SPERM CENTRIOLES AND THEIR DUAL ROLE IN FLAGELLOGENESIS AND CELL CYCLE OF THE ZYGOTE

HéCTOR E. CHEMES

The centrosome

Humana Press (Springer Science+Business Media LLC)

Lugar: Totowa, NJ, USA; Año: 2010;

SPERM CENTRIOLES AND THEIR DUAL ROLE IN FLAGELLOGENESIS AND CELL CYCLE OF THE ZYGOTE STRUCTURE, FUNCTION AND PATHOLOGY Hector E. Chemes CENTROSOMES, CENTRIOLES and BASAL BODIES Centrosomes are ubiquitous organelles found in eukaryotic cells. They are composed of a pair of barrel shaped centrioles, hollow cylindrical structures with their walls composed of nine triplet microtubules in a “pinwheel” arrangement. The two centrioles, perpendicular to each other (diplosomes), are surrounded by a dense fibro-granular “cloud” of pericentriolar material (PCM) that constitutes the microtubule organizing center (MOCT) of the cell (Figure 1). The centrosome is involved in numerous cell functions, among them the organization of the mitotic spindle and the cytoskeleton, translocation of signal transduction molecules and movement of cell organelles along microtubules. The PCM is organized as a framework that supports microtubular motor proteins like kinesins and dynein, coiled coil proteins, centrin, pericentrin, speriolin, Cdc20 (spindle checkpoint protein) and NuMA (Nuclear Mitotic Apparatus protein)  among about other 100 proteins (reviewed by Schatten and Sun, 2009). Microtubules do not originate from centrioles themselves but from the centrosome ã- tubulin ring complex, a collection of ã- tubulin annular structures contained in discrete densities of the PCM with no direct contact with centriolar triplets (Figure 2). The ã-tubulin ring serves as a nucleation site for á and â-tubulin heterodimers, the building blocks of microtubules, polarized structures with a minus end anchored to the PCM and a distal plus end where microtubules elongate by polymerization of tubulin heterodimers.             Centrioles and basal bodies are structurally similar and functionally interconvertible. During mitosis, centrosomes organize the mitotic spindle for chromosome alignment, duplication and partition between daughter cells. In ciliated and flagellated cells, centrosomes migrate to the cell periphery where distal centrioles dock to the cell membrane to become basal bodies from which ciliary and flagellar axonemes originate. When these cells enter mitosis, basal bodies move back to the cytoplasm and reconstitute centrosomes. This alternating dual role is essential to understand the functioning of spermatids and spermatozoa.