Zentrosom

Zentrosom is a term used in speculative and theoretical discussions to denote a proposed subcellular organelle that functions as a microtubule organizing center (MTOC). Unlike the centrosome of many animal cells, which contains a pair of centrioles surrounded by pericentriolar material, the Zentrosom is described as a centriole-free MTOC that can localize near the nucleus or at the cell cortex depending on cell type and developmental stage.

Structure and composition of a Zentrosom are hypothetical. Proponents describe a dense protein matrix enriched in γ-tubulin ring complexes and scaffolding factors, sometimes accompanied by specialized linker proteins that organize and stabilize surrounding microtubules. Some models envisage a dynamic core that assembles in mitosis to help nucleate spindle poles, while others position it as a steady-state organizer during interphase.

Functionally, Zentrosoms are proposed to nucleate, anchor, and organize microtubules, contributing to spindle assembly, intracellular transport, and cell polarity. In this framework, they may operate independently of centrioles, enabling alternative modes of spindle formation and cytoskeletal arrangement.

Evidence and status: The Zentrosom concept appears primarily in speculative reviews and limited experimental reports. It is not widely accepted as a standard MTOC in established biology, and many researchers regard centrosomes or spindle pole bodies as the primary MTOCs in most lineages. Ongoing work and future discoveries could clarify whether Zentrosoms exist in any natural systems or represent an extreme form of MTOC plasticity. Related concepts include the centrosome, spindle pole body, and broader microtubule organizing centers.