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障碍，但在某些情况下，升高温度或降低睾丸激素水平可以克服这种障碍。这表明，在这些病理病例中，阴囊低温和睾丸内高睾酮可能不是精原细胞和精母细胞发育的最佳条件，睾酮抑制的恢复效应和升高的温度可能存在机制联系。我们假设，抑制睾丸激素可提高睾丸温度，从而增强一般或特定代谢事件，以克服遗传或毒物引起的阻滞。幼鼠精原细胞缺失（jsd）突变体是研究温度升高和激素抑制减轻精原细胞分化障碍机制的一个模型。Jsd是参与核糖体RNA加工的Utp14b基因突变。Utp14b是广泛表达的（除精母细胞外）与X相关的Utp14a基因的拷贝。Utp14b主要在生殖细胞中表达。我们提出，在jsd小鼠中，睾酮抑制导致温度逐渐升高，通过上调精原细胞和/或精母细胞中的Utp14a来恢复核糖体RNA加工。我们将在该模型和替代模型之间进行测试，具体目的如下：(1)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，以及体外温度而非睾酮是否会影响分化。（II）确定在阴囊温度下jsd小鼠精原细胞和精母细胞中的18S核糖体RNA加工是否存在缺陷，以及在体温下加工是否更有效。（三）确定通过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缺陷。如果温度升高恢复jsd小鼠的18S rRNA加工，那么生殖细胞中Utp14a水平的增加将作为一种特定的补偿机制进行研究。此外，（IV）我们将评估睾酮抑制和升高温度在辐照小鼠（一种毒物诱导的低精子发生模型）中促进精原细胞发育的应用。这些结果将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。这一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。

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.