Aspects Of Testicular Function Research Articles

The evolutionary ecology of testicular function: size isn't everything

Larger testes are considered the quintessential adaptation to sperm competition. However, the strong focus on testis size in evolutionary research risks ignoring other potentially adaptive features of testicular function, many of which will also be shaped by post-mating sexual selection. Here we advocate a more integrated research programme that simultaneously takes into account the developmental machinery of spermatogenesis and the various selection pressures that act on this machinery and its products. The testis is a complex organ, and so we begin by outlining how we can think about the evolution of testicular function both in terms of the composition and spatial organisation of the testis ('testicular histology'), as well as in terms of the logical organisation of cell division during spermatogenesis ('testicular architecture'). We then apply these concepts to ask which aspects of testicular function we can expect to be shaped by post-mating sexual selection. We first assess the impact of selection on those traits most strongly associated with sperm competition, namely the number and kind of sperm produced. A broad range of studies now support our contention that post-mating sexual selection affects many aspects of testicular function besides gross testis size, for example, to maximise spermatogenic efficiency or to enable the production of particular sperm morphologies. We then broaden our focus to ask how testicular function is affected by fluctuation in sperm demand. Such fluctuation can occur over an individual's lifetime (for example due to seasonality in reproduction) and may select for particular types of testicular histology and architecture depending on the particular reproductive ecology of the species in question. Fluctuation in sperm demand also occurs over evolutionary time, due to shifts in the mating system, and this may have various consequences for testicular function, for example on rates of proliferation-induced mutation and for dealing with intragenomic conflict. We end by suggesting additional approaches that could be applied to study testicular function, and conclude that simultaneously considering the machinery, products and scheduling of spermatogenesis will be crucial as we seek to understand more fully the evolution of this most fundamental of male reproductive traits.

Endocrine Regulation of Male Fertility by the Skeleton

Interactions between bone and the reproductive system have until now been thought to be limited to the regulation of bone remodeling by the gonads. We now show that, in males, bone acts as a regulator of fertility. Using coculture assays, we demonstrate that osteoblasts are able to induce testosterone production by the testes, though they fail to influence estrogen production by the ovaries. Analyses of cell-specific loss- and gain-of-function models reveal that the osteoblast-derived hormone osteocalcin performs this endocrine function. By binding to a G protein-coupled receptor expressed in the Leydig cells of the testes, osteocalcin regulates in a CREB-dependent manner the expression of enzymes that is required for testosterone synthesis, promoting germ cell survival. This study expands the physiological repertoire of osteocalcin and provides the first evidence that the skeleton is an endocrine regulator of reproduction.

The treatment of adolescents presenting with a varicocele

In the last 10 years there have been many reports of children and adolescents with varicocele, but virtually none from the UK. There is an increasing incidence with age, to 19% by the age of 19 years. There is some evidence that a varicocele impairs the development of the affected testis; 9.3% of boys of 19 years old have a small testis as a result. Some aspects of testicular function are compromised. Treatment of the varicocele allows compensatory growth and testicular function. The surgical technique must be meticulous to avoid complications, particularly the formation of a hydrocele. Despite much research, the effect on fertility is unknown. The incidence of varicocele is much higher than that of male factor infertility. It is not known whether varicocele in adolescence impairs fertility or whether surgery restores fertility. At present the main indications for surgery are persistent delay in growth of >20%, bilateral varicocele and impaired spermatogenesis persisting beyond 18 years old.

Spermatogonial stem cell transplantation and testicular function

Spermatogonial stem cells (SSCs) are responsible for the continual production of spermatozoa throughout adult life. Interactions between SSCs and the surrounding cells in the seminiferous tubules regulate the biological activity of these cells. Factors involved in the regulation of SSCs are beginning to be defined by animal models and the culture of SSCs in defined media. A critical development in the characterization of SSCs has been the development of the germ cell transplantation technique, which provides the only assay for the presence of SSCs in a population of cells, and which allows the determination of whether SSCs are proliferating or differentiating in culture. This approach has accelerated SSC-focused research and promises to provide a better understanding of the factors and mechanisms that regulate these cells. The knowledge provided by this work is also critical to an appraisal of the components of the SSC niche in the seminiferous epithelium. Thus, many aspects of testicular function can be defined by the investigation of SSCs and the factors, cells, and environment that regulate SSCs, thereby leading to a more comprehensive understanding of spermatogenesis.

Testicular function in transsexual men.

Although the sperm counts of 5 of 8 adult male-to-female transsexuals were low, other aspects of testicular function were normal. Plasma production rates of testosterone averaged 6.4 mg/24 hours, a value similar to the 5.7 mg/24 hours produced by heterosexual adult men. Production rates of 17β-estradiol and estrone, 55µg/24 hours and 52 µg/24 hours, were also normal. Observed abnormalities of pituitary function and pituitary response to LHRH cannot be explained by abnormal testicular steroidogenesis.

BOOK REVIEWS

Book Reviewed in this article:The Biology of Human Fetal Growth. Edited by D. F. Roberts and A. M. ThomsonProstaglandins (Two volumes). Edited by S. M. M. KarimRecent Advances in Human Reproduction. Edited by A. Composda Paz, V. A. Drill, M. Hayashi, W. Rodrigues and A. V. Schally.Surgical Treatment of Endocrine Disorders. Edited by William HamiltonPolypeptide Hormones: Molecular and Cellular Aspects.Inborn Errors of Calcium and Bone Metabolism. Edited by H. Bickel and J. SternManual of Endocrine Surgery. By Anthony J. Edis, Luis A. Ayala and Richard H. Egdahl.Thyroid Research. Edited by Jacob Robbins and Lewis E. BravermanBiological Rhythms and Endocrine Function. Edited by L. W. Hedlund, J. M. Franz and A. D. Kenny.Contemporary Topics in the Study of Diabetes and Metabolic Endocrinology. Edited by Eleazor Shafrir.General Comparative and Clinical Endocrinology of the Adrenal Cortex, Vol. 1. Edited by I. Chester Jones and I. W. Henderson.Immunologic Aspects of Testicular Function. By R. E. Mancini

Actions of mammalian pituitary gonadotropins (FSH and LH) in reptiles: I. Male snakes

Ovine FSH and LH were tested in hypophysectomized male snakes, Thamnophis sauritus and T. sirtalis. FSH was considerably more potent than LH and appeared capable of stimulating testis growth, spermatogenesis, and interstitial cell activity (androgenesis). The effects of relatively large amounts of LH were comparable to a low dose of FSH in promoting slight spermatogenic activity; LH did not differentially affect steroiodogenesis. Testosterone did not affect spermatogenesis in T. sirtalis. These results confirm previous findings with purified mammalian hormones in lizards, and suggest that all aspects of testicular function in squamate reptiles may be accounted for by a single FSH-like gonadotropin.