Pleiotropy in microdeletion syndromes: neurologic and spermatogenic abnormalities in mice homozygous for the p6H deletion are likely due to dysfunction of a single gene.

Abstract

Variability and complexity of phenotypes observed in microdeletion syndromes can be due to deletion of a single gene whose product participates in several aspects of development or can be due to the deletion of a number of tightly linked genes, each adding its own effect to the syndrome. The p6H deletion in mouse chromosome 7 presents a good model with which to address this question of multigene vs. single-gene pleiotropy. Mice homozygous for the p6H deletion are diluted in pigmentation, are smaller than their littermates, and manifest a nervous jerky-gait phenotype. Male homozygotes are sterile and exhibit profound abnormalities in spermiogenesis. By using N-ethyl-N-nitrosourea (EtNU) mutagenesis and a breeding protocol designed to recover recessive mutations expressed hemizygously opposite a large p-locus deletion, we have generated three noncomplementing mutations that map to thep6H deletion. Each of these EtNU-induced mutations has adverse effects on the size, nervous behavior, and progression of spermiogenesis that characterize p6H deletion homozygotes. Because EtNU is thought to induce primarily intragenic (point) mutations in mouse stem-cell spermatogonia, we propose that the trio of phenotypes (runtiness, nervous jerky gait, and male sterility) expressed in p6H deletion homozygotes is the result of deletion of a single highly pleiotropic gene. We also predict that a homologous single locus, quite possibly tightly linked and distal to the DJSS12 (P) locus in human chromosome 15qll-q13, may be associated with similar developmental abnormalities in humans.

Functional annotation of mammalian genomic DNA sequence by chemical mutagenesis: A fine-structure genetic mutation map of a 1- to 2-cM segment of mouse chromosome 7 corresponding to human chromosome 11p14-p15

“…Thus, all lethal p deletions used for fine-structure mapping were maintained by crosses of p x ͞Del(p) heterozygotes to p x ͞p x mates. The prenatally lethal Del(ru2 p) 46DFiOD deletion (22) was used to detect recessive mutations in the hemizygosity screen (see below) (15). For these crosses, Del(ru2 p) 46DFiOD was maintained by alternate crosses of ϩp͞Del(ru2 p) 46DFiOD and ru2ϩ͞Del(ru2 p) 46DFiOD heterozygotes to ru2ϩ͞ru2ϩ and ϩp͞ϩp mice, respectively.…”

“…We previously reported initial results of a hemizygosity-screen strategy for recovering ENU-induced recessive mutations within the 4-to 5-cM Del(ru2 p) 46DFiOD deletion (15); this strategy is similar to a mutation-recovery experiment carried out for a 6-to 11-cM deletion at the more distally mapping Chr 7 tyrosinase [Tyr; previously, albino (c)] locus (14,16). The initial phase of this ''p-region screen'' (like the entire Tyr-region screen) used simple phenotyping criteria such as recognizing lethality and externally visible characters or behaviors in mutant lines.…”

“…Consequently, it is possible to use phenotype-driven strategies to recover new ENU-induced mutations in specific, preselected loci for the generation of new alleles (1)(2)(3)(4), in whole-genome screens for genes comprising components of complex pathways or phenotypes (5-10), or, with the use of chromosomal rearrangements, in a wide variety of genes within specific chromosomal regions (11)(12)(13)(14)(15)(16)(17)(18). The phenotyping protocols used in such strategies can range from simple to complex and can be narrowly or broadly focused, with the output of any experiment dependent largely on the discriminating power of the phenotyping used.…”

“…The phenotyping protocols used in such strategies can range from simple to complex and can be narrowly or broadly focused, with the output of any experiment dependent largely on the discriminating power of the phenotyping used. The extensive homologies between the genomes of mouse and human make it feasible to use the mouse for discovery of new mutations and phenotypes that aid in the functional annotation of the corresponding human DNA sequence and transcription maps.The region of mouse chromosome (Chr) 7 surrounding the pink-eyed dilution (p) locus that shares homology with human genomic regions 15q11-q13 and 11p14-p15 is being characterized by both genetic and molecular approaches (15,(19)(20)(21)(22)(23)(24)(25)(26). We previously reported initial results of a hemizygosity-screen strategy for recovering ENU-induced recessive mutations within the 4-to 5-cM Del(ru2 p) 46DFiOD deletion (15); this strategy is similar to a mutation-recovery experiment carried out for a 6-to 11-cM deletion at the more distally mapping Chr 7 tyrosinase [Tyr; previously, albino (c)] locus (14,16).…”

“…The region of mouse chromosome (Chr) 7 surrounding the pink-eyed dilution (p) locus that shares homology with human genomic regions 15q11-q13 and 11p14-p15 is being characterized by both genetic and molecular approaches (15,(19)(20)(21)(22)(23)(24)(25)(26). We previously reported initial results of a hemizygosity-screen strategy for recovering ENU-induced recessive mutations within the 4-to 5-cM Del(ru2 p) 46DFiOD deletion (15); this strategy is similar to a mutation-recovery experiment carried out for a 6-to 11-cM deletion at the more distally mapping Chr 7 tyrosinase [Tyr; previously, albino (c)] locus (14,16).…”