RUI: Role of the haploidizer gene in genome elimination by a selfish B chromosome

This project aims to elucidate how selfish genetic elements disrupt normal genetic inheritance patterns. A certain class of selfish elements – B chromosomes – are pervasive among plants and animals. In certain cases, B chromosomes cause harmful effects to reproduction and extreme sex ratio distortion.

In the jewel wasp, Nasonia vitripennis, one such B chromosome destroys the part of the genome that comes from the father, resulting in all-male broods of progeny carrying hereditary material only from the mother and the B chromosome. Recent work has revealed a toxin-like gene expressed by this B chromosome; this gene is needed for the B chromosome’s genome elimination activity, making it the only gene known to underlie selfish chromosome behavior in any organism.

This research aims to uncover how this gene functions at the molecular level, providing insights into how other selfish genetic elements alter inheritance patterns. The project will facilitate rigorous research training opportunities for a diverse group of undergraduate students and a postdoctoral researcher. A new laboratory-based course will be developed around one of the proposal’s aims; in this course, students will perform the research, learning the practice of science through hands-on experimentation.

Students from the two-year college level will be involved in the research, helping to enhance their retention in STEM and the likelihood of their continuation to 4-year degree-granting institutions. Collectively, this work will help to train the rising STEM workforce.

An implicit assumption of genetics is that elements of the genome function cooperatively for organismal fitness. However, certain genetic elements do not behave in this manner. Such elements, deemed selfish, disobey the normal rules of genetics to gain a transmission advantage.

This opposition between the benefits gained by a selfish genetic element and the harm incurred by the organism represents a poorly understood condition known as intragenomic conflict. This project will utilize a combination of modern genomic, genetic, molecular, and cytological methods to study how a B chromosome-expressed gene called haploidizer causes genome elimination in the jewel wasp Nasonia vitripennis.

The main activities include: (1) using transgenesis and other gene manipulation approaches to test if the haploidizer gene functions alone or instead with other B-chromosome expressed genes; (2) using high-resolution fluorescence microscopy to understand the properties of haploidizer’s encoded protein at the sub-cellular level; (3) using genetics to identify protein interactors of the haploidizer protein; and (4) using genomics approaches to determine if a similar B chromosome in a different wasp species also expresses a haploidizer-like toxin gene to cause genome elimination. This study will provide a detailed investigation of how B chromosomes alter genetic inheritance through the expression of individual genes.

Broadly, the study will help to elucidate how B chromosomes behave so differently from the standard chromosomes in the genome, and it may facilitate efforts to build more effective artificial gene expression systems aimed at controlling disease-carrying insect pests.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.