The Collaborative Cross Consortium reports here on the development of a unique genetic resource population. The Collaborative Cross (CC) is a multiparental recombinant inbred panel derived from eight laboratory mouse inbred strains. Breeding of the CC lines was initiated at multiple international sites using mice from The Jackson Laboratory. Currently, this innovative project is breeding independent CC lines at the University of North Carolina (UNC), at Tel Aviv University (TAU), and at Geniad in Western Australia (GND). These institutions aim to make publicly available the completed CC lines and their genotypes and sequence information. We genotyped, and report here, results from 458 extant lines from UNC, TAU, and GND using a custom genotyping array with 7500 SNPs designed to be maximally informative in the CC and used a novel algorithm to infer inherited haplotypes directly from hybridization intensity patterns. We identified lines with breeding errors and cousin lines generated by splitting incipient lines into two or more cousin lines at early generations of inbreeding. We then characterized the genome architecture of 350 genetically independent CC lines. Results showed that founder haplotypes are inherited at the expected frequency, although we also consistently observed highly significant transmission ratio distortion at specific loci across all three populations. On chromosome 2, there is significant overrepresentation of WSB/EiJ alleles, and on chromosome X, there is a large deficit of CC lines with CAST/EiJ alleles. Linkage disequilibrium decays as expected and we saw no evidence of gametic disequilibrium in the CC population as a whole or in random subsets of the population. Gametic equilibrium in the CC population is in marked contrast to the gametic disequilibrium present in a large panel of classical inbred strains. Finally, we discuss access to the CC population and to the associated raw data describing the genetic structure of individual lines. Integration of rich phenotypic and genomic data over time and across a wide variety of fields will be vital to delivering on one of the key attributes of the CC, a common genetic reference platform for identifying causative variants and genetic networks determining traits in mammals.

The lactate dehydrogenase (LDH) protein family members characteristically are distributed in tissue- and cell type-specific patterns and serve as the terminal enzyme of glycolysis, catalyzing reversible oxidation reduction between pyruvate and lactate. They are present as tetramers, and one family member, LDHC, is abundant in spermatocytes, spermatids, and sperm, but also is found in modest amounts in oocytes. We disrupted the Ldhc gene to determine whether LDHC is required for spermatogenesis, oogenesis, and/or sperm and egg function. The targeted disruption of Ldhc severely impaired fertility in male Ldhc(-/-) mice but not in female Ldhc(-/-) mice. Testis and sperm morphology and sperm production appeared to be normal. However, total LDH enzymatic activity was considerably lower in Ldhc(-/-) sperm than in wild type sperm, indicating that the LDHC homotetramer (LDH-C(4)) is responsible for most of the LDH activity in sperm. Although initially motile when isolated, there was a more rapid reduction in the level of ATP and in motility in Ldhc(-)(/-) sperm than in wild-type sperm. Moreover, Ldhc(-/-) sperm did not acquire hyperactivated motility, were unable to penetrate the zona pellucida in vitro, and failed to undergo the phosphorylation events characteristic of capacitation. These studies showed that LDHC plays an essential role in maintenance of the processes of glycolysis and ATP production in the flagellum that are required for male fertility and sperm function.

Lactate dehydrogenase C (LDHC) was, to the best of our knowledge, the first testis-specific isozyme discovered in male germ cells. In fact, this was accomplished shortly before ''isozymes or isoenzymes'' became a field of study. LDHC was detected initially in human spermatozoa and spermatogenic cells of the testes by gel electrophoresis. Immunohistochemistry was used to localize LDHC first in early-pachytene primary spermatocytes, with an apparent increase in quantity after meiosis, to its final localization in and on the principal piece of the sperm tail. After several decades of biologic, biochemical, and genetic investigations, we now know that the lactate dehydrogenase isozymes are ubiquitous in vertebrates, developmentally regulated, tissue and cell specific, and multifunctional. Here, we will review the history of LDHC and the work that demonstrates clearly that it is required for sperm to accomplish their ultimate goal, fertilization.