Ultrastructure of the early ovary and testis in pig embryos

Abstract

Pig embryos aged 26-27 days were used for an ultrastructural study of the early ovary and testis. Sex was identified by both chromosomal analysis and gonadal histology, with consistent results. The gonads occupied their original site in the medial coelomic angles in both sexes. The female gonad was composed of three tissues: the surface epithelium, the gonadal blastema and the mesenchyme. The gonadal structure was similar to that seen earlier at the age of 24 days. At 26 days the testis had distinctly differentiated into four tissues. The new components were the testicular cords and the interstitium, both derived from the gonadal blastema. The testicular cords resembled anastomosing sheets more than cords. The ultrastructure of the tissues and their cell types are described and compared to the previous indifferent stage at the age of 24 days. The cells of the surface epithelium, of the primitive cords, of the mesenchyme, and the primordial germ cells had an ultrastructure that was similar in both sexes. The sustentacular cells of the testicular cords resembled the primitive cord cells and the spermatogonia were similar to the primordial germ cells. No Leydig cells were present yet. The process of testicular differentiation is described on the basis of the present and a previous study, and a new hypothesis, based on the vascular organization, is presented.

Expression levels of Mullerian-inhibiting substance, GATA4 and 17alpha-hydroxylase/17,20-lyase cytochrome P450 during embryonic gonadal development in two diverse breeds of swine

“…Testicular cords were detected morphologically by 26 dpc in both breeds, consistent with previous reports in domestic pigs (Pelliniemi 1975, McCoard et al 2001a. Coincident with the formation of testicular cords, MIS protein was observed in the cytoplasm of Sertoli cells in embryos of both breeds at 26 dpc, indicative of their functional differentiation (Tran et al 1977).…”

“…In occidental pig breeds, genetically determined gonads begin to form on the ventromedial surfaces of the mesonephroi around 20-21 days postcoitum (dpc) (Pelliniemi 1975, McCoard et al 2001a. Male sexual differentiation occurs around 26 dpc (Pelliniemi 1975, Tung et al 1984, Tung & Fritz 1987, McCoard et al 2001a, characterized by the formation of testicular cords.…”

“…Male sexual differentiation occurs around 26 dpc (Pelliniemi 1975, Tung et al 1984, Tung & Fritz 1987, McCoard et al 2001a, characterized by the formation of testicular cords. Shortly thereafter, Leydig cells of the testicular interstitium differentiate, resulting in androgen-stimulated development of the male phenotype.…”

The functional maturation of the Sertoli cell and Leydig cell in the mammalian testis

“…The former are believed to arise from the gonadal blastema and the latter from undifferentiated mesenchymal cells in the interstitium (see Pelliniemi & Dym, 1980). Thus, sexual differentiation of the male gonad starts with the formation of the testicular or seminiferous cords at 13 days of gestation in the rat (Jost, Magre, Cressent & Perlman, 1974;Jost, Magre & Ageloupoulou, 1981), 26 days in the pig (Pelliniemi, 1975;Pelliniemi & Lauteala, 1981) and 42 days in the human (Pelliniemi & Dym, 1980). The testicular cords are believed to be directed by the presence of the H-Y antigen and its bind¬ ing to receptors on the somatic gonadal blastema cells (Wachtel, Ohno, Koo & Boyse, 1975;Ohno, 1976;Wachtel & Koo, 1981;Silvers, Gasser & Eicher, 1982; Gore-Langton, Tung & Fritz, 1983;see Ritzen & Syed, 1985).…”

A comparative study of the development of the fetal testis and ovary in the monkey (Macaca fascicularis)

“…Since the mesonephric tubules-rete blastema continuities are established at the time the ovary begins to form a « cortex » and a « medulla », it may be that the mesonephric tubule cells join the mesenchymal cells of the rete ovarii blastema to constitute the perioocyte (follicular) cell population. Unfortunately, due to the small number of samples, and especially to the scarcity of specific cell markers such as those found in the fetal mouse (Byskov, 1979) (Mauger and Clermont, 1974 ;Merchant-Larios, 1976), rabbits (Gondos and Conner, 1973), pigs (Pelliniemi, 1975) (Fouquet et al, 1978) and in the cells of the peripheral epithelium.…”