Reversal of Spermatogonial Arrest in Mice

描述(申请人提供)：遗传缺陷或有毒物质暴露通常会导致生殖细胞早期发育受阻，但在某些情况下，提高温度或降低睾酮水平可以克服这一障碍。这表明，在这些病理情况下，阴囊温度低和睾丸内睾酮水平高可能不是精原细胞和精母细胞发育的最佳条件，睾酮抑制和温度升高的恢复作用可能是机械联系的。我们假设，抑制睾丸素会提高睾丸温度，从而增强一般或特定的代谢事件，以克服遗传或毒物诱导的障碍。幼年精原细胞耗竭(JSD)突变小鼠是研究高温和激素抑制缓解精原细胞分化障碍的机制的一种模型。JSD是参与核糖体RNA加工的Utp14b基因的突变。Utp14b是广泛表达的(除精母细胞外)X连锁的Utp14a基因的拷贝。Utp14b主要在生殖细胞中表达。我们认为，在JSD小鼠中，睾酮抑制导致温度逐渐升高，这通过上调精原细胞和/或精母细胞中的Utp14a来恢复核糖体RNA的加工。我们将在这个模型和替代模型之间进行测试，具体目标如下：(I)确定体内睾酮抑制是否会提高睾丸温度，睾酮是否通过作用于参与温度调节的细胞来抑制精原细胞分化，以及温度是否而不是睾酮影响体外分化。(Ii)确定在阴囊温度下JSD小鼠的精原细胞和精母细胞的18S核糖体RNA处理是否有缺陷，以及在体温下处理是否更有效。(3)确定因温度升高而改变的特定或一般代谢过程，以克服生殖细胞分化方面的缺陷。如果温度升高恢复了JSD小鼠的18S rRNA处理，那么生殖细胞中Utp14a水平的增加将被视为一种特殊的补偿机制。此外，(Iv)我们将评估睾丸激素抑制和高温在促进辐射小鼠精原发育方面的应用，辐射小鼠是一种毒物诱导的生精不足模型。这些结果将为深入了解温度和雄激素对精子发生的影响提供潜在的分子机制，并揭示这两个调节器之间的直接机制联系。这些信息将大大有助于我们对精子发生的生物学机制的基本理解，以及对男性少精子症或无精子症的可能治疗。 部分或完全阻断精子发生的早期阶段会导致精子数量减少或为零，这一问题在男性中似乎正在加剧。阐明这些障碍的原因，以及在实验动物模型中温度升高和激素抑制可以逆转这些障碍的机制，可能适用于人类遗传或环境原因导致的男性不育的治疗。此外，证明我们的假设，即睾丸激素抑制和体温升高的影响是机械联系的，将导致对已发表的研究的新见解和解释。

DESCRIPTION (provided by applicant): Genetic defects or toxicant exposure often result in blocks in early germ cell development, but in some cases elevation of temperature or lowering testosterone levels can overcome this block. This suggests that the low scrotal temperatures and high intratesticular testosterone may not be optimal for spermatogonial and spermatocyte development in these pathological cases, and that effects restorative of testosterone suppression and elevated temperature might be mechanistically linked. We hypothesize that suppression of testosterone elevates testicular temperature, which then enhances general or specific metabolic events to overcome genetic or toxicant induced blocks. The juvenile spermatogonial depletion (jsd) mutant mouse is one model to study the mechanisms by which elevated temperature and hormone suppression can alleviate the block in spermatogonial differentiation. Jsd is a mutation in the Utp14b gene, which is involved in ribosomal RNA processing. Utp14b is a copy of the widely expressed (except spermatocytes) X linked Utp14a gene. Utp14b is mainly expressed in germ cells. We propose that in jsd mice, testosterone suppression leads to a gradual temperature increase, which restores ribosomal RNA processing by upregulating Utp14a in spermatogonia and/or spermatocytes. We will test between this model and alternatives with the following Specific Aims: (I) Determine whether testosterone suppression elevates testicular temperature in vivo, whether testosterone inhibits spermatogonial differentiation by acting on cells involved in temperature regulation, and whether temperature but not testosterone affects differentiation in vitro. (II) Determine if 18S ribosomal RNA processing is defective in both spermatogonia and spermatocytes of jsd mice at scrotal temperatures, and if processing is more efficient at body temperature. (III) Determine the specific or general metabolic processes that are altered by elevation of temperature to overcome the defects in germ cell differentiation. If temperature elevation restores 18S rRNA processing in jsd mice, then increases in Utp14a levels in germ cells will be examined as a specific compensatory mechanism. In addition, (IV) we will evaluate the application of testosterone suppression and elevated temperature to enhance spermatogonial development in irradiated mice, a toxicant induced model of hypospermatogenesis. These results will provide insight into the molecular mechanisms underlying aspects of temperature and androgen effects on spermatogenesis and reveal a direct mechanistic link between these two modulators. This information would significantly contribute to both our basic understanding of the biological mechanisms involved in spermatogenesis, and to possible treatments for oligospermia or azoospermia in men. Partial or complete blocks at the early stages of spermatogenesis results in low or zero sperm counts, a problem that appears to be increasing in men. Elucidation of the causes of such blocks and the mechanisms by which temperature elevation and hormone suppression can reverse them in experimental animal models could apply to treatment of genetically or environmentally caused male infertility in humans. Further, proof of our hypothesis that the effects of testosterone suppression and temperature elevation are mechanistically linked would lead to new insights and interpretations of published research.