Total RNA was extracted from pooled tammar fetuses and neonatal gonads
and analysed for SRY expression using reverse transcription and polym
erase chain reaction (RT-PCR). In the tammar, the gonadal primordium i
s first apparent at day 21 of the 26.5 day gestation. By day 25 the cy
toplasmic:nuclear ratio in male pre-Sertoli cells is greater than in f
emale cells, but it is not until two days post-partum that seminiferou
s cords are obvious with putative Leydig cells appearing in the inters
titium(9). We initially tested for the presence of SRY transcripts fro
m the day after the genital ridge is established (day 22 of gestation)
until two days after the development of seminiferous tubules (day 4 p
ost partum). Surprisingly, SRY expression was detected throughout this
entire developmental period in male fetal tissue and in gonads from m
ale pouch young (Fig. 1a). We therefore extended our sampling period f
rom day 19 of gestation (early head-fold; similar to 20 somites) to 40
days after birth and established that in the tammar SRY is expressed
from at least 6 days before the appearance of Sertoli cells until long
after the immature testis has bully differentiated (Fig. 1b). Thus, e
xpression of the tammar SRY gene does not result in immediate Sertoli
cell differentiation.