Combined approaches identify known and novel genes associated with sheep litter size and non-seasonal breeding

Improvement of ewe reproduction is considerable by appropriately increasing litter size and sustaining non-seasonal breeding. However, their genetic makeups have not been entirely elucidated. Genome-wide analyses of 821 individuals were performed by combining three genomic approaches (genome-wide association study, XP-nSL, and runs of homozygosity). Consequently, 35 candidate genes including three domestication genes (TSHR, GTF2A1, and KITLG) were identified. Other than the FecB mutation at BMPR1B, we described a significant association of a missense mutation rs406686139 at seasonal lambing-associated TSHR gene with litter size. Some promising novel genes may be relevant for sheep reproduction by multitude biological processes, such as FETUB functioning in fertilization, HNRNPA1 in oogenesis, DCUN1D1 in spermatogenesis, and HRG in fertility outcome. The present study suggests that improvement of ewe reproduction is attributed to selective breeding, and casts light on the genetic basis and improvement of sheep reproduction.

Delayed Postnatal Growth and Anterior Pituitary Development in Growth-Retarded (grt) Female Mice

Growth-retarded (grt) mice display primary congenital hypothyroidism due to the hyporesponsiveness of their thyroid glands to thyroid-stimulating hormone (TSH). We examined somatic growth, anterior pituitary development, and hormonal profiles in female grt mice and normal ones. Although growth in grt females was suppressed 2 weeks after birth, the measured growth parameters and organ weights gradually increased and finally reached close to the normal levels. Grt mice exhibited delayed eye and vaginal openings and remained in a state of persistent diestrus thereafter, plasma estrogen levels being lower than those in normal mice. Grt mice that received normal-donor thyroids showed accelerated growth and their body weights increased up to the sham-normal levels, indicating the importance of early thyroid hormone supplementation. In the anterior pituitary, there were fewer growth hormone (GH) and prolactin (PRL) cells in grt mice than in normal mice as examined at 12 weeks after birth, but the numbers of these cells did not differ from those in normal mice after 24 weeks. Grt mice had more TSH cells than normal mice until 48 weeks. Plasma GH levels in grt mice were lower than those in normal mice at 2 weeks, but did not differ substantially after 5 weeks. Compared with normal mice, grt mice had significantly lower plasma PRL and thyroxine levels, but notably higher TSH levels until 48 weeks. These findings indicate that thyroid hormone deficiency in grt mice causes delayed development and growth, and inappropriate development of GH, PRL and TSH cells, followed by the abnormal secretion of hormones by these pituitary cells.

Zebrafish duox mutations provide a model for human congenital hypothyroidism

Thyroid dyshormonogenesis is a leading cause of congenital hypothyroidism, a highly prevalent but treatable condition. Thyroid hormone (TH) synthesis is dependent on the formation of reactive oxygen species (ROS). In humans, the primary sources for ROS production during thyroid hormone synthesis are the NADPH oxidases DUOX1 and DUOX2. Indeed, mutations in DUOX1 and DUOX2 have been linked with congenital hypothyroidism. Unlike humans, zebrafish has a single orthologue for DUOX1 and DUOX2. In this study, we investigated the phenotypes associated with two nonsense mutant alleles, sa9892 and sa13017, of the single duox gene in zebrafish. Both alleles gave rise to readily observable phenotypes reminiscent of congenital hypothyroidism, from the larval stages through to adulthood. By using various methods to examine external and internal phenotypes, we discovered a strong correlation between TH synthesis and duox function, beginning from an early larval stage, when T₄ levels are already noticeably absent in the mutants. Loss of T₄ production resulted in growth retardation, pigmentation defects, ragged fins, thyroid hyperplasia/external goiter and infertility. Remarkably, all of these defects associated with chronic congenital hypothyroidism could be rescued with T₄ treatment, even when initiated when the fish had already reached adulthood. Our work suggests that these zebrafish duox mutants may provide a powerful model to understand the aetiology of untreated and treated congenital hypothyroidism even in advanced stages of development.

This article has an associated First Person interview with the first author of the paper.

Summary: Zebrafish harbouring two loss-of-function alleles of the single duox gene exhibit various adult phenotypes reminiscent of human congenital hypothyroidism.

Restoration of corpus luteum angiogenesis in immature hypothyroid rdw rats after thyroxine treatment: morphologic and molecular evidence

Thyroxine (T4) plus gonadotropins might stimulate ovarian follicular angiogenesis in immature infertile hypothyroid rdw rats by upregulating mRNA expression of major angiogenic factors. Development of growing corpus luteum (CL) is strongly related to angiogenesis and to morphofunctional development of microcirculation. Our aim was to investigate if T4 is involved in CL angiogenesis and in the activation of capillary cells and angiogenic factors after ovulation in a spontaneous model of hypothyroidism, the rdw rat. Rdw rats were treated with T4 plus gonadotropins (equine chorionic gonadotropin plus human chorionic gonadotropin; eCG+hCG) or gonadotropins alone in order to evaluate the effects of T4 on early luteal angiogenesis, on microvascular cells and on expression of major growth factors which are involved in the regulation of angiogenesis. Wistar-Imamichi rats treated with gonadotropins were used as controls. The ovaries were collected 4 days after hCG administration and analyzed using morphologic and molecular approaches. Thyroxine plus gonadotropins stimulated the growth of CLs and follicles as in controls, differently from rdw rats treated only with gonadotropins, in which CLs were not found and only small follicles, often atretic, could be recognized. In T4 plus gonadotropin-treated rdw rats CLs showed increased microvasculature, numerous activated capillaries characterized by sprouting and other angiogenic figures, and associated pericytes. Quantitative analysis revealed that the number of pericytes in T4 plus gonadotropin-treated rdw rats was comparable with that found in control rats and was significantly higher than that found in gonadotropin-treated rdw rats. The mRNA expression of vascular endothelial growth factor and basic fibroblast growth factor was significantly higher in control rats and in T4 plus gonadotropin-treated rdw rats than in gonadotropin-treated rdw rats. mRNA expression of tumor necrosis factor α, transforming growth factor β, and epidermal growth factor did not show significant changes. Our data originally demonstrated that T4 promoted the growth of an active microcirculation in developing CLs of gonadotropin-primed hypothyroid rdw rats, mainly by inducing sprouting angiogenesis, pericyte recruitment, and upregulation of mRNA expression of vascular endothelial growth factor and basic fibroblast growth factor. In conclusion, we suggest that T4 plays a key role in restoring luteal angiogenesis in ovaries of immature hypothyroid rdw rats.

Hypothyroid phenotype of the Tpst2 mutant mouse is dependent upon genetic background

DW/J-grt is a congenital hypothyroid mouse model that is characterized by growth retardation, significantly lowered T3 and T4 levels, and severe thyroid hypoplasia related to TSH hyporesponsiveness. Previously, we identified the point mutation of the Tpst2 gene in DW/J-grt mice that causes a decrease in the enzymatic activity, and demonstrated that the Tpst2 transgene rescues the mutant phenotypes both in vitro and in vivo. The severity of hypothyroidism is highly variable indicating the influence of modifier genes in humans. In this study, to identify the modifier/resistant gene(s) to hypothyroidism, we produced congenic strains carrying this Tpst2(grt) mutation on the C57BL/6J and 129/SvJcl (129) genetic backgrounds and analyzed growth rate and thyroid function. Interestingly, the 129 congenic mice exhibited normal growth and thyroid function. The result suggests that 129 strain has the modifier(s) of attenuation of hypothyroidism. Therefore, the identification of the modifier loci of 129 mice will provide important new information about the gene(s) related to congenital hypothyroidism.

Inducible male infertility by targeted cell ablation in zebrafish testis

To generate a zebrafish model of inducible male sterility, we expressed an Escherichia coli nitroreductase (Ntr) gene in the male germ line of zebrafish. The Ntr gene encodes an enzyme that can convert prodrugs such as metronidazole (Met) to cytotoxins. A fusion protein eGFP:Ntr (fusing Ntr to eGFP) under control of approximately 2 kb putative promoters of the zebrafish testis-specific genes, A-kinase anchoring protein-associated protein (Asp), outer dense fibers (Odf), and sperm acrosomal membrane-associated protein (Sam) was expressed in the male germ line. Three independent and four compound transgenic zebrafish lines expressing eGFP:Ntr were established. Female carriers were fertile, while males exhibited different levels of sterility and appeared normal, otherwise. Developmental analysis shows that germ cells survived and testes were normal before Met treatment, but that the testes of all male transgenic zebrafish exhibited variously depleted prospermatogonia after Met treatment. Particularly in a triple-transgenic line, Tg(AOS-eGFP:Ntr)[Tg(Asp-eGFP:Ntr; Odf-eGFP:Ntr; Sam-eGFP:Ntr)], the transgenic males had very small testes that were virtually devoid of germ cells, and the residual germ cells had almost completely disappeared after 2 weeks of Met treatment. These zebrafish transgenic lines show the complete testis specificity of inducible male sterility after Met treatment and reveal a period of the Ntr/Met ablation activity just prior to formation of the definitive adult spermatogonial cell population. This study demonstrates that combined genetic and pharmacological methods for developing an "infertile breeding technology" have practical application in controlling genetically modified (GM) fish breeding and meet the standards of biological and environment safety for other GM species.

Impaired Development of Somatotropes, Lactotropes and Thyrotropes in Growth-Retarded (grt) Mice

Congenitally primary hypothyroid growth-retarded (grt) mice exhibit a characteristic growth pause followed by delayed onset of pubertal growth. We characterized the developmental pattern of somatotropes, lactotropes and thyrotropes in the anterior pituitary, as well as plasma levels of their secretory hormones, in grt mice. Compared with normal mice, the weight of grt pituitary gland was similar at 8 weeks of age but significantly heavier after 12 weeks of age. Compared with normal mice, there were significantly fewer somatotropes in the grt pituitary until 8 weeks of age, but the number gradually increased up to 48 weeks. The number of lactotropes in grt mice was consistently lower than that in normal mice from 2 through 48 weeks, whereas the number of thyrotropes in the grt pituitary was consistently higher than in the normal pituitary. Thyrotropes in the grt pituitary exhibited hypertrophy and hyperplasia with less intensive thyroid-stimulating hormone (TSH) immunoreactivity than normal thyrotropes. In normal mice, the sum of the relative proportions of these cells plateaued at 8 weeks, where it remained up to 48 weeks of age. In grt mice, these proportions almost reached normal levels at 12 weeks of age but gradually declined after 24 weeks. Plasma growth hormone concentrations did not differ between grt and normal mice until 24 weeks of age. Compared with normal mice, grt mice exhibited significantly lower plasma prolactin and thyroxine levels but higher TSH levels. These findings indicate that development of somatotropes, lactotropes and thyrotropes in grt mice is impaired, being followed by altered hormone secretion.