Splice site m6A methylation prevents binding of U2AF35 to inhibit RNA splicing

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Coordination of spermatogenic processes in the testis: lessons from cystic spermatogenesis

A common observation in the vertebrate testis is that new germ cell clones enter spermatogenesis proper before previously formed clones have completed their development. The extent to which the developmental advance of any given germ cell clone in any phase of spermatogenesis is dependent on that of neighboring clones and/or on the coordinating influence of associated Sertoli cells in the immediate vicinity or of others further away remains unclear. This review presents an overall synthesis of findings in an ancient vertebrate, the spiny dogfish shark and shows that, even at this phyletic level, the developmental advance of a given germ cell clone is the outcome of various processes emanating from its spatiotemporal relationship with (1) its own complement of Sertoli cells in the anatomically distinct spermatocyst and (2) Sertoli cells associated with other germ cell clones that lie upstream or downstream in the spermatogenic progression and that secrete, among others, androgen and estrogen destined for target sites upstream. Analysis of the protracted spermatogenic cycle shows the coordination in space and time of spermatogenic and steroidogenic events. Furthermore, the natural withdrawal of pituitary gonadotropin support in the dogfish causes a distinct and highly ordered gradient of apoptosis among the spermatogonial generations; this in turn is a major contributing factor to the cyclic nature of sperm production observed in this lower vertebrate. Because of the simplicity of their testicular organization, their cystic spermatogenesis and their phylogenetic position, cartilaginous fishes constitute a valid vertebrate reference system for comparative analysis with higher vertebrates.     

Non-identity of cystine lyase with β-cystathionase in turnip roots

An active preparation of cystine lyase (EC 4.4.1.-) was prepared from turnip roots and its substrate specificity examined. Only L-cysteine, cysteine-S-SO₃, and the sulphoxides of L-djenkolic acid, S-methyl-and S-ethyl-L-cysteine were substrates. L-Cystathione, L-djenkolic acid, S-methyl-and S-ethyl-cysteines were not cleaved by this enzyme. The K_m for L-cystine was 1.3 mM and L-cystathionine acted as an effective competitive inhibitor with a K_i of 0.7 mM. After dialysis against 10 mM potassium phosphate buffer pH 7.5, added pyridoxal phosphate was absolutely necessary for activity. In addition a marked stimulation was observed in the presence of ammonium sulphate. The products of the reaction were cysteine persulphide, pyruvate and presumably ammonia. The persulphide was easily demonstrated by cleavage with CN^? to yield SCN^? under conditions in which elemental sulphur was unreactive.     

Structure-activity studies of modified citrus limonoids as antifeedants for Colorado potato beetle larvae, Leptinotarsa decemlineata

Limonin and ten structurally modified limonins were evaluated as antifeedants against 4th instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata Say, in no-choice leaf dics assays. The epoxide and furan groups were shown to be essential structural requirements for high antifeedant activity.

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Résumé Le pouvoir phagodissuasif de la limonine et de 10 limonines dont la structure avait été modifiée a été évalué sur des disques de feuilles de Solanum tuberosum offerts à des larves du 4ème stade de L. decemlineata. Aucune activité dissuasive n'ayant été observée avec le tétrahydrolimonine ou le déoxylimonine, l'anneau furane et le groupe époxy sont donc nécessaires pour obtenir cette activité. Ni la réduction de la fonction 7-kéto, ni la rupture de l'anneau A de la limonine n'ont eu d'effêt sur cette activité. La réduction des fonctions 16-carbonyl et 7-kéto de la limonine ont diminué l'activité, mettant en évidence une action possible de l'anneau D-lactone dans l'activité phagodissuasive. Tandis que la déépoxydation de la limonine entraîne une perte d'activité totale, une restauration partielle de cette activité a pu être obtenu par une réduction ultérieure de la fonction 7-kéto.

     

Protein reactions with methyl and ethyl vinyl sulfones

Disulfide bonds of bovine serum albumin and wool were reduced byn-tributylphosphine to sulfhydryl groups that were then modified by methyl or ethyl vinyl sulfone in a nucleophilic addition reaction toS-(-ethylsulfonylmethyl)-l-cysteine andS(-ethylsulfonylethyl)-l-cysteine, respectively. The reductive alkylation was carried out either simultaneously, with both the reducing and alkylating agents present in the reaction mixture, or sequentially, with the reduced proteins first isolated before alkylation. Amino acid analysis studies showed that authentic, syntheticS-(-ethylsulfonylethyl)-l-cysteine eluted as a well-resolved peak after serine but that the peak associated with the corresponding methyl derivative overlapped the corresponding peak due to threonine. The extent of alkylation of the sulfhydryl groups of cysteine, -NH₂ of lysine, and NH groups of the imidazole ring of histidine was also measured by amino acid analysis. The results show that alkyl vinyl sulfones have a strong chemical affinity for protein functional groups.     

A slow wave frequency complex of the canine small intestine during the fasting state

The electrical activity of the duodenum and proximal jejunum was studied in conscious healthy dogs implanted with unipolar silver electrodes. A computerized method was used for the calculation of the mean frequency of the slow wave for each consecutive minute of the electromyographic signal. A "slow wave frequency complex" was identified in the fasted animals. It was characterized by an increase of the mean frequency of the slow wave which ranged, from one dog to another, between 1 and 3 cycles/min. The complex lasted about 30 min. It consisted of two distinct phases: a phase of increasing frequency of the slow wave which lasted about one-third of the total duration of the complex and a phase of progressive return of the frequency to its precomplex value. Each phase III of the migrating myoelectric complex occurring in both the duodenum and the jejunum was associated with one slow wave frequency complex. The phase III began a few minutes before the start of the slow wave frequency complex and ended a few minutes before the slow wave frequency reached its maximum. Ectopic phase IIIs which occurred in the jejunum but not in the duodenum were not associated with slow wave frequency complexes. The slow wave frequency complex was never seen in the fed dogs.     

Phylogenetic Analysis of Components of the Eukaryotic Vesicle Transport System Reveals a Common Origin of Adaptor Protein Complexes 1, 2, and 3 and the F Subcomplex of the Coatomer COPI

Eukaryotic vesicular transport requires the recognition of membranes through specific protein complexes. The heterotetrameric adaptor protein complexes 1, 2, and 3 (AP1/2/3) are composed of two large, one small, and one medium adaptin subunit. We isolated and characterized the cDNA for Arabidopsisγ-adaptin and performed a phylogenetic analysis of all adaptin subunits (proteins) in the context of all known homologous proteins. This analysis revealed (i) that the large subunits of AP1/2/3 are homologous and (ii) two subunits of the heptameric coatomer I (COPI) complex belong to this gene family. In addition, all small subunits and the aminoterminal domain of the medium subunits of the heterotetramers are homologous to each other; this also holds for two corresponding subunits of the COPI complex. AP1/2/3 and a substructure (heterotetrameric, F-COPI subcomplex) of the heptameric COPI had a common ancestral complex (called pre-F-COPI). Since all large and all small/medium subunits share sequence similarity, the ancestor of this complex is inferred to have been a heterodimer composed of one large and one small subunit. The situation encountered today is the result of successive rounds of coordinated gene duplications of both the large and the small/medium subunits, with F-COPI being the first that separated from the ancestral pre-F-COPI. Received: 1 October 1998 / Accepted: 4 January 1999     

Simulated hypogravity and proline incorporation into salt-extractable macromolecules from cell walls

Proline [U-¹⁴C] was fed to shoots of intact Tagetes patula grown normally, on horizontal clinostats, or on vertical clinostats rotating at 15 rev/hr. After various periods the incorporation of ¹⁴C into salt-extractable material from the cell walls of stems, petioles, leaves and flowers was determined. The cell walls of the gravity-compensated plants (grown on horizontal clinostats) has the highest amount of salt-extractable radioactivity. A 2- to 9-fold increase was observed in comparison to either the normal or vertical clinostat plant controls. Some physico-chemical properties of the salt-extractable fraction suggest that it consists of highly charged, low MW entities, possibly short chain peptides. On acid hydrolysis this material yields radioactive aspartic acid, glutamic acid and proline. The presence of labelled hydroxyproline is suggested. After acid hydrolysis of the cell walls of leaves, it was found that ca 4 times the amount of ¹⁴C was incorporated in the hypogravity-grown plant compared to the controls. It appears likely that extensibility changes in tissues under simulated hypogravity required additional cell wall protein.