Biology Reference
In-Depth Information
In the mouse, Chiquoine used alkaline phosphatase (AP) staining to
identify PGCs, a significant advancement over the previously used morpho-
logical criteria (
Chiquoine, 1954
). He was able to identify PGCs as early as
E8 residing in the allantoic and yolk sac mesoderm and at the caudal end of
the primitive streak (
Chiquoine, 1954
), the same location as the earliest
PGCs in human embryos (
Fig. 5.1
A). Indeed, mouse PGCs were found
to follow a similar course along the “germ tract” from yolk sac to genital
ridges via the hindgut and its mesentery. In mouse, PGCs begin to enter
the developing hindgut at around E8.5 and reside there by E9, while entry
to the genital ridges begins at E10 and is largely complete by E11. Sex-
specific differences in the gonads are evident by E12.5 and this represents
a convenient endpoint of PGC development (
Sasaki & Matsui, 2008
).
Modifications to the AP staining protocol enabled mouse PGCs to be
identified a day earlier at E7 and allowed a detailed description of their loca-
tion during gastrulation (
Ginsburg, Snow, & McLaren, 1990
).The earliest
PGCs that can be discerned are in the posterior primitive streak in the
A
B
C
Chiquoine, 1954
Mclaren, 1990
Surani, 2005
Figure 5.1 History of mouse PGC specification. Schematic diagrams of embryos
depicting the earliest developmental stage at which PGCs were observed in landmark
studies. (A) Chiquoine observed PGCs in early E8 embryos in the allantoic and yolk sac
mesoderm (
Chiquoine, 1954
). (B) Modifications to the AP staining protocol allowed
PGCs to be detected a day earlier emerging from the posterior primitive streak, in extra-
embryonic mesoderm (
Ginsburg, Snow, & McLaren, 1990
). (C) Using Blimp1-transgenic
reporter mice, four to eight PGCs were observed in the E6.25 prestreak epiblast (
Ohinata
et al., 2005
).
