Re‐examination of spermatogonial renewal in the rat by means of seminiferous tubules mounted “in toto”

Abstract

Observations on dissected tubules, fked in Carnoy, stained with hematoxylin and mounted "in toto" revealed that there were five distinct classes of type A spermatogonia. The type AI found in stages 11-VIII of the cycle of the seminiferous epithelium had round, pale-stained nuclei, typically arranged in linear clusters of four or eight along the tubular wall. They all divided at stage IX to produce type A2 cells. These in turn divided at stage XI1 to produce type As spermatogonia. The type A2 and As cells had large ovoid nuclei containing globular masses of deeply stained chromatin and were randomly distributed in the space between Sertoli nuclei. The type A3 spermatogonia divided a t stage XIV to produce type A4 cells. These had smaller nuclei, sometimes lobulated, containing more deeply stained chromatin granulation, free in the nucleus or adhering to the nuclear membrane. They divided in stage I of the cycle to yield two classes of spermatogonia: intermediate type and new type Al. Hence, type Al-type A4 spermatogonia were considered as '<renewing stem cells." The fifth class of type A spermatogonia (A,) was found at all stages of the cycle. Rare, isolated or in pairs, they had oval nuclei with deeply stained chromatin granulations. Seldom seen to divide, they did not appear to be actively involved in cell renewal and were tentatively considered as "reserve stem cells."The renewal of the spermatogonial stem cell population has been investigated in several mammalian species and, amongst these, the rat has received the greatest attention (see reviews by Roosen-Runge, '62; Clermont, '67). It was soon observed that, between the initial spermatogonial stem cell and the spermatocytes, several intermediate generations of spermatogonia were being produced. In the rat, five distinct generations of spermatogonia were described, three of type A, one of intermediate type and one of type B spermatogonia (Clermont and Leblond, ' 5 3 ) . It was also indicated that at each cycle of the seminiferous epithelium, while spermatocytes were being generated, some new spermatogonial stem cells were produced and set aside to serve in the production of future generations of spermatogonia and spermatocytes. It was also demonstrated that the new stem cells arose from the proliferating type A spermatogonia, before the production of the more differentiated intermediate and type B spermatogonia. More recently, Clermont ('62) suggested that the new stem cells were produced by divisions of the third generation of type A spermatogonia.The main data used in these investigations (Roosen-Runge and Giesel, '50; Roosen-Runge, '51; Clermont and Leblond, 53; Clermont, '62) were average cell counts AM. J. ANAT., 122: 237-248.obtained after enumerating large numbers of spermatogonia in tubular cross-sections. Therefore, on account of the statistical nature of these results, the exact time of formation and the source of the new stem cells remained a matter of speculation. In the present study, information bearing on this particular subject was obt...

Three-dimensional profile of three types of spermatogonia and their topographies in adolescent or adult rats.

“…The latter seem to be differentiated cells and the former undifferentiated ones. From LM (light microscope), TEM and SEM criteria such as morphology of nuclei and cytoplasm (CLERMONT and BUSTOS-OBREGON, 1968;CLERMONT, 1972), the presence of cytoplasmic processes (MOENS and Go, 1972), contour and size of the cells (EDDY and KAHRI,1976;HAMASAKI and MURAKAMI, 1981), it has been suggested that the large and the medium cells in both rat groups correspond to undifferentiated spermatogonia and the small cells to differentiated ones.…”

“…Rat spermatogonia are roughly divided into undifferentiated (A) and differentiated (B) cells, but a more detailed clarification by TEM has not yet been sufficiently performed in rats, although seven types of rat spermatogonia have already been ascertained by light microscopy (LM) (CLERMONT and BUSTOS-OBREGON, 1968;CLERMONT,1972;HUCKINS and OAKBERG, 1978;DYM and FAWcETT, 1971). The types of spermatogonia in rats are generally identified from LM or TEM criteria such as shape and stainability of the nucleus, cell arrangement and location related to the basement membrane, but the cell-contour along close spermatogonial lines is apt to be similar.…”

“…The spermatogonia and their daughter cells often overlap during individual stages in the first cycle of rat spermatogenesis (CLERMONT and BUSTOS-OBREGON, 1968;HUCKINS and OAKBERG, 1978). Therefore, there is a possibility of misjudging cell types when only nuclear morphology is taken into account after a single TEM study.…”

Elucidating the identity and behavior of spermatogenic stem cells in the mouse testis

“…First, precise judgment of spermatogonial interconnection in whole-mounted seminiferous tubule specimen (Clermont & Bustos-Obregon 1968) is difficult because intercellular bridges are not always visible under microscope, and identification of syncytia was practically based on the distance between nuclei with similar appearance that reflect their cell cycle phase (de Rooij & Russell 2000). More fundamentally, what one needs to know more is the behavior of spermatogonia over time (i.e.…”

Male germline stem cells in non-human primates

“…In rodents SSCs undergo highly synchronous mitotic and meiotic divisions, and A single differentiate into A paired , further dividing into chains of up to 16 cells; whereas in primates, stem cells are classified as A dark , the irregularly dividing reserve stem cells, and A pale , the self-renewing population. These cells further undergo mitotic and meiotic divisions to differentiate into spermatozoa Leblond, 1953, 1959;Clermont and Bustos-Obregon, 1968;Huckins, 1971;Oakberg, 1971;.…”