Sex Dimorphic Proliferation Profiles and Its Regulation in Chicken Germ Cells during Embryonic Development

Abstract

Germ cell is the only cells undergoing two types of cell cycle changes during lifetime. This cell cycle changes is the process that is necessary to halve the number of chromosomes for formation of haploid germ cells. The cell cycle change of primordial germ cells (PGCs) indicates the initiation of germ cell differentiation leading to the highly specialized gametes, oocyte or sperm.

Usually, mammals and bird undergo the first cell cycle changes by sex is occurred during embryonic development. Female initiate the first meiotic division in embryonic day, while male pause the mitotic division and enter the G0/G1 arrest. Through this differentiation pathway, strict controls of cell cycle event both proliferation and meiosis induction is required at proper timing to establish the formation of functional gametes. Under aberrant regulations, germ cells undergo excessive apoptosis, formation of TGCT (Testicular Germ Cell Tumor), infertility (Jorgensen et al., 2013). Despite the importance of regulation of cell cycle in germ cells during sex differentiation, the clear definition and mechanisms remained as questions in chicken. In this study, we try to definite the proliferation and cell cycle profiles in chicken germ cells. And also, we focused on the mitotic arrest in male germ cells and try to elucidate the biological meaning of this mechanisms involved in sex differentiation.

We try to examine the proliferation profiles in chicken germ cells during sex differentiation. To examine the dynamics, we performed the comparison study of germ cells based on DNA replication cell cycle and mitosis dynamics during embryonic development. From these studies, we showed that chicken germ cells undergo proliferation and cell cycle changes in sex dimorphic pattern prior to germ cell differentiation. It have been showed that female germ cells progress the cell cycle changes with high proliferation than male germ cells. And also, from embryonic day 16, the population of G2 phase were increased drastically. On the other hand, male germ cells continues the cell cycle changes with low proliferation phase during overall embryonic development. In addition, at embryonic day 14, almost germ cells enter the mitotic arrest. However, some germ cells lasting DNA synthesizing are existed in both embryonic testis and ovary after onset of sexual differentiation. Collectively, chicken germ cells trigger the sex dimorphic proliferation and differentiation in asynchronous pattern in their gonad.

In our research, the proliferation profiles based on DNA contents was investigated for the first time in chicken germ cells and it was revealed that chicken germ cell differentiation has the distinguished mechanism compared with mammal. This study can contribute to the studies on relationship of cell cycle changes and sex differentiation in chicken germ cells.