Evolutionary aspects of cell differentiation

Biology of hypothalamic neurons and pituitary cells

Results obtained by examining hypothalamic neurons producing precursors to neurohormones, and pituitary cells synthesizing peptide and glycoprotein families of hormones, and recent advances in comparative endocrinology, have been summarized and considered from the following viewpoints: species specificity in the organization and communication of the hypothalamic neurons with different brain areas lying inside the BBB and with CVOs; sensitivity of hypothalamic neurons and pituitary cells to the environmental stimuli; gonadal steroids as modulators of gene expression needed for neuronal differentiation and synaptogenesis; dose(s)-dependent pituitary cell proliferation and differentiation; an inverse relationship between PRL and GH synthesis and release and also between degree of hyperplasia and hypertrophy of PRL cells and retardation of GTH cell differentiation; and responsiveness of neurons producing CRH, and of neurons and pituitary cells synthesizing POMC hormones, to stress and glucocorticosteroids. These data show that growth of the animals may be stimulated, retarded, or inhibited; reproductive properties and behavior may be under hormonal control; and character of responsiveness in reaction to stress, and ability for adaptation and other related functions, may be controlled.

Methods of successive multiparametric cytochemistry and microfluorometry on identical cells with special reference to cell cycle phases in a chick embryo

The study of cell cycle kinetics in relation to regulatory mechanisms in embryonic development is considered quite important, but many technical difficulties still remain owing to the complexity of embryonic systems. To facilitate such study, a novel method of multiparametric microfluorometry was developed and is presented here. In many other multiparametric methods, various cytochemistries and fluorometries are conducted at the same time, whereas in our system only one type of cytochemistry and its microfluorometry are performed first and then other types subsequently. Our system is composed of two parts, a method for combining various types of quantitative cytochemistries to be performed in succession on identical cells and a method that permits the implementation of cytochemistries and microfluorometries in succession using in combination a microfluorometer, TV camera, video recorder, digital Telopper, and microcomputers. A method for the evaluation and normalization of microfluorometric data on DNA content is described. The cell cycle phases of each cell can be accurately distinguished on the basis of DNA content and BrdU uptake, using a statistical method. A cell cycle traverse study using embryonic avian scale dermal cells was carried out in which the four parameters of DNA content, double labeling with BrdU and [3H]AdR, and time lapse between the two labelings were included. As an example of its application to molecular cytochemistry, in situ nick translation was conducted on developing scale dermal cells. The special features and scope of application of the present system are discussed.

Chromosome markers and karyology of selachians

Among vertebrates, chondrichthyans exhibit peculiar karyotypes and total amount and composition of DNA very different from those of tetrapods and teleosteans. Selachians have relatively large genome sizes (more than 30 pg/N), which are inversely related to the fraction rich in adenine-thymine. Moreover, they show a high chromosome number (2n = 60-100), decreasing in the most specialized species. The karyotypes of Scyliorhinus stellaris, Torpedo ocellata, and T. marmorata have been investigated by several techniques in order to distinguish particular genome fractions along the chromosome arms. C-banding appears to be positive in most telomeric regions in Scyliorhinus and at the interstitial level in the two torpedo species. Studies with restriction enzymes (RE) have just been started in selachians, employing ALU I and HIND III in Scyliorhinus stellaris. The former digests the whole chromosome except the telomeric regions, revealing patterns similar to the C-bands. The latter cuts the chromosomes into several interstitial regions, producing G-bands. Other RE are being studied, which will allow identification in situ of qualitative differences in the various DNAs.