Genomic organization and role of the sperm surface protein, fertilin

Date of Completion

January 1998


Biology, Molecular|Biology, Animal Physiology




The sperm surface protein fertilin is a heterodimer composed of $\alpha$ and $\beta$ subunits that are the first identified members of the ADAM family. The present dissertation describes the chromosomal localization and gene structure of fertilin, and the functional characterization of fertilin $\beta$ using a gene knockout approach.^ Chromosomal locations of four mouse ADAM family genes including fertilin $\alpha$ and fertilin $\beta$ were determined by genetic mapping. These genes have been given the locus symbols Ftna (fertilin $\alpha),$ Ftnb (fertilin $\beta),$ Adam4 (ADAM 4), and Adam5 (ADAM 5). They were mapped to mouse chromosomes, 5, 14, 9 and 8, respectively, revealing a dispersed localization.^ Analysis of the mouse fertilin $\beta$ gene revealed that the gene is present as a single copy, spanning about 55 kb in the genome. The fertilin $\beta$ gene consists of at least 20 exons that average 114 bp in size, interrupted by 19 introns. Comparison of genomic organization between mouse fertilin $\beta$ and the previously sequenced ADAM family gene, human MDC, showed 12 conserved exon-intron boundaries, revealing their evolutionary relationship. Additionally, it was found that more than one gene for fertilin $\alpha$ is present in the mouse genome.^ Mice carrying a targeted mutation in the fertilin $\beta$ gene were generated to test hypotheses that fertilin acts in sperm-egg binding and fusion, and egg activation. Adhesion of sperm lacking fertilin $\beta$ to the egg plasma membrane is dramatically decreased. Fusion of mutant sperm with the egg membrane occurs with only a slight reduction. When mutant sperm fuse with the egg membrane, eggs are activated normally. Furthermore, it was found that mutant sperm are defective in additional steps of fertilization. The progression of mutant sperm from the uterus into the oviduct is severely impaired and mutant sperm fail to adhere to the egg coat, the zona pellucida. Male homozygous mutants are infertile despite normal mating. These results indicate that fertilin is important for multiple sperm functions in fertilization. ^