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**Oogonia Development in Mammals**:
– Oogonia form in large numbers through mitosis during fetal development.
– Human oogonia development occurs between weeks 4 and 8 of gestation.
– Oogonia are distinguishable from somatic cells by their nuclei.
– Degenerating oogonia exhibit distinct characteristics under an electron microscope.
– Oogonia are present in the fetus from weeks 5 to 30.

**Structure and Differentiation of Oogonia**:
– Normal human oogonia are spherical or ovoid with prominent nucleoli in their nuclei.
– Oogonia cytoplasm contains large round mitochondria and underdeveloped endoplasmic reticulum.
– Degenerating oogonia show swollen and disrupted mitochondria.
– Oogonia differentiate into primary oocytes through asymmetric division.
– Most oogonia have differentiated or degenerated into primary oocytes by birth.

**Regulation of Oogonia Differentiation**:
– RSPO1 activates the β-catenin signaling pathway for ovary differentiation.
– Up-regulation of Stra8 is essential for germ cell differentiation.
– RSPO1 acts on germ cells in a paracrine mode.
– RSPO1 deficiency can lead to sex reversal of gonads in female mice.
– Multiple factors are involved in Stra8 regulation.

**Oogonial Stem Cells and Research**:
– Recent studies suggest the presence of renewable oogonia in adult females.
– Mitotically active germ cells may migrate to the ovaries from the bone marrow.
– Active germ cells in adult females could aid in fertility research.
– Germ cells have been grown in vitro for fertility restoration in mice.
– Adult mammalian females may lack a population of regenerating germ cells.

**Thallophyte Oogonia and Fertilization**:
– Oogonia of certain Thallophyte species are round or ovoid.
– Male antheridia contain several nuclei and fertilize oogonia in certain species.
– Fertilization involves haploid nucleus transfer forming a diploid oospore.
– Oospore germinates into an adult diploid somatic stage.
– Different Thallophyte species exhibit variations in oogonia and antheridia structure and location.

Oogonium (Wikipedia)

An oogonium (pl.: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes.

Anatomical terminology
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