Quantitative studies of steroid bioconversions in the seminal vesicles of spawning male African catfish, Clarias gariepinus (Burchell), under natural conditions, and of non-spawning catfish under natural and fish farm conditions

1. Steroid bioconversions in the seminal vesicles of Clarias gariepinus were studied quantitatively in vitro by tissue incubations with [3H]pregnenolone, [3H]androstenedione and [14C]11 beta-hydroxyandrostenedione, respectively. 2. Spawning and non-spawning catfish, collected in the Hula nature reserve in northern Israel during the spawning period, and non-spawning animals, collected from a fish pond in the same region during the same period, were studied. 3.Spawning animals showed a significantly higher production of 17 alpha-hydroxyprogesterone, 5 beta-pregnan-17 alpha-ol-3,20-dione and 5 beta-reduced androgens than non-spawning feral and pond catfish, as a result of a significantly increased contribution of the enzymes 5 beta-reductase and 3 alpha-hydroxysteroid dehydrogenase (HSD). 4. In spawning catfish the concentration of gonadotropin in blood plasma were also significantly higher than in the plasma of non-spawning feral and pond catfish. This increase in gonadotropin level might have induced the rise in enzyme activity of 5 beta-reductase and 3 alpha-HSD. 5. It is concluded that the absence of a shift in steroidogenesis towards the production of 5 beta-reduced steroids may be among the factors preventing spontaneous spawning in male African catfish under husbandry conditions.     

Assembly of splicing complexes on exon 11 of the human insulin receptor gene does not correlate with splicing efficiency in-vitro

Background  

Incorporation of exon 11 of the insulin receptor gene is both developmentally and hormonally-regulated. Previously, we have shown the presence of enhancer and silencer elements that modulate the incorporation of the small 36-nucleotide exon. In this study, we investigated the role of inherent splice site strength in the alternative splicing decision and whether recognition of the splice sites is the major determinant of exon incorporation.