Cloning, localization and differential expression of Neuropeptide-Y during early brain development and gonadal recrudescence in the catfish, Clarias gariepinus

Cloning and expression profiling of peptide YY in the brain of common carp, Cyprinus carpio

Peptide YY (PYY) is an anorectic brain-gut pancreatic peptide that helps in feeding regulation by reducing appetite and is well characterized in mammals. The role of PYY in relation to brain is least studied in mammals as well as in lower vertebrates including fish, however high expression was evident in male reproductive tissue. In this regard, this study attempts to evaluate the significance of PYY in the brain of common carp, Cyprinus carpio. As a first step, the cDNA of PYY from brain of adult male carp was cloned. Following which expression analysis was performed using juvenile and adult fish. The differential distribution pattern in various regions of brain and ontogeny expression analysis indicated that PYY may involve in physiological processes related to brain-pituitary axis. In addition, a significant decrease in neuropeptide Y expression was observed upon PYY- endoribonuclease-prepared small interfering RNA transfection in brain cells, in vitro indicating plausible PYY-NPY interaction in brain-pituitary axis of common carp.

Impact of gonadotropin on certain testis-related genes identified through testicular transcriptome analysis in the Asian and the African catfish

Induction of spawning in catfish is well demonstrated in females while stimulation of spermiation in males seems difficult. This has led to least understanding of gene profile changes during testicular maturation. Expression of the factors after hormonal induction that control reproductive processes has become an intense research area in fish endocrinology. In view of this, de novo assemblies of testicular transcriptomes of the Asian catfish, Clarias batrachus and the African catfish, C. gariepinus, were performed to identify genes/factors involved in testicular maturation. For testicular induction, human chorionic gonadotropin (hCG) was administered in vivo to both the catfish species during active phase of reproduction. 1,68,071 and 1,26,232 assembled transcripts were obtained from C. batrachus and C. gariepinus testicular transcriptomes and were annotated using different databases. Further, in silico analysis suggested the presence of several transcripts that were involved in steroidogenesis and male reproduction. Comparison of transcriptomes of both species revealed the presence of certain unique genes related to reproduction differentially. Expression profiles after hCG induction in testis showed higher expression of certain steroidogenesis related genes such as star, cyp11b1, cyp17a and cyp21a in both the species. Further, expression levels of crucial factors related to testis, such as dmrt1/2/3, were also found to be significantly higher after gonadotropin induction. However, amh, tgfα and dmrt4/5 expression levels were significantly low. Factors related to male reproduction i.e., tekt1, tekt2, sox9, spag1, spata2 and spata7 were found to be differentially upregulated in hCG treated testicular tissues of both the species. Histology analysis indicated that the gonadotropin induction either short or long term is a better strategy to highlight expression profile changes during testicular maturation in teleost.

Neuropeptide Y in Spotted Scat (Scatophagus Argus), Characterization and Functional Analysis towards Feed Intake Regulation

Neuropeptide Y (Npy) is an intricate neuropeptide regulating numerous physiological processes. It is a highly conserved peptide known to improve feed intake in many vertebrates, including fishes. To enlighten the mechanism of Npy in spotted scat feed intake control, we cloned and identified the Npy cDNA sequence. We further examined its expression in some tissues and explored its expression effects at different time frames (hours and days). Here, we discovered that spotted scat Npy comprised a 300 bp open reading frame (ORF) and a 99 amino acid sequence. Npy was identified to be expressed in all tissues examined. Using in situ hybridization examination, we proved that npy has a wide expression in the brain of the spotted scat. Furthermore, the expression of npy in the hypothalamus significantly increased one hour after feeding (p < 0.05). Further, it was revealed that npy expression significantly increased in fish that were fasted for up to 5 days and significantly increased after refeeding from the 8th to the 10th day. This suggests that Npy is an orexigenic peptide, and hence, it increases food intake and growth in the spotted scat. Additionally, results from in vitro and in vivo experiments revealed that Npy locally interacts with other appetite-regulating peptides in the spotted scat hypothalamus. This research aimed to set a fundamental study in developing the feed intake regulation, improving growth and reproduction, which is significant to the aquaculture industry of the spotted scat.

Advances in Reproductive Endocrinology and Neuroendocrine Research Using Catfish Models

Catfishes, belonging to the order siluriformes, represent one of the largest groups of freshwater fishes with more than 4000 species and almost 12% of teleostean population. Due to their worldwide distribution and diversity, catfishes are interesting models for ecologists and evolutionary biologists. Incidentally, catfish emerged as an excellent animal model for aquaculture research because of economic importance, availability, disease resistance, adaptability to artificial spawning, handling, culture, high fecundity, hatchability, hypoxia tolerance and their ability to acclimate to laboratory conditions. Reproductive system in catfish is orchestrated by complex network of nervous, endocrine system and environmental factors during gonadal growth as well as recrudescence. Lot of new information on the molecular mechanism of gonadal development have been obtained over several decades which are evident from significant number of scientific publications pertaining to reproductive biology and neuroendocrine research in catfish. This review aims to synthesize key findings and compile highly relevant aspects on how catfish can offer insight into fundamental mechanisms of all the areas of reproduction and its neuroendocrine regulation, from gametogenesis to spawning including seasonal reproductive cycle. In addition, the state-of-knowledge surrounding gonadal development and neuroendocrine control of gonadal sex differentiation in catfish are comprehensively summarized in comparison with other fish models.

Developmental aspects of the hypothalamic-pituitary network related to reproduction in teleost fish

The hypothalamic-pituitary-gonadal axis is the main system that regulates reproduction in vertebrates through a complex network that involves different neuropeptides, neurotransmitters, and pituitary hormones. Considering that this axis is established early on life, the main goal of the present work is to gather information on its development and the actions of its components during early life stages. This review focuses on fish because their neuroanatomical characteristics make them excellent models to study neuroendocrine systems. The following points are discussed: i) developmental functions of the neuroendocrine components of this network, and ii) developmental disruptions that may impact adult reproduction. The importance of the components of this network and their susceptibility to external/internal signals that can alter their specific early functions and/or even the establishment of the reproductive axis, indicate that more studies are necessary to understand this complex and dynamic network.

Role of sox30 in regulating testicular steroidogenesis of common carp

Expression of transcription factors is crucial for the regulation of steroidogenesis and gonadal development in fish. SRY-related box (SOX) proteins regulate gene expression of various events related to vertebrate reproduction. This study reports the role of sox30 and its influence on sox9a/b in regulating testicular steroidogenesis of the common carp, Cyprinus carpio. Tissue distribution showed predominant expression of sox30 in gonads, while gonadal ontogeny indicated significant dimorphic expression of sox30 from 120 days post hatch. Higher sox30 transcripts during the spawning season, an elevation of sox30 after human chorionic gonadotropin induction, and 11-ketotestosterone (11-KT) treatment authenticate gonadotropin dependency. Treatment of 17α-methyl-di-hydroxy-testosterone to juvenile common carp for mono-sex induction, vis-à-vis elevated sox30 expression. Sox30 protein was detected abundantly in spermatocytes and spermatid/sperm of carp testis. Transient silencing of sox30 using small interfering RNAs decreased sox9a/b expression, lead to downregulation of certain molecule/factor, transcription factor, germ/stem cell marker, and steroidogenesis-related enzyme genes. Serum testosterone and 11-KT decreased significantly upon transient silencing of sox30, in vivo. Concomitantly, a reduction in testicular microsomal 11-β hydroxysteroid dehydrogenase activity was observed. These results demonstrate the influence of sox30 as well as sox9a/b in the regulation of testicular steroidogenesis in common carp.

Photo-thermal regulation of neuropeptide Y (NPY) expression in ovarian follicles and ovarian activity of the catfish, Clarias batrachus

Authors have recently reported a gradual increase in neuropeptide Y expression in the ovarian follicles of Clarias batrachus with the progression of oogenesis, coinciding with increasing photoperiod and temperature. This indicates the involvement of photoperiod and temperature in controlling NPY expression. Therefore, a study was designed to investigate the role of photoperiod and temperature in regulation of NPY expression in ovarian follicles. The catfish were exposed to different photo-thermal regimes during the late-quiescence and late-recrudescence phases for one month, and the expression of NPY was analyzed along with other ovarian activities. Though the exposure of catfish to long photoperiod induced a marginal increase (1.5 fold) in NPY expression in follicular cells, the high temperature stimulated its expression more effectively (6-10 fold), irrespective of photoperiodic exposures. Exposure to long photoperiod and high temperature together induced NPY expression maximally in granulosa and thecal cells of fully grown oocytes, but exposure to low temperature decreased its expression significantly. The oogenic and steroidogenic activities were also promoted simultaneously after the exposure to high temperature and long photoperiod alone or in combination. However, the low temperature exposure suppressed the ovarian activities leading to atresia of advanced follicles. Thus it is suggested that photoperiod and temperature both affect NPY expression and ovarian recrudescence in fish but the influences of temperature seem to be more prominent.

Metabolic hormones and the regulation of spermatogenesis in fishes

Metabolic hormones play essential regulatory roles in many biological processes, including morphogenesis, growth, and reproduction through the maintenance of energy balance. Various metabolic hormones originally discovered in mammals, including ghrelin, leptin, and nesfatin-1 have been identified and characterized in fish. However, physiological roles of these metabolic hormones in regulating reproduction are largely unknown in fishes, especially in males. While the information available is restricted, this review attempts to summarize the main findings on the roles of metabolic peptides on the reproductive system in male fishes with an emphasis on testicular development and spermatogenesis. Specifically, the primary goal is to review the physiological interactions between hormones that regulate reproduction and hormones that regulate metabolism as a critical determinant of testicular function. A brief introduction to the localization of metabolic hormones in fish testis is also provided. Besides, the consequences of fasting and food deprivation on testicular development and sperm quality will be discussed with a focus on interactions between metabolic and reproductive hormones.

Expression profiling of c-kit and its impact after esiRNA silencing during gonadal development in catfish

Receptor, c-Kit is a member of a family of growth factor receptors that have tyrosine kinase activity, and are involved in the transduction of growth regulatory signals across plasma membrane by activation of its ligand, kitl/scf. The present study analyzed mRNA and protein expression profiles of c-kit in the gonads of catfish, Clarias gariepinus, using real time PCR, in situ hybridization and immunohistochemistry. Tissue distribution analysis revealed higher expression mainly in the catfish gonads. Ontogeny studies showed minimal expression during early developmental stages and highest during 50-75 days post hatch, and the dimorphic expression in gonads decreased gradually till adulthood, which might suggest an important role for this gene around later stages of sex differentiation and gonadal development. Expression of c-kit was analyzed at various phases of gonadal cycle in both male and female, which showed minimal expression during the resting phase, and higher expression during the pre-spawning phase in male compared to females. In vitro and in vivo induction using human chorionic gonadotropin elevated the expression of c-kit indicating the regulatory influence of hypothalamo-hypophyseal axis. In vivo transient gene silencing using c-kit-esiRNA in adult catfish during gonadal recrudescence showed a decrease in c-kit expression, which affected the expression levels of germ cell meiotic marker sycp3, as well as several factors and steroidogenic enzyme genes that are involved in germ cell development. Decrease in the levels of 11-ketotestosterone and testosterone in serum were also observed after esiRNA silencing. The findings suggests that c-kit has an important role in the process of germ cell proliferation, development and maturation during gonadal development and recrudescence in catfish.

GDNF family receptor α-1 in the catfish: Possible implication to brain dopaminergic activity

Glial cell line-derived neurotrophic factor (GDNF)is a potent trophic factor that preferentially binds to GDNF family receptor α-1 (GFRα-1)by regulating dopaminergic (DA-ergic) neuronsin brain. Present study aimed to evaluate the significance of GFRα-1 expression during early brain development in catfish. Initially, the full-length cDNA of GFRα-1 was cloned from adult brain which showed high homology with other vertebrate counterparts. Quantitative PCR analysis of tissue distribution revealed ubiquitous expression of GFRα-1 in the tissues analyzed with high levels in female brain and ovary. Significant high expression was evident in brain at 75 and 100 days post hatch females than the respective age-match males. Expression of GFRα-1 was high in brain during the spawning phase when compared to other reproductive phases. Localization of GFRα-1 revealed its presence in preoptic area-hypothalamus which correlated well with the expression profile in discrete areas of brain in adult catfish. Transient silencing of GFRα-1through siRNA lowered expression levels of GFRα-1, which further down regulated the expression of certain brain-specific genes. Expression of GFRα-1 in brain declined significantly upon treatment with the 1-methyl-1,2,3,6-tetrahydropyridinecausing neurodegeneration which further correlated with catecholamines (CA), L-3,4-dihydroxyphenylalanine, DA and norepinephrine levels. Taken together, GFRα-1 plausibly entrains gonadotropin-releasing hormone and gonadotropin axiseither directly or indirectly, at least by partially targeting CA-ergic activity.

Seasonal variations in cellular expression of neuropeptide Y (NPY) in testis of the catfish, Clarias batrachus and its potential role in regulation of steroidogenesis

The present study demonstrates seasonal variation in the cellular expression of neuropeptide Y (NPY), a known orexigenic neuropeptide, in the testis of the catfish, Clarias batrachus and its relation with testicular steroids. In vitro effects of NPY on androgen production and activities of steroidogenic enzymes were also analyzed to reaffirm the relation between NPY and steroids. NPY-immunoprecipitation was observed in Sertoli cells, interstitial cells and germ cells in recrudescing testis. Intensity of NPY-immunoreaction in the interstitial cells increased steadily with initiation of spermatogenesis and reached maximal in fully grown testes, and then decreased suddenly in the spermiating/spent testis. NPY was also expressed considerably in Sertoli cells in recrudescing testis, but disappeared in the fully grown testis. A moderate NPY-immunoreactivity was also seen in spermatogonial cells in recrudescing testis, but intense NPY-immunoprecipitation was detected in advanced germ cells (spermatids/spermatozoa) in fully mature testis. NPY-immunoreation intensity in interstitial cells showed positive correlation with increasing levels of testicular testosterone and 11-ketotestosterone, and with activities of 3β-HSD & 17β-HSD coinciding with advancing testicular activities. NPY treatment of testicular fragments in vitro stimulated the activities of 3β-HSD & 17β-HSD and increased testosterone & 11-ketotestosterone levels. This study for the first time demonstrates the existence of NPY peptide at cellular levels in fish testis, which stimulates androgen production by acting directly at testicular level.

Seasonal ovarian immunolocalization of neuropeptide Y and its role in steriodogenesis in Asian catfish, Clarias batrachus

The present study was undertaken to examine the cellular localization and potential steroidogenic role of neuropeptide Y (NPY) in the ovary of the freshwater catfish, Clarias batrachus. NPY-immunoreaction was observed in the follicular cells (granulosa and thecal cells) in the growing ovarian follicles, and the intensity of staining increased steadily from the initiation of follicular development until follicles were fully grown. Thereafter as follicles matured the stain intensity decreased. Positive correlations were found between NPY expression and the ovarian levels of 17β-estradiol, testosterone, and activities of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) in the ovary. In vitro NPY treatment stimulated the production of the two steroids and the activities of two enzymes. This is the first report of NPY immunoreactivity at the cellular level in the fish ovary and implicates this orexigenic peptide in the modulation of ovarian steroidogenesis.