A germline clone screen on the X chromosome reveals novel meiotic mutants in Drosophila melanogaster

Abstract

In an effort to isolate novel meiotic mutants that are severely defective in chromosome segregation and/or exchange, we employed a germline clone screen of the X chromosome of Drosophila melanogaster. We screened over 120,000 EMS-mutagenized chromosomes and isolated 19 mutants, which comprised nine complementation groups. Four of these complementation groups mapped to known meiotic genes, including mei-217, mei-218, mei-9, and nod. Importantly, we have identified two novel complementation groups with strong meiotic phenotypes, as assayed by X chromosome nondisjunction. One complementation group is defined by three alleles, and the second novel complementation group is defined by a single allele. All 19 mutants are homozygous viable, fertile, and fully recessive. Of the 9 mutants that have been molecularly characterized, 5 are canonical EMS-induced transitions, and the remaining 4 are transversions. In sum, we have identified two new genes that are defined by novel meiotic mutants, in addition to isolating new alleles of mei-217, mei-218, mei-9, and nod.

Keywords: chromosome segregation; meiosis; mutant screens.

Figure 1

Schematic representing the cross schemes used in the screen to isolate new meiotic mutants on the X chromosome. Specifics of the screen are detailed in Materials and Methods.

Figure 2

Schematic representing mutations of mei-218 alleles. Mutations are shown for the alleles identified in this screen (with the exception of mei-218¹⁰⁵⁷) as well as for the following previously identified alleles: mei-218⁴, mei-218^g9, mei-218⁶, mei-218^j2, mei-218^hfnd, mei-218^g2, mei-218⁸, mei-218^j1, mei-218^g4, mei-218⁵, mei-218¹, and mei-218^6-7. The mutation in mei-218⁷ is not shown because it encodes for a splice acceptor mutation prior to the 4^th exon.

Figure 3

Metaphase I preparations reveal multiple chromosome masses in novel mei-218 and mei-9 mutants. The number of oocytes with multiple chromosome masses is indicated above each representative figure. (A) Metaphase I preparations of y¹ w¹¹¹⁸ FRT19A oocytes show one chromosome mass, indicating that chromosome congression is complete. (B–D) Metaphase I preparation of y¹ w¹¹¹⁸ mei-218¹²⁵ FRT19A (B), y¹ w¹¹¹⁸ mei-218¹³⁶ FRT19A (C), and y¹ w¹¹¹⁸ mei-9¹⁴⁰ FRT19A (D) oocytes show multiple chromosome masses, suggestive of a defect in recombination. Scale bar: 5 μ.