Hormonal control of meiosis reinitation in starfish oocytes. New evidence for the absence of efficient intracellular receptors for l-methyladenine recognition.

Nuclei isolated from testes of the house cricket were centrifuged in a gradient of colloidal silica with a density range of about 1.12 to 1.18 g/ml. Fractions were collected from the bottom to the top of the gradient, and the types of nuclei in them were classified by phase microscopy. The distribution of nuclear types in the gradient indicated relatively large increases in nuclear density during spermatogenesis, and that silica-gradient centrifugation can readily yield fractions enriched for nuclei of specific developmental stages needed to study basic protein changes during sperm development. Basic proteins could be extracted from nuclei spun through silica if they were washed with polyvinylpyrrolidone. The histones in different fractions of nuclei were analysed electrophoretically. Fractions of spermatocyte and early spermatid nuclei contained histones of the somatic types as their only basic proteins. Fractions with mixtures of mid-spermatid and earlier nuclei also yielded somatic histones primarily. Essentially pure samples of late spermatid nuclei were obtained. They lacked somatic histones. In one fraction of late nuclei, the spermatid-specific histones TH1 and TH2 were the major proteins present. In another, two additional histone-like components, not detected in previous studies, were also prominent.     

Why and how do Hebrew verbs change their form? A morpho-thematic account

This paper examines the criteria that are responsible for morphological variation in the verbal system of Modern Hebrew. The Hebrew verbal system consists of configurations called binyanim (and binyan in sg.): CaCaC, niCCaC, hiCCiC, CiCeC and hitCaCeC. The relation between Hebrew binyanim is manifested via valence changing operations (e.g. ni?ek ‘kiss’ and hitna?ek ‘kiss each other’). Some verbs demonstrate morphological variation with regard to their binyan. I define morphological variation as cases where two verbs occur in (at least) two different binyanim, but share the same (i) stem consonants (ii) thematic grid and (iii) denotation. For example, the verbs nirtav and hitratev are formed in niCCaC and hitCaCeC respectively; they are both intransitive verbs that denote ‘get wet’ and they share the stem consonants r-t-v. Morphological variation results from a change that takes place in the verbal system, where a verb takes another form. I analyze the factors that bring about the development of a new morphological form alongside the existing form, and are responsible for the choice of a specific binyan during that process. The main claim is that the addition of another binyan results from both morpho-phonological and thematic-syntactic factors. With respect to the former, the morphological mechanism changes the binyan of verbs in cases where their inflectional paradigm consists of prosodic or segmental alternation. With respect to the latter, verbs that are stored in the lexicon as thematically derived entries have a greater chance of undergoing binyan change than do basic entries. Verbs that are the output of syntactic operations do not undergo morphological change. In addition, verbs which are morphologically neutral with respect to transitivity change into a binyan that is marked as transitive or intransitive.     

Tumor-Associated Antigen Peptides as Anti-Metastatic Vaccines

Cytotoxic T-lymphocytes (CTLs) kill abnormal cells. CTLs recognize major histocompatibility complex class I molecules in complex with peptides derived from relevant antigens. The identification of tumor associated antigen peptides enabled the design of anti-tumor and anti-metastatic vaccines in a murine lung carcinoma.     

Expression of cell surface sialic acid and galactose by normal adult human melanocytes in culture

Normal adult human melanocytes grown either in the presence of phorbol ester or dialyzed hypothalamic extract were analyzed for their cell surface sialic acid and galactose content. In both cases, cells expressed large amounts of sialic acid, whereas they differed in their terminal nonreducing beta-D-galactosyl residues linked to N-acetyl galactosamine; such residues were accessible to peanut agglutinin and Bauhinia purpurea lectin on cells grown in phorbol ester and inaccessible on cells grown with dialyzed hypothalamic extract. In addition, striking differences in morphology and growth characteristics were observed between adult melanocytes grown with phorbol ester or with dialyzed hypothalamic extract. Thus, pure cultures of normal adult human melanocytes grown in the presence of dialyzed hypothalamic extract displayed cell surface properties different from those of melanocytes grown with phorbol ester. Cultures of melanocytes with dialyzed hypothalamic extract are likely to reflect known cell surface characteristics of human melanocytes in the skin. Such cultures could represent a useful model to study normal behavior and tumor progression of pigmented cells.