Germ Cell-Somatic Cell Dichotomy of a Low-Density Lipoprotein Receptor Gene Family Member in Testis

Abstract

Members of the low-density lipoprotein receptor (LDLR) supergene family interact with a large number of diverse ligands. One of the relevant receptors is the recently characterized LDLR relative with eight ligand-binding repeats, termed LR8, which exists in two splice variant forms. The gonads, relying on receptor-mediated lipoprotein supply for steroidogenesis, and on interplay of germ cells with somatic cells, provide a particularly attractive setting to study details of the expression of LR8. Here we show by polymerase chain reactions and Northern analysis, as well as by in situ hybridization, that the longer of the two splice variants (LR8+), containing an additional region defining an O-linked sugar domain, is produced in the somatic cells of chicken testis, whereas the shorter form lacking this domain (LR8-) is expressed in the male germ cells. Interestingly, as shown by transcript analysis and at the functional level by ligand blotting, LR8- expression in the spermatoids increases with germ cell maturation, but is absent from ejaculated sperm. This constitutes a scenario reminiscent of the situation in growing vitellogenic oocytes, which express very high levels of LR8-, but lack the receptor following ovulation. Thus, the cell-specific expression of different LR8 splice variants may relate to the requirements of extensive communication and cooperation between germ cells and somatic cells in the gonads.