Fig. 1. T^C/T^C homozygous mutants produce a single but persistent mRNA transcript and transient protein. (A) RT-PCR reactions for +/+ (LHF to 8-s), T^C/+ (LHF to 8-s) and T^C/T^C (LHF, 5-s) conceptuses. A single T transcript was detected in +/+ samples, a strong T and a faint T^C band were detected at all stages in T^C/+ samples, and a single T^C transcript was detected in T^C/T^C samples. Minus reverse-transcriptase (-RT) control was negative for all reactions. M indicates marker, a 100 bp gene ruler. ß-actin RT-PCR product was used as a loading control for each corresponding T RT-PCR reaction. (B) Immunohistochemical detection of T and T^C (brown) in +/+ (a,b) and T^C/T^C (c,d) conceptuses in sagittally oriented histological sections. T (a) and T^C (c) were localized to the primitive streak (ps) at the EB stage. At LHF, T (b) was localized to the allantoic core and primitive streak, and, with the exception of the ectoplacental endoderm (not shown), T^C (d) was not detected in the T^C/T^C conceptus. The slanted black line in b indicates the previously defined boundary between the allantois and posterior primitive streak (Downs and Harmann, 1997). (e-g) Transverse immunohistochemical sections (6 µm) through a 2-s allantois to highlight the T-defined core domain. The total length of this allantois was 258 µm after fixation. (e) The distalmost T(+) section at 102 µm (39.5% of the total fixed allantoic length). (f) A mid-region section at 48 µm. (g) The most proximal section at 6 µm. ac, amniotic cavity; al, allantois; am, amnion; bi, yolk sac blood island; eve, embryonic visceral endoderm; ps, primitive streak; x, exocoelomic cavity; xve, extraembryonic visceral endoderm. Scale bars: in d, 100 µm for a-d; in g, 100 µm for e-g.