Multinucleated smooth muscles and mononucleated as well as multinucleated striated muscles develop during establishment of the male reproductive organs of Drosophila melanogaster

Abstract

The adult musculature in D. melanogaster forms during metamorphosis. Much is known about the flight and leg musculature, but not about the muscles surrounding the male reproductive tract. The inner genitalia of males consist of the testes, which emerge from the gonads; the remaining genital organs, i.e., paragonia (or accessory glands), ejaculatory duct, sperm pump, and seminal vesicles, develop out of the genital imaginal disc. We analyzed the myoblasts forming the muscle layers of these organs. In myoblasts derived from the genital imaginal disc, the regulatory region of the transcription factor DMef2 is active. DMef2 is also needed for specification and differentiation of embryonic and adult myoblasts. We could discriminate three different muscle types: (i) multinucleated muscles that resemble vertebrate smooth muscles surround the testes, (ii) multinucleated muscles that resemble striated muscles comprises seminal vesicles and the sperm pump, and (iii) mononucleated striated musculature encloses the paragonia and ejaculatory duct. Members of the immunoglobulin superfamily involved in embryonic myogenesis, Dumbfounded (Duf) and Sticks and Stones (Sns), were also expressed in the genital imaginal disc, in the muscle sheath of the testes during muscle differentiation and in the secretory secondary cells, which are part of the binucleated epithelia enclosing the paragonia.

Female-biased dimorphism underlies a female-specific role for post-embryonic Ilp7 neurons inDrosophilafertility

“…By contrast, the male seminal vesicle is lined by thin striated muscle that receives only Ilp7/serotonergic innervation and has no NMJs characteristic of fast excitatory transmission. Male seminal vesicle contractility has not been examined, but peristaltic activity of the adjacent ejaculatory duct is under serotonergic modulation; however, innervation is not essential for this (Susic-Jung et al, 2012). Together with our data here, it appears that innervation of the seminal vesicle is not a requirement for the passage of sperm.…”

<em>Ex vivo</em> Culture of <em>Drosophila</em> Pupal Testis and Single Male Germ-line Cysts: Dissection, Imaging, and Pharmacological Treatment

“…Third-instar larvae show small, round testes surrounded by a layer of future pigment cells and embedded in fat body tissue (Figure 2A). Testes in adult male flies are long, coiled tubes, which are covered by a layer of muscle cells originating from the genital disc and a pigment layer 24 . Interestingly, larval testes contain only germ-line cells of pre-meiotic and meiotic stages until the primary spermatocyte stage, which corresponds to meiotic prophase (see also Figure 1) 23 .…”

“…Testes dissected at 36 hr APF appear elongated and in some cases already begin to curl ( Figure 2D). They have already attached to the tissues of the genital tract growing out from the genital imaginal disc 23,24 . Furthermore, they frequently contain the first spermatids beyond the H-P switch, as indicated by the ProtamineB-eGFP signal (Figures 1 and 2D, arrow).…”

“…This is possibly due to a lack of positional and growth signals normally sent from the developing genital tract contacting the testis at its posterior tip 23,29 . Furthermore, the muscle layer of the testis sheath does not develop because nascent myotubes cannot migrate from the genital disc to the testis 24 . The testis sheath-in this situation solely the thin pigment layer-does not seem to grow sufficiently in culture to envelope the increasing number of developing germ cells within.…”

“…For this purpose, pupal testes at around 24 hr after puparium formation (APF) are dissected (see Figures 1 and 2). At this time, the testes have not made connections to other tissues and are surrounded by only a thin outer sheath, which allows better penetration by the inhibitor compounds 23,24 . The testes are bean-or pear-shaped organs that can be easily taken into culture.…”