ISOLATION AND CHARACTERIZATION OF A PRESPORE SPECIFIC STRUCTURE OF THE CELLULAR SLIME MOLD, DICTYOSTELIUM DISCOIDEUM

A method was described for isolation of the prespore specific vacuole (PSV) from slugs of the cellular slime mold, D. discoideum . A cellular component, which was fractionated in accordance with immunohistochemical staining using heteroplastic antispore serum, was found to consist of only the PSV. It was thus concluded that the PSV is identical with the cytoplasmic granule which has been shown by the antiserum to be specifically present in the prespore cell, and hence that the PSV is the only structure which contains the prespore specific substance (antigenic mucopolysaccharide). The isolated PSV contained polysaccharide equivalent to 14% of its protein content, and antigenic mucopolysaccharide constitutes about 60% of the total polysaccharide.     

Genetic Regulation of Melanocyte Differentiation

Melanocytes originate from the neural crest in vertebrates and migrate to the body surface where they differentiate into functional cells. Genes involved in melanocyte differentiation can be classified into two groups. One of them consists of the functional genes that control proteins specific to the function of the melanocyte. As the representative gene of this category, albino (c) locus in the mouse is considered to control tyrosinase, the key enzyme in melanogenesis. cDNA for mouse tyrosinase has been cloned and sequenced. The cDNA can be used to detect tyrosinase mRNA synthesized during melanocyte differentiation. On the other hand, genes such as brown (b) or pink-eyed dilution (p) have been assumed to control melanosome proteins. The other category consists of genes that regulate the expression of these functional genes directly or indirectly. In the mouse, so-called white-spotting genes and genes of the agouti series are considered to fall into this category. Based on the fact that mutations at the white-spotting loci result in the absence of melanocytes in a particular area of skin, it is assumed that some of these loci control the factors that promote either differentiation or migration of melanoblasts and are candidates for the classic regulator genes Genes at the agouti (a) locus in the mouse determine the type of melanin synthesized in hair follicle melanocytes, that is eumelanin or pheomelanin. An interesting feature of this locus is that the site of gene action is not within the melanocytes but in the cells surrounding them. The results of our study indicate that the gene product of the a-locus interacts with α-MSH at the α-MSH receptor site, regulates the cellular cAMP level via a signal transduction system and, in turn, determines the type of melanin synthesized in the cells.     

Differentiation of Extracutaneous Melanocytes in Embryos of the Turtle,Trionyx sinensis japonicus

The present study investigates the mode of differentiation of neural crest-derived melanocytes in the embryos of the soft-shell turtle, Trionyx sinensis japonicus. DOPA reaction-positive melanoblasts were first detected in 10-day-old embryos. Melanocyte differentiation in terms of pigmentation takes place from the day 16 of development. Melanin pigments were found in the dorsal integument as well as in various extracutaneous tissues such as skeletal muscle, dorsal aorta, peritoneum, blood vessels, choroid, lung, bone marrow, fat tissues and in the connective tissue of the nose. These results suggest the presence of a specific environmental regulation of the melanoblast differentiation in the soft-shell turtle.     

ON PROPAGATION OF CORTICLA FACTOR AND CYTOPLASMIC FACTOR PARTICIPATING IN CLEAVAGE FURROW FORMATION OF THE NEWT'S EGG*

From Cynops pyrrhogaster eggs just after the start of the first cleavage, a fragment of cortical layer with a small entire cleavage furrow was cut out. In the fragment, the cortex had already acquired susceptibility to and the subcortical cytoplasm had already accquired inducibility for furrow formation. The fragment was transplanted to the animal hemisphere of uncleaved fertilized eggs or eggs immediately after the onset of the first cleavage, from which a portion of the host cortex was removed. Observation was made on division of the graft, and on propagation of the cortical susceptibility and the cytoplasmic inducibility of the graft onto the host egg. The transplant divided succesively on the host egg in many cases, but the furrow of the graft never advanced to the surface of the host egg. Neither the cortical factor nor the cytoplasmic factor was transmitted across the graft to the recipient egg.     

Persistent Nucleoli in Early Postimplantation of Rat Embryos

Ultrastructural changes of the nucleolus in mitotic embryonic ectodermal cells of 7 1/2-day and 7 2/3-day rat embryos were examined. It was found that the nucleolus was broken down into small fragments during late prophase and metaphase, and that some of these fragments persisted in the cytoplasm of telophase cell (persistent nucleoli). No interphase embryonic ectodermal cells contained persistent nucleoli. Persistent nucleoli were also found in telophase cells of extraembryonic ectoderm, extraembryonic visceral endoderm and parietal endoderm of the embryos, but they disappeared in interphase cells. Persistent nucleoli in telophase cells tended to decrease in size with embryonic age, and they had almost completely disappeared in neuroectodermal cells of the telencephalon in 14 1/2-day embryos. They were concluded to be remnants of disappearing nucleoli in embryonic cells that were cycling too rapidly to permit their nucleoli to disappear completely.     

Effect of Bicuculline on the GABA Receptor of the Crayfish Neuromuscular Junction

SINCE it was reported that bicuculline is a specific antagonist of γ-aminobutyric acid (GABA)^1–3, much attention has been paid to the action of this alkaloid on cortical neurones^4–6. Thus it seemed worthwhile to test the mode of action of bicuculline on the inhibitory neuromuscular junction of the crayfish, where the action of GABA has been well documented^7,8.