The Expression of Multiple Connexins Throughout Spermatogenesis in the Rainbow Trout Testis Suggests a Role for Complex Intercellular Communication1

Abstract

Certain fish, such as rainbow trout (Oncorhynchus mykiss), are seasonal breeders. Spermatogenesis in rainbow trout is synchronous; therefore, at any time point during this process, germ cells are predominantly at the same stage of development. As such, rainbow trout represent an excellent model in which to study spermatogenesis. Gap junctions are composed of connexons, which are themselves formed by six transmembrane proteins termed connexins (Cxs). The objectives of this study were to assess which Cxs are expressed in the rainbow trout testis, and if their expression was stage specific during gonadal maturation. Rainbow trout were killed at various stages of maturation, and total cellular RNA was isolated from the testes. RT-PCR using degenerate primers recognizing all vertebrate Cxs indicates that there are several different Cxs in trout testes. Amplicons were cloned and sequenced. Homology comparisons indicate that these were cx43, cx43.4, cx31, and cx30. Immunolocalization of these Cxs indicate that Cx43 was localized primarily to Sertoli cells, while Cx43.4 was localized along the lateral plasma membranes between adjacent spermatocytes. Cx30 was localized to the interstitial Leydig cells, and Cx31 was localized primarily to the endothelium of interstitial blood vessels. The expression of each Cx varied as a function of the stage of spermatogenesis, suggesting that the expression of these proteins is highly regulated. Together, these results indicate that intercellular communication in the testis is complex, involves several different Cxs, and is a highly regulated process.

The mechanism of reproduction and hormonal function in finfish species: A review

“…This process has been described at the morphological level, but its control remains poorly understood, although it is known that it requires the actions of both gonadotropins (follicle-stimulating hormone, FSH and luteinizing hormone, LH), as well as intratesticular testosterone (T) (Saito et al, 2000). Similar to mammals, there is a close morphological and functional intercellular communication between Sertoli cells and germ cells during fish spermatogenesis (De Montgolfier et al, 2007;Mylonas et al, 2010;Loir et al, 1995).…”

Cell junctions in fish seminiferous epithelium

“…The presence of several different connexins in rainbow trout (Oncorhynchus mykiss) testes at various stages of maturation corroborates these data. Immunolocalization of these connexins indicated that connexin 43 was localized primarily in SC (de Montgolfier et al 2007), suggesting that the role of this connexin in the testis is highly conserved and may play a similar role in fish as it does in mammals (Batias et al 2000;Points et al 2005;Brehm et al 2007). Given the cystic arrangement of spermatogenesis, it is reasonable to expect that SC communicate through gap junctions, providing an adequate coordination among them to support the synchronous development of GC within a given cyst.…”

“…According to these authors, testicular connexin 43 mRNA levels in the brook trout, Salvelinus fontinalis, were significantly increased, and spermatogenesis was advanced in individuals after exposure to wastewater effluent. On the other hand, the functionality of SC gap junctions has never been demonstrated, and it remains unknown if these gap junctions reported in fish (Marina et al 2002;Batlouni et al 2005;de Montgolfier et al 2007) are capable of allowing the sharing of substances among these cells. Therefore, it would be very interesting to develop dye-coupling experiments to test the functionality of these junctions between SC.…”

“…Despite species-specific variations, in general, the seminiferous epithelium structure of teleosts shifts from a Sertoli cell monolayer that contains some spermatogonia (non-reproductive season) to an active spermatogenic arrangement composed of spermatocysts and spermatozoa that fill the tubular lumen (reproductive season) (Grier and Taylor 1998;Brown-Peterson et al 2002;Cinquetti and Dramis 2003;Batlouni et al 2006 and others). These structural changes have been demonstrated to have direct effects on the types and distribution of cell junctions on the seminiferous epithelium (Batlouni et al 2005;de Montgolfier et al 2007) (Fig. 1).…”

“…In this respect, the majority of available knowledge on fish refers to the morphofunctional characteristics of adhesive (Sprando and Russell 1987;Loir et al 1995;Pfeiffer and Vogl 2002), gap (Loir et al 1995;Marina et al 2002;Batlouni et al 2005) and tight (Abraham et al 1980;Silva and Godinho 1989;McClusky 2006) junctions. However, more recent investigations have started to reveal the molecular composition of these junctions (Batlouni et al 2005;Prisco et al 2007), their turnover during the reproductive cycle (de Montgolfier et al 2007) and that they represent a specific target for environmental toxicants, such as cadmium (McClusky 2006), or compounds present in wastewater effluents (de Montgolfier et al 2008).…”