Differentiation of somatic cells in the ovariuteri of the apoikogenic scorpion Euscorpius italicus (Chelicerata, Scorpiones, Euscorpiidae) Izabela Je ˛ drzejowska * , Kamil Szymusiak, Marta Mazurkiewicz-Kania, Arnold Garbiec Institute of Experimental Biology, University of Wroclaw, Sienkiewicza 21, 50-335 Wroclaw, Poland article info Article history: Received 5 July 2013 Received in revised form 22 November 2013 Accepted 23 November 2013 Keywords: Follicular cells Stalk cells Chelicerate type ovary Epithelial morphogenesis Cellecell adhesion abstract In apoikogenic scorpions, growing oocytes protrude from the gonad (ovariuterus) and develop in follicles exposed to the mesosomal (i.e. hemocoelic) cavity. During subsequent stages of oogenesis (previtello- genesis and vitellogenesis), the follicles are connected to the gonad surface by prominent somatic stalks. The aim of our study was to analyze the origin, structure and functioning of somatic cells accompanying protruding oocytes. We show that these cells differentiate into two morphologically distinct sub- populations: the follicular cells and stalk cells. The follicular cells gather on the hemocoelic (i.e. facing the hemocoel) surface of the oocyte, where they constitute a cuboidal epithelium. The arrangement of the follicular cells on the oocyte surface is not uniform; moreover, the actin cytoskeleton of these cells undergoes significant modifications during oocyte growth. During initial stages of the stalk formation the stalk cells elongate and form F-actin rich cytoplasmic processes by which the stalk cells are tightly connected to each other. Additionally, the stalk cells develop microvilli directed towards the growing oocyte. Our findings indicate that the follicular cells covering hemocoelic surfaces of the oocyte and the stalk cells represent two distinct subpopulations of epithelial cells, which differ in morphology, behavior and function. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Animal eggs are produced in the course of the process called oogenesis. During oogenesis oocytes undergo remarkable growth which proceeds in two consecutive stages: previtellogenesis and vitellogenesis. Previtellogenic growth results from the accumula- tion of organelles and macromolecules, whereas vitellogenic growth relies on storage of various reserve materials such as gly- coproteins, lipids and glycogen in the oocyte cytoplasm (ooplasm). The oocytes growth is very often supported by additional cells of germline and/or somatic origin. The germline cells supporting the oocyte growth are called trophocytes or nurse cells. Comparative studies of the nurse cells functioning in insects have revealed that the main function of the nurse cells is the synthesis of macromol- ecules and their transport, together with organelles, to the oocyte cytoplasm (Büning, 1994; de Cuevas et al., 1997; Matova and Cooley, 2001; Mazurkiewicz and Kubrakiewicz, 2001; Tworzyd1o and Kisiel, 2010). The somatic cells accompanying growing oocytes are usually referred to as the follicular cells. Numerous comparative studies of different animal groups have shown that the follicular cells may exhibit different organization and play diverse functions. In most cases, the follicular cells constitute a simple epithelium overlying either the germline clusters or individual oocytes. It has been found that among many functions, in invertebrates, the follicular cells may contribute to vitellogenesis and formation of the eggshell (reviewed in Dobens and Raftery, 2000). Moreover, based on studies of insect ovaries, it has been shown that the follicular cells are able to diversify into several distinct subpopulations that differ in morphology, behavior, function and position in relation to the germline cells (Zawadzka et al., 1997; Deng and Bownes, 1998; Dobens and Raftery, 2000; Kubrakiewicz et al., 2003; Mazurkiewicz and Kubrakiewicz, 2005, 2008; Tworzyd1o et al., 2005; _ Zelazowska, 2005; Ogorza1ek, 2007; Jaglarz et al., 2008, 2009, 2010; Garbiec and Kubrakiewicz, 2012). Among chelicerates, nutrimentary, i.e. supported with nurse cells, egg development is unique for some acarine groups (Alberti and Hänel, 1986; Alberti and Zeck-Kapp, 1986; Witali  nski et al., 1990; Alberti and Coons, 1999; Di Palma and Alberti, 2002). In scorpions, like in most chelicerates, all germline cells differentiate into the oocytes and the oocytes growth is supported solely by the somatic cells. * Corresponding author. Department of Animal Developmental Biology, Institute of Experimental Biology, University of Wroc1aw, Sienkiewicza 21, 50-335 Wroc1aw, Poland. Tel.: þ48 71 3754027; fax: þ 48 71 3754118. E-mail addresses: izabela.jedrzejowska@uni.wroc.pl (I. Je ˛ drzejowska), kamil. szymusiak@uni.wroc.pl (K. Szymusiak), marta.kania@uni.wroc.pl (M. Mazurkiewicz-Kania), arnold.garbiec@uni.wroc.pl (A. Garbiec). Contents lists available at ScienceDirect Arthropod Structure & Development journal homepage: www.elsevier.com/locate/asd 1467-8039/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.asd.2013.11.004 Arthropod Structure & Development xxx (2013) 1e10 Please cite this article in press as: Je ˛ drzejowska, I., et al., Differentiation of somatic cells in the ovariuteri of the apoikogenic scorpion Euscorpius italicus (Chelicerata, Scorpiones, Euscorpiidae), Arthropod Structure & Development (2013), http://dx.doi.org/10.1016/j.asd.2013.11.004