Mammalian oocytes and spermatozoa derive from fetal cells shared by the sexes. These primordial germ cells (PGCs) migrate to the developing somatic gonad, giving rise to oocytes or spermatozoa. These opposing sexual fates are determined not by the PGCs’ own sex chromosome constitution (XX or XY), but by the sexual identity of the fetal gonad that they enter. We asked whether PGCs undergo a deve...

AIM To examine the expression and regulation of integral membrane protein 2b (Itm2b) in rat male reproductive tissues during sexual maturation and under different treatments by in situ hybridization. METHODS Testis, epididymis, and vas deferens were collected on days 1-70 to examine Itm2b expression during sexual maturation. To further examine the regulation of Itm2b, adult rats underwent sur...

The planarian Dugesia ryukyuensis reproduces both asexually (fissiparous) and sexually (oviparous) and can switch from the asexual mode to the sexual mode. By feeding with mature Bdellocephala brunnea oviparous worms, the fissiparous worms, which do not possess sexual organs, can be converted to fully sexualized worms in a process termed sexualization. As sexualization proceeds, the sexual orga...

Sexual selection reflects the joint contributions of precopulatory selection, which arises from variance in mating success, and postcopulatory selection, which arises from variance in fertilization success. The relative importance of each episode of selection is variable among species, and comparative evidence suggests that traits targeted by precopulatory selection often covary in expression w...

The role of sex chromosomes in sex determination has been well studied in diverse groups of organisms. However, the role of the genes on the sex chromosomes in conferring sexual dimorphism is still being experimentally evaluated. An unequal complement of sex chromosomes between two sexes makes them amenable to sex-specific evolutionary forces. Sex-linked genes preferentially expressed in one se...

  Since the stress influences the biological processes, in the present study the effect of prenatal immobilization stress on the sexual activity of male rats was studied. Adult male and female Wistar rats (Pasteur Institute, Tehran) were copulated. After observing the vaginal plugs, pregnant rats were divided into control and two experimental groups. All groups were kept under the laboratory co...

Arguably the most defining moment in our lives is fertilization, the point at which we inherit either an X or a Y chromosome from our father. The profoundly different journeys of male and female life are thus decided by a genetic coin toss. These differences begin to unfold during fetal development, when the Y-chromosomal Sry ("sex-determining region Y") gene is activated in males and acts as a...

Testis determination in mammals is initiated by expression of SRY in somatic cells of the embryonic gonad. Genetic analyses in the mouse have revealed a requirement for mitogen-activated protein kinase (MAPK) signaling in testis determination: targeted loss of the kinases MAP3K4 and p38 MAPK causes complete XY embryonic gonadal sex reversal. These kinases occupy positions at the top and bottom ...