Unconventional myosin that functions as actin-based motor protein with ATPase activity (PubMed:12719468, PubMed:15853803). Plays a role in endosomal protein trafficking, and especially in the transfer of cargo proteins from early to recycling endosomes (By similarity). Required for normal planar cell polarity in ciliated tracheal cells, for normal rotational polarity of cilia, and for coordinated, unidirectional ciliary movement in the trachea. Required for normal, polarized cilia organization in brain ependymal epithelial cells (PubMed:26446290). Interacts (via the two IQ motifs) with calmodulin (PubMed:8034741, PubMed:12719468, PubMed:15853803). Binds an additional calmodulin chain via a third, C-terminal region (PubMed:8034741). Interacts with F-actin (PubMed:12719468, PubMed:15853803). Colocalizes with the actin cytoskeleton in the cell cortex close to the apical cell membrane (PubMed:26446290). Colocalizes with cytoplasmic puncta that are reminiscent of transport vesicles (PubMed:8034741). Detected on tracheal epithelial cells, and on epithelial cells and brush border cells in duodenum, jejunum and ileum (PubMed:26446290). Detected on myelinated white matter in the cerebellum, and the myelinated part of the optic nerve. Detected on mature oligodendrocites. Detected on the outside of the myelin sheet that surrounds axons (at protein level) (PubMed:24903835). Ubiquitous. Highest levels in adult brain, and spinal chord. Moderate levels in lung, kidney, liver and spleen. Low levels in testis and heart (at protein level). Not detected in brain one week after birth, prior to the onset of myelination, and levels are low two weeks after birth. Expressed at high and constant levels in brain after three weeks and later (at protein level) (PubMed:24903835). Expression is developmentally regulated during brain ontogeny, rising 2-3 week postnatally, and is maximal in adult brain (PubMed:8034741, PubMed:24903835). Binds a calmodulin chain via each of the two IQ domains (PubMed:12719468, PubMed:15853803). IQ domain 1 mediates interaction with calmodulin both in the presence and in the absence of Ca(2+). IQ domain 2 mediates interaction with calmodulin in the presence of Ca(2+) (PubMed:8034741, PubMed:15853803). The TH1 domain is required for activity in complementing zebrafish defects in Kupffer's vesicle lumen size. Mutants display no defects in body left-right asymmetry, no obvious motor defects, and normal kidney and liver morphology. Tracheal epithelial cells display aberrant ciliary bending angles and disordered ciliary bending patterns. Likewise, planar cell polarity is disrupted in ependymal epithelial cells. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family. Contrary to the situation in zebrafish, xenopus and drosophila, rat Myo1d defects have no effects on left-right body asymmetry. Represents an unconventional myosin. This protein should not be confused with the conventional myosin-1 (MYH1).