Human myometrium - the ultrastructural 3D network of telocytes

Abstract

Telocytes (TCs), a novel type of interstitial cells, were recently described in the interstitial space of tissues (www.telocytes.com). Telocytes TCs have several very long, moniliform extensions, namely telopodes (Tps). However, the functional role(s) of TCs is not yet understood. Successive photomicrographs of ultrathin sections were concatenated to capture the entire length of Tps which usually measure tens to hundreds of micrometres. Besides the podoms (dilations) and podomers (thin segments), ultrastructural features of Tps include the dichotomous branching and establishing homo- and heterocellular contacts. Telopodes make a labyrinthine system by 3D convolution and overlapping, their number being roughly estimated at approximately 20 per 1000 μm(2) . Moreover, the presence of extracellular vesicles (shedding vesicles/exosomes) along the Tps suggests an active intercellular signalling (micro- and macromolecules), with possible significance in regulating uterine contractility.

Fig. 1

Representative ultrathin section of human non-pregnant myometrium. Two-dimensional sequenced concatenation from eight serial electron micrographs depicting the 3D network of telocytes. Oblique section through smooth myocytes (brown) (SMC) are bordered by numerous Tps (blue) interconnected by homocellular junctions (dotted circles) forming a 3D network. The inset illustrates the diagram of the interstitial network built-up by TCs and Tps with uneven calibres: podoms and podomers. Exosomes and shedding vesicles (arrowheads) are digitally coloured in purple. coll: collagen; m: mitochondria; mvb: multivesicular bodies; N: nucleus. Scale bar = 5 μm.

Fig. 2

Representative ultrathin section of human pregnant myometrium. Two-dimensional sequenced concatenation from 11 serial electron micrographs depicting the 3D network of TCs (blue) interconnected by homocellular junctions (dotted circles). Smooth myocytes (SMC) are depicted in cross section digitally coloured in brown. In their vicinity, numerous Tps (blue) establish a network and release extracellular organelles (exososomes and shedding vesicles) (arrowheads) digitally coloured in purple. One mast cell (green) is in the vicinity of this network. Some vesicles are captured at the moment of being shed from Tps (marked with *). Cav: caveolae; coll: collagen; m: mitochondria; rER: rough endoplasmic reticulum; N: nucleus. Scale bar = 3 μm.