The physiologic forms of vitamin A are quite water insoluble. This property is circumvented by a number of specific
binding or carrier proteins for these compounds. Six such proteins have been well characterized: serum retinol-binding
protein (180250); cellular retinol-binding protein (CRBP; 180260); cellular retinoic acid-binding protein; cellular
retinol-binding protein, unique to visual tissue; interphotoreceptor retinol-binding protein, also unique to visual tissue;
and cellular retinol-binding protein, type II (CRBP2; 180280), present in small intestine.
NCBI Summary:
A number of specific carrier proteins for members of the vitamin A family have been discovered. Cellular retinoic acid-binding protein is assumed to play an important role in retinoic acid-mediated differentiation and proliferation processes. CRABP1 is structurally similar to the cellular retinol-binding proteins, but binds only retinoic acid. CRABP1 is constitutively expressed and is believed to have different functions in the cell than the related CRABP2.
General function
Intracellular protein transport
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Comment
Expression regulated by
Comment
Ovarian localization
Luteal cells
Comment
Schweigert FJ, et al reported the immunolocalization of retinol-binding protein, cellular
retinoic acid-binding protein I and retinoid X receptor beta in
the porcine reproductive tract during the oestrous cycle.
Retinoid-binding proteins and nuclear receptors are expressed in the
reproductive tissues of different species and their expression is hormonally
regulated. In the present study, the authors demonstrated immuno cyto chemically the
temporal and spatial localization of retinol-binding protein (RBP), cellular
retinoic acid-binding protein I (CRABPI) and retinoid X receptor beta (RXR
beta) in porcine ovary, oviduct and uterus during the oestrous cycle. RBP and
CRABPI were localized in the cytoplasm, whereas RXR beta occurred in the
nucleus. CRABPI was present in luteal cells of the ovary only
during dioestrus and in glandular and ciliated cells of the oviduct during
oestrus. In the ovary, RXR beta was always present in granulosa cells and
germinal epithelium, with highest levels observed during oestrus. The results show that the
occurrence of retinoid-binding proteins and nuclear receptors in individual
tissues of the reproductive tract are strongly dependent on the stage of the
oestrous cycle. The association of expression in different
sections of the reproductive tissues investigated shows that the presence of
specific proteins involved in retinoid metabolism was dependent on events
associated with ovulation, the migration of the oocyte through the oviduct and
the possible implantation of the blastocyst into the uterus.