L. Saltercid et al., EXPRESSION OF MHC CLASS IA AND CLASS IB DURING ONTOGENY - HIGH EXPRESSION IN EPITHELIA AND COREGULATION OF CLASS IA AND LMP7 GENES, The Journal of immunology, 160(6), 1998, pp. 2853-2861
The amphibian Xenopus permits the examination of immune responses in a
species that progresses through two distinct lives, tadpole and adult
, in which animals are free-living and immunocompetent. MHC gene expre
ssion as well as general features of the immune system change profound
ly at metamorphosis, In this study gene expression of class Ia, class
Ib, and the immune proteasome component lmp7 was investigated by North
ern blotting at all stages of development, Class Ia genes are expresse
d in most adult tissues, with highest levels in intestine, Class Ib ge
nes are expressed at lower levels, and their tissue distribution is so
mewhat more restricted than that of class Ia, Consistent with the idea
that particular class Ib isotypes can perform distinct functions, pre
ferential expression of class Ib genes is found in some tissues, with
one family being expressed exclusively in epithelia, The onset of MHC
expression is not simultaneous in all tissues: class Ia transcripts ar
e first present in tadpole lung, gill, and intestine, organs with epit
helial surfaces in contact with the environment, In every tissue excep
t colon and muscle, class Ia expression increases markedly after metam
orphosis, Interestingly, expression of the MHC-linked proteasome compo
nent lmp7 mirrored class Ia expression, while the constitutive lmp7 ho
mologue X was expressed ubiquitously at all stages. Class Ib transcrip
ts were never detected before metamorphosis, suggesting that the Xenop
us class Ib proteins identified to date do not subserve class Ia funct
ions in tadpole life.