Anthony R. Bellvé

T-type Ca2+ channels and α1E expression in spermatogenic cells, and their possible relevance to the sperm acrosome reaction

There is pharmacological evidence that Ca2+ channels play an essential role in triggering the mammalian sperm acrosome reaction, an exocytotic process required for sperm to fertilize the egg. Spermatozoa are small terminally differentiated cells that are difficult to study by conventional electrophysiological techniques. To identify the members of the voltage‐dependent Ca2+ channel family possibly present in sperm, we have looked for the expression of the α 1A, α 1B, α 1C, α 1D and α 1E genes in mouse testis and in purified spermatogenic cell populations with RT‐PCR. Our results indicate that all 5 genes are expressed in mouse testis, and in contrast only α 1E, and to a minor extent α 1A, are expressed in spermatogenic cells. In agreement with these findings, only T‐type Ca2+ channels sensitive to the dihydropyridine nifedipine were observed in patch‐clamp recordings of pachytene spermatocytes. The results suggest that low‐threshold Ca2+ channels are the dihydropyridine‐sensitive channels involved in the sperm acrosome reaction.

Defects in Nuclear and Cytoskeletal Morphology and Mitochondrial Localization in Spermatozoa of Mice Lacking Nectin-2, a Component of Cell-Cell Adherens Junctions

ABSTRACT Nectin-2 is a cell adhesion molecule encoded by a member of the poliovirus receptor gene family. This family consists of human, monkey, rat, and murine genes that are members of the immunoglobulin gene superfamily. Nectin-2 is a component of cell-cell adherens junctions and interacts with l-afadin, an F-actin-binding protein. Disruption of both alleles of the murine nectin-2 gene resulted in morphologically aberrant spermatozoa with defects in nuclear and cytoskeletal morphology and mitochondrial localization. Homozygous null males are sterile, while homozygous null females, as well as heterozygous males and females, are fertile. The production by nectin-2−/−mice of normal numbers of spermatozoa containing wild-type levels of DNA suggests that Nectin-2 functions at a late stage of germ cell development. Consistent with such a role, Nectin-2 is expressed in the testes only during the later stages of spermatogenesis. The structural defects observed in spermatozoa ofnectin-2 −/− mice suggest a role for this protein in organization and reorganization of the cytoskeleton during spermiogenesis.

The Occurrence and Distribution of Lamin Proteins during Mammalian Spermatogenesis and Early Embryonic Developmenta

Based on current evidence it is apparent that the lamins undergo a dynamic reorganization during both spermatogenesis and early embryonic development, processes that presumably underscore unusual requirements in germ-cell differentiation and embryonic development.

Pleiotypic actions of the seminiferous growth factor on two testicular cell lines: comparisons with acidic and basic fibroblast growth factors.

Bovine seminiferous growth factor (SGF) stimulated different pleiotypic responses in TM3 Leydig and TM4 Sertoli cells from those obtained with bovine acidic and basic fibroblast growth factors (aFGF, bFGF). First, the three growth factors had distinct mitogenic effects. SGF increased TM3 and TM4 cell numbers, whereas aFGF was mitogenic only for TM3 cells, and bFGF was inactive on both cell lines. Second, only SGF and bFGF stimulated TM4 cells to produce 3- and 2-fold, respectively, greater levels of extracellular, sulfated glycoprotein-1. By Northern analyses, SGF increased the steady-state levels of sulfated glycoprotein-1 mRNA approximately 1.34-fold relative to those of actin mRNA during a 48-hr period. Third, the cell lines secreted different [35S]methionine-labeled proteins. With TM3 cells, some proteins were secreted specifically, whereas other were up- or down-regulated differentially in response to SGF, aFGF, or bFGF. Likewise, with TM4 cells, the three growth factors induced qualitative and quantitative changes in the secretion of specific proteins. On immunoblots, SGF did not bind antibodies specific for an internal domain of aFGF or FGF-5, nor those directed against N-terminal, internal, and C-terminal regions of bFGF. These data suggest SGF, aFGF, and bFGF acted on TM3 Leydig and TM4 Sertoli cells through different receptors and/or diverging pathways of signal transduction to induce different pleiotypic effects.

Dynamic Changes in the Perinuclear Matrix during Spermiogenesis and Sperm Maturation in the Mouse

During mammalian spermatogenesis the germ cell undergoes mitotic proliferation, meiosis, and spermiogenesis (Bellve, 1979). In meiosis the nucleus passes through distinctive cytological events that reflect the molecular processes of genetic recombination, chromosome segregation and two reduction divisions. Later, during early spermiogenesis, the nucleus acquires polarity by forming a cap of heterochromatin, fusing the justaposed region of nuclear membranes and depositing a layer of perinuclear material. Then, as the nucleus condenses and becomes falciform in shape, the histones are replaced by protamines and quantitatively the bulk of the nonhistone proteins are lost. Of the many “non-histone” or “nonprotamine” proteins that remain associated with the nucleus after spermiation, nothing is known about their functions (Bellve and O’Brien, 1983). Yet, these proteins may have structural or regulatory roles essential to sperm maturation, capacitation, acrosome reaction and/or fertilization.