Different Stages Of Gametogenesis Research Articles

Gap junctions mediate discrete regulatory steps during fly spermatogenesis.

Gametogenesis requires coordinated signaling between germ cells and somatic cells. We previously showed that Gap junction (GJ)-mediated soma-germline communication is essential for fly spermatogenesis. Specifically, the GJ protein Innexin4/Zero population growth (Zpg) is necessary for somatic and germline stem cell maintenance and differentiation. It remains unknown how GJ-mediated signals regulate spermatogenesis or whether the function of these signals is restricted to the earliest stages of spermatogenesis. Here we carried out comprehensive structure/function analysis of Zpg using insights obtained from the protein structure of innexins to design mutations aimed at selectively perturbing different regulatory regions as well as the channel pore of Zpg. We identify the roles of various regulatory sites in Zpg in the assembly and maintenance of GJs at the plasma membrane. Moreover, mutations designed to selectively disrupt, based on size and charge, the passage of cargos through the Zpg channel pore, blocked different stages of spermatogenesis. Mutations were identified that progressed through early germline and soma development, but exhibited defects in entry to meiosis or sperm individualisation, resulting in reduced fertility or sterility. Our work shows that specific signals that pass through GJs regulate the transition between different stages of gametogenesis.

Reproduction and development of the brooding sea urchin Austrocidaris canaliculata from deep-sea off Argentina

Even though brooding behavior show an unusual high level of incidence in Austral cidaroids, the genus Austrocidaris has a particularly original developmental feature, is the only cidaroid to brood its young on the aboral side of the test. This study describes several features of the reproductive and development mode of the widely distributed sea urchin Austrocidaris canaliculata (Agassiz, 1863). For this, 216 specimens were collected from deep-sea off Argentina including the Mar del Plata submarine canyon area and the Marine Protected Area Namuncurá/Burdwood Bank. Histological analyses revealed specimens presenting gonads at different stages of development. Ovaries contained oocytes at different stages of gametogenesis; the largest intra-ovarian oocyte recorded was 1300 µm in diameter. Fully testes were found showing spermatozoa with elongated heads (9 µm in length). Eleven brooding females were collected. A single mother was recorded carrying up to 536 broods simultaneously. All the offspring in the same marsupium were at a single stage of development. The deepest record for A. canaliculata (up to 1398 m) is also reported in this study. The main finding confirm that A. canaliculata is a brooding cidaroid with a direct, lecithotrophic developmental mode from the Southwestern Atlantic Ocean.

Zebrafish as a Model to Screen the Potential of Fatty Acids in Reproduction.

Sperm quality is an important topic in general health, chemotherapy, and gamete preservation technology. Fatty acid (FA) composition of membranes, which is influenced by the diet, plays key roles in sperm biology and quality. Dietary supplementation with natural products can be used as a technique to screen potential agents to protect, modify, and recover sperm quality. In this study, zebrafish (male [♂-ZF] and female [♀-ZF]) were fed a single cultivar olive oil (OO) bioencapsulated in Artemia. OO-treated ♂-ZF had higher (p < 0.05) sperm density and motility compared to the Artemia nauplii (AN). A significant difference was also observed in follicle abundance at different stages of gametogenesis, and a nonsignificant increase in total fecundity between OO-treated ♀-ZF and the AN, although in OO-treated ♀-ZF, mature follicles had a smaller diameter. A higher fertility rate (FR) was observed in OO-treated pairs compared to the other groups. Hatching in the OO-treated fish was accelerated, although no significant differences could be found in terms of hatching rate (HR) and embryo/larval survival rate (SR). These findings in FR, HR, and SR were also confirmed in male and female replacement mating trials. Taken together, this study shows that altering the FA ratios in the diet has a clear impact on several reproductive parameters in the zebrafish, adding new information about the nutritional requirement of this model species.

New evidence of brooding in the deep-sea brittle star Astrotoma agassizii Lyman, 1876 from a South Western Atlantic Canyon

The reproduction of the brittle star Astrotoma agassizii was studied from deep waters of the South Atlantic Ocean, based on samples collected in August 2012, and May and September 2013. Ten samples from 800 to 1400m depths off Mar del Plata Canyon were studied. The species was found to be a brooding simultaneous hermaphrodite. Hermaphroditic gonads contained testis and ovaries inside the same sacs. Both, ovary and testis contained different stages of gametogenesis development simultaneously. Gonads contained several stages of oocytes in different stages of gametogenesis. The largest oocyte recorded was 800µm diameter. Free spermatozoa were observed in the lumen of the testis, together with spermatogenic columns. Five individuals, from a total of 30 examined, resulted brooding, and most contained mature ovotestis at the same time. Incubation occurs in five of the ten bursal sacs, containing 15–20 young juveniles each. Maximum disc diameter recorded for a brood was 1100µm. Herein we hypothesize that Astrotoma agassizii could be continuous breeder species in the deep-sea.

Reference gene selection for qPCR in mussel, Mytilus edulis, during gametogenesis and exogenous estrogen exposure

The aim of this study is to develop a normalization method for real-time PCR data by analyzing the most stably expressed control genes in mussel (Mytilus edulis) reproductive tissue. To facilitate this, six candidate genes, including several commonly used in the literature, were investigated in mussels at different stages of gametogenesis and following experimental exposure to a model estrogen (17b-estradiol). GeNorm and NormFinder softwares were employed to assess the stability of the reference genes. Our results demonstrate that the most stable reference genes are not the same in mussels at different stages of gametogenesis and in experimentally E2-exposed mussels. Interestingly, HEL (helicase) and ACT (actin) mRNA expression levels were most affected by the stage of gametogenesis and yet, in molluscan studies, ACT is possibly the most frequently used reference gene. We demonstrate that the experimental results are highly dependent on the reference gene chosen and that statistically significant contrasting differences between sample groups are present or absent depending on the reference gene employed.

Spermidine Is a Morphogenetic Determinant for Cell Fate Specification in the Male Gametophyte of the Water FernMarsilea vestita

Here, we show that the polyamine spermidine plays a key role as a morphogenetic determinant during spermatid development in the water fern Marsilea vestita. Spermidine levels rise first in sterile jacket cells and then increase dramatically in spermatogenous cells as the spermatids mature. RNA interference and drug treatments were employed to deplete spermidine in the gametophyte at different stages of gametogenesis. Development in spermidine-depleted gametophytes was arrested before the completion of the last round of cell divisions. In spermidine-depleted spermatogenous cells, chromatin failed to condense properly, basal body positioning was altered, and the microtubule ribbon was in disarray. When cyclohexylamine, a spermidine synthase (SPDS) inhibitor, was added at the start of spermatid differentiation, the spermatid nuclei remained round, centrin failed to localize into basal bodies, thus blocking basal body formation, and the microtubule ribbon was completely abolished. In untreated gametophytes, spermidine made in the jacket cells moves into the spermatids, where it is involved in the unmasking of stored SPDS mRNAs, leading to substantial spermidine synthesis in the spermatids. We found that treating spores directly with spermidine or other polyamines was sufficient to unmask a variety of stored mRNAs in gametophytes and arrest development. Differences in patterns of transcript distribution after these treatments suggest that specific transcripts reside in different locations in the dry spore; these differences may be linked to the timing of unmasking and translation for that mRNA during development.

Effects of estrogen exposure in mussels, Mytilus edulis, at different stages of gametogenesis

Mytilus edulis were exposed to 17β-estradiol (E2) and the synthetic estrogens ethinyl estradiol (EE2) and estradiol benzoate (EB) for 10 days. Two exposures were performed to determine their effect on vitellogenin ( VTG) and estrogen receptor 2 ( ER2) mRNA expression at different stages of the reproductive cycle. Significant natural variation was not observed in VTG mRNA expression, though ER2 mRNA expression displayed significantly lower values during January, February and July compared with other times of the year. A significant increase in VTG and ER2 mRNA expression was observed in mussels exposed to estrogens at the early stage of gametogenesis. In contrast, mature mussels displayed no statistically significant change in the VTG or ER2 mRNA expression. The data presented suggests that the reproductive physiology of molluscs, in terms of VTG and ER2 mRNA expression, may be susceptible to damage by environmental estrogens at certain points in their gametogenesis process.

When fragmented coral spawn? Effect of size and timing on survivorship and fecundity of fragmentation in Acropora formosa

In order to determine competency of sexual reproduction and survival rate after fragmentation, the branching coral Acropora formosa was fragmented and fragments in three different sizes (ca. 5, 10 and 20 cm long) and three different stages of gametogenesis were transplanted on coral pavement. Their oocyte development and fecundity, as well as spawning were monitored for a 3-year period. The oocyte development was affected by both fragment size and by the developmental stage of oocytes when fragmented. In small fragments, the oocytes were resorbed while in large fragments they continued development. Oocytes in the early vitellogenic stage at the time of fragmentation were resorbed, whereas those in the late stage continued developing. Smaller fragments showed a lower survival rate and histological observations of their gonads revealed resorption of oocytes, suggesting that there was a trade-off of energy between reproduction and survival. Transplanted fragments often spawned one month earlier than the donor colonies in the first year, but spawning occurred in the same month as the donors or did not occur at all in the second year and none spawned in the third year. The risk of colony death may cause the fragments to re-allocate energy for sexual reproduction.

Testing for the Effects of Seasonal and Lunar Periodicity on the Reproduction of the Edible Sea Urchin Tripneustes gratilla (L) in Kenyan Coral Reef Lagoons

The annual and lunar reproductive cycle of the widely distributed edible sea urchin Tripneustes gratilla (L) was examined through measurements of gonad index, histological examination of gametogenesis, and induction of spawning with KCl injections. The population density and morphological characteristics of urchins at Diani, Kanamai, and Vipingo reef lagoons were also studied as well as the effects of seawater temperature and light on reproduction. Gonad growth started early during the northeast monsoon and reached a peak in June at the beginning of the southeast monsoon followed by a sharp decrease in gonad size of 50% in July and August towards the end of the southeast monsoons. Histological examination of gonads, revealed many different stages of gametogenesis with gametes present throughout the year, indicating continuous reproduction. There was a significant relationship between gonad index and lunar day with spawning occurring between lunar day 7 and 21, but spawning was not in perfect synchrony in the population. The population density of urchins at each reef is variable from year to year and was highest on average at Vipingo. Urchins at Kanamai had the lowest gonad indices, the largest jaws and smallest individuals an indication of food limitation. The gonads (roe) of T. gratilla at all three sites, were perpetually ‘runny’ an attribute that is not suitable for urchin fisheries. Studies to develop techniques to improve roe quality are recommended.

Seeking new meiotic genes.

Human infertility is a major worldwide health problem for individuals and their partners (1). Because genetic defects are thought to underlie many of the unexplained pathologies in infertility cases, animal models are expected to provide valuable clues to the underlying defects. More than 200 infertile or subfertile genetic mouse models have already been generated, defining key DNA repair and signaling pathways and other processes involved in mammalian reproduction (2). Many of these models were generated by targeted disruption of known genes or were fortuitously identified as spontaneously arising mutants. Because of the complexity of reproduction, however, this number almost certainly represents only a small fraction of the genes controlling this process (3). To discover new genes in gametogenesis, John Schimenti and colleagues have undertaken an ambitious phenotypebased screen in mice based on chemical mutagenesis of either embryonic stem cells (ethylmethanesulfonate) or whole animals (ethylnitrosourea). In a pilot study, 11 mouse fertility mutants have thus far been generated that affect several different stages of gametogenesis in one or both sexes, including meiosis (4). In this issue of PNAS, Libby et al. (5) report the positional cloning of the first of the mutant genes, Mei1 (meiosis defective 1). Mei1 is expressed almost exclusively in the gonads, in particular, in the testis of prepubertal and adult males and in the ovary of late embryonic females (i.e., embryonic day 17.5), the time of meiotic prophase. The human MEI1 gene is predicted to encode a protein with 79% identity to the mouse protein, and other vertebrate homologs have also been identified. However, the encoded protein contains no significant homology to previously described proteins, and homologs are not evident in yeast, worms, or flies. Thus, with this forward genetic approach, a novel vertebrate meiosis gene has been identified, highlighting the power of the chemical mutagenesis …

Expression of sGnRH mRNA in gonads during rainbow trout gametogenesis

The salmon gonadotropin-releasing hormone (sGnRH) is the major form of GnRH decapeptide expressed in the salmonid brain and it acts as a gonadotropin releaser. In rainbow trout, sGnRH-1 and sGnRH-2 mRNA forms were found in brain and gonads. We analyzed the expression of both forms in trout gonads at different stages of gametogenesis. Northern blot demonstrated that sGnRH-2 mRNA was the major sGnRH form in testis and ovary. In testis but not in ovary, brain or pituitary, alternatively spliced sGnRH-2 transcripts which coded for prepro-sGnRH with a truncated GnRH-associated peptide due to a premature stop codon in retained intron 2 were detected. In testis, sGnRH mRNA was highly expressed before the onset of spermatogenesis, it disappeared at stage II and then increased progressively up to stage VI. In ovary, the expression of sGnRH was high in immature pre-vitellogenic fish and progressively decreased throughout vitellogenesis. At ovulation it reached its maximum and came down again after stripping. The decrease of sGnRH mRNA expression during the period of active spermatogonial proliferation in testis and increase during meiosis occurrence in testis and ovary suggest an anti-proliferative and meiosis-stimulating effect of sGnRH during rainbow trout gametogenesis.

Levels of the Native Forms of GnRH in the Pituitary of the Gilthead Seabream,Sparus aurata, at Several Characteristic Stages of the Gonadal Cycle

Brains of the gilthead seabream,Sparus aurata, contain three different forms of gonadotropin-releasing hormone (GnRH): seabream (sb) GnRH, chicken (c) GnRH-II, and salmon (s) GnRH. In the present study, we developed three specific enzyme-linked-immunosorbent assays (ELISA) for sbGnRH, cGnRH-II, and sGnRH and used them to measure the levels of each GnRH form in the pituitary of male and female seabream at different stages of gametogenesis. The sensitivity was 6 pg/well for the sbGnRH assay, 7 pg/well for the cGnRH-II assay, and 2 pg/well for the sGnRH assay. Levels of each of the three GnRH forms were measured in pituitaries from fish sampled at the beginning of gonadal recrudescence and during the spawning season. Of the three forms, only sbGnRH and cGnRH-II were detected in the pituitary, irrespective of reproductive state or sex. Recrudescent fish had similar levels of sbGnRH and cGnRH-II in the pituitary. In sexually mature fish, the levels of sbGnRH were higher than those in recrudescent fish while pituitary cGnRH-II content remained unchanged. Consequently, sbGnRH levels were 3- to 17-fold higher than cGnRH-II levels in mature fish. Positive correlations also existed between pituitary sbGnRH content and pituitary and plasma gonadotropin (GtH) II levels. Surprisingly, mature 1-year-old males had significantly higher levels of sbGnRH in the pituitary than mature 3-year-old males, while pituitary and plasma GtH II levels were similar between these two groups. Although the reason for this difference in sbGnRH levels is unclear, a possible role of sbGnRH in the processes of puberty or sex-inversion is implied. Based on the present results, it can be suggested that in the gilthead seabream, sbGnRH is the most relevant form of GnRH in the control of reproduction.

Effects of age and body size on gonadal development of Atlantic sturgeon

Three hundred and five Atlantic sturgeon caught in the Hudson River and Hudson Bight were examined for age, body size and gonadal development (histology). Sampled fish ranged in age from 1·5 to 43 years and fork length (LF) 48–244 cm, and included 144 females and 161 males. All young sturgeon (age 1·5–4 years) caught in the river had sexually differentiated gonads. Age and size distributions of subadults and adults at different stages of gametogenesis were sex‐specific and conformed with von Bertalanffy growth curves. Males mature faster and at a younger age compared to the females. Females with mid‐vitellogenic ovaries were not found and their absence may be related to fishing gear selectivity or out‐migration into the ocean during ovarian recrudescence. Mature males and females caught during the spring spawning migration into the Hudson River, ranged in age from 12 to 19 and from 14 to 43 years, and LF 117–185 and 173–244 cm, respectively. Individual fecundity and diameter of fully grown ovarian follicles increased with age and body size, but this increase was dampened in older females. Three hermaphroditic fish were found and all exhibited sparse pre‐vitellogenic ovarian follicles embedded in normally developing testicular tissue.

Permissive Effect of Insulin-like Growth Factor I (IGF-I) on Gonadotropin Releasing-hormone Action on In Vitro Growth Hormone Release, in Rainbow Trout ( Oncorhynchus mykiss)

The aim of the work was to study the influence of insulin-like growth factor I (IGF-I) on GnRH-induced GH release by cultured pituitary cells of normally growing rainbow trout ( Oncorhynchus mykiss), collected at different stages of gametogenesis. When pituitary cells were pre-incubated with human IGF-I (10 −8 M) for 48 hours they became responsive to sGnRH (10 −8 to 10 −6 M) in the subsequent 24-hour incubation period, depending on the sexual stage, while not IGF-I pre-incubated cells were always non-responsive to GnRH. The permissive effect of IGF-I was detected in immature fish or those at the beginning of the gametogenesis, but not in mature fish. IGF-I inhibition of GH release during the preincubation period varies also with the sexual stage and is greater in immature than in mature fish. The permissive effect of IGF-I seems specific to somatotropes since IGF-I does not modify GnRH action on GtH 2 release. This work suggests that GnRH action on GH release can vary for a particular fish species depending on the physiological status.

Alteration of starfish oocyte adenylate cyclase properties in gametogenesis

1. The properties of the oocyte membrane adenylate cyclase system of the starfish Aphelasterias japonica at different stages of gametogenesis were studied. 2. The adenylate cyclase activity of fully grown oocytes was insensitive to catecholamines whereas activity in growing oocytes was increased. 3. Forskolin and NaF stimulated catalytic activity of growth and fully grown oocytes to various degrees. The stimulated effect of these modifiers was more considerable in grown oocytes. 4. We believe that the interaction between components of the adenylate cyclase system is altered in gametogenesis.

Pituitary response to LH-RH at different stages of gametogenesis in the rainbow trout (Salmo gairdneri)

Pituitary response to LH-RH at different stages of gametogenesis in the rainbow trout (Salmo gairdneri)

Influence de la température sur la spermatogenèse et l'activité neurosécrétrice d' Hirudo medicinalis L. (Hirudinée Gnathobdelliforme)

Temperature is shown to act on spermatogenesis in Hirudo medicinalis in a manner which permits the production of animals at different stages of gametogenesis throughout the year. Staining properties of fuchsinophilic cells and neurons of type β 2 of the central nervous system has been followed in relation to gametogenic activity in the testis. The possible gonadotropic role of the fuchsinophilic cells, as well as the problem of the release of their secretions, are discussed.