FEMALE MOUSE GERM-CELLS FORM SYNCHRONOUSLY DIVIDING CYSTS

Oocytes from many invertebrates initiate development within distinctiv e cysts of interconnected cells, which are formed through synchronous divisions of a progenitor cell. Recently, processes underlying cyst fo rmation have been extensively characterized at the molecular le level in Drosophila, Defects in this process cause sterility in female flies . Early female mouse germ cells are organized as cell clusters as well , but it is uncertain whether these groups are similar to the cysts of invertebrates. We find that mouse germ cells are connected by interce llular bridges in the ovaries of 11.5 to 17.5 days postcoitum embryos; microtubules and organelles have been observed within these bridges. Confocal microscopy shows that cells within mouse clusters divide sync hronously and frequently correspond in number to powers of two. Thus, female mouse germ cell clusters exhibit key characteristics of inverte brate germline cysts indicating that the process of germline cyst form ation is conserved in the mouse.