Research

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1) General introduction to lab research

Our research is focused on centriole, centrosome and cilium biology, which are interconnected subcellular organelles with unique developmental programs, physiological roles and evolutionary fates.  The centriole is a critical core component of centrosomes and cilia.  A pair of mother and daughter centrioles recruit pericentriolar material to form the centrosome, which serves as an astral microtubule nucleation center. In many cells the mother centriole matures to form a basal body which templates the formation of the cilium.  To assure that cells maintain the same exact number of centrioles and cilia, centrioles are formed only once during the cell cycle and each of the two centrioles give rise to only one additional centriole.  How centrioles duplicate is still a mystery.

Figure 1: Generalized schema for centriole duplication cycle and cilium formation in vertebrate cells. Blue marks a procentriole from its formation in S phase, through its elongation and maturation, until it becomes, 2 cell cycle later in G1/G0, a basal body and gives rise to a cilium.

Centrioles, centrosomes and cilia are conserved eukaryotic organelles that are not found in prokaryotes. During eukaryotic evolution several lines independently lost these structures demonstrating their interconnection as well as dispensability for basic cellular life.  However, in organisms where these structures are found they are highly advantagous, providing the cells with motility and sensory antennae and became essential for complex organism viability. Therefore, the underlying  of our research is that the centriole, centrosome and cilium represent distinct developmental and functional stages of the same organelle.  To test this hypothesis we examine various aspects of the program that interconnects them physiologically, developmentally and evolutionarily using our preferred model organism, the fly Drosophila melanogaster.

Centrosomes are most commonly associated with cell division being located at the spindle poles.  However, it is now clear that centrioles or centrosomes are not essential for cell division to occur.  Therefore, the role of the centrosome at this site is not clear.  Our hypothesis is that the centrosome and microtubule aster it nucleates plays an important role in assuring that centriole duplicates and segregates precisely.  The end result is that in humans, after cell division the 2 daughter cells each inherit one daughter centriole and one mother centriole that transforms to a basal body and assembles a single cilium.

Cilia are most commonly associated with cellular motility, propagating the movement of unicellular organisms and animal spermatozoa. However, most cell types in the human body express these organelles, where they also serve as chemical and mechanical sensors. Dramatic examples of specialized sensory cilia are found in rod and cone cells of the eye, where they house the entire photoreceptor signal transduction machinery. Given the central role of cilia in so many physiological processes, it is not surprising that their malformation or dysfunction can lead to a variety of disorders, such as: sterility, blindness, lung dysfunction, situs inversus polycystic kidney disease and has been recently implicated in obesity and mental retardation.

In spite of the importance of centrioles and cilia in many biological systems, the mechanism(s) and the inventory of proteins required for their formation are poorly understood.  Our goal is to understand the molecular underpinnings of centriole and cilia biology.  Therefore, we continually develop novel approaches and tools that aim to identify the set of proteins that mediate this process, elucidate their roles and mechanism of action.

2)Drosophila melanogaster a powerful genetic model organism

To dissect centriole and cilium formation we employ Drosophila melanogaster a powerful genetic model organism where large-scale forward and reveres genetic screens for basal body and ciliogenesis mutations can be achieved, allowing for the identification of novel  genes, as well as the determination of their specific role in this process. Further more, fruit flies are particularly suited to study centriole and cilium formation for the following reasons:

  1. Centrioles, basal bodies and cilia are not required for fly development and unlike in other organisms do not result in early organismal lethality or cell death, however they do participate in the same cellular processes as in humans. Their essential role in fertility and sensory perception, providing a clear and distinguishable phenotype for genes involved in centriole/basal body/cilia formation.
  2. Unlike other model organisms, centriole transformation to basal body and ciliogenesis occurs in Drosophila only during spermatogenesis and sensory neuron development, providing a very distinct expression pattern for genes specifically involve in these processes.
  3. Sperm basal bodies in flies are extremely large - 2.6µm versus 0.5µm in other model organisms. Therefore protein localization in sub-domains of the basal body can be studied using conventional florescent microscopy and provide important insight to the protein function.

Recently, we have generated series of flies with GFP labeled basal bodies, ciliary transport components and ciliary cargo, allowing us to perform detailed analysis of the many aspect of cilium biology. Further more, we have identified and obtained a large repertoire of mutant flies to many of the ciliary genes identified in the bioinformatic approach.