Expression study of an alpha-l-fucosidase gene in the Drosophilidae family

The plasma membrane of Drosophila (Sophophora) melanogaster spermatozoa contains an alpha-l-fucosidase that might be involved in fertilization by interacting with alpha-l-fucose residues on the micropyle of the eggshell. D. (S.) melanogaster has a single gene called CG6128 or Fuca encoding for a putative alpha-l-fucosidase. Two transcripts have been annotated, RA of 3514 bp, and RB of 1673 bp. While both transcripts encode an alpha-l-fucosidase, RA contains an upstream open reading frame, translated into a polypeptide containing a predicted BTB/POZ domain. We demonstrate that Fuca is expressed in male and female germ lines. RT-PCR analysis indicated a broader tissue expression. Homologous genes are expressed in the same tissues in several drosophilid flies belonging to the genera Drosophila and Scaptodrosophila. However, the long transcript is restricted to species belonging to the subgenus Sophophora. The presence of two transcripts in species of the subgenus Sophophora and only one in species belonging to the subgenus Drosophila might be related to the phylogenetic relationships of these subgenera. Immunofluorescence demonstrated that the gene product, localized to the sperm plasma membrane, is absent from Scaptodrosophila lebanonensis spermatozoa. These findings support the hypothesis that the enzyme is involved in the molecular events of primary gamete interactions that are conserved among drosophilids belonging to Drosophila genus.