Mapping and cloning recombinant breakpoints demarcating the Hybrid Sterility 6-specific sperm tail assembly defect

Variants of the mouse t complex known as t haplotypes it express factors th at perturb sperm differentiation, resulting in the non-Mendelian transmissi on of t from +/t heterozygous males and the sterility of t/t homozygous mal es. Previous studies of mice carrying heterospecific combinations of the t complex have revealed a 1-cM candidate locus, Hst6, for the distal-most of these factors, Tcd/Tcs2. Males heterozygous for the M. spretus allele of Hs t6 and a t haplotype (Hst6(s)/t) are sterile, expressing an abnormality in sperm flagellar curvature ("curlicue") indistinguishable from one exhibited by sperm from t/t homozygotes. Hsr6(s)/Yst6(s) males are also sterile: how ever, sperm produced by these males are completely immotile owing to the ab sence of assembled flagella. Recent studies have shown that the complete pr esentation of ''curlicue'' derives from expression of at least two factors within the locus, Curlicue a (Ccua) proximally and Curlicue b (Ccub) distal ly, with a factor affecting sperm-oolemma penetration, Stoplp mapping betwe en them, in the present report, we have examined expression of the Hst6-spe cific flagellar assembly phenotype in sperm from mice homozygous for M. spr erus-M. In. domesticus recombinant Chr 17 homologs whose breakpoints map wi thin the Hst6 locus. SSLP analysis of these homologs has demonstrated that the flagellar assembly defect maps to less than 0.2 cM between D17Mit61 and D17Mit135. coincident with Ccua. SSR content analysis of 23 BACs mapping t o four contigs within the Hst6 locus has resulted in isolation of proximal and distal recombinant breakpoints circumscribing the flagellar assembly ph enotype/Ccua factor. In addition. we have provided increased high-resolutio n mapping of the Sroplp and Ccub factors. These new data enhance our abilit y to isolate and characterize candidates for Tcd/Tcs2.