Table 1.

Observations of cytonemes and TNTs in vitro and in vivo

	Cell type and organism	Transmitted signals and cargo	Function	Size: length; diameter	Cytoskeleton element	References
Cytonemes
In cell culture
	Xenopus fibroblasts	Wnt2b–EGFP	Wnt secretion	n/a	Actin and microtubules	Holzer et al. (2012)
	Mouse C3H/10T1/2 mesenchymal cells	FGF: FGFR elongation via cytonemes	FGF reception	Up to > 60 µm; n/a	Actin	Koizumi et al. (2012)
	Zebrafish pigment cells	Membrane-associated signal to trigger depolarization	Pigment pattern formation	20–30 µm; n/a	Actin	Hamada et at. (2014)
In tissue
	Wing disc tracheal cells or peripodial layer of the eye disc	Dpp/Tkv; Spi/EgfR reception	Imaginal disc pattering	Up to > 80 µm; 200 nm	Actin	Sato and Kornberg et al. (2002); Hsiung et al. (2005); Roy et al. (2011)
	Drosophila myoblasts	Wg/Fzd uptake and delta/notch interaction	Relay system for Wg and Notch signals	Up to 25 µm; 200 nm	Actin	Huang and Kornberg (2015)
	Drosophila germ cells	Dpp transport	Maintenance of stem cells	Up to 4 µm	Microtubules	Inaba et al. (2015)
	Basal cytonemes in the Drosophila wing pouch	Hh/patched reception	Imaginal disc pattering	Up to 70 µm; n/a	Actin	Bischoff et al. (2013); Gradilla et al. (2014); González-Méndez et al. (2017)
	Zebrafish neural plate	Wnt transport to Fzd/Lrp6 containing cells	Neuroectoderm AP patterning	Up to 50 µm; <1.5 µm	Actin	Stanganello et al. (2015), Mattes et al. (2018)
	Chick limb bud	Shh ligand caintaining cytonemes connect Cdo and Boc coreceptors cytonemes	Patterning of mesenchymal cells	Up to 150 µm; 200 nm	Actin	Sanders et al. (2013)
Tunnelling nanotubes
In cell culture
	Primary rat pheochromocytoma (PC12)	Membrane vesicles, membrane-anchored proteins, and small organelles	Intercellular transfer of cellular components	Thin: 20 µm; 70–200 nm	Actin	Rustom et al. (2004)
	Primary rat pheochromocytoma (PC12)	Mitochondria and intracellular vesicles such as endosomes and lysosomes	Recovery mechanism for stressed cells	Thick: n/a; > 700 nm	Actin and microtubules	Wang and Gerdes (2015)
	Human monocyte-derived macrophages	Mitochondria and intracellular vesicles	Intercellular transfer of cellular components	Thick: n/a; > 700 nm	Actin and microtubules	Onfelt et al. (2006)
	Humanperipheral blood NK cells, macrophages, and B cells	Bacteria ; GFP-tagged cell surface class I MHC protein	Communication mechanism in immunology	10–50 µm; <700 nm	Actin	Onfelt et al. (2006)
	Between adult human endothelial progenitor cells and neonatal rat cardiomyocytes	Mitochondria, soluble GFP	Cell fate decisions in adult progenitor cells	Up to 120 µm; 50–800 nm	Actin	Koyanagi et al. (2005)
	Neuronal CAD cells and between astrocytes to granule neurons	PrPSC prions	Propagation of infectious particles	Up to 80 µm; 180–800 nm	Actin	Gousset et al. (2009); Zhu et al. (2015)
	NRK cells, HEK293, HUVEC, and NCC	Electrical signals	Electrical coupling via gap junctions	Up to 70 µm; 50–200 nm	Actin	Wang et al. (2010)
In tissue
	Neural Crest cells in chick embryos	Cytoplasmic material; cytosolic and membrane-tethered fluorescent proteins	Delivering positional information during migration	Up to 100 µm; 0.5–2 µm	N/a	Teddy and Kulesa (2004); McKinney et al. (2011)
	Gastrulating zebrafish embryo cells	Cytosolic and membrane-tethered fluorescent proteins	Cell–cell communication during gastrulation	Up to 350 µm; <1 µm	Actin; tubulin only in proximal part	Caneparo et al. (2011)
	Myeloid cells in the mouse cornea	Smaller molecules such as MHC and/or MHC-antigen complexes	Immunological response	> 300 µm; 200–300 nm	Actin; n/a	Chinnery et al. (2008); Seyed-Razavi et al. (2013)
	Patient-derived malignant pleural mesothelioma	Organelles and other cytosolic components	Role in pathogenesis and invasion	Up to 100–200 µm; n/a	Actin; n/a	Lou et al. (2012)