Timing in the Testis

Abstract

The testis provides not just one but several models of temporal organization. The complexity of its rhythmic function arises in part from its compartmentalization and diversity of cell types: not only does the testis produce gametes, but it also serves as the major source of circulating androgens. Within the seminiferous tubules, the germ cells divide and differentiate while in intimate contact with Sertoli cells. The tubule is highly periodic: a spermatogenic wave travels along its length to determine the timing of the commitment of spermatogonia to differentiate, the phases of meiotic division, and the rate of differentiation of the postmeiotic germ cells. Recent evidence indicates that oscillations of retinoic acid play a major role in determining periodicity of the seminiferous epithelium. In the interstitial space, Leydig cells produce the steroid hormones required both for the completion of spermatogenesis and the development and maintenance of male sexual characteristics throughout the body. This endocrine output also oscillates; although the pulse generator lies outside the gonad, the steroidogenic function of Leydig cells is tuned to a regular episodic input. While the oscillations of the intratubular and interstitial cells have multihour (ultradian) and multiday (infradian) periodicities, respectively, the functions of both compartments also display dramatic seasonal rhythms. Furthermore, circadian rhythms are evident in some of the cell types, although their amplitude and pervasiveness are not as great as in many other tissues of the same organism, and their detection may require methods that recognize the heterogeneity of the testis. This review examines the periodicity of testicular function along multiple time scales.

Day-night and seasonal variation of human gene expression across tissues

“…In contrast, we did not detect any of them as day-night in testis and vagina, consistent with their overall low number of day-night changes (Fig. 2A) and with previous studies in testis in rodents ( 27 ). Clock genes showed a largely consistent pattern of day-night expression across tissues (i.e.…”

Expression of retinoic acid‐metabolizing enzymes, ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, CYP26B1 and CYP26C1 in canine testis during post‐natal development

“…Mammalian spermatogenesis is a highly regulated process of cell division and differentiation, consisting of spermatogonial proliferation, meiosis of spermatocytes, spermiogenesis of haploid spermatids and production of sperm (Johnson et al., ; de Kretser, Loveland, Meinhardt, Simorangkir, & Wreford, ). Spermatogenesis is organized temporally and spatially and is carefully controlled by several signalling molecular processes (Bittman, ; Murta et al., ; Okuda et al., ; Takashima et al., ; Walker, ; Yao et al., ). Among these signalling events, retinoic acid (RA) signalling could have a critical role in spermatogenesis by promoting spermatogonia differentiation, adhesion of germ cells to Sertoli cells and release of mature spermatids (Busada & Geyer, ; Busada et al., ; Chapman, Medrano, Chaudhary, & Hamra, ; Griswold, Hogarth, Bowles, & Koopman, ; Kasimanickam, Kasimanickam, & Dernell, ; Mark, Teletin, Vernet, & Ghyselinck, ; Nicholls, Harrison, Rainczuk, Wayne Vogl, & Stanton, ).…”

Ultradian and Infradian Rhythms in the Dynamic of Testosterone Concentration in the Serum of the White-Breasted Hedgehog Erinaceus roumanicus

“…Thus, the phase of some ultradian biorhythms, including the dynamics of the concentration of testosterone in the blood serum, is not determined by the light/dark mode. Perhaps this 8-hour rhythm of testosterone is needed to synchronise sperm maturation processes 3 , whose frequency is not affected by the duration of the circadian rhythm 29 .…”