Germ cells during gonadal sex differentiation in the teleost

We reported previously that two isoforms of vasa mRNA and protein are present in tilapia (Kobayashi et al. 2002). One (vas-s) lacks a part of the N-terminal region found in the other isoform (vas). Both isoforms are expressed in oocytes through the embryonic stages when PGCs localize in the lateral plate mesoderm. After PGCs localized in the gonadal anlagen, vas-s expression increased and vas expression became undetectable. Expression of both isoforms was observed again after morphological gonadal sex differentiation, irrespective of genotypic sexes. These changes are in accordance with sex differences in number of gonial germ cells during this period, suggesting that molecular sexual dimorphism occurs in germ cells between both sexes during this period.     

Mechanisms of synthesis and action of 17α,20β-dihydroxy-4-pregnen-3-one,a teleost maturation-inducing substance

This article briefly reviews the current status of investigations, mainly based on the amago salmon,Oncorhynchus rhodurus, on the mechanisms of synthesis and action of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog). Pituitary gonadotropin is of primary importance in triggering meiotic maturation in teleost oocytes. However, the maturational action of gonadotropin is not direct, but is mediated by the follicular production of maturation-inducing substance (MIS). It is now well established that 17α,20β-diOHprog is the major MIS of salmonids. Production of this steroid occursvia the interaction of two distinct cell layers, the thecal and granulosa cell layers (2-cell type model). The first step of the stimulating effect of gonadotropin in both layers is the receptor-mediated activation of adenylate cyclase and formation of cAMP. Our findings suggest that the major stimulating action of gonadotropin on 17α,20β-diOHprog biosynthesis is due to the stimulation of 17α-hydroxyprogesterone production by the thecal layer and the selective induction of thede novo synthesis of 20β-hydroxysteroid dehydrogenase in the granulosa layer. 17α,20β-diOHprog acts at the surface of the oocyte. The early steps following 17α,20β-diOHprog action involve the formation of the major cytoplasmic mediator of this steroid, maturation-promoting factor (MPF). It was shown that goldfish MPF induces meiotic maturation inXenopus oocytes andvice versa. The chemical characterization of fish MPF is important for our understanding of the precise mode of maturational action of 17α,20β-diOHprog.     

Specific binding of [3H]17α,20β-dihydroxy-4-pregnen-3-one to oocyte cortices of rainbow trout (Oncorhynchus mykiss)

Specific binding of [³H]17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP) to plasma membranes prepared from defolliculated oocytes of rainbow trout (Onchorhynchus mykiss) was identified and characterized. Binding was rapid and reached equilibrium in 30 min. 17α,20β-DP strongly inhibited [³H] 17α,20β-DP binding in a competitive manner. Scatchard analysis revealed two different binding sites: a high affinity binding site with a K_d of 18 nM and a B_max of 0.2 pmoles/mg protein; and a low affinity binding site with a K_d of 0.5 μM and a B_max of 1 pmoles/mg protein. This binding activity was successfully solubilized with n-heptyl-β-D-thioglucoside. [³H]17α,20β-DP binding to solubilized preparations reached equilibrium in 1h, and was competitively inhibited with 17α,20β-DP and 17α,20β,21-trihydroxy-4-pregnen-3-one. However, Scatchard analysis showed a single binding site with a K_d of 0.3 μM. The reason for the disappearance of the high affinity binding site in solubilized preparations remains unclear. These results demonstrate that a specific binding site for 17α,20β-DP exists in the plasma membrane of rainbow trout oocytes.

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Résumé Une liaison spécifique de le [³H]17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP), avec des membranes plasmiques d'ovocytes défollicularisés de truite arc-en-ciel (Onchorhynchus mykiss), a été identifiée et caractérisée. Sa cinétique est rapide et atteint son équilibre en 30 minutes. Le 17α,20β-DP inhibe fortement, et de manière compétitive, la liaison de la [³H] 17α,20β-DP. Une étude de Scatchard a mis en évidence deux sites diffŕents de liaison: un site de forte affinité, de K_d 18 nM et de B_max 0,2 pmoles/mg de protéine; et un site de faible affinité, de K_d 0,5 μM et de B_max 1 pmoles/mg de protéine. L'activité de liaison a été solubilisée, avec succés, par le n-heptyl-β-D-thioglucoside. Dans la fraction soluble, la liaison de le [³H]17α,20β-DP atteint un équilibre en 1h.; et elle est complétement inhibiée par la 17α,20β-DP et le 17α,20β,21-trihydroxy-4-pregnen-3-one. Cependant, une étude de Scatchard ne permet de déceler qu'un seul site de liaison, de K_d 0,3 μM. La disparition du site de liaison de forte affinité dans la fraction soluble reste inexpliquée. Ces résultats démontrent l'existence d'un site spécifique de liaison du 17α,20β-DP dans les membranes plasmiques des ovocytes de truite arc-en-ciel.

     

Steroidogenic shift is a critical event for ovarian follicles to undergo final maturation

The steroidogenesis in the granulosa-thecal layers of fish ovarian follicles undergo a distinct shift from the production of estradiol-17β (E₂) to 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP, maturation-inducing hormone, MIH) prior to meiotic maturation. This review attempts to explain the underlying mechanisms of steroidogenic shift.     

Effects of enzymatic deamidation by protein-glutaminase on structure and functional properties of alpha-zein

The performance of novel protein-glutaminase (PG) purified from Chryseobacterium proteolyticumon alpha-zein was investigated. Highly insoluble alpha-zein was able to be deamidated to the extent of deamidation degree 62% by using 50 mM potassium phosphate (pH 8) containing 11.7% ethanol, at 40 degrees C for 137 h. Analysis by sodium dodecyl sulfate polyacrylamide-gel electrophoresis showed that deamidated and non-deamidated zeins have different mobilities. Results of circular dichroism spectra revealed the decline in alpha-helix contents of alpha-zein by deamidation. Besides, Fourier transform infrared spectroscopy analysis demonstrated alterations in the secondary structure of alpha-zein by deamidation. The assignment of the amide I region showed a remarkable decrease in antiparallel intermolecular beta-sheets (around 1690 cm(-1)) as an indication of the weakening aggregation ability of the deamidated molecules. Solubility and emulsification properties of alpha-zein, particularly at pH 7, were remarkably improved after the deamidation by PG. Gas chromatography and peroxide value studies pointed out that deamidated alpha-zein in powder form exhibited an inferior antioxidative property as compared with the non-deamidated one.     

Enhanced Urinary Bladder, Liver and Colon Carcinogenesis in Zucker Diabetic Fatty Rats in a Multiorgan Carcinogenesis Bioassay: Evidence for Mechanisms Involving Activation of PI3K Signaling and Impairment of p53 on Urinary Bladder Carcinogenesis

In the present study, modifying effects of diabetes on carcinogenesis induced in type 2 diabetes mellitus model Zucker diabetic fatty (ZDF) rats were investigated using a multiorgan carcinogenesis bioassay. Our re sults demonstrated enhancement of urinary bladder, colon and liver carcinogenesis in ZDF rats treated with five types of carcinogens (DMBDD). Elevated insulin and leptin and decreased adiponectin levels in the serum may be responsible for the high susceptibility of type 2 diabetes mellitus model rats to carcinogenesis in these organs. Possible mechanisms of increased susceptibility of diabetic rats to bladder carcinogenesis could be activation of the PI3K pathway and suppression of p53 in the urothelium in consequence of the above serum protein alterations.     

Spin-polarized resonant tunneling in magnetic tunnel junctions

Insertion of a thin nonmagnetic copper Cu(001) layer between the tunnel barrier and the ferromagnetic electrode of a magnetic tunnel junction is shown to result in the oscillation of the tunnel magnetoresistance as a function of the Cu layer thickness. The effect is interpreted in terms of the formation of spin-polarized resonant tunneling. The amplitude of the oscillation is so large that even the sign of the tunnel magnetoresistance alternates. The oscillation period depends on the applied bias voltage, reflecting the energy band structure of Cu. The results are encouraging for the development of spin-dependent resonant tunneling devices.     

Collagen content and architecture of the pectoralis muscle in male chicks and broilers reared under various nutritional conditions

Varying chicken growth rates were induced with different nutritional regimes, and the collagen content and architecture of M. pectoralis (PT) were compared among 21‐day‐old chicks and broilers at 80 or 95 days of age. The percentage of muscle weight to live weight was higher in rapid growing chicks (8.4%) than slow growing chicks (6.3%). The 80‐day‐old broilers engaged in compensatory growth after the early slow growth period producing PT muscle at 11% of live weight. The 80‐ and 95‐day‐old chicks with restricted late growth after an early rapid growth period showed PT weight at 8% and 9% of live weight, respectively. Collagen content of the PT muscle markedly decreased from the chicks to the broilers. The collagen concentration was higher in the late‐growth restricted broilers (1.67–1.88 mg/g) than the compensatory growth broilers (1.01–1.10 mg/g). Collagen concentration did not differ between the rapid and slow growing chicks (2.72 and 2.94 mg/g). Scanning electron micrographs showed thick and thin perimysia, and honeycomb endomysia. In the perimysia, a stack layer of collagen platelets and a reticular layer of collagen fiber cords were distinguished and collagen baskets of adipocytes were observed. The perimysial collagen fibers became thicker during growth of the chicks to broilers. However, in the late‐growth restricted broilers, the perimysial collagen fibers seemed to have retarded development compared with the compensatory growth birds. The PT muscle of chickens develops optimally when body growth is enhanced. The PT muscle of the compensatory growth broilers had improved collagen architecture regardless of the marked decrease in collagen content.     

Phage conversion of exfoliative toxin A in Staphylococcus aureus isolated from cows with mastitis

An exfoliative toxin produced by Staphylococcus aureus is the causative agent of staphylococcal scalded-skin syndrome (SSSS) in young children. Recently, we reported that only few isolates of S. aureus from bovine mastitis contained the eta gene encoding exfoliative toxin A (ETA) and produced ETA in vitro. In this study, we isolated temperate phages from two ETA-positive bovine isolates of S. aureus by treatment with mitomycin C. Polymerase chain reaction (PCR) assay of the phage genomes suggested that the temperate phages carried the structural gene for ETA. Moreover, the nucleotide sequence analysis of the PCR products revealed that the eta gene was located very close to an amidase gene on the phage genomes. The nucleotide sequence for the amidase gene of the bovine phage (bovine phi ETA) differed at nine positions from that of the amidase gene of phi ETA from a human isolate reported by Yamaguchi et al. [Mol. Microbiol. 38 (2000) 694], suggesting that eta-converting phages are heterogeneous. Bovine phi ETA had a head with a hexagonal outline and a non-contractile and flexible tail. Bovine phi ETA was able to lysogenize ETA-negative bovine isolates of S. aureus, and the lysogenized S. aureus isolates had the ability to produce ETA. These results suggest the possibility of horizontal transmission of the eta gene by temperate bacteriophages among bovine isolates of S. aureus.     

Effects of Estradiol on Expression of Estrogen Receptor and Collagen mRNAs in Chick Skin

Skin thickness and strength differ between male and female chickens. This study aimed to clarify the effects of estradiol on the expression of estrogen receptors and collagen mRNA in chicken skin. Estradiol was administered to male chicks for 3 weeks, then cryosections of skin collected from the cervical, thoracic, dorsal, and pelvic limb regions were stained with hematoxylin and eosin, and dermal thickness was measured. Estrogen receptor and collagen mRNA expression was assessed using real-time RT-PCR, and collagen contents were determined. Estradiol did not alter dermal thickness or the collagen content of the skin from any tested region. Among the estrogen receptors, significantly more ESR1 mRNA was expressed in the thoracic skin of chicks administered with estradiol compared with vehicle (control), and in the thoracic skin compared with skin from other regions within each group. Estradiol did not affect ESR2, GPER, and COL1A1 mRNA expression. These results suggested that estradiol stimulates ESR1 expression in thoracic skin, but does not affect collagen synthesis in skin from any other region of male chicks.