Postnatal somatic cell proliferation and seminiferous tubule maturation in pigs: a non-random event

Abstract

Although seminiferous tubule maturation in horses begins in the central area of the testis, this process is thought to occur randomly throughout the testis in most mammals. Studies in our laboratory revealed that the establishment of spermatogenesis may not be a synchronous event in the testicular parenchyma of pigs. The objectives of the present study were to evaluate the pattern of seminiferous cord/tubule maturation and the morphological and functional characteristics of testicular somatic cells during postnatal development in three regions of the pig testis: a) near the tunica albuginea (TA); b) in the transitional area between the seminiferous tubules and mediastinum (TR); and c) in the intermediate area (ID) between the TA and TR. Based on the diameter of seminiferous cords/tubules, nucleus size of Sertoli cells and fluid secretion, mainly at 90 and 120 d of age, seminiferous tubule maturation was more advanced in the ID and TR. The mitotic activity of Sertoli cells was higher (P<0.05) in the TR than the ID and TA at 7 and 120 d. Except for the mitotic index of the Leydig cells, which was lower (P<0.05) in the ID at 7, 30, and 180 d than in the TA and TR, other Leydig cell ebd points, e.g., individual cell size, nuclear volume, and cytoplasmic volume, were consistently higher (P<0.05) in the ID, suggesting that steroidogenesis was more active in this region during the period investigated. Overall, we inferred that Leydig cells in the ID may play a pivotal role in postnatal testis development in pigs and this type of cell is likely related to asynchronous testicular parenchyma development, with the transitional area providing the primary zone for growth of seminiferous tubules.

Fig. 1

Illustration of the three testicular parenchyma regions in pigs from which the samples were taken; TA, tunica albuginea region; ID, intermediate region; TR, transitional region.

Fig. 2

Biometric data (mean ± SEM) during postnatal development in pigs. (A) body weight; (B) testis weight; (C) gonadosomatic index (GSI).

Fig. 3

Seminiferous cords and tubular diameter (mean ± SEM) in three regions of the testicular parenchyma during postnatal development in pigs. Different uppercase letters denote significant differences between ages for the same region (P < 0.05).

Fig. 4

Tubular compartment volume density (mean ± SEM) in three regions of testicular parenchyma during postnatal development in pigs. Different lowercase letters denote significant differences between regions, whereas different uppercase letters denote significant differences between ages for the same region (P < 0.05).

Fig. 5

Intertubular compartment volume density (mean ± SEM) in three regions of testicular parenchyma during postnatal development in pigs. Different lowercase letters denote significant differences between regions, whereas different uppercase letters denote significant differences between ages for the same region (P < 0.05).

Fig. 6

Sertoli cell nuclei at 7 (A), 30 (B), 60 (C), 90 (D), 120 (E) and 180 (F) d of age in pigs. In all prepubertal ages investigated (A to E), immature Sertoli cells exhibited two different nuclear patterns: round/ovoid (arrows) or elongated (arrowheads). After puberty (F), only typically mature Sertoli cell nuclei (*) with evident nucleolus were found. A–E, bar = 30 μm; F, bar = 20 μm.

Fig. 7

Sertoli cell nuclear volume (mean ± SEM) in three regions of the testicular parenchyma during postnatal development in pigs. Different lowercase letters denote significant differences between regions, whereas different uppercase letters denote significant differences between ages for the same region (P < 0.05).

Fig. 8

Leydig cells in different regions of testicular parenchyma in pigs at 7, 90 and 180 days of age. Leydig cells near or under the tunica albuginea (A, D, G) and near the mediastinum (transitional region, C, F, I) are smaller in comparison to those in the intermediate region (B, E, H). TA, tunica albuginea; TR, transitional region; SC, seminiferous cords; ST, seminiferous tubules; L, Leydig cell (bar = 40 μm).

Fig. 9

Leydig cell end points (mean ± SEM) in three regions of testicular parenchyma during postnatal development in pigs. Different lowercase letters denote significant differences between regions, whereas different uppercase letters denote significant differences between ages for the same region (P < 0.05).

Fig. 10

Testicular somatic cell proliferation index (mean ± SEM) in three regions of testicular parenchyma during postnatal development in pigs. Different lowercase letters denote significant differences between regions, whereas different uppercase letters denote significant differences between ages for the same region (P < 0.05).