Pattern and density of vascularization in mammalian testes, ovaries, and ovotestes

According to the classical paradigm, the vasculature of the embryonic testis is more dense and complex than that of the ovary, but recent studies based on whole-mount detection of Caveolin-1 (CAV1) as an endothelial cell marker, have suggested that the level of ovarian vascularization is higher than previously assumed. However, this new hypothesis has been neither tested using alternative methodology nor investigated in other mammalian species. In this paper, we have studied the vascularization process in the gonads of males and females of two mammalian species, the mouse (Mus musculus) and the Iberian mole (Talpa occidentalis). Our results show that the pattern of testis vascularization is very well conserved among mammals, including both pre- and postnatal stages of development and, at least in the mole, it is conserved irrespectively of whether the testicular tissue is XY or XX. We have shown that CAV1 is present not only in endothelial cells but also in prefollicular oocytes and in an ovarian population of somatic cortical cells. These data clearly establish that: (1) according to the classical hypothesis, the degree of vascularization of the developing ovary is lower than that of the testis, (2) ovarian vascularization is also evolutionarily conserved as it occurs similarly both in moles and in mice, and (3) that the degree of vascular development of the mammalian ovary is age-dependent increasing significatively at puberty. The expression of CAV1 in the ovary of most animal taxa, from nematodes to mammals, strongly suggests a role for this gene in the female meiosis.