Mary F. Lyon

Transmission ratio distortion in mouse t-haplotypes is due to multiple distorter genes acting on a responder locus

Transmission ratios of male mice heterozygous for various combinations of partial t-haplotypes provide evidence in support of a model for the genetic basis of ratio distortion, involving two or more distorter genes acting on a responder locus. The t form of the responder locus, Tcr, in the medial part of the haplotype, must be present and heterozygous for distortion to occur. When the responder alone is present, as in t low haplotypes, the chromosome carrying it is transmitted in a low ratio (less than 50%). The t forms of the distorter loci act additively, in cis or trans, to raise the transmission of whichever chromosome carries Tcr. Identified distorter loci are Tcd-1, in the proximal part of the haplotype, Tcd-2, distal to Tcr, and probably Tcd-3, lying between Tcr and Tcd-2. In the absence of Tcr the distorters are transmitted normally. The system is compared with the SD system of Drosophila.

Male sterility of the mouse t-complex is due to homozygosity of the distorter genes

Evidence is presented that the male sterility produced by the mouse t-complex is due to interaction of at least three sterility factors. These factors are carried in the same partial haplotypes as the three distorter genes, Tcd-1, Tcd-2, and Tcd-3 and are suggested to be identical with them. When heterozygous, the distorter/sterility genes act on the wild-type form of the responder gene, rendering sperm carrying it nonfunctional, thus leading to high transmission of the t form of the responder. When homozygous, the harmful effects of the distorter genes are stronger and affect both forms of the responder, leading to sterility. If homozygous sterility is an inescapable part of ratio distortion, then the t-lethals confer a selective advantage in removing sterile males from the population. Thus, the relationship between the various properties of the t-complex can now be understood.

Molecular probes define different regions of the mouse t complex

Four genomic clones obtained from microdissected fragments of the proximal portion of mouse chromosome 17 have been used to identify a series of t-haplotype-specific restriction fragments. Their specificity is defined by presence in eight complete t haplotypes and absence from 18 inbred strains of wild-type mice. Partial t haplotypes contain subsets of the t-specific fragments, and each can be classified according to the t-specific fragments it contains. This is the first molecular evidence that independent partial t haplotypes contain different lengths of t haplotype DNA. Recombination studies indicate that partial t haplotypes suppress recombination in proportion to the extent of t haplotype DNA they contain. Molecular analysis of partial t haplotypes shows that the t-specific fragments map to and thus define different regions of the t complex. Certain regions of t haplotype DNA defined by t-specific restriction fragments can be correlated with loci involved in the control of transmission ratio distortion.

The t complex polypeptide 1 (TCP-1) is associated with the cytoplasmic aspect of Golgi membranes

The t complex polypeptide 1 (TCP-1) is a protein of unknown function expressed in large amounts during spermatogenesis. Rat monoclonal antibodies recognizing TCP-1 have been prepared and used to immunoprecipitate and Western blot a 57 kd protein from germ cell and tissue culture cell extracts. In tissue culture cells, indirect immunofluorescent localization of antigen indicated a perinuclear distribution similar to that of the Golgi apparatus. Analysis of the TCP-1 distribution in tissue culture cells showed that the polypeptide was associated with the cytoplasmic aspect of membranes of the trans-Golgi network (TGN). The distribution in spermatids suggested that TCP-1 was localized to structures often associated with the developing acrosome. The TCP-1 antigenic epitopes are highly conserved, allowing the protein to be identified in cells across a wide variety of vertebrate species and tissues. These experiments suggest that TCP-1 may be essential for transport of proteins through the exocytic pathway in all cells and required in large amounts for acrosome formation in developing spermatids.

The major brain isoform of Kif1b lacks the putative mitochondria-binding domain

Kinesin and kinesin superfamily proteins are molecular motors involved in important intracellular functions such as organelle transport and cell division. They are microtubule-activated ATPases composed of a motor domain that binds to microtubules and a cargo-binding domain that binds to specific organelles. While searching for the slow Wallerian degeneration mutation (WldS) on distal mouse Chromosome (Chr) 4, we have identified a member of the kinesin superfamily whose predicted gene product has the N-terminal motor domain of Kif1b and a novel C-terminal cargo-binding domain homologous to Kif1a. Kif1b is responsible for the movement of mitochondria along the axon, but the novel isoform containing the alternative C-terminal domain is likely to have a different cargo-binding specificity. cDNA library screening and Northern blot analysis indicate that the alternatively spliced form of Kif1b containing the novel 3′end accounts for the most part of Kif1b expression. We also found more alternatively spliced exons that can give rise to heterogeneous transcripts. Therefore, alternative splicing, as well as multiple genes, may contribute to the selective movement of diverse organelles by anterograde axonal transport. Kif1b maps on distal mouse Chr 4, within the Wld genetic candidate interval, but outside the recently identified triplication. There is, however, no evidence that Kif1b is the Wld gene.

THE ARRANGEMENT OF H‐2 CLASS I GENES IN MOUSE t HAPLOTYPES

The t haplotypes of mouse chromosome 17 bear a number of interesting mutations and rearrangements, some of which map close to the H‐2 complex. Since there are many H‐2 class I genes of unknown function, we have investigated their arrangement in t haplotypes using genomic Southern blots. We present a detailed chart of the H‐2w30(tw12) complex, and compare it with the arrangement in other t haplotypes and standard mouse haplotypes. The chart shows duplications, deletions, and reshuffling of conserved and divergent regions. The two major features of the t arrangement‐large deletions in the Qa and Tla regions–have analogues in some standard strains, so it is unlikely that these deletions are responsible for t‐specific phenotypes. The differences between t and standard mouse strains are similar, in nature and in degree, to those between different standard strains.

Genetic analysis of the organic cation transporter genes Orct2/Slc22a2 and Orct3/Slc22a3 reduces the critical region for the t haplotype mutant t w73 to 200 kb

Abstract. Here we report an analysis of two candidate genes for the tw73 implantation mutation. The tw73 gene maps to a 20-cM region of mouse Chromosome (Chr) 17 known as the t-complex, which exists in a wild-type and t haplotype form in present-day mice. The t haplotype variants contain several mutant alleles affecting male fertility and embryonic viability and offer the opportunity to identify genes critical for these processes. tw73 homozygous embryos are defective in trophoblast production and fail to implant adequately, with death occurring at approximately 7.5 days post coitum (pc). Two recently described organic cation transporter genes, Slc22a2 (Orct2) and Slc22a3 (Orct3), fulfill criteria predicted for tw73 candidate genes, since both map to the previously defined 500-kb tw73 minimal region and both are also expressed in 7.5 days pc post-implantation embryos. The genomic locus of the Orct2 gene appears similar in wild-type and tw73 chromosomes. In contrast, the genomic locus of Orct3 is amplified and displays an altered expression profile in all t haplotype variant chromosomes tested. In addition, Orct3 shows a tw73 specific polymorphism. To test whether either Orct2 or Orct3 is involved in the tw73 phenotype, we have performed a genetic rescue experiment using YAC transgenes overexpressing Orct2, and genetic complementation with an allele in which the Orct3 gene was inactivated by homologous recombination. The results eliminate both Orct2 and Orct3 as candidates and further reduce the critical region containing the tw73 mutant from 500 kb to 200 kb.

ISOLATION AND CHARACTERIZATION OF A CDNA CLONE CORRESPONDING TO THE MOUSE T-COMPLEX GENE TCP-1X

The mouse t complex on chromosome 17 is known to harbour many genes which have an important role in spermatogenesis. One of these, Tcp-1 has been cloned and shown to code for a protein probably essential for acrosome formation. During the isolation of a cDNA for Tcp-1 two other homologous sequences were recognized and described as Tcp-1x and Tcp-1y. In this paper we describe the isolation of a cDNA which has been shown by in situ hybridization to correspond to the Tcp-1x gene. Sequence analysis has confirmed that a 140 bp region of homology between Tcp-1 and Tcp-1x lies in the 3 portion of both genes. Northern blotting has revealed that the Tcp-1x gene is expressed abundantly in liver where two transcripts are detectable and hybrid selection shows that the gene codes for a 37 kDa protein. A search of the DNA database has failed to find any significant homology between Tcp-1x and any other sequences apart from Tcp-1.

An answer to a complex problem: cloning the mouse t-complex responder

Abstract. The t-complex is maintained in wild mouse populations by its high transmission (up to 99%) from heterozygous males and provides an example of ``meiotic drive. Its molecular basis has remained obscure despite long and intensive study. In a major advance, the t-complex responder gene, thought to be the key gene on which several distorters act, has now been cloned.

Margaret C. Green

necessary conversion to electronic data-keeping and analysis, and setting the groundwork for the Laboratorys leadership in the area of mouse genetic databases. He also believed strongly in the Laboratorys training program, and often took the time to personally sponsor a student in the Laboratorys summer internship program. An annual Short Course in Medical and Mammalian Genetics, jointly taught by The Jackson Laboratory and Johns Hopkins University, was begun during his directorship. He oversaw the building of high-quality animal facilities for research (named by the Trustees the.Earl L. Green Mammalian Genetics Laboratory at the time of his retirement) and a new Library-Conference Center. Overall, he enhanced the Laboratorys reputation as a center for mouse genetics. Prior to his years as director, the Laboratory was known primarily as a cancer research facility. His management style and organization of the smallest details of Laboratory life were often viewed as either comical, tyrannical, or both, depending on the observer and circumstance. New staff and postdoctoral fellows were obliged to attend a weekly seminar at which he lectured on the organization and workings of the Laboratory and on basic concepts in genetics and statistics. Postdocs who were later promoted to staff positions got to attend these seminars a second time, While his 19-year directorship was not without controversy, he made major contributions, and his devotion to the Laboratory was unquestionable. After retiring from the Laboratory in 1975, he continued a number of professional pursuits. He wrote a book entitled Genetics and Probability in Animal Breeding Experiments, which was published in 1981. It is a concise, clearly written explication of common genetic paradigms. He learned to program a personal computer, and wrote a program to obtain maximum likelihood estimates of recombination frequencies from a wide variety of linkage crosses. He also taught courses in genetics and statistics at a local college. Dr. Green was honored by election to Phi Beta Kappa at Allegheny College and to Sigma Xi at Brown University. He was awarded a Doctor of Science degree, honor& causa, by Allegheny College in 1960. In 1978, he was among a group of eight honored by the National Cancer Institute, the National Institute of Allergy and Infectious Diseases, and the Cancer Research Institute for their pioneering efforts in the development of inbred strains of mice. In 1980 he received a Graduate Citation for Distinguished Achievement at the Brown University Graduate Convocation. Earl Green had a strong sense of duty, not only toward his profession, but also toward civic, political, and cultural causes, to which he generously contributed both time and money. He served on the boards of several private research, educational and philanthropic organizations. He was by nature curious and philosophical. He liked puzzles, both physical and mathematical. He enjoyed writing, and produced a series of essays, mostly about everyday experiences, which he distributed to friends. He also enjoyed physical activity as demonstrated by the fact that he cut and split his own firewood throughout his retirement years. The Greens were avid hikers and cross-country skiers. He was devoted to his wife Margaret, who predeceased him by two days. He and Margaret were cordial and frequent hosts to Laboratory visitors and friends, and they will surely be missed.