Developmental rescue of an embryonic-lethal mutation in the retinoblastoma gene in chimeric mice.

Abstract

The requirement for a functional retinoblastoma gene, Rb‐1, in murine development around days 12‐15 of gestation precludes monitoring the effect of loss of Rb‐1 function on later stages of development and on tumorigenesis in adult mice. Here we describe the developmental rescue of embryonic stem cells carrying two inactive Rb‐1 alleles in chimeric mice. Rb‐1‐ cells contributed substantially to most tissues in adult chimeras, including blood, liver and central nervous system, which were severely affected in pure Rb‐1‐ embryos. The adult chimeric erythroid compartment appeared completely normal, but an increased number of nucleated red cells was observed during fetal liver erythropoiesis in highly chimeric embryos. No ostensive abnormalities were seen in the developing and adult CNS. However, the developing retina of chimeric Rb‐1‐ embryos showed ectopic mitoses and substantial cell degeneration, while the contribution of Rb‐1‐ cells to the adult retina was much reduced. Moreover, the formation of lens fibre cells was severely disturbed. No retinoblastomas developed in any of these mice. Instead, nearly all animals died of pituitary gland tumours which were exclusively derived from Rb‐1‐ cells.

Rb regulates proliferation and rod photoreceptor development in the mouse retina

“…Indeed, the microarray data are consistent with p107 upregulation in Rb-deficient retinas. Findings from previous genetic studies are consistent with this conclusion [26][27][28] …”

“…This result may indicate that loss of Rb alone is not sufficient for the formation of these particularly large clones, and redundancy or compensation by p107 or p130 may prevent proliferation when Cre is used to inactivate Rb1. The earlier genetic studies [26][27][28] better understanding of the complex compensatory and redundant mechanisms of Rb, p107 and p130 in mouse retinal progenitor cells will form a valuable foundation for understanding how mouse retinal progenitor cells are resistant to deregulated proliferation, which in humans ultimately causes retinoblastoma.…”

The retinoblastoma gene family is differentially expressed during embryogenesis

“…RB1 transcripts were detected in the ganglion cell layer of the developing retina from E13.5 through E17.5 (Figure 3c ± j). Although there is no evidence for retinal abnormalities in E13.5 RB 7/7 embryos, reduced contribution of RB 7/7 cells and increased cell death have been observed in the developing retina of RB 7/7 : RB +/+ chimeric mice (Maandag et al, 1994;Williams et al, 1994). RB1 transcripts were not detected in the embryos in the outer half of the retina, which di erentiates after birth.…”

“…Development of the lens ®bers is greatly impaired in RB 7/7 mice (Maandag et al, 1994;Morgenbesser et al, 1994;Williams et al, 1994) with a marked increase in apoptosis. Accordingly, RB1 transcripts were detected in the lens by E11.5 through E17.5, with maximal expression attained by E13.5 ( Figure 3).…”

A dynamic switch in Rb+/− mediated neuroendocrine tumorigenesis

“…Tumor susceptibility is highly penetrant, in mice reaching nearly 100%. Furthermore, tumorigenesis is rate-limited by the loss of the remaining wild-type allele, as demonstrated by the fact that chimeras constructed with Rb-deficient embryonic stem cells succumb to ILP tumors much earlier than the Rb þ /À animals (Maandag et al, 1994;Williams et al, 1994b). The most obvious difference in tumors developing in RB þ /À humans and Rb þ /À mice is the tissue specificity that is displayed.…”