The cycle of the seminiferous epithelium can be viewed in microscope slides of the testis in most mammals. It is an orderly arrangement of successive generations of germ cells developing in tandem within the seminiferous tubules. There are usually about five generations, each forming a circular layer, with the youngest generation at the periphery of the tubule, and the oldest associated with the tubule lumen. In any tubule cross section, viewed with the microscope, you can see the generations, but they look different from one tubule to the next. This is because you are seeing various stages in a cycle of the seminiferous epithelium. These stages in the rat testis were described in 1952 by Leblond and Clermont (Ann. NY Acad. Sci. 55:548-73), who defined 14 stages. If you are interested in the testis, then you may already have some familiarity with the cycle. If you are doing molecular studies involving the testis, then you are probably aware that a serious evaluation of results may require histological examination to see how the cycle is perturbed, suggesting effects at the molecular and cellular levels.
In the past, becoming familiar with the cycle has required study with a light microscope and a suitable histological slide, which may not have been easy for those who were uncomfortable with microscopes. However, in modern histology courses it has become customary to make digital images of histological sections, so they can be studied on the screen of any computer. These digitized images are called "virtual slides." This web page offers virtual slides of both rat and mouse testis that are favorable for study of the cycle of the seminiferous epithelium.
To see the virtual slides, click either "View virtual slide of rat testis," or "View virtual slide of mouse testis" below. In order to view these slides your computer needs to have an Aperio ImageScope viewer, which can be downloaded free from the Aperio web page. You will be able to view the whole section on your computer screen, and you can then enlarge any area of the image to magnifications of up to 40X. Unfortunately, it only works with PCs, not with Macintosh computers (unless they have an Intel processor and can run Microsoft Windows).
For study of the rat testis, see the diagram showing the 14 stages of the cycle (from Perey, Clermont and Leblond 1961). For general information on the cycle of the seminiferous epithelium in rat testis, click here. For help in finding examples of stages on the rat virtual slide, click here.
The glass histological slide from which the virtual slide was made came from Philip E. Smith, who gave it to A. K. Christensen at Stanford University about 1963. To prepare the glass histological slide, rat testis was fixed in Bouin's fixative, embedded in paraffin, and sectioned at 6 µm thickness. Sections were mounted on a 1 x 3 inch glass slide, and were stained with PAS-Weigert iron hematoxylin. The virtual slide was prepared by J. Matthew Velkey, using an Aperio ScanScope XT in the Pathology Department at the University of Michigan Medical School.
Modern molecular studies on the mammalian testis are apt to be carried out in laboratory mice, because of the extensive genetic information that is available for this species. To evaluate the results of these experiments, it may be necessary to include histological observations on the testis to ascertain the effect on spermatogenesis, as reflected in the cycle of the seminiferous epithelium.
When you click the virtual slide of mouse testis, you will see several objects in the section. These are identified in the figure below. Examine both testes in the virtual slide at about 20X magnification. For help in finding examples of stages on the mouse virtual slide, click here.
The cycle of the seminiferous epithelium has not been documented as extensively in mice as it has in rats. In general, the organization of the seminiferous tubules is similar in the two species. If you are familiar with the rat cycle, you will find it easy to interpret the mouse sections. The main study on the mouse cycle is Oakberg EF, 1956, "A description of spermiogenesis in the mouse and its use in analysis of the cycle of the seminiferous epithelium and germ cell renewal," Amer J Anat 99:391-413.
The histological glass slide from which the virtual slide was prepared was obtained from Jiandie Lin, a faculty member in the Life Science Institute, and in the Department of Cell and Developmental Biology, at the University of Michigan Medical School. The mouse strain?, any details about the histological preparation?. The virtual slide was prepared by J. Matthew Velkey, director of the histology course at the University of Michigan Medical School.