Differentiation of Somatic Components of the Human Fetal Testis
The somatic components of human fetal testis were identified using specific antibodies, and the structural organization in the first- and second-trimester samples were compared (Fig. 1). In all samples obtained during the second trimester (14-19 wk), Sertoli cells that were immunoposi-tive for mullerian-inhibiting substance (MIS) were identified within clearly defined testicular cords (Fig. 1, b and c). The surrounding interstitial portion of the testis contained populations of functional Leydig cells (3-p-hydroxy-steroid dehydrogenase [3pHSD]) (Fig. 1, e and f).
Most cells that were immunopositive for androgen receptor (AR) were located around the base of the seminiferous cords (putative peritubular myoid cells) (Fig. 1, h and i). All samples from the first trimester (7-9 wk) were immunonegative for 3pHSD and AR; the examples in Figure 1, d and g, are taken from the same fetus, the gestational age of which was estimated to be 64 days. In this testis (Fig. 1a), MIS-im-munopositive cells are present, but testis cords are not as well defined as in samples from the second trimester In the individual samples from the first trimester, the degree of cord formation based on the pattern of MIS staining was highly variable, ranging from none (54 days) to well defined (63 days).
FIG. 1. General organization and gene expression in somatic cells in fetal human testes during the first and second trimester. Sections obtained from fetuses at 7-9 wk (a, d, and g), 14 wk (b, e, and h), and 19 wk (c, f, and i) are shown. All testes obtained during the second trimester contained well-organized testicular cords containing MIS-immunopositive Sertoli cells (b and c). Within the interstitial region of the same set of testes, 3HSD-positive Leydig cells (Lc; e and f) and AR-immunopositive peritubular cell populations were detected. The morphological appearance of first-trimester samples was variable, and although all contained MIS-positive immunostaining (a, arrows), clearly defined testis cords were rare. Immunopositive staining for 3pHSD and AR was not detected in the interstitium (In; b and c). The inset in i shows a typical control in which normal rabbit serum was used in place of primary antibody. Magnification, X40.