Reversal of Spermatogonial Arrest in Mice

描述（由申请人提供）：遗传缺陷或有毒物质暴露通常会导致早期生殖细胞发育受阻，但在某些情况下，温度升高或睾酮水平降低可以克服这种阻滞。这表明，在这些病理情况下，低阴囊温度和高睾丸内睾酮可能不是精原细胞和精母细胞发育的最佳条件，睾酮抑制的恢复效果和升高的温度可能是机械相关的。我们假设，抑制睾酮升高睾丸温度，然后增强一般或特定的代谢事件，以克服遗传或毒物诱导的块。幼年型精原细胞耗竭（jsd）突变小鼠是研究高温和激素抑制缓解精原细胞分化阻滞机制的模型之一。Jsd是Utp 14 b基因中的突变，其参与核糖体RNA加工。Utp 14 b是广泛表达的（除精母细胞外）X连锁Utp 14 a基因的拷贝。utp 14 b主要在生殖细胞中表达。我们建议，在jsd小鼠，睾酮抑制导致温度逐渐升高，这恢复核糖体RNA加工上调Utp 14 a在精原细胞和/或精母细胞。我们将在该模型和替代模型之间进行测试，具体目的如下：（I）确定睾酮抑制是否在体内升高睾丸温度，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，以及温度而不是睾酮是否影响体外分化。(II)确定在阴囊温度下，jsd小鼠精原细胞和精母细胞的18 S核糖体RNA加工是否有缺陷，以及在体温下加工是否更有效。(III)确定特定或一般的代谢过程，通过温度升高改变，以克服生殖细胞分化的缺陷。如果温度升高恢复了jsd小鼠的18 S rRNA加工，那么生殖细胞中Utp 14 a水平的增加将被视为一种特定的补偿机制。此外，（IV）我们将评估睾酮抑制和升高温度在辐射小鼠（一种毒物诱导的精子生成障碍模型）中促进精原细胞发育的应用。这些结果将提供深入了解温度和雄激素对精子发生影响的分子机制，并揭示这两种调节剂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。 在精子发生的早期阶段部分或完全阻断导致精子数量低或为零，这一问题在男性中似乎越来越严重。在实验动物模型中阐明这种阻滞的原因以及温度升高和激素抑制可以逆转它们的机制，可以适用于治疗遗传或环境引起的人类男性不育症。此外，证明我们的假设，即睾酮抑制和温度升高的影响是机械联系将导致新的见解和解释发表的研究。

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.