nest association on host reproductive success, is necessary before the nature of this nesting symbiosis can be characterized.     

Cytomorphology of primary small-cell (Merkel-cell) carcinoma of the skin in fine needle aspirates

The histologic appearance of primary small-cell carcinoma of the skin (the so-called Merkel-cell tumor) is similar to other small-cell tumors that may metastasize to the dermis. Significance has been placed on the electron microscopic appearance of this tumor since the ultrastructural features of this neoplasm are helpful in distinguishing it from most of the other neoplasms considered in the differential diagnosis. To determine whether any additional morphologic criteria might exist to distinguish this neoplasm, the fine needle aspirate appearance of a primary small-cell carcinoma of the skin was studied and compared to that of similar preparations of other small-cell tumors that could potentially involve the dermis. Cells of this unusual tumor were round and showed neither cohesiveness nor nuclear molding. Mitoses were numerous. The chromatin pattern was bland. The cytologic features of this tumor can aid in the distinction of primary small-cell carcinoma of the skin from other metastatic small-cell neoplastic lesions in the dermis of adults.     

The isolation of new DNA synthesis mutants in the yeast Saccharomyces cerevisiae

Summary Sixty-eight new conditional cell cycle mutants have been isolated on the basis of their terminal cellular morphology (dumbbells). Fifteen mutants falling into nine complementation groups, were grossly defective in DNA replication and have been assigned the provisional gene symboldbf (fordumbbellformer). Dbf1 and2 stop DNA synthesis immediately on transfer to 37°C and are presumably defective in enzymes required for polymerization. Neither, however, possess a thermolabile DNA polymerase A or B.Dbf3 and4 show a pattern of synthesis consistent with their being deficient in initiation of DNA synthesis. This is confirmed in the accompanying paper.The remaining mutants are deficient in the synthesis of RNA as well as DNA. Indeed the four members of one complementation group are allelic withrna3, one of the group of mutants originally isolated as defective in RNA synthesis, and which do not exhibit a cell cycle phenotype. A re-examination of this group of mutants however, showed the bulk of them also to be defective in DNA synthesis. Furthermore, in preliminary experimentsrna3 and our four new alleles of it, together withrna6 anddbf5 and6, showed enhanced spontaneous mutation frequency.     

Mutants of yeast with depressed DNA synthesis

Summary Seven temperature-sensitive mutants have been isolated in Saccharomyces cerevisiae which show a reproducible defect in DNA synthesis at the restrictive temperature. One of these is allelic with rnal1 (Hartwell et al., 1970) but the remaining mutants define six complementation groups and probably represent six different genes. The gene symbol dds (for depressed DNA synthesis) is proposed.At the restrictive temperature, rnal1-2, dds2-1 and dds6-1 show a rapid and almost total cessation of DNA and RNA synthesis, whilst protein synthesis continues for several hours. The remaining dds mutants show a reduced rate of DNA synthesis from the time of temperature shift (dds1, dds3, dds4) or a cessation of DNA synthesis at a later time (dds5). In some cases, RNA synthesis is affected concomitantly with, or soon after, the depression in DNA synthesis. Possible reasons for the phenotypes of these mutants, and for the relative absence of yeast mutants which are unambiguously and specifically affected in DNA synthesis, are discussed.In addition, we report the isolation of seven new alleles of known cdc genes and ten new mutants with a cell cycle phenotype that complement those already known.     

On the mechanism of premeiotic DNA synthesis in the yeast Saccharomyces cerevisiae

Premeiotic DNA synthesis in synchronously sporulating cultures of the yeast, Saccharomyces cerevisiae, was analysed by sedimentation in alkaline sucrose gradients and by DNA-fibre autoradiography. The gradient profiles of cells pulse-labelled for varying times were essentially identical with those obtained with mitotic cultures, revealing a close resemblance between the meiotic and mitotic replication mechanisms. This was supported by the finding that exposure of meiotic cells to a specific concentration of hydroxyurea led to the accumulation of completed, but unjoined replicons, just as it does in mitotic cells. The results of DNA-fibre autoradiography confirmed that replicons in meiotic cells are the same size (20–180 Kb, averaging around 90 Kb) as in mitotic cells, and assuming replication is bi-directional, replication forks must move at round the same rate as in mitosis, i.e. about 0.7 μm/min.     

Xenopus temporal retinal neurites collapse on contact with glial cells from caudal tectum in vitro.

Nasal and temporal retinal neurites were confronted in culture with glial cells from the rostral and caudal parts of the optic tectum and with glial cells from the diencephalon. Twenty of each of the six classes of encounter between individual growth cones and isolated glial cells were analysed by time-lapse videorecording. The results show that growth cones from the temporal retina collapse when they contact glial cells from the caudal tectum, but do not collapse when they contact glia from other areas. Growth cones of nasal retinal fibres do not collapse on contact with any of the glial types examined. This suggests that the inhibitory phenomena described by others are in part due to the cell surface characteristics of glial cells, and that there are differences between glia from the front and back of the optic tectum.     

The cytopathology of cerebrospinal fluid. II. Metastatic cancer, meningeal carcinomatosis and primary central nervous system neoplasms

The evaluation of cerebrospinal fluid (CSF) requires adaption of basic cytopathologic principles to the specific neoplasms that involve the central nervous system (CNS). In this review, general criteria for detecting malignant cells in CSF are presented. The incidence and cytologic characteristics of specific metastatic tumors that involve CSF are reviewed, and the incidence, pathogenesis and natural history of meningeal carcinomatosis are discussed. The role of cytopathology in the detection and management of primary CNS tumors is presented. Emphasis is placed on the cytologic characteristics of individual types of primary brain tumors and the application of fine needle aspiration biopsy to intracranial lesions.