Page 16 - 71_04

FLORA DE PABLO Y COLS. AN. R. ACAD. NAC. FARM.

The fact that the cells from mice lacking IGF-I managed to
maintain normal proliferation in culture suggested that perhaps they
were overproducing other proteins of the insulin family or they were
upregulating the IGF-I receptor to compensate. We set out RT-PCR
analysis of the proinsulin I and proinsulin II mRNAs from wild type
mice in a way that we could determine if one or both of the genes
were expressed. In the mouse pancreas, the two mRNAs are co-
expressed, whereas in the proliferating neural stem cells, only
proinsulin II mRNA was found (Fig. 6). Additional experiments
compared the wild type neural stem cells with those from IGF-I
knockout mice and the results were variable (Fig. 7). We would need
to analyze a larger number of mice to be certain that there was
overcompensation at the level of proinsulin II expression in the
absence of IGF-I. Even with similar amounts of proinsulin mRNA,
however, different transcripts with distinct translational capacity
might be present, an aspect that remains to be elucidated. More

FIGURE 7. Expression of proinsulin, IGF-II and IGF-I receptor in O.B. stem cells
from wild type (WT) and IGF-I knockout mice (KO). RNA from the proliferative O.B.
stem cells derived from normal mice or mice null for IGF-I was subjected to RT-PCR
followed by Southern blot for the indicated genes, proinsulin, IGF-II, the IGF-I recep-
tor and the control GAPDH (corresponding in each case to the sample(s) above.

778