Using Sex-reversed Chickens To Identify Core Spermatogenic Regulatory Genes

在过去的几十年里，由于肉类和鸡蛋等禽类产品含有丰富的蛋白质，商业鸡肉产量呈指数级增长，预计在未来10年内，它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。商业家禽的管理依赖于相对较少的繁殖雄性的最佳精子产生，而保持和提高雄性生育能力是大规模生产的关键因素。为了维持繁殖雄性的繁殖力和繁殖性能，需要选择性繁殖和限制喂养方案。影响精子质量的特征是精子数量、活动率、形态和活力，以及完整的顶体。在这项研究中，我们旨在通过研究鸡的精子发生来了解与生产可存活配子相关的分子网络。特别是，我们将利用我们开发的一个独特的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，性染色体含有生育的主要调节因子，这种新的方法将使我们能够快速识别与性别相关的精子发生调节因子。在鸟类中，雄性有两个Z染色体副本，雌性Z染色体和W染色体各有一个副本。原始生殖细胞(PGC)是具有生殖线能力的细胞，可产生动物的功能性配子。以前人们认为PGCs只能发育成精子(如果ZZ)或卵母细胞(如果ZW)。然而，我们最近发现，鸟类的生殖细胞具有双能，基于性腺内周围细胞的细胞信号，它可以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，当女性生殖细胞(ZW)被移植到不育的男性宿主(ZZ)中时，ZW细胞可以形成功能正常的精子。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Z染色体存活下来，为下一代做出贡献。我们将研究这些性反转细胞与正常的ZZ精子发生的比较，以了解在这个模型系统中W-精子的丢失是由于W染色体的存在还是第二个Z染色体的缺失。无论是哪种情况，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细胞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，我们还将收集鸟类精子发生的基本生物学数据，重点放在两个鲜为人知的领域。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不活跃(这一过程被称为MSCI，减数分裂性染色体失活)。在鸡身上，MSCI的证据是模棱两可的，因为在发育的这个阶段很难获得卵母细胞。我们的新模型是独一无二的，因为它允许我们在精子发生期间研究MSCI，在那里生殖细胞更容易获得。我们的研究将解决这一争议，并为鸟类中是否存在性染色体转录沉默机制提供确凿证据。其次，来自哺乳动物的证据表明，在精子产生过程中，X和Y被分割成单独的细胞后，它们继续跨越发育中的细胞之间的“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的背景下被研究过。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.