**1. Introduction**

The spermatogenesis of Urodeles occurs in longitudinal course into the testis. The structure of the testis forms abundant longitudinal lobules which contain the germinal cells. The lobules are separated by trabeculae of thin and vascularized connective tissue, which are the continuation of the tunica albuginea. The spermatogonia are situated in the cephalic edge of the testis, and the development of spermatozoa occurs during the way of the spermatogenesis through the testicular lobules to the caudal edge of the testis (**Figure 1A**–**C**). At the end of the lobules, the spermatozoa are discharged to the deferent duct system [1, 2]. Consequently, the disposition of spermatogenesis in Urodeles is longitudinal, in cephalocaudal progression, where the

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For the description of this type of spermiogenesis of Urodeles, we consider convenient detailed illustration in this chapter of the progressive histological changes of the spermatids during the development of the spermatozoa, taking the species *Ambystoma dumerilii* (Ambystomatidae) as a model. The histological sections were stained with hematoxylin-eosin (H-E), Masson's trichrome, periodic acid-Schiff (PAS), and alcian blue. *A. dumerilii* is an endemic species, which habits at the southern edge of the Mexican Plateau in Michoacán State, Mexico, in the Lake

Sequence of Germ Cells Differentiation During Spermiogenesis of the Amphibian Urodele *Ambystoma dumerilii*

*A. dumerilii* is a neotenic species, because lack metamorphosis, maintaining during all the life

Spermatogenesis in Urodeles was studied by several authors who described stages of germ cell maturation in a variety of species as: in *Desmognathus fusca* [7]; in *Ambystoma tigrinum* [8–10]; in *Trituroides hongkongensis* [11]; in *Necturus maculosus* [12]; in *Salamandrina terdigitata* [13]; in *Salamandra salamandra* [14, 15]; in *A. mexicanum* [16, 17]; Ricote et al. in *Triturus marmo-*

The spermatogenic cells of *A. dumerilii*, as in all Urodeles, are in synchronous groups called cysts, where all the cells are at the same stage of development. A cyst is formed when a spermatogonium becomes surrounded by a Sertoli cell. Then, the distribution of cysts in the testicular lobules displays a longitudinal sequence of stages of spermatogenesis, in respect to the cephalocaudal gradient: spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids in spermiogenesis, and spermatozoa. The Sertoli cells are involved in essential functions of the spermatogenesis: they maintain a permeability barrier to the germinal cells into the cyst during all the process of differentiation, determine the endocrine activity that controls the spermatogenesis, and phagocytose degenerating spermatogenic cells, residual

Spermatogonia of *A. dumerilii* are spherical cells with 45–55 μm in diameter (**Figure 2A**). These cells are diploid and have mitotic activity. When spermatogonia initiate the meiotic

The primary spermatocytes are also spherical cells; their size is 40–45 μm in diameter. These cells initiate the meiosis; then, their nuclei contain duplicated chromosomes at different stages of prophase I of meiosis exposed clearly in the chromatin changes: leptotene with fine reticular chromatin, zygotene with fine fibrillar pattern of duplicated chromosomes, pachytene with more thick fibrillar pattern of duplicated chromosomes in crossing-over, and diplotene when occurs the separation of homologous duplicated chromosomes, remaining some chiasms (**Figure 3A** and **B**). The primary spermatocytes enter metaphase I, anaphase I, and telo-

Secondary spermatocytes are spherical cells and are smaller than primary spermatocytes; they have in average 18–20 μm in diameter. As the result of the first division of meiosis, the secondary

*ratus* [18]; in *A. dumerilii* [1, 3, 17, 19]; and in *Salamandrella keyserlingii* [20].

bodies, and abnormal spermatozoa during the spermiogenesis [1, 17, 19].

process become a primary spermatocyte (**Figure 2A**–**C**).

phase I (**Figure 3C**), resulting in two secondary spermatocytes.

, moderately shallow to 11 m, and high elevation at 2035 m up sea level).

http://dx.doi.org/10.5772/intechopen.71508

11

Pátzcuaro (260 km<sup>2</sup>

cycle as paedomorphic aquatic larva [6].

**2. Spermatogenesis in Urodeles**

**Figure 1.** Testis of *Ambystoma dumerilii* in longitudinal sections. Spermatogenesis advancing in successive regions along the cephalocaudal axis of the testis, where the different types of spermatogenic cells are seen. (A) Panoramic morphology of the testis. H-E. Bar = 0.3 mm. (B, C) Testicular lobules containing the spermatogenic cells and surrounded of connective tissue. H-E. Bar = 0.1 mm. Spermatogonia (Sg), primary spermatocytes (S1), spermatids (St), spermatozoa (Z), and interlobular connective tissue (c).

earliest stages are more cephalic and the latest stages are more caudal, in contrast with the tubular structure with radial disposition of the spermatogenesis in the testis of amniotes.

Spermatogenic cells of Urodeles are quite big, compared to amniotes germ cells, as example, the spermatogonia may attain 55 μm in *A. dumerilii* [1, 3] and the spermatozoa may attain 840 μm long in *Necturus maculosus* [4, 5].

For the description of this type of spermiogenesis of Urodeles, we consider convenient detailed illustration in this chapter of the progressive histological changes of the spermatids during the development of the spermatozoa, taking the species *Ambystoma dumerilii* (Ambystomatidae) as a model. The histological sections were stained with hematoxylin-eosin (H-E), Masson's trichrome, periodic acid-Schiff (PAS), and alcian blue. *A. dumerilii* is an endemic species, which habits at the southern edge of the Mexican Plateau in Michoacán State, Mexico, in the Lake Pátzcuaro (260 km<sup>2</sup> , moderately shallow to 11 m, and high elevation at 2035 m up sea level). *A. dumerilii* is a neotenic species, because lack metamorphosis, maintaining during all the life cycle as paedomorphic aquatic larva [6].
