Mesenchymal cell differentiation and diseases: involvement of translin/TRAX complexes and associated proteins

TSNAXIP1 is required for sperm head formation and male fertility

Purpose

TRANSLIN (TSN) and its binding partner TSNAX have been reported to contribute to a wide spectrum of biological activities including spermatogenesis. TSN accompanies specific mRNA transport in male germ cells through intercellular bridges. A testis-expressed protein TSNAXIP1 was reported to interact with TSNAX. However the role of TSNAXIP1 in spermatogenesis remained unclear. This study aimed to elucidate the role of TSNAXIP1 in spermatogenesis and male fertility in mice.

Methods

TSNAXIP1 knockout (KO) mice were generated using the CRISPR-Cas9 system. The fertility, spermatogenesis, and sperm of TSNAXIP1 KO males were analyzed.

Results

TSNAXIP1, and especially its domains, are highly conserved between mouse and human. Tsnaxip1 was expressed in testis, but not in ovary. TSNAXIP1 KO mice were generated, and TSNAXIP1 KO males were found to be sub-fertile with smaller testis and lower sperm count. Although no overt abnormalities were observed during spermatogenesis, lack of TSNAXIP1 induced sperm head malformation, resulting in a unique flower-shaped sperm head. Moreover, abnormal anchorage of the sperm neck was frequently observed in TSNAXIP1 null sperm.

Conclusion

A testis-expressed gene TSNAXIP1 has important roles in sperm head morphogenesis and male fertility. Moreover, TSNAXIP1 could be a causative gene for human infertility.

Translin restricts the growth of pubertal mammary epithelial cells estrogen-independently in mice

Translin, a ubiquitous RNA/DNA-binding protein that forms a hetero-octamer together with Translin-associated factor X (TRAX), possesses endoribonuclease activity and plays a physiological role in restricting the size and differentiation of mesenchymal precursor cells. However, the precise role of Translin in epithelial cells remains unclear. Here, we show evidence that Translin restricts the growth of pubertal mammary epithelial cells. The mammary epithelia of Translin-null females exhibited retarded growth before puberty, but highly enhanced growth and DNA synthesis with increased ramification after the onset of puberty. Primary cultures of Translin-null mammary epithelial cells showed augmented DNA synthesis in a ligand-independent and ligand-enhanced manner. Translin-null ovariectomized mice implanted with slow-release estrogen pellets showed enhanced length and ramification of the mammary glands. Mammary epithelial growth was also observed in ovariectomized Translin-null mice implanted with placebo pellets. Luciferase reporter assays using embryonic fibroblasts from Translin-null mice showed unaltered estrogen receptor α function. These results indicate that Translin plays a physiological role in restricting intrinsic growth, beyond mesenchymal cells, of pubertal mammary epithelial cells.

Deletion of translin (Tsn) induces robust adiposity and hepatic steatosis without impairing glucose tolerance

Objective:

Translin knockout (KO) mice display robust adiposity. Recent studies indicate that translin and its partner protein, trax, regulate the microRNA and ATM kinase signaling pathways, both of which have been implicated in regulating metabolism. In the course of characterizing the metabolic profile of these mice, we found that they display normal glucose tolerance despite their elevated adiposity. Accordingly, we investigated why translin KO mice display this paradoxical phenotype.

Methods:

To help distinguish between the metabolic effects of increased adiposity and those of translin deletion per se, we compared three groups: (1) wild-type (WT), (2) translin KO mice on a standard chow diet, and (3) adiposity-matched WT mice that were placed on a high-fat diet until they matched translin KO adiposity levels. All groups were scanned to determine their body composition and tested to evaluate their glucose and insulin tolerance. Plasma, hepatic and adipose tissue samples were collected and used for histological and molecular analyses.

Results:

Translin KO mice show normal glucose tolerance whereas adiposity-matched WT mice, placed on a high-fat diet, do not. In addition, translin KO mice display prominent hepatic steatosis that is more severe than that of adiposity-matched WT mice. Unlike adiposity-matched WT mice, translin KO mice display three key features that have been shown to reduce susceptibility to insulin resistance: increased accumulation of subcutaneous fat, increased levels of circulating adiponectin and decreased Tnfα expression in hepatic and adipose tissue.

Conclusions:

The ability of translin KO mice to retain normal glucose tolerance in the face of marked adipose tissue expansion may be due to the three protective factors noted above. Further studies aimed at defining the molecular bases for this combination of protective phenotypes may yield new approaches to limit the adverse metabolic consequences of obesity.

Translin modulates mesenchymal cell proliferation and differentiation in mice

Translin, a highly conserved DNA/RNA binding protein that forms a hetero-octamer together with Translin-associated factor X (TRAX), possesses a broad variety of functions, including RNA processing and DNA repair. Recent studies have reported that Translin is involved in mesenchymal cell physiology. Thus, here we analyzed the intrinsic role of Translin in mesenchymal cell proliferation and differentiation. Translin-deficient E11.5 mouse embryonic fibroblasts showed enhanced growth. Translin-deficient bone marrow-derived mesenchymal stem cells showed substantial expansion in vivo and enhanced proliferation in vitro. These cells also showed enhanced osteogenic and adipocytic differentiation. Histological analyses showed adipocytic hypertrophy in various adipose tissues. Translin knockout did not affect the growth of subcutaneous white adipose tissue-derived stem cells, but enhanced adipocytic differentiation was observed in vitro. Contrary to previous reports, in vitro-fertilized Translin-null mice were not runted and exhibited normal metabolic homeostasis, indicating the fragility of these mice to environmental conditions. Together, these data suggest that Translin plays an intrinsic role in restricting mesenchymal cell proliferation and differentiation.