Molecular characterization and gene expression in the eye of the apolipophorin II/I precursor from Locusta migratoria

The transport of lipids via the circulatory system of animals constitutes a vital function that uses highly specialized lipoprotein complexes. In insects, a single lipoprotein, lipophorin, serves as a reusable shuttle for the transport of lipids between tissues. We have found that the two nonexchangeable apolipoproteins of lipophorin arise from a common precursor protein, apolipophorin II/I (apoLp-II/I). To examine the mechanisms of transport of lipids and liposoluble substances inside the central nervous system, this report provides the molecular cloning of a cDNA encoding the locust apoLp-II/I. We have recently shown that this precursor protein belongs to a superfamily of large lipid transfer proteins (Babin et al. [1999] J. Mol. Evol. 49:150-160). We determined that, in addition to its expression in the fat body, the locust apoLp-II/I is also expressed in the brain. Part of the signal resulted from fat body tissue associated with the brain; however, apoLp-II/I was strongly expressed and the corresponding protein detected, in pigmented glial cells of the lamina underlying the locust retina and in cells or cellular processes interspersed in the basement membrane. The latter finding strongly suggests an implication of apolipophorins in the transport of retinoids and/or fatty acids to the insect retina.