Abstract
Oogonia are characterized by diploidy and mitotic proliferation. Human and mouse oogonia express several factors such as OCT4, which are characteristic of pluripotent cells. In human, almost all oogonia enter meiosis between weeks 9 and 22 of prenatal development or undergo mitotic arrest and subsequent elimination from the ovary. As a consequence, neonatal human ovaries generally lack oogonia. The same was found in neonatal ovaries of the rhesus monkey, a representative of the old world monkeys (Catarrhini). By contrast, proliferating oogonia were found in adult prosimians (now called Strepsirrhini), which is a group of ‘lower’ primates. The common marmoset monkey (Callithrix jacchus) belongs to the new world monkeys (Platyrrhini) and is increasingly used in reproductive biology and stem cell research. However, ovarian development in the marmoset monkey has not been widely investigated. Herein, we show that the neonatal marmoset ovary has an extremely immature histological appearance compared with the human ovary. It contains numerous oogonia expressing the pluripotency factors OCT4A, SALL4, and LIN28A (LIN28). The pluripotency factor-positive germ cells also express the proliferation marker MKI67 (Ki-67), which has previously been shown in the human ovary to be restricted to premeiotic germ cells. Together, the data demonstrate the primitiveness of the neonatal marmoset ovary compared with human. This study may introduce the marmoset monkey as a non-human primate model to experimentally study the aspects of primate primitive gonad development, follicle assembly, and germ cell biology in vivo.
Highlights
Primates can be subdivided into two large groups: Strepsirrhini and Haplorhini (Finstermeier et al 2013)
We demonstrated that SALL4 protein expression is restricted to premeiotic germ cells in the human and non-human primate (NHP) testes including the common marmoset monkey testis (Eildermann et al 2012)
We show that the neonatal marmoset ovary is, compared with the human ovary, extremely primitive at birth, as it contains numerous premeiotic germ cells
Summary
Primates can be subdivided into two large groups: Strepsirrhini (the former group of prosimians excluding tarsiers) and Haplorhini (the former group of simians plus tarsiers) (Finstermeier et al 2013). Anthropoidea include Platyrrhini (new world monkeys) and Catarrhini (old world monkeys, and Hominoidea, which include humans, great apes, and gibbons) (Perelman et al 2011, Finstermeier et al 2013). The first oogonia enter meiosis during embryonic week 9 (Bendsen et al 2006). During weeks 10–12 of ovarian development, oogonia constitute 50–60% of all ovarian germ cells (Maheshwari & Fowler 2008). During weeks 12–18, the number of oocytes increases reflecting the entry into meiosis of most germ cells (Maheshwari & Fowler 2008). The vast majority of oogonia had entered meiosis by the end of the second trimester (Stoop et al 2005, Bendsen et al 2006), so that the late fetal human ovary already contains almost only proliferation-arrested germ cells. Synaptonemal complex formation is a major hallmark of meiotic prophase
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