Motiivides

Motiivides are a proposed class of subcellular, motile vesicle-like bodies observed in a subset of unicellular eukaryotes. The term motiivide is derived from motus (movement) and dividere (to divide), reflecting their reported mobility and potential for duplication under certain conditions. As of the current literature, motiivide are not universally accepted as a distinct organelle, and descriptions vary among studies.

Morphology and biochemistry: Motiivides are typically 0.2 to 1.5 micrometers in diameter, bounded by a single membrane or proteinaceous coat, with an electron-dense interior. Some samples reveal a light crystalline core or lipid-rich inclusions. Their surfaces often display protein complexes that appear to interface with cytoskeletal filaments, suggesting a link to intracellular transport or organization.

Distribution and detection: Reports originate from select single-celled eukaryotes within the Amoebozoa and some Excavata lineages, identified by high-resolution fluorescence microscopy and, in some cases, cryo-electron tomography. Attempts to reproduce findings have yielded mixed results, and concerns about artefacts in sample preparation and image processing have been raised, contributing to ongoing debate about their existence.

Proposed function and interpretation: Hypotheses include roles in intracellular lipid transport, signaling, or stress responses, and in some instances a mechanism for local cargo segregation. Some researchers propose that motiivides participate in primitive division or organelle turnover, while others view them as transient assemblies or imaging artefacts. The lack of consensus has limited their inclusion in standard cellular inventories.

Status and outlook: The concept of motiivides remains controversial and experimental. Ongoing work aims to standardize detection methods, confirm lineage conservation, and clarify whether motiivides constitute a true organelle or a byproduct of cellular processes. Further replication and functional studies are needed.