Seasonal Testicular Cycle Research Articles

Transcriptome-wide changes in testes reveal molecular differences in photoperiod-induced seasonal reproductive life-history states in migratory songbirds.

We investigated the molecular basis of seasonal testicular states in black-headed buntings (Emberiza melanocephala), in which seasonal migrations limit reproduction to a narrow time-window during the year. We examined testicular gene expressions in buntings during short day-induced photosensitive nonreproductive state (SDSE), and during long day-induced early (LDES) and late (LDLS) gonadal maturation and regressed photorefractory (LDRF) seasonal states. Using Kallisto, we pseudoaligned the RNA-Seq transcripts and calculated the transcript abundance. We found 1,799 differentially expressed genes (DEGs) between the four photoperiod-induced seasonal states. Further pairwise comparison with SDSE revealed 1,187, 1,224, and 1,238 DEGs in LDES, LDLS, and LDRF, respectively; 852 genes were common to three comparisons. We then identified genetic pathways putatively involved in seasonal testicular cycle. DEGs that enriched calcium ion binding were highly expressed in testicular maturation states. Similarly, DEGs that enriched glycolytic pathway were highly expressed in LDES and LDRF states. More specifically, quantitative polymerase chain reaction showed significant differences between the photoperiod-induced states in testicular expression of genes (HOOK1, RGS2, PRDX4, BCL6, CYFIP2, PDCD4, P2RX4, and GABRA1) involved in gametogenesis and associated pathways. Overall, these results show significant transcriptional differences, and provide insights into the molecular basis of seasonal changes in the reproductive life-history states in a photoperiodic species.

Molecular cloning, expression analysis and transcript localization of testicular orphan nuclear receptor 2 in the male catfish, Clarias batrachus

Testicular receptor 2 (TR2; also known as Nr2c1) is one of the first orphan nuclear receptors identified and known to regulate various physiological process with or without any ligand. In this study, we report the cloning of full length nr2c1 and its expression analysis during gonadal development, seasonal testicular cycle and after human chorionic gonadotropin (hCG) induction. In addition, in situ hybridization (ISH) was performed to localize nr2c1 transcripts in adult testis and whole catfish (1day post hatch). Tissue distribution and gonadal ontogeny studies revealed high expression of nr2c1 in developing and adult testis. Early embryonic stage-wise expression of nr2c1 seems to emphasize its importance in cellular differentiation and development. Substantial expression of nr2c1 during pre-spawning phase and localization of nr2c1 transcripts in sperm/spermatids were observed. Significant upregulation after hCG induction indicate that nr2c1 is under the regulation of gonadotropins. Whole mount ISH analysis displayed nr2c1 expression in notochord indicating its role in normal vertebrate development. Taken together, our findings suggest that nr2c1 may have a plausible role in the testicular and embryonic development of catfish.

Distribution and male reproductive system of the Bridled Mabuya, Trachylepis vittata (Olivier, 1804) (Reptilia: Scincidae), in Lebanon

The distribution of the Bridled Mabuya, Trachylepis vittata, in Lebanon is described and the male reproductive cycle was studied in a population living at 2000 m a.s.l. on Mount Sannine. Males emerge from hibernation in March, one month earlier than females. They show a short seasonal testicular cycle in which spermiogenesis occurs in spring, followed by testicular regression and subsequent recrudescence in summer. Hibernation starts in October and lasts 5 months. The development of secondary sexual characteristics was in synchrony with the testicular cycle. There was a significant difference between the reproductive stages and the testicular volume. The species is assigned to an associated reproductive cycle with short vernal spermiogenesis.

Circadian and Seasonal Responses in Indian Weaver Bird: Subjective Interpretation of Day and Night Depends Upon Both Light Intensity and Contrast Between Illuminations

This study investigated whether changes in illumination modify perception of day and night conditions in a diurnal species, the Indian weaver bird. Birds were initially subjected to a 12-h light:12-h dark regime (12L:12D; L = 20 lux, D = 0.5 lux). After every 2 wks, the combinations of light illumination in L and D phases were changed as follows: 20:2 lux, 20:5 lux, 20:10 lux, 20:20 lux, 20:100 lux, and 20:200 lux. Finally, birds were released into dim constant light (0.5 lux) for 2 wks to determine the phase and period of the circadian activity rhythm. They were also laparotomized at periodic intervals to examine the effects of the light regimes on the seasonal testicular cycle. All individuals showed a consistently similar response. As evident by the activity pattern under these light regimes, both in total activity during contrasting light phases and during the 2 h in the beginning and end of first light phase, birds interpreted the period of higher light intensity as day, and the period of lower intensity as the night. During the period of similar light intensity, i.e., under LL, birds free-ran with a circadian period (∼24 h). In bright LL (20 lux), the activity rhythm was less distinct, but periodogram analysis revealed the circadian period for the group as 24.46 ± 0.41 h (mean ± SE). However, in dim LL at the end of the experiment, all birds exhibited a circadian pattern with average period of 25.52 ± 0.70 h. All birds also showed testicular growth and regression during the 16-wks study. It is suggested that weaver birds interpret day and night subjectively based on both the light intensity and contrast between illuminations during two phases over the 24 h. (Author correspondence: drskumar7@yahoo.com)

Cloning, expression and enzyme activity analysis of testicular 11β-hydroxysteroid dehydrogenase during seasonal cycle and after hCG induction in air-breathing catfish Clarias gariepinus

A full-length cDNA encoding 11β-hydroxysteroid dehydrogenase type 2 ( 11β-HSD2) was cloned from testis of air-breathing catfish, Clarias gariepinus which showed high sequence homology to zebrafish and eel. The open reading frame of 11β-HSD2 was then transfected to COS-7 cells, which converted 11β-hydroxytestosterone (11-OHT) to 11-ketotestosterone (11-KT). Using NAD +, 11β-HSD2 from testicular microsomes oxidized 11-OHT with apparent K m 56 ± 4 nM and V max 55 ± 6 pmol/h/mg protein values. Tissue distribution analysis revealed prominent expression in testis, anterior kidney, liver and gills. Expression of 11β-HSD2 in testis and serum levels of 11-KT were high in the prespawning phase. Administration of human chorionic gonadotropin (hCG) during prespawning and resting phases revealed initial rise in 11β-HSD2 transcript at 4 h followed by gradual increase at 8 h, 12 h and peaking at 24 h, only in testis of prespawning phase. Rate of conversion of 11-OHT to 11-KT by testicular microsomes during different testicular phases and after hCG administration corroborated well with the expression of 11β-HSD2. Ontogeny study indicated that this enzyme is expressed during testicular development. Thus the spatio-temporal expression supported with putative dehydrogenase activity and circulating 11-KT levels clearly suggest a major role for 11β-HSD2 during testicular differentiation and seasonal testicular cycle in catfish.

Reproductive cycle of the Namibian striped skink, Trachylepis sparsa (Squamata: Scincidae) from southern Africa

ABSTRACT The reproductive cycle of the Namibian striped skink is described from a histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which sperm were produced primarily during spring and summer. Testes in regression were present mainly in March. Females with oviductal eggs or corpora lutea were present September to March and May to June. Not all females reproduced annually. Clutch (= litter size) for 23 females was 4.9 ± 0.97 S.D., range: 3–6.

Reproductive cycle of the Namib giant ground gecko, Chondrodactylus angulifer (Squamata: Gekkonidae)

The reproductive cycle of the Namib giant ground gecko, Chondrodactylus angulifer, from southern Africa was described from a histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which (based on available specimens) the major period of spermiogenesis occurred between September and December. The onset of spermiogenesis is not known as specimens from May to August were not available. Testes in regression were found in January, February and March. Testes in recrudescence were found in January, February, March and April. Females with enlarged ovarian follicles (>5mm length) were found in January/February and September to December. Mean clutch size for 36 females was 1.7 ± 0.47 S.D., range: 1–2. Evidence is presented that more than one clutch may be produced in the same reproductive season.

Reproductive cycle of the Namib giant ground gecko, Chondrodactylus angulifer (Squamata: Gekkonidae)

ABSTRACT The reproductive cycle of the Namib giant ground gecko, Chondrodactylus angulifer, from southern Africa was described from a histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which (based on available specimens) the major period of spermiogenesis occurred between September and December. The onset of spermiogenesis is not known as specimens from May to August were not available. Testes in regression were found in January, February and March. Testes in recrudescence were found in January, February, March and April. Females with enlarged ovarian follicles (>5 mm length) were found in January/February and September to December. Mean clutch size for 36 females was 1.7 ± 0.47 S.D., range: 1–2. Evidence is presented that more than one clutch may be produced in the same reproductive season.

Reproductive cycle of the Namaqua sand lizard, Pedioplanis namaquensis (Squamata: Lacertidae), from southern Africa

The reproductive cycle of the Namaqua sand lizard, Pedioplanis namaquensis, from southern Africa is described from histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which sperm was produced in January–March and September–December. Testes in regression were present in March and May. Females with enlarged ovarian follicles (>4 mm length) or oviductal eggs were collected between November and February. Clutch size for 14 females was 3.8 ± 0.97 S.D. eggs, range 3–5. Histological evidence is presented that two clutches may be produced in the same reproductive season.

Reproductive cycle of the Namaqua sand lizard, Pedioplanis namaquensis (Squamata: Lacertidae), from southern Africa

The reproductive cycle of the Namaqua sand lizard, Pedioplanis namaquensis, from southern Africa is described from histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which sperm was produced in January–March and September–December. Testes in regression were present in March and May. Females with enlarged ovarian follicles (>4 mm length) or oviductal eggs were collected between November and February. Clutch size for 14 females was 3.8 ± 0.97 S.D. eggs, range 3–5. Histological evidence is presented that two clutches may be produced in the same reproductive season.

Role of FSH, numbers of FSH receptors and testosterone in the regulation of inhibin secretion during the seasonal testicular cycle of adult rams

The regulation of inhibin secretion has not been elucidated fully in male ruminants. The aim of this study was to determine the relative importance of FSH and testosterone concentrations, and FSH receptors, in the control of secretion of immunoactive inhibin in rams. In Expt 1, temporal changes in hormone concentrations and testicular FSH binding were determined for two groups of rams (n = 4) kept under opposite, alternating 4 month periods of long (16 h light:8 h dark) and short (8 h light:16 h dark) days. Testicular biopsies (1-2 g) were collected when the testes were regressed, redeveloping, redeveloped and regressing. In Expt 2, separate groups of rams (n = 4) kept under natural photoperiod (latitude 45 degrees 48 minutes N) were designated as controls or passively immunized (for 3 weeks) with sufficient oestradiol antiserum to increase testosterone secretion without altering LH and FSH; this was done when the testes were regressed (non-breeding season) and redeveloped (breeding season). In both groups of rams (Expt 1), 'seasonal' increases in FSH concentrations began a few weeks earlier than did increases in inhibin concentrations. FSH reached maximum concentrations during testicular recrudescence, whereas numbers of FSH receptors in the testis and circulatory inhibin concentrations did not reach peak values until the testes were fully developed. Numbers of FSH receptors per testis, but not FSH concentration, were positively correlated (r = 0.65) with inhibin concentrations across the four stages of the testicular cycle. Near the end of testicular recrudescence early in the breeding season (Expt 2), relatively high FSH concentration was associated with increased abundance of FSH receptor mRNA (90%) and number of receptors (45%) in the testis and increased inhibin concentrations (50%), compared with when the testes were regressed. Moderate, physiological increases in testosterone secretion in immunized rams did not affect inhibin in either season. These results indicate that: (i) FSH stimulation of immunoactive inhibin secretion by Sertoli cells as testes recrudesce is via increases in secretion (early) and cognate receptors (late); (ii) FSH upregulates the synthesis of its own receptor late in recrudescence; and (iii) the positive correlation (r = 0.70) observed between circulatory testosterone and immunoactive inhibin does not reflect a causal relationship.

Role of FSH, numbers of FSH receptors and testosterone in the regulation of inhibin secretion during the seasonal testicular cycle of adult rams

The regulation of inhibin secretion has not been elucidated fully in male ruminants. The aim of this study was to determine the relative importance of FSH and testosterone concentrations, and FSH receptors, in the control of secretion of immunoactive inhibin in rams. In Expt 1, temporal changes in hormone concentrations and testicular FSH binding were determined for two groups of rams (n = 4) kept under opposite, alternating 4 month periods of long (16 h light:8 h dark) and short (8 h light:16 h dark) days. Testicular biopsies (1-2 g) were collected when the testes were regressed, redeveloping, redeveloped and regressing. In Expt 2, separate groups of rams (n = 4) kept under natural photoperiod (latitude 45 degrees 48 minutes N) were designated as controls or passively immunized (for 3 weeks) with sufficient oestradiol antiserum to increase testosterone secretion without altering LH and FSH; this was done when the testes were regressed (non-breeding season) and redeveloped (breeding season). In both groups of rams (Expt 1), 'seasonal' increases in FSH concentrations began a few weeks earlier than did increases in inhibin concentrations. FSH reached maximum concentrations during testicular recrudescence, whereas numbers of FSH receptors in the testis and circulatory inhibin concentrations did not reach peak values until the testes were fully developed. Numbers of FSH receptors per testis, but not FSH concentration, were positively correlated (r = 0.65) with inhibin concentrations across the four stages of the testicular cycle. Near the end of testicular recrudescence early in the breeding season (Expt 2), relatively high FSH concentration was associated with increased abundance of FSH receptor mRNA (90%) and number of receptors (45%) in the testis and increased inhibin concentrations (50%), compared with when the testes were regressed. Moderate, physiological increases in testosterone secretion in immunized rams did not affect inhibin in either season. These results indicate that: (i) FSH stimulation of immunoactive inhibin secretion by Sertoli cells as testes recrudesce is via increases in secretion (early) and cognate receptors (late); (ii) FSH upregulates the synthesis of its own receptor late in recrudescence; and (iii) the positive correlation (r = 0.70) observed between circulatory testosterone and immunoactive inhibin does not reflect a causal relationship.

Reproduction in an Introduced Population of the Brown Anole, Anoles sagrei, from O'ahu, Hawai'i

The reproductive cycle of an introduced population of the brown anole, Anolis sagrei, from O'ahu, Hawai'i, was studied from a histological examination of monthly samples collected July 1999 to June 2000. Males undergo a seasonal testicular cycle in which all males > 38 mm snout-vent length are in spermiogenesis from January to August. Although some ovarian activity was found in all months, the period of greatest ovarian inactivity was October- December, which corresponds to the time of male gonadal regression. The reproductive cycle of A. sagrei in Hawai'i resembles that of populations in Belize, Florida, and Jamaica, where minimum gonadal activity was recorded from November through February. Body sizes at reproductive maturity were similar in all four localities. Anolis sagrei in Hawai'i has an ovarian cycle typical of other Anolis lizards with a prolonged breeding season and production of single eggs in succession. Because A. sagrei has been in Hawai'i for only approximately 20 yr, sufficient time has not elapsed to allow evolution of its reproductive cycles, but this study presents baseline reproductive data that can be used for future studies to see if the A. sagrei reproductive cycles are modified as the lizards adapt to the environmental conditions of their newly colonized range.

Sex Accessories Morphology and Functions during the Seasonal Testicular Cycle of a Subtropical Wild Avian Species, the Yellow-Throated Sparrow Petronia xanthocollis Burton

Annual changes in the male sex accessories (tubuli recti, rete testis, vasa efferentia, epididymis, vas deferens and seminal glomus) were studied during the annual testicular cycle of the yellow-throated sparrow (Petronia xanthocollis Burton). All the segments of genital tract and the seminal glomus became enlarged during the progressive phase (January to March), were maximally enlarged during breeding (April), began to decrease during regression (May and June) and became maximally regressed during the nonbreeding phase (July to December). But the sialic acid level of the seminal glomus increased to maximum already during the progressive phase, remained high during breeding and declined subsequently. The findings suggest that the male sex accessories functions vary distinctly with the annual testicular cycle presumably due to alterations in the testicular androgen production in the yellow-throated sparrow.

Evidence for the role of light intensity in the seasonal testicular cycle of a wild bird, black headed munia

Abstract The effects of various light intensity levels (0.11, 0.48, 0.96 and 1.86 mW/cm2) of constant white light on the testicular cycle of a wild bird, Black headed munia were investigated. While in higher intensity (0.96 and 1.86 mW/cm2) treated birds precocious gonadal development was observed, low intensity illumination prevented gonadal regression, indicating a better maintenance of testicular activity under low intensity lighting in Black headed munia. Since the total hours of light exposure (24 hr/day) were the same for all the four experimental groups, and higher intensities could not prevent gonadal regression, it would seem that light intensity is more important than the hours of illumination in the reproduction of this bird.

Localization of melatonin binding sites in the pars tuberalis of the mink at three times during the seasonal testicular cycle

The strict photoperiodic dependence of gonadotropic function observed in mink provides an excellent physiological model for studying the activity of GnRH hypothalamic neurons. In mink, exposure to more than 10 h light inhibits the activity of this neurohormonal system. Melatonin plays an essential role in this type of regulation of gonadotropic function. In mink, contrary to results in many other photosensitive species, melatonin was observed to mediate the gonadostimulating effect of short days. However, the binding sites and action of this substance have not yet been defined. We thus attempted to identify melatonin binding sites in the mink brain. The study was carried out at three times during the seasonal testicular cycle in male minks maintained under natural environmental conditions. Coronal sections were taken from the whole brain and pituitary gland. Using 2-[ 125I]iodomelatonin, we observed a strong concentration of binding sites in the pars tuberalis and not in the part of the median eminence surrounded by the pars tuberalis. This concentrated localization of melatonin binding sites brings up the problem of defining the action of this substance in photoregulating the activity of the GnRH neurohormonal system.

Influences of environmental factors and pineal gland on seasonal testicular cycle in white‐throated munia(Lonchura malabarica)

Abstract Histological studies of the seasonal testicular cycle in white‐throated munia, Lonchura malabarica (Passeriformes : Ploceidae) Tevealed that this bird breeds from September to January in India. The gametogenesis in the male gonad starts in May when the day length is maximum and the temperature high. The initiation of sexual cycle starts in May‐July. Active spermatogenesis occurs in September to October. The Leydig cell nucleus diameter increases in August just before the onset of spermatogenesis. The diameter of pinealocyte nucleus increases in non‐breeding stage of the bird and decreases during breeding period.

The reproductive cycle of the newt Triturus italicus

AbstractThis paper describes the reproductive cycle in male and female newts Triturus italicus (Peracca, 1898) from a mountain population living in southern Italy. The male shows a well-defined seasonal testicular cycle: spermatogenesis almost stops from November to March, resuming in April-May; the maturative stage of spermatogenesis occurs in summer and spermiohistogenesis is completed by late October. Spermiation starts in late autumn and culminates in the next spring. The female shows a seasonal ovarian cycle. Vitellogenesis starts in September; ovulation and egg deposition occur between late January and early June. Thus potentially long reproductive activity is demonstrated in both males and females of T italicus. Testicular and ovarian weights seem to be reliable indices of the reproductive status of an animal. Annual variation in gonadal weight appears unrelated to annual variation in fat body weight in both sexes.

Maintaining a high physiological rate of testosterone secretion in the adult ram by estradiol immunoneutralization partially prevents testicular regression

The seasonal testicular cycle of 10 adult Dorset × Leicester × Suffolk rams was entrained to alternating 4-mo periods of long-inhibitory (16 h light) and short-stimulatory (8 h light) day lengths. Beginning in the third month of a short-day period, when the testes were fully redeveloped, five rams were passively immunized with a low titre (1:200) of estradiol antiserum for 13 wk. During this time the testes of the remaining (control) rams regressed almost completely. Estradiol immunoneutralization reliably maintained most characteristics of testosterone secretion (mean and base-line concentrations, and pulse amplitude) at "breeding season" values and had a minor but persistent effect on the hypothalamic–pituitary axis. When both the immunization period and the following 6 mo were considered, LH pulses were 50% larger in the immunized rams than in the control rams. Testicular regression was partially prevented in the immunized rams. However, their 1.5- to 1.7-cm larger scrotal circumference during most of the regression stage was not associated with a greater daily sperm output (based on sperm voided in urine) early in the redevelopment stage. Mean LH and FSH concentrations were increased by 200% in all rams during testicular recrudescence, and maximum testis size was achieved 1 mo earlier in the immunized rams than in the control rams. Immunization of rams against estradiol effectively maintained a high physiological rate of testosterone secretion, but was not able to prevent the normal decline in quantitative spermatogenesis. Key words: Estradiol immunoneutralization, testicular regression, testosterone, adult ram

Testicular response to melatonin or suprachiasmatic nuclei ablation in the spotted skunk

Testes of the Western spotted skunk enlarge and regress seasonally. The pineal hormone, melatonin, may be important in timing this seasonal reproductive activity. Likewise, the suprachiasmatic nuclei (SCN) have been implicated as possible neural regulators of pineal and reproductive events. These experiments were conducted to determine whether ablation of the SCN or constant administration of melatonin alters timing of the seasonal pattern of testicular regression and recrudescence. Male skunks (n = 24) were treated as follows: six received two empty Silastic capsules, six received two melatonin-filled Silastic capsules, six received sham lesions to the SCN, and six received lesions to the SCN (SCNx). All skunks were exposed to a natural photoperiod and had regressed testes at the onset of the experiment. Four of six males from the SCNx group had an average of 94 +/- 11.3% of these nuclei destroyed. Sham SCNx, animals with less than 40% of the SCN ablated, and males with empty capsules did not have fully enlarged testes until October. SCNx and melatonin-treated skunks exhibited a hastening of testicular recrudescence with maximal testis size being reached in June. Skunks with lesions to the SCN maintained enlarged testes for 5 months while all other groups exhibited rapid regression after attaining maximal testis size. Testicular regression occurred from July through October in animals receiving continuous melatonin, while controls exhibited recrudescence during this same period. Our data suggest that the SCN, melatonin, and thus the pineal gland, play a role in regulating the seasonal testicular cycle of the spotted skunk.