Lawson K A, Dunn N R, Roelen B A, Zeinstra L M, Davis A M, Wright C V, Korving J P, Hogan B L
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, 3584 CT Utrecht, The Netherlands.
Genes Dev. 1999 Feb 15;13(4):424-36. doi: 10.1101/gad.13.4.424.
In many organisms the allocation of primordial germ cells (PGCs) is determined by the inheritance of maternal factors deposited in the egg. However, in mammals, inductive cell interactions are required around gastrulation to establish the germ line. Here, we show that Bmp4 homozygous null embryos contain no PGCs. They also lack an allantois, an extraembryonic mesodermal tissue derived, like the PGCs, from precursors in the proximal epiblast. Heterozygotes have fewer PGCs than normal, due to a reduction in the size of the founding population and not to an effect on its subsequent expansion. Analysis of beta-galactosidase activity in Bmp4(lacZneo) embryos reveals that prior to gastrulation, Bmp4 is expressed in the extraembryonic ectoderm. Later, Bmp4 is expressed in the extraembryonic mesoderm, but not in PGCs. Chimera analysis indicates that it is the Bmp4 expression in the extraembryonic ectoderm that regulates the formation of allantois and primordial germ cell precursors, and the size of the founding population of PGCs. The initiation of the germ line in the mouse therefore depends on a secreted signal from the previously segregated, extraembryonic, trophectoderm lineage.
在许多生物体中，原始生殖细胞（PGC）的分配是由卵中沉积的母体因子的遗传决定的。然而，在哺乳动物中，原肠胚形成前后需要诱导性细胞相互作用来建立生殖系。在这里，我们表明Bmp4纯合缺失胚胎不含PGC。它们也没有尿囊，尿囊是一种胚外中胚层组织，与PGC一样，源自近端上胚层的前体。杂合子的PGC比正常情况少，这是由于起始群体的大小减小，而不是对其随后扩增的影响。对Bmp4（lacZneo）胚胎中β-半乳糖苷酶活性的分析表明，在原肠胚形成之前，Bmp4在胚外外胚层中表达。后来，Bmp4在胚外中胚层中表达，但不在PGC中表达。嵌合体分析表明，正是胚外外胚层中的Bmp4表达调节了尿囊和原始生殖细胞前体的形成，以及PGC起始群体的大小。因此，小鼠生殖系的起始取决于来自先前分离的胚外滋养外胚层谱系的分泌信号。
