Periódicos Brasileiros em Medicina Veterinária e Zootecnia

p. 82-88

Recent developments in the spermatogonial stem cell field

Rooij, Dirk G. de

This review aims at putting in perspective the many new developments in our understanding of spermatogonial multiplication and stem cell renewal in non-primate mammals. In the rodent seminiferous epithelium, the spermatogonial compartment can be subdivided into A, In and B spermatogonia, that show no, some or abundant nuclear het erochromatin, respectively. At first, it was thought that all A spermatogonia were spermatogonial stem cells while In and B spermatogonia were in the differentiation pathway. Then there appeared to be a class of so -called undifferentiated A spermatogonia, subdivided according to their topographical arrangement in to singles (As), pairs (Apr) and chains of 4, 8 and 16 A Al spermatogonia. Four (in mouse and rat) subsequent generations of A spermatogonia together with In and B spermatogonia were called differentiating type spermatogonia. A socalled As model was proposed in which the As spermatogonia are the stem cells that self -renew by forming new singles or give rise to Apr spermatogonia that eventually will become spermatozoa. The As model was challenged by the fragmentation model in which stem cell renewal was supposed to occur by way of fragmentation of clones of A al spe rmatogonia.(AU)

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