This study deals with the structure and ultrastructure of the epithelial cells of the lizard (Lacerta vivipara Jacquin) epididymis as related to secretory activity. The epithelium contains only two types of cells, secretory cells and basal cells. The secretory cells undergo an annual cycle which has been divided into 10 stages. In its most active secretory state, epithelium forms 65.3% of the organ volume. The secretory cell is a tall columnar cell (from 55 ± 3.4 μm to 74.3 ± 2.4 μm height) with a basal nucleus and a supranuclear cytoplasm almost entirely occupied by numerous large secretory granules (5 to 7 μm in diameter). At the ultrastructural level, secretory cells contain rough endoplasmic reticulum (RER), Golgi complex, and secretory granules at various stages of synthesis before being discharged into the lumen. Each granule is membrane-limited and contains a spherical electron dense central core and a peripheral vacuole which varies in density. The secretory cell originates from small cubic cells (13.8 ± 0.7 μm) with few organelles (stage 1). The height of the cell increases gradually and free ribosomes appear first (stage 2), followed by scarce elements of RER (stage 3). The step preceding the secretion period (stage 4) is characterized by a conspicuous increase in volume of RER and Golgi complex. From stage 7 to stage 10, the cell undergoes a dramatic involution. After a transient hypertrophy of the RER, numerous autophagic vacuoles invade the cytoplasm. This degeneration can lead to a complete lysis of the cell and to its rebuilding after elimination of the greatest part of the cytoplasm. The volume of the epithelium falls to 15.6% of the total volume. With antibodies raised against the protein family which constitutes the main part of the secretion (L proteins of 19 kDa), it is shown by immunohistochemistry that these proteins are concentrated into secretory granules which are discharged into the lumen to finally bind to the heads of the spermatozoa.
The lizard epididymis provides a model for studying the control, by testosterone, of a secretory activity related to the physiology of spermatozoa. To evaluate seasonal changes and to establish chronological correlations between the structure of the epididymis and its testosterone content, lizards (Lacerta vivipara) were killed between March (emergence) and October (retreat). The epididymal tissue was examined histologically and assayed for testosterone content. Ten stages of development were defined, mainly on the basis of the epithelial structure and the morphological features of secretory activity. Degeneration of the epithelium after the breeding period and its subsequent renewal also were considered. Increased epithelial height and secretory activity coincided with a progressive rise of the testosterone level, and a severe atrophy followed a sudden reduction of blood testosterone. Reorganization of the epithelium takes place when testosterone is at its lowest level, and the hormonal dependency of this stage is questionable. This study confirms in vivo, during a sexual cycle, experimental evidence previously obtained concerning testosterone's control of the secretory activity of the lizard epididymis.
The lizard epididymis is an androgen-dependent organ whose epithelial cells undergo marked changes in structure and secretory activity during the annual cycle. These changes are connected to fluctuations of testosterone levels. During the breeding season, the epididymis produces a major protein secretion, the L-proteins. In the present work we studied the fluctuations of RNA synthesis and accumulation during the annual cycle by means of histoautoradiographic methods. Total RNA synthesis was determined by uridine incorporation; accumulation of rRNAs and L-protein mRNAs were determined by in situ hybridization. Total RNA synthesis began during reorganization (Phase I), then increased gradually during differentiation and growth (Phase II). The synthesis peaked during maturation (Phase III), but stopped abruptly during hypersecretory activity (Phase IV). The rRNAs were very abundant from Phase II to Phase IV, which is related to the presence of many ribosomes as revealed by electron microscopy. The mRNAs of L-proteins were detected only during Phases III and IV in all epithelial cells. For every phase of the sexual cycle there exists a strong correspondence between the changes in transcriptional activity (rRNA and specific mRNA) of the epithelial cells and changes in the testosterone levels.
The I factor is a functional non-viral retrotransposon, or LINE, from Drosophila melanogaster. Its mobility is associated with the I-R hybrid dysgenesis. In order to study the expression pattern of this LINE in vivo, a translational fusion between the first ORF of the I factor and the lacZ gene of Escherichia coli has been carried out and introduced in the genome of reactive (R) flies. Homozygous transgenic Drosophila lines have been established and analysed. ORF1 expression is limited to germ-line cells (nurse cells and oocyte) between stage 2 and 10 of oogenesis. No somatic expression is found. Position effects may limit the level of expression of a given transgene but do not modify its basic pattern of expression during the development of the fly. This reproducible control demonstrates both that I factor is driven by its own promoter, probably the internal one suggested by Mizrokhi et al. (Mizrokhi, L.J., Georgevia, S.G. and Ilying, Y.V. (1988). Cell 54, 685–691), and that tissue-specific regulatory sequences are present in the 5′ untranslated part of the I factor. The nuclear localization of the fusion protein reveals the presence of nuclear localization signals (NLS) in the ORF1-encoded protein correlating with the possible structural and/or regulatory role of this protein. This expression is restricted to dysgenic and reactive females, and is similar in the two conditions. All the results obtained in this work suggest that I factor transposition occurs as a meiotic event, between stage 2 and 10 of the oogenesis and is regulated at the transcriptional level. It also appears that our transgene is an efficient marker to follow I factor expression.
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