In contrast, a striking increase in the number of MAGE-A4-immunopositive cells was detected in testes collected on and after the 17th week of gestation; the immunopositive reaction was intense and usually associated with groups of germ cells at the periphery of the seminiferous cords. An example of this staining pattern can be seen in Fig. 2l. canadian helth& care mall
Morphological Appearance of Germ Cells Within Human Fetal Testis During the Second Trimester
In sections of testes from the first trimester, germ cells were easily distinguished from the Sertoli cells, because they had larger, rounder nuclei. They also all had a similar morphology, with a high nuclear:cytoplasmic ratio. In contrast, variation in the morphological appearance of the germ cells within the individual seminiferous cords was evident in sections from the second trimester (Fig. 3). Three populations of germ cells were identified based on the appearance of their nuclei and their nuclear:cytoplasmic ratio. Cells in population 1 had round nuclei containing a prominent nucleolus but very little cytoplasm (labeled 1 in Fig. 3). Those in population 2 often appeared in pairs at the periphery of the cords; although their nuclei contained a prominent nucleolus, they had a larger volume of cytoplasm than the cells in population 1.
FIG. 3. Identification of germ cells with differing morphology in second-trimester testis. Hematoxylin-and-eosin-stained section from a fetal testis recovered at 18 wk of gestation shows the different morphological appearance of germ cells. Based on the appearance of the nucleus and the nuclear:cytoplasmic ratio, three different populations were identified. Population 1: small, round cells; high nuclear:cytoplas-mic ratio: prominent nucleolus: usually single cells, often in the center of a cord. Population 2: round nuclei, usually in pairs, more cytoplasm/irregular outline compared with population 1. Population 3: largest of the germ cell types, irregular outline, clear cytoplasm, usually in groups at the periphery of a cord. Magnification, X100
FIG. 4. Identification of OCT4-positive germ cells. OCT4 was immunolocalized to germ cell nuclei at all ages examined (719 wk). In the first trimester (7 wk; a and b), intense immunopositive staining was detected in the majority of germ cells. However, in all second-trimester samples (15 wk [c] and 18 wk [d]), some immuno-negative cells were detected (arrows). Double-staining of cells for OCT4 (blue nuclei) and C-KIT (brown membrane) revealed that all OCT4-positive cells also expressed C-KIT (16 wk; e and f). Some oCT4neg/C-KITneg cells were detected in second-trimester samples (arrows in f). Magnification, X20 (b) and X100 (a, c, d, and inset of b).