Vacuole segregation and mycelial development of Candida albicans

白色念珠菌是与危及生命的感染有关的最常见的真菌。它是许多真菌中的一种，它既可以作为卵形酵母生长，通过形成扩张的芽生长，也可以作为一种霉菌生长，使分枝的管状细胞形成菌丝体。由于感染与这两种形式之间的转换有关，酵母到菌丝的转换过程在最近几年得到了大量研究。然而，这些研究大多集中在刺激转变的信号上，而不是初级生殖管及其相关分支的生长。这一点很重要，因为菌丝生长对组织入侵可能是至关重要的，而且已经清楚地表明，菌丝白色念珠菌的过程是不寻常的，并使关于真核细胞一般细胞分裂的生理要求的新假说能够得到检验。因此，我们将从菌丝细胞在真菌疾病中的作用以及它对细胞周期的细胞生物学的洞察的角度来研究菌丝细胞是如何生长和分裂的。我们观察到，在胚管的生长过程中，在生长的顶端后面形成了一个大液泡，填满了大部分细胞。虽然这个细胞的整体尺寸与其他细胞相似，但它的细胞质较少。我们认为它没有足够的细胞质来在细胞分裂周期中进行。在细胞周期中称为起始的特定时间点，细胞必须达到一定的最小细胞尺寸。因此，我们假设，细胞分裂后留下的大液泡阻止这些细胞在分裂周期中通过START。我们还发现，液泡不是在细胞分裂后形成的两个子细胞之间平均分配的，年轻的子细胞获得了大部分细胞质，母细胞保留了大部分空泡。液泡分裂和遗传是一个严格调控的过程，我们已经从相关的酵母样真菌酿酒酵母那里学到了很多东西。为了验证液泡遗传和分布决定细胞生长或生长停滞是发生在菌丝体内的假说，我们将在调节细胞分裂时液泡分裂的基因中进行明确的突变。从对酿酒酵母的研究中，我们可以准确地预测我们需要进行哪些突变才能改变细胞中的正常空泡模式。这些突变体将使我们不仅能够发现液泡如何控制细胞分裂，而且还可以解决高等真核细胞中细胞周期如何调控的问题。有了一系列突变体，我们将能够剖析菌丝和菌丝分支生长的调节途径。我们还将能够评估正常的分枝是否对这种真菌在动物组织中建立病损的能力很重要。重要的是，许多其他重要的真菌，包括许多植物病原体，通过形成或多或少的液泡来控制它们所经历的生长类型。因此，通过对液泡化和真菌生长之间的遗传联系进行首次深入研究，我们将能够推动真菌生理学领域的发展。

Candida albicans is the most common fungus that is associated with life-threatening infection. It is one of many fungi that can grow either as an ovoid yeast that grows by forming expanding buds or as a mould that elaborates branching tubular cells to form a mycelium. Because infections are associated with transitions between these two forms the process of yeast-to-hypha transition has been heavily studied in recent years. However, most of these investigations have focussed on the signals that stimulate the transitions rather than the growth of the primary germ tube and its associated branches. This is important because mycelial growth may be vital for tissue invasion, and because it has become clear that the process of hyphal C. albicans is unusual and enables novel hypotheses to be tested about the physiological requirements for cell division of eukaryotic cells in general. Consequently we will investigate how mycelial cells grow and divide both from the point of view of its role in fungal disease and the insights it can provide into the cell biology of the cell cycle. We have observed that during the growth of germ tubes, a large vacuole forms behind the growing tip that fills up most of the cell. Although the overall dimensions of this cell are similar to other cells, it has less cytoplasm. We propose that it does not have sufficient cytoplasm to progress through the cell division cycle. At a specific point in the cell cycle called START, cells must achieve a certain minimal cell size. We therefore hypothesise that the large vacuole left behind after cell division prevents these cells from passing through START in the division cycle. We have also shown that the vacuole is not equally divided between the two daughter cells formed after cell division, and that the younger daughter cell acquires most of the cytoplasm and the mother cell retains most of the vacuole. Vacuole division and inheritance is a carefully regulated process about which we have learned much from the related yeast-like fungus Saccharomyces cerevisiae. To test out hypothesis that vacuole inheritance and distribution determines whether growth or growth arrest of cells occurs within the mycelium, we will make defined mutations in genes that regulate vacuole partitioning at cell division. We can predict from studies in S. cerevisiae exactly what mutations we will need to make to be able to alter the normal vacuole pattern in cells. These mutants will enable us not only to find out how vacuoles control cell division, but also to address questions about how the cell cycle in regulated in higher eukaryotic cells. With a range of mutants we will be able to dissect the regulatory pathways through which hyphae and branches of mycelia grow. We will also be able to assess whether normal branching is important for the ability of this fungus to establish diseased lesions in animal tissues. Importantly, many other important fungi, including many plant pathogens, control the type of growth they undergo by forming a greater or lesser amount of vacuole. We will therefore be able to advance the field of fungal physiology, by undertaking the first in- depth study of the genetic links between vacuolation and fungal growth.