The ultrastructures of germ cells and the functions of Leydig cells and Sertoli cells during spermatogenesis in male Kareius bicoloratus (Pleuronectidae) were investigated by electron microscope observation. Each of the well-developed Leydig cells during active maturation division and before spermiation contained an ovoid vesicular nucleus, a number of smooth endoplasmic reticula, well-developed tubular or vesicular mitochondrial cristae, and several lipid droplets in the cytoplasm. It is assumed that Leydig cells are typical steroidogenic cells showing cytological characteristics associated with male steroidogenesis. No cyclic structural changes in the Leydig cells were observed through the year. However, although no clear evidence of steroidogenesis or of any transfer of nutrients from the Sertoli cells to spermatogenic cells was observed, cyclic structural changes in the Sertoli cells were observed over the year. During the period of undischarged germ cell degeneration after spermiation, the Sertoli cells evidenced a lysosomal system associated with phagocytic function in the seminiferous lobules. In this study, the Sertoli cells function in phagocytosis and the resorption of products originating from degenerating spermatids and spermatozoa after spermiation. The spermatozoon lacks an acrosome, as have been shown in all teleost fish spermatozoa. The flagellum or sperm tail of this species evidences the typical 9+2 array of microtubules.

Mammalian spermatogenesis takes place in the seminiferousepithelium, which is composed of Sertoli cells and germ cells. The interaction between spermatogenic and Sertoli cells as well as elongated spermatids and Sertoli cells is tightly regulated by junctional adhesion molecules (JAMs). JAMs, which are cell adhesion molecules, are known to play roles in various biological processes such as fertilization, neurogenesis, cancer progression, and spermatogenesis. Members of the JAM family have a unique structure: they contain an N-terminal signal peptide domain, immunoglobulin (Ig)-like domains, transmembrane and cytoplasmic tail domains, each of which has distinct functions. The extracellular Ig-like domains interact in a homophilic or heterophilic manner, whereas cytoplasmic tail domain mediates the tight junction assembly. Although members of the JAM family are exclusively present in or restricted to the testis, their precise roles in spermatogenesis and fertilization have not yet been completely explored. The functional roles of Nectin-2, Nectin-3, JAM-C, cell adhesion molecule1 (CADM1), coxsackie and adenovirus receptor (CAR) have been evaluated by analysis of null mutant mice. Unfortunately, CAR-deficient mice had an embryonic lethal phenotype; this demonstrates the importance of CAR in development, but its physiological role in spermatogenesis is not known. The loss of CADM1, Nectin-3 and JAM-C resulted in male infertility caused by loss of adhesion between germ and Sertoli cells. A variety of JAMs participate in the interaction between germ and Sertoli cells. Recently, human VSIG1 has been characterized, which was originally known as A34, as a new member of the JAM family; VSIG1 is composed of two extracellular Ig-like domains, a transmembrane domain, and a cytoplasmic domain. However, this molecule has not been functionally characterized, so this was one of the aims of our present study. RT-PCR and immunoblot analyses were used to study VSIG1 expression, VSIG1 was specifically expressed in testicular germ cells but not in sperm. Pull-down assay with glutathione S-transferase (GST) or His-fused first Ig and second Ig domains of VSIG1 and SDS-PAGE under mild non-reducing conditions demonstrated that VSIG1 functions as an in vitro homophilic adhesion molecule. Furthermore, cells expressing a deletion of the C-terminus of VSIG1 failed to interact with ZO-1, the central structural protein of the tight junction. These findings suggest mouse VSIG1 interacts with an unknown molecule in Sertoli cells via its extracellular domain, while its cytoplasmic domain is needed for binding to ZO-1. Thus, we suggest mouse VSIG1 may play an important role in spermatogenesis rather than fertilization by forming heterophilic complex with a molecule similar to JAM family.

TM4 Sertoli cell의 체외 관강형성 유도에 미치는 세포외기질 (ECM) 및 hepatocyte growth factor (HGF)의 역할과 세포분화 과정에서 MMP의 발현의 변화를 조사하였다. Matrigel bed(60%, v/v) 상에서 배양한 TM4 cell은 무혈청 조건하에서 chain 분화단계를 거쳐 cord의 구조로 분화하였다. 그러나 이후의 분화는 일어나지 않았다. TM4 cell에서 c-MET (HGF receptor)의 발현을