BCL-X(L) DISPLAYS RESTRICTED DISTRIBUTION DURING T-CELL DEVELOPMENT AND INHIBITS MULTIPLE FORMS OF APOPTOSIS BUT NOT CLONAL DELETION IN TRANSGENIC MICE
Dam. Grillot et al., BCL-X(L) DISPLAYS RESTRICTED DISTRIBUTION DURING T-CELL DEVELOPMENT AND INHIBITS MULTIPLE FORMS OF APOPTOSIS BUT NOT CLONAL DELETION IN TRANSGENIC MICE, The Journal of experimental medicine, 182(6), 1995, pp. 1973-1983
The survival of T lymphocytes is tightly controlled during development
. Here, we show that Bcl-x(L), a protein homologue of Bcl-2, is highly
regulated in the thymus in a pattern different than that of Bcl-2. Th
e maximum expression was in CD4(+)CD8(+) thymocytes, a developmental s
tage where Bcl-2 is downregulated. To assess the role of Bcl-x(L) in t
hymocyte apoptosis, we generated mice overexpressing an E mu-bcl-x tra
nsgene within the T cell compartment. Constitutive expression of Bcl-x
(L) resulted in accumulation of thymocytes and mature T cells in lymph
oid organs. Thymocytes overexpressing Bcl-x(L) exhibited increased via
bility in vitro and were resistant to apoptosis induced by different s
ignals, including glucocorticoid, gamma irradiation, calcium ionophore
, and CD3 cross-linking. However, Bcl-x(L) was unable to block clonal
deletion of thymocytes reactive with self-superantigens or H-Y antigen
. These studies demonstrate that Bcl-2 and Bcl-x(L), two functionally
related proteins, are regulated independently during T cell developmen
t. In contrast to Bcl-2, which has been implicated in the maintenance
of mature T cells, Bcl-x(L) appears to provide a survival signal for t
he maintenance of more immature CD4(+)CD8(+) thymocytes before positiv
e selection.