Peritubular Myoid Cells from Rat Seminiferous Tubules Contain Actin and Myosin Filaments Distributed in Two Independent Layers1

Abstract

In the mammalian testis, peritubular myoid cells (PM cells) surround the seminiferous tubules (STs), express cytoskeletal markers of true smooth muscle cells, and participate in the contraction of the ST. It has been claimed that PM cells contain bundles of actin filaments distributed orthogonally in an intermingled mesh. Our hypothesis is that these actin filaments are not forming a random intermingled mesh, but are actually arranged in contractile filaments in independent layers. The aim of this study is to describe the organization of the actin cytoskeleton in PM cells from adult rat testes and its changes during endothelin-1-induced ST contraction. For this purpose, we isolated segments of ST corresponding to the stages IX-X of the spermatogenic cycle (ST segments), and analyzed the actin and myosin filament distribution by confocal and transmission electron microscopy. We found that PM cells have actin and myosin filaments interconnected in thick bundles (AF-MyF bundles). These AF-MyF bundles are distributed in two independent layers: an inner layer toward the seminiferous epithelium, and an outer layer toward the interstitium, with the bundles oriented perpendicularly and in parallel to the main ST axis, respectively. In endothelin-1 contracted ST segments, PM cells increased their thickness and reduced their length in both directions, parallel and perpendicular to the main ST axis. The AF-MyF bundles maintained the same organization in two layers, although both layers appeared significantly thicker. We believe that this is the first time this arrangement of AF-MyF bundles in two independent layers has been shown in smooth muscle cells, and that this organization would allow the cell to generate contractile force in two directions.

The cell–cell junctions of mammalian testes: II. The lamellar smooth muscle monolayer cells of the peritubular wall are laterally connected by vertical adherens junctions—a novel architectonic cell–cell junction system

“…15c). Our observations of coaxially oriented myofilament bundles in a given LSMC are obviously in contrast to claims of some other authors that-at least in rodents-in the same LSMC region myofilament bundles may exist that are oriented in different directions (see e.g., Losinno et al 2012Losinno et al , 2016. Some AJ-like structures connecting LSMCs appear-at relatively low frequency-as rather short end-on-end junctions.…”

Advanced immunostaining approaches to study early male germ cell development

“…Alexa Fluor-633, Invitrogen) so that it does not interfere with the green and red confocal channels, allowing for those to be used for co-immunostaining with separate antibodies. Phalloidin binds with high affinity to filamentous (F)-actin, which is particularly abundant in peritubular myoid cells in the testis ( Tung and Fritz, 1990 ; Losinno et al, 2012 ). This staining essentially outlines the testis cords in the neonate and seminiferous tubules in the adult, allowing for diameter measurement facile determination of the position of cells (inside the cords = Sertoli and germ cells, periphery of the cords = peritubular myoid cells, and outside the cords = interstitial cells such as Leydig cells, endothelial cells, and macrophages).…”

Human testicular peritubular cells: more than meets the eye

“…Local factors, e.g. endothelin 1 (Romano et al 2007, Losinno et al 2012, platelet-derived growth factor (PDGF; Romano et al 2006), prostaglandins, and neurotransmitters (Miyake et al 1986, Tripiciano et al 1998, may play a role, as do hormones, including sex steroids (Yamamoto et al 1989) and the pituitary hormone vasopressin. In rat peritubular cells, receptors for vasopressin (V1a), in contrast to endothelin receptors, appear to be under developmental control.…”