Molecular characterization of an allelic series of mutations in the mouse Nox3 gene.

The inner ear consists of the cochlea (the organ of hearing) and the vestibular system (the organs of balance). Within the vestibular system, linear acceleration and gravity are detected by the saccule and utricle. Resting above the neurosensory epithelia of these organs are otoconia, minute proteinaceous and crystalline (calcite) inertial masses that shift under the physical forces imparted by linear movements and gravity. It is the transduction and sensation of these movements and their integration with vision and proprioceptive inputs that contribute to the sensation of balance. It has been proposed that a reactive oxygen species- (ROS-) generating NADPH oxidase comprising the gene products of the Nox3, Noxo1, and Cyba genes plays a critical and constructive role in the process of inner-ear development, specifically, the deposition of otoconia. Inactivation in mouse of any of the NADPH oxidase components encoded by the Nox3, Noxo1, or Cyba gene results in the complete congenital absence of otoconia and profound vestibular dysfunction. Here we describe our use of PCR, reverse transcription-PCR (RT-PCR), and rapid amplification of cDNA ends (RACE) with traditional and high-throughput (HTP) sequencing technologies to extend and complete the molecular characterization of an allelic series of seven mutations in the Nox3 gene. Collectively, the mutation spectrum includes an endogenous retrovirus insertion, two missense mutations, a splice donor mutation, a splice acceptor mutation, premature translational termination, and a small duplication. Together, these alleles provide tools to investigate the mechanisms of otoconial deposition over development, throughout aging, and in various disease states.

Generation of a conditional null allele of NADPH oxidase activator 1 (NOXA1).

NADPH oxidase complexes are multiprotein assemblies that generate reactive oxygen species in a variety of mammalian tissues. The canonical phagocytic oxidase consists of a heterodimeric, enzymatic core comprised of the transmembrane proteins, CYBB andCYBA and is regulated, in part, by an "organizing" function of NCF1 and an "activating" activity of NCF2. In contexts outside of the phagocyte, these regulatory functions may be encoded not only by NCF1 and NCF2, but also alternatively by their respective paralogues, NOXO1 and NOXA1. To allow tissue-specific dissection of Noxa1 function in mouse, we have generated an allele of Noxa1 suitable for conditional inactivation. Moreover, by crossing Noxa1 conditional allele carriers to B6.129S4-Meox2(tm1(Cre)Sor)/J mice, we have generated first, Noxa1-null heterozygotes, and ultimately, Noxa1-null homozygotes. Through the thoughtful use of tissue-specific, Cre-expressing mouse strains, the Noxa1 conditional allele will offer insight into the roles of NOXA1 in the variety of tissues in which it is expressed.

Identification of EOMES-expressing spermatogonial stem cells and their regulation by PLZF.

Long-term maintenance of spermatogenesis in mammals is supported by GDNF, an essential growth factor required for spermatogonial stem cell (SSC) self-renewal. Exploiting a transgenic GDNF overexpression model, which expands and normalizes the pool of undifferentiated spermatogonia between Plzf +/+ and Plzf lu/lu mice, we used RNAseq to identify a rare subpopulation of cells that express EOMES, a T-box transcription factor. Lineage tracing and busulfan challenge show that these are SSCs that contribute to steady state spermatogenesis as well as regeneration following chemical injury. EOMES+ SSCs have a lower proliferation index in wild-type than in Plzf lu/lu mice, suggesting that PLZF regulates their proliferative activity and that EOMES+ SSCs are lost through proliferative exhaustion in Plzf lu/lu mice. Single cell RNA sequencing of EOMES+ cells from Plzf +/+ and Plzf lu/lu mice support the conclusion that SSCs are hierarchical yet heterogeneous.

Sex Steroid Hormones Regulate Leptin Transcript Accumulation and Protein Secretion in 3T3-L1 Cells.

Leptin is an adipokine produced by fat cells that regulates food consumption and metabolic activity. Sexual dimorphism in leptin and fat stores have been observed in humans and rodents with females having more leptin and greater levels of subcutaneous fat than males. One potential mechanism leading to this dimorphism is steroid hormone regulated synthesis of transcripts encoding leptin. Identification of direct regulatory mechanisms is difficult in animals or primary adipocytes due to these intertwined dimorphisms. We used well-characterized 3T3-L1 murine adipocytes to demonstrate that dihydrotestosterone (DHT) reduced Leptin (Lep) transcript abundance and cytosolic and secreted leptin protein. The magnitude of this effect was greatest on secreted leptin, which was decreased by DHT to 30% of the control. In contrast, 17ß-estradiol significantly increased the abundance of transcripts encoding leptin and increased secreted leptin to 230% of the control. Treatment with estrogen and androgen receptor antagonists had opposite effects on Lep transcript abundance to steroid treatments, indicating that these transcriptional effects are mediated through the canonical steroid hormone signaling pathways. These results indicate that short-term treatments with steroid hormones are sufficient to alter both Lep transcript accumulation and leptin protein secretion, and may play a role in the sexual dimorphism of this adipokine.

Spontaneous 8bp Deletion in Nbeal2 Recapitulates the Gray Platelet Syndrome in Mice.

During the analysis of a whole genome ENU mutagenesis screen for thrombosis modifiers, a spontaneous 8 base pair (bp) deletion causing a frameshift in exon 27 of the Nbeal2 gene was identified. Though initially considered as a plausible thrombosis modifier, this Nbeal2 mutation failed to suppress the synthetic lethal thrombosis on which the original ENU screen was based. Mutations in NBEAL2 cause Gray Platelet Syndrome (GPS), an autosomal recessive bleeding disorder characterized by macrothrombocytopenia and gray-appearing platelets due to lack of platelet alpha granules. Mice homozygous for the Nbeal2 8 bp deletion (Nbeal2gps/gps) exhibit a phenotype similar to human GPS, with significantly reduced platelet counts compared to littermate controls (p = 1.63 x 10-7). Nbeal2gps/gps mice also have markedly reduced numbers of platelet alpha granules and an increased level of emperipolesis, consistent with previously characterized mice carrying targeted Nbeal2 null alleles. These findings confirm previous reports, provide an additional mouse model for GPS, and highlight the potentially confounding effect of background spontaneous mutation events in well-characterized mouse strains.

A 5' distal palindrome within the mouse mammary tumor virus-long terminal repeat recruits a mammary gland-specific complex and is required for a synergistic response to progesterone plus prolactin.

Progesterone (P) and prolactin (PRL) fulfill crucial roles during growth and differentiation of the mammary epithelium, and each has been implicated in the pathogenesis of mammary cancer. We previously identified that these hormones synergistically stimulate the proliferation of mouse mammary epithelial cells in vivo, although the mechanism(s) underlying their cooperative effect are unknown. We now report a novel pathway by which P and PRL synergize to activate transcription from the long terminal repeat (LTR) of the mouse mammary tumor virus-LTR (MMTV-LTR) in T47D breast cancer cells. Using serial 5' and 3' deletions of the MMTV-LTR, in addition to selective mutations, we identified that a previously uncharacterized inverted palindrome on the distal enhancer (-941/-930), in addition to a signal transducer and activator of transcription 5 site, was essential for the synergistic activation of transcription by P and PRL. Notably, hormone synergy occurred via a mechanism that was independent of the P receptor DNA-binding elements found in the proximal MMTV-LTR hormone-response element. The palindrome specifically recruited a protein complex (herein termed mammary gland-specific complex) that was almost exclusive to normal and cancerous mammary cells. The synergy between P and PRL occurred via a Janus kinase 2 and c-Src/Fyn-dependent signaling cascade downstream of P and PRL receptors. Combined, our data outline a novel pathway in T47D cells that may facilitate the action(s) of P and PRL during mammary development and breast cancer.