As was shown in this study along with many other
As was shown in this study, along with many other previous studies, TALEN and double-nicking CRISPR/Cas9 genome-editing techniques are significantly accurate, with only a negligible risk of random gene disruption, in the drug-selected clones. This result indicates that disrupting a particular gene without disturbing any other genes in GS AMG-900 could replace gene-manipulating technologies with ESCs in the study of spermatogenesis. When GS cells of species other than mice become available for gene targeting as well, it may become possible to study the role of particular genes in their spermatogenesis, which would be rather difficult or practically impossible with ESC technology. In fact, culturing of the SSCs of the rat, hamster, and rabbit was reported to be feasible (Hamra et al., 2005; Kanatsu-Shinohara et al., 2008b; Kubota et al., 2011; Ryu et al., 2005), making this research strategy realistic. In addition, whole-genome sequencing is now available, owing to the many technological innovations in that field. Based on such a huge volume of genome information along with sophisticated analysis methods, genetic analysis of infertile patients (azoospermia in particular) could reveal genes responsible for spermatogenic failure. The genome-modifying technologies shown in this study will be extremely useful to examine such candidate genes responsible for spermatogenic defects in the future.
Introduction Frontotemporal dementia (FTD) comprises a group of neurodegenerative diseases and is the second most common early-onset dementia after Alzheimer’s disease (AD), having a prevalence of ∼15–22/100,000 person-years (Boxer and Miller, 2005; Knopman and Roberts, 2011). FTD is characterized by cortical degeneration of the frontal and temporal lobes (frontotemporal lobar degeneration [FTLD]) leading to impairment of behavior, language, and cognition (Boxer and Miller, 2005; Goedert et al., 2012). About 20%–30% of patients have hereditary forms of FTD, and up to 15%–20% of these patients carry mutations in the MAPT gene located on chromosome 17q21, which encodes the microtubule-associated protein TAU (Goedert and Spillantini, 2011). FTD patients with MAPT mutations present with dementia and Parkinson-like motor impairment due to additional degeneration of subcortical brain areas, including the substantia nigra (SN). Thus, this form of FTD was termed FTD and Parkinsonism linked to chromosome 17 (FTDP-17; for review, see Ghetti et al., 2015). TAU is a neuronal protein that stabilizes microtubules and axoplasmic transport, establishes neuronal polarity, mediates axonal outgrowth and dendritic positioning, and protects DNA from heat damage and oxidative stress (Noble et al., 2013). Six different TAU isoforms are expressed in the adult human brain as a result of alternative splicing of exons 2, 3, and 10 (Goedert et al., 1989). While exons 2 and 3 encode for amino-terminal TAU domains, exon 10 encodes for one of the four microtubule-binding domains in the carboxy-terminal half of TAU (Goedert et al., 1989). In the normal brain, the ratio of isoforms including exon 10 (4R isoforms) to those isoforms devoid of exon 10 (3R isoforms) is usually balanced, but in some FTDP-17 patients, this ratio is shifted toward 4R isoforms, leading to increased deposition of 4R TAU protein within neurons and glial cells (Goedert and Spillantini, 2011). A pathological hallmark of FTDP-17 is the deposition of excessive amounts of hyperphosphorylated TAU (p-TAU) protein in neurons and glial cells in affected brain areas, including neural cells within the temporal cortex and dopaminergic (DA) neurons of the SN. Hyperphosphorylation of TAU is thought to suppress its ability to stabilize microtubules, resulting in axonal degeneration and eventual cell death (for review, see Noble et al., 2013). Deposition of p-TAU is not limited to FTD caused by mutant MAPT but is seen in about 40%–45% of all FTD patients, grouped together with FTDP-17 as FTLD-TAU, and includes patients with Pick’s disease, progressive supranuclear palsy (PSP), and corticobasal degeneration (Goedert et al., 2012; Irwin et al., 2015). Furthermore, excessive accumulation of p-TAU is found in patients with AD, which together with FTLD-TAU forms the large group of neurodegenerative tauopathies.