Using Sex-reversed Chickens To Identify Core Spermatogenic Regulatory Genes

在过去的几十年里，由于肉类和蛋类等家禽产品富含蛋白质，商业鸡肉产量呈指数级增长，预计在未来10年里，鸡肉仍将是最受欢迎的畜产品之一。为了满足全球对家禽产品日益增长的需求，需要不断扩大鸡的生产，这取决于雄性和雌性（亲本）鸡群的生育力和繁殖能力。商业家禽管理依赖于相对较少的繁殖雄性的最佳精子产量，保持和提高雄性生育能力是大规模生产的关键因素。为保持育龄雄鱼的繁殖力和繁殖性能，需要进行选择性育种和限制性饲养计划。影响精子质量的特征是精子数量、活动性、形态和活力，以及完整的顶体。在本研究中，我们旨在通过研究鸡精子发生来了解与活配子产生相关的分子网络。特别是，我们将利用我们开发的独特模型系统来研究具有非典型性染色体的鸟类的精子产生。众所周知，在许多物种中，性染色体包含生育的主要调节因子，这种新方法将使我们能够快速识别精子发生的性别相关调节因子。在鸟类中，雄性有两条Z染色体，雌性各有一条Z和W染色体。原始生殖细胞（PGCs）是一种能产生动物配子的生殖细胞系细胞。以前认为PGCs只能发育成精子（如果是ZZ）或卵母细胞（如果是ZW）。然而，我们最近发现鸟类PGCs具有双能性，可以通过生殖腺周围细胞的信号传导成为精子或卵母细胞。当携带ZZ的雄性PGCs被移植到不育的雌性宿主（ZW）中时，ZZ细胞形成卵母细胞。同样，当雌性PGCs （ZW）被移植到不育的雄性宿主（ZZ）中时，ZW细胞可以形成功能精子。然而，令人惊讶的是，在精子产生过程中，Z染色体和W染色体分离后，只有携带Z染色体的细胞存活下来，为下一代做出贡献。我们将研究这些性别逆转的细胞，并与正常的ZZ精子发生进行比较，以了解该模型系统中携带W的精子的损失是由于W染色体的存在还是由于缺少第二条Z染色体。无论哪种情况，这些发现都将突出对调节细胞存活、细胞死亡和发育中的精子受精能力至关重要的关键基因。然后，这些基因可以作为选择的目标，以提高公鸡的生育能力。此外，我们将收集鸟类精子发生的基本生物学数据，重点关注两个知之甚少的领域。首先，在哺乳动物中，性染色体在精子发生的减数分裂细胞阶段变得失活（这一过程被称为MSCI，减数分裂性染色体失活）。在鸡中，由于在这个发育阶段难以获得卵母细胞，因此MSCI的证据是模棱两可的。我们的新模型的独特之处在于，它允许我们研究精子发生过程中的MSCI，在精子发生过程中，生殖细胞更容易获得。我们的研究将解决这一争议，并为鸟类性染色体转录沉默机制的存在与否提供确凿的证据。其次，来自哺乳动物的证据表明，在精子产生过程中，X染色体和Y染色体被分割成不同的细胞后，它们继续通过发育细胞之间的“桥梁”共享基因产物（mRNA和蛋白质）。然而，这一过程从未在哺乳动物之外进行过研究。ZW精子发生提供了一个独特的比较系统来理解发育中的精子细胞之间转录物共享的机制和原理。

Over the past decades, due to the protein rich contents of poultry products such as meat and eggs, there has been an exponential increase in commercial chicken production, and it is projected to remain one of the most popular livestock products by volume over the next 10 years. To meet the increasing global demand for poultry products, the production of chickens needs to be constantly expanded, which is dependent on the fertility and reproductive capacity of the male and female (parental) flocks. Commercial poultry management depends on optimal sperm production of relatively few breeding males, and maintaining and enhancing male fertility is a critical factor for large scale production. Selective breeding and restrictive feeding programmes are needed to maintain the fertility and breeding performance of the breeding males. The characteristics that influence the quality of sperm are sperm count, mobility, morphology, and viability, and intact acrosomes. In this research, we aim to understand the molecular network associated with the production of viable gametes by studying spermatogenesis in chickens. In particular, we will make use of a unique model system we have developed to study sperm production in birds with non-typical sex chromosomes. The sex chromosomes are well known to contain master regulators of fertility in many species, and this novel approach will allow us to rapidly identify sex-linked regulators of spermatogenesis.In birds, males have two copies of the Z chromosome and females have one copy each of the Z and W chromosomes. Primordial germ cells (PGCs) are germline-competent cells that give rise to the functional gametes of an animal. It was previously thought that PGCs could only develop into either sperm (if ZZ) or oocytes (if ZW). However, we have recently shown that avian PGCs are bipotent, and can become either sperm or oocyte based on cellular signalling by the surrounding cells within the gonad. When male PGCs (carrying ZZ) are transplanted into a sterile female host (ZW), the ZZ cells form oocytes. Similarly, when female PGCs (ZW) are transplanted into a sterile male host (ZZ), the ZW cells can form functional sperm. Surprisingly, however, after the Z and W chromosomes separate during sperm production only Z-bearing cells survive to contribute to the next generation. We will study these sex-reversed cells in comparison to normal ZZ spermatogenesis, to understand whether the loss of W-bearing sperm in this model system is due to the presence of the W chromosome or the absence of a second Z chromosome. In either case, the findings will highlight key genes that are crucial for regulating cell survival, cell death and fertilizing ability of developing sperm cells. These genes can then be used as targets for selection to improve fertility in roosters.Additionally, we will gather data on the basic biology of spermatogenesis in birds, focusing on two areas that are poorly understood. Firstly, in mammals, the sex chromosomes become inactive (a process known as MSCI, meiotic sex chromosome inactivation) during the meiotic cell stage of spermatogenesis. In chickens, evidence for MSCI is equivocal due to the difficulty accessing oocytes at this stage of development. Our new model is unique in that it allows us to study MSCI during spermatogenesis, where germ cells are much more accessible. Our research will resolve this controversy and offer conclusive evidence for the presence or absence of a sex chromosome transcription silencing mechanism in birds. Secondly, evidence from mammals shows that after the X and Y have been partitioned into separate cells during sperm production, they continue to share gene products (mRNA and protein) across "bridges" between developing cells. This process has however never been studied outside a mammalian context. ZW spermatogenesis offers a unique comparative system to understand the mechanisms and principles underpinning transcript sharing between developing sperm cells.