The Journal of Neuroscience, June 1, 1999, 19(11):4349-4359
c-jun Is Dispensable for Developmental Cell Death and
Axogenesis in the Retina
Karl-Heinz
Herzog,
Shu-Cheng
Chen, and
James I.
Morgan
Department of Developmental Neurobiology, St. Jude Children's
Research Hospital, Memphis, Tennessee 38105
Although a number of studies have implicated c-Jun in neuronal
death and axonal regeneration, it is unknown whether Jun function is
essential for either response. One approach to resolve this issue is to
analyze knock-out mice. However, c-jun-null mice die at
midgestation, precluding critical investigation. Therefore, a xenograft
paradigm was used in which retinas from embryonic day 12.5 (E12.5)
c-jun nullizygous or wild-type mice were transplanted onto the superior colliculus of newborn rats. The rats were allowed to
develop, and the grafts were assayed at various times for cell death
and axon growth. Histologically, grafts of both genotypes developed in
identical manners and had morphological characteristics of retinas. A
functional c-jun allele was not essential for
axogenesis, because ganglion cells in retinal grafts from
c-jun nullizygous mice developed axons that projected
into the colliculus. Programmed cell death (PCD) was also evident in
the age-appropriate regions of the retina in both wild-type and
c-jun-null grafts. Furthermore, there were no
discernible differences in the number or location of dying cells in the
two genotypes. That c-jun was not essential for PCD was
supported by two additional findings. First, a
c-jun-lacZ reporter gene was expressed in
many cells in developing and grafted retinas, although only a few of
these cells were destined to die. Second, in E12.5
c-jun-null embryos there were normal levels of PCD in
the trigeminal ganglion. Together, these data indicate that c-Jun is
not essential for axon growth in the retina or for PCD in the retina
and trigeminal ganglion.
Key words:
c-jun; AP-1; knock-out mice; programmed cell
death; axogenesis; retinal grafts
Copyright © 1999 Society for Neuroscience 0270-6474/99/19114349-11$05.00/0