Gonadal Development Research Articles

Salmonid Pituitary Cells as a Test System for Identifying Endocrine-Disrupting Compounds.

The pituitary gland is a central regulator of reproduction, producing two gonadotropins, follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), which regulate gonadal development, sex steroid synthesis, and gamete maturation. The present study sought to optimize an in vitro test system using pituitary cells isolated from previtellogenic female coho salmon and rainbow trout, focusing on fshb and lhb subunit gene expression. Initially, we optimized culture conditions for duration and benefits of culturing with and without addition of endogenous sex steroids (17β-estradiol [E2] or 11-ketotestosterone) or gonadotropin-releasing hormone (GnRH). The results suggest that culturing with and without E2 was valuable because it could mimic the (+) feedback effects on Lh that are observed from in vivo studies. After optimizing assay conditions, a suite of 12 contaminants and other hormones was evaluated for their effects on fshb and lhb gene expression. Each chemical was tested at four to five different concentrations up to solubility limitations in cell culture media. The results indicate that more chemicals alter lhb synthesis than fshb. The more potent chemicals were estrogens (E2 and 17α-ethynylestradiol) and the aromatizable androgen testosterone, which induced lhb. The estrogen antagonists 4-OH-tamoxifen and prochloraz decreased the E2-stimulated expression of lhb. Among several selective serotonin reuptake inhibitors tested, the sertraline metabolite norsertraline was notable for both increasing fshb synthesis and decreasing the E2 stimulation of lhb. These results indicate that diverse types of chemicals can alter gonadotropin production in fish. Furthermore, we have shown that pituitary cell culture is useful for screening chemicals with potential endocrine-disrupting activity and can support the development of quantitative adverse outcome pathways in fish. Environ Toxicol Chem 2023;42:1730-1742. © 2023 SETAC.

Identification and Characterization of C-Mos in Pearl Mussel Hyriopsis cumingii and Its Role in Gonadal Development

C-Mos, a proto-oncogene, regulates oocyte maturation by activating the classical MAPK pathway in cells. To examine the function of C-Mos in Hyriopsis cumingii, C-Mos was identified in this study. The full-length cDNA of C-Mos was 2213 bp, including 144 bp in the 5′ UTR, 923 bp in 3′ the UTR, and 1146 bp in the open reading frame (ORF) region. During early gonad development, the expression of C-Mos from 4 to 6 months of age in H. cumingii was significantly higher than that in other months, with the highest expression in 6-month-old H. cumingii, suggesting that C-Mos may be involved in early gonadal development in H. cumingii. Clear hybridization signals were found by in situ hybridization in the oocytes, oocyte nucleus and oogonium, and a small number of hybridization signals were found in the follicular wall of the male gonads. In addition, the C-Mos RNA interference (RNAi) assay results showed that the knockdown of C-Mos caused a down-regulation of ERK and P90rsk. In summary, these results indicate that C-Mos has a crucial part to play in gonadal development in H. cumingii.

Function of secretoneurin in regulating the expression of reproduction-related genes in ovoviviparous black rockfish (Sebastes schlegelii).

Secretoneurin (SN), a conserved peptide derived from secretogranin-2 (scg2), also known as secretogranin II or chromogranin C, plays an important role in regulating gonadotropin in the pituitary, which affects the reproductive system. This study aimed to clarify the mode of action of scg2 in regulating gonad development and maturation and the expression of mating behavior-related genes. Two scg2 cDNAs were cloned from the ovoviviparity teleost black rockfish (Sebastes schlegelii). In situ hybridization detected positive scg2 mRNA signals in the telencephalon and hypothalamus, where sgnrh and kisspeptin neurons were reported to be located and potentially regulated by scg2. In vivo, intracerebral ventricular injections of synthetic black rockfish SNa affected brain cgnrh, sgnrh, kisspeptin1, pituitary lh and fsh and gonad steroidogenesis-related gene expression levels with sex dimorphism. In vitro, a similar effect was found in primary cultured brain and pituitary cells. Thus, SN could contribute to the regulation of gonadal development, as well as reproductive behaviors, including mating and parturition.

Blue LED light treatment of pregnant mares is not detrimental to gonadal development in their offspring

A light program transmitted via blue LED light directed at one eye from individual light masks (Equilume, Kildare, Ireland) to pregnant mares from the middle of December onwards advanced the onset of foaling with birth of mature and healthy foals, but they were slightly smaller than foals from untreated control pregnancies (Lutzer et al., Domestic Anim Endocrinol 2022;78:106675). Differences, however, equilibrated within the first year of life. In this study we followed the hypothesis that light treatment of pregnant mares is without detrimental effects on body size and gonadal development of offspring after puberty. A total of 47 warmblood horses born and raised on the same stud farm to blue LED light-treated (17 males and 9 females) or control mares (14 males and 9 females) were included. At 24 months of age, their body weight, height at withers and cannon bone circumference was determined. In males, the external genitalia were examined, testis size was measured by transcutaneous ultrasound. The total testicular volume (TTV) was calculated. In females, a transrectal ultrasound examination of the genital tract was performed, the presence of corpora lutea was detected via plasma progesterone concentration and the antral follicle count (AFC) was assessed. Statistical comparisons weremade by analysis of variance (general linear model) with group (blue light vs. control) and sex (male vs. female) as between subject factors (IBM SPSS 27). Results are given as mean ± SEM. There were no group or sex differences with regard to bodyweight or height at the withers. The cannon bone circumference was larger in male vs. female horses (p<0.001) but not affected by blue light treatment during pregnancy. Testes were classified as normal in size and location (Love et al., J Reprod Fertil Suppl 1991;44:99-105) in 13 of 17 blue light and 11 of 14 control colts (n.s., chi2 analysis). The TTV was 232±14cm3 in the blue light and 218±11cm3 in the control group (n.s.). Abnormal testicular development was diagnosed in 7 males with unequal testicular size in 3 blue light and 2 control animals, both testes too small (1 blue light) or unilaterally cryptorchid (1 control). In females, no abnormalities were present. A corpus luteum (progesterone >1ng/ml) was present in 8 / 9 females from the blue light and 5 / 8 from the control group. The AFC was 20.6±2.5 in blue light and 22.1±3.7 in control females (n.s.). Results demonstrate that blue LED light treatment of pregnant mares has no detrimental effects on body and genital tract development of their offspring at two years of age.

Expression characteristics of Hsd3b7 in the gonads of Paralichthys olivaceus.

Steroidogenesis is an important biological process for gonadal differentiation and development. In mammals, 3β-hydroxysteroid dehydrogenase 7 (HSD3B7) could convert 3β-hydroxy of 7α-hydroxycholesterol into a ketone and form 7α-hydroxy-4-cholesten-3-one, which may affect steroidogenesis. However, in fish, the study of Hsd3b7 is still lacking. In this study, Hsd3b7 was identified in the olive flounder Paralichthys olivaceus, an important mariculture fish. According to bioinformatics analysis, Hsd3b7 belongs to a Rossmann-fold NAD(P)(+)-binding protein and can interact in a predictable manner with Hsd17b2, -3, and - 4, which play a role in steroidogenesis. In the adult flounder, Hsd3b7 was expressed in various tissues, at particularly high level in male muscle. The expression levels of Hsd3b7 at gonadal development stages I-V initially increased and then decreased, with an inflection point in the ovary at stage III and in the testis at stage IV. At stage III, the expression level of Hsd3b7 was significantly higher in the ovary than in the testis (P < 0.01). The results of in situ hybridization (ISH) revealed that it was mainly expressed in oocytes of phases I-IV or around oocytes of phases IV-V in the ovaries and around spermatid lobules at stages IV-V in the testes. Three regulatory sites of SRY-box transcription factor 9 (Sox9), a transcription factor involved in steroidogenesis and gonadal differentiation, were predicted in the promoter of Hsd3b7. After intraperitoneal injection with the recombination flounder Sox9a, the expression of Hsd3b7 was significantly up-regulated (P < 0.01). During the flounder gonadal differentiation, 17β-estradiol (E2, 5 μg/g feed) and 17α-methyltestosterone (T, 5 μg/g feed) were used to obtain the phenotypic female or male flounder, and the results showed that in the E2 group, Hsd3b7 expression was highest at 2 cm TL, the primordial gonad stage, which was significantly higher than that at 12 cm TL (P < 0.05). In the T group, Hsd3b7 expression level was also highest at 2 cm TL and significantly higher than at 10 and 12 cm TL (P < 0.05). Moreover, Hsd3b7 was detected to be localized mainly around oogonia and spermatogonia during the differentiated gonads with ISH. These findings first introduce the expression characteristics of Hsd3b7 and the effect of Sox9a on its expression, which contribute to our understanding of the function of Hsd3b7 in fish gonads.

Histological demonstration of gonad development in the banana shrimp, Fenneropenaeus merguiensis

The genetic diversity of the banana shrimp Fenneropenaeus merguiensis is at risk because of over-harvesting, which consequently reduces food security. This endangerment is exacerbated because this species is not commonly cultivated by farmers. Overall, these factors necessitate conservation of this shrimp species across its natural habitat. Information on the migration of primordial germ cells (PGCs) to form a gonad is essential for shrimp preservation techniques such as broodstock preparation, sex differentiation, and germ cell transplantation. In this study, histological analysis and in situ hybridization of vasa expression (from embryo to testis development) were used to demonstrate the movement of PGCs. Hematoxylin and Eosin staining and in situ hybridization with the VASA probe revealed that the PGCs migrated retrogradely along the midgut, colonizing the area between the hepatopancreas and heart, a region that becomes the genital ridge in the postlarval stage. External sexual organs appeared at approximately 4 months of age. Through real-time PCR, the expression of the vasa gene was detected early on postlarval day 7, whereas its abundant expression was detected in the ovaries and testes of adult shrimp. This study could help with the identification and monitoring of PGCs or spermatogonia in banana shrimp and facilitate the implementation of other germ cell-relevant techniques in the future.

Identification and characterization of gonadotropin-releasing hormone (GnRH) in Zhikong scallop Chlamys farreri during gonadal development.

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on neuroendocrine control of gonadal function, such as the function of GnRH during gonadal development is limited. In this study, we investigated the morphology and structure of the nerve ganglia of Zhikong scallop Chlamys farreri by physiological and histological observations. We also cloned the ORF and studied the expression patterns of GnRH in the scallop. Tissue expression analysis showed that GnRH was highly expressed in parietovisceral ganglion (PVG). The in situ hybridization result further confirmed that GnRH mRNA only distributed in some good-sized neurons in the posterior lobe (PL) and some pint-sized neurons in the lateral lobe (LL). In addition, by examining the expression of GnRH during gonadal development in ganglia, we found GnRH displayed higher expression in the female scallops, and showed significant high expression at the growing stage of female scallops in PVG. This study would contribute to gaining insight into the mechanism underlying reproduction regulation by GnRH in the scallop and help to provide a better understanding of reproductive neuroendocrine in mollusks.

A PITX2-HTR1B pathway regulates the asymmetric development of female gonads in chickens.

All female vertebrates develop a pair of ovaries except for birds, in which only the left gonad develops into an ovary, whereas the right gonad regresses. Previous studies found that the transcription factor Paired-Like Homeodomain 2 (PITX2), a key mediator for left/right morphogenesis in vertebrates, was also implicated in asymmetric gonadal development in chickens. In this study, we systematically screened and validated the signaling pathways that could be targeted by Pitx2 to control unilateral gonad development. Integrated chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) analyses indicated that Pitx2 directly binds to the promoters of genes encoding neurotransmitter receptors and leads to left-biased expression of both serotonin and dopamine receptors. Forcibly activating serotonin receptor 5-Hydroxytryptamine Receptor 1B (HTR1B) signaling could induce ovarian gene expression and cell proliferation to partially rescue the degeneration of the right gonad. In contrast, inhibiting serotonin signaling could block the development of the left gonad. These findings reveal a PITX2-HTR1B genetic pathway that guides the left-specific ovarian growth in chickens. We also provided new evidence showing neurotransmitters stimulate the growth of nonneuronal cells during the early development of reproductive organs well before innervation.

Who is sensitising whom? A participatory interview guide development as an awareness tool within a health care research project

Who is sensitising whom? A participatory interview guide development as an awareness tool within a health care research project

Polystyrene nanoplastics decrease nutrient accumulation, disturb sex hormones, and inhibit reproductive development in juvenile Macrobrachium nipponense

The biological effects of nanoplastics has grown exponentially over the past few years. However, little is known about the effects of nanoplastic exposure on gonadal development in crustaceans. Thus, juvenile oriental river prawns (Macrobrachium nipponense) were exposed to different concentrations of 75-nm polystyrene nanoplastics (0, 5, 10, 20, and 40 mg/L) for 28 days to study the effects of exposure to nanoplastics on gonadal development. The genes encoding extracellular signal-regulated kinase (ERK) and mitogen-activated protein kinase kinase (MEK) were selected and the nutrient composition, sex hormone level, and gonad development-related gene expression were determined. Crude lipid and crude protein decreased with exposure to higher concentrations of nanoplastics, whereas there were no significant differences in levels of ash or moisture (P > 0.05). Full-length Mn-ERK and Mn-MEK cDNAs were cloned from M. nipponense and homologous comparisons showed that the genes had conserved functional sequences and had evolved consistently in invertebrates. With nanoplastics concentration increased, the serum sex hormone (estradiol, progesterone, and testosterone) levels of juvenile shrimp first increased and then decreased. In addition, the expression of gonad development-related genes (Vitellogenin, Vitellogenin receptor, Cyclin B, Gametocyte Specific Factor 1, Vasa, and PL10), MEK and ERK initially increased and then decreased with increasing nanoplastic concentration. This suggests that polystyrene nanoplastics reduce the accumulation of nutrients and lead to suppression of gonadal development in juvenile M. nipponense and, thus, provides basic information on the toxic effects of nanoplastics that could extend to other crustaceans.

Inhibition of the NF-κB signaling pathway affects gonadal differentiation and leads to male bias in Paramisgurnus dabryanus

In recent years, sex-controlled breeding has emerged as an effective strategy to enhance the yields of economic animals with different growth characteristics, while increasing the economic benefits of aquaculture. It is known that the NF-κB pathway participates in gonadal differentiation and reproduction. Therefore, we used the large-scale loach as a research model for the present study and selected an effective inhibitor of the NF-κB signaling pathway (QNZ). This, to investigates the impacts of the NF-κB signaling pathway on gonadal differentiation during a critical period of gonad development and after maturation. Simultaneously, the sex ratio bias and the reproductive capacities of adult fish were analyzed. Our results indicated that the inhibition of the NF-κB signaling pathway influenced the expression of genes related to gonad development, regulated the gene expression related to the brain-gonad-liver axis of juvenile loaches, and finally impacted the gonadal differentiation of the large-scale loach and promoted a male-biased sex ratio. Meanwhile, high QNZ concentrations affected the reproductive abilities of adult loaches and inhibited the growth performance of offspring. Thus, our results deepened the exploration of sex control in fish and provided a certain research basis for the sustainable development of the aquaculture industry.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

Molecular characterization of Smtdc-1 and Smddc-1 discloses roles as male-competence factors for the sexual maturation of Schistosoma mansoni females.

Schistosomes are the only mammalian flatworms that have evolved separate sexes. A key question of schistosome research is the male-dependent sexual maturation of the female since a constant pairing contact with a male is required for the onset of gonad development in the female. Although this phenomenon is long known, only recently a first peptide-based pheromone of males was identified that contributes to the control of female sexual development. Beyond this, our understanding of the molecular principles inducing the substantial developmental changes in a paired female is stillrudimentary. Previous transcriptomic studies have consistently pointed to neuronal genes being differentially expressed and upregulated in paired males. These genes included Smp_135230 and Smp_171580, both annotated as aromatic-L-amino-acid decarboxylases (DOPA decarboxylases). Here, we characterized both genes and investigated their roles in male-female interaction of S. mansoni. Sequence analyses indicated that Smp_135230 represents an L-tyrosine decarboxylase (Smtdc-1), whereas Smp_171580 represents a DOPA decarboxylase (Smddc-1). By qRT-PCR, we confirmed the male-specific and pairing-dependent expression of both genes with a significant bias toward paired males. RNA-interference experiments showed a strong influence of each gene on gonad differentiation in paired females, which was enhanced by double knockdown. Accordingly, egg production was significantly reduced. By confocal laser scanning microscopy, a failure of oocyte maturation was found in paired knockdown females. Whole-mount in situ hybridization patterns exhibited the tissue-specific occurrence of both genes in particular cells at the ventral surface of the male, the gynecophoral canal, which represents the physical interface of both genders. These cells probably belong to the predicted neuronal cluster 2 of S. mansoni. Our results suggest that Smtdc-1 and Smddc-2 are male-competence factors that are expressed in neuronal cells at the contact zone between the genders as a response of pairing to subsequently control processes of female sexual maturation.

Insulin-like growth factor 1 promotes the gonadal development of Pampus argenteus by regulating energy metabolism†.

Insulin-like growth factor 1 (Igf1) is known to promote ovarian maturation by interacting with other hormones. However, the limited research on the role of Igf1 in the energy metabolism supply of gonads has hindered further exploration. To explore the role of Igf1 in gonadal development of silver pomfret, we analyzed the expression levels and the localization of igf1 mRNA and protein during testicular and ovarian development of silver pomfret. The results of the study showed upregulation of Igf1 in the critical period of vitellogenesis and sperm meiosis, which was found to be mainly expressed in the somatic cells of the gonads. Upon adding E2 and Igf1 to cultured gonadal tissues, the expression of energy-related genes was significantly increased, along with the E2-enhanced effect of Igf1 in the testis. Importantly, stimulation of both ovaries and testes with E2 and Igf1 led to a remarkable increase in the expression of vitellogenesis and meiosis-related genes. Therefore, we conclude that Igf1 promotes vitellogenesis and sperm meiosis by regulating gonadal energy production. Moreover, the expression of Igf1 in gonads is significantly regulated by E2. These findings provide new insights for the research of Igf1 in fish breeding, thus allowing the regulation of energy metabolism between growth and reproduction for successful reproductive outcomes.

Fecundity, an overlooked life-history trait for coastal management of commercial molluscs?

Gonadal development in limpets is well-known. However, the integration of fecundity data on coastal management actions remains overlooked. Here, we use fecundity of two exploited limpets (Patella ordinaria and P. aspera) to demonstrate its potential as a conservation tool to preserve the harvested populations of both species. From October 2021 to June 2022, 158 females of P. ordinaria and 70 of P. aspera were collected from the coastal rocky shores of the archipelago of Madeira (NE Atlantic Ocean). The fecundity in both species appears to be determinate, and estimated batch fecundity 365,638 ± 204,462 oocytes for P. ordinaria and 73,029 ± 43,496 oocytes for P. aspera. The presence of spawning individuals of both species until May is of significant relevance to their management and conservation. A harvest-ban (November-March) is currently implemented in the coastal governance actions of P. ordinaria and P. aspera. Based on the fecundity results, small adjustments can be made to further improve the conservation of adult individuals, which are important for the continuity of future generations. So far, fecundity data constitute an overlooked life trait of key importance to preserve populations of exploited species, primarily those with limited mobility such as semi-sessile littoral limpets.

Mass synchronization of gonadal maturation in banded knifefish broodstock (Gymnotus cf. carapo)

The banded knifefish Gymnotus cf. carapo (Pisces, Gymnotidae), also known locally as tuvira, is a natural resource of great importance to the Pantanal biome that has been used as live bait in sport fishing. This study investigated the mass synchronization of gonadal development of banded knifefish in captivity by subjecting them to different water electrical conductivity at different time intervals (pre and post conductivity change) and also evaluated the use of ultrasound imaging to identify the sex and phases of ovarian recrudescence of the captive broodstock. Fish were exposed to three different combinations of time intervals (Group 1: 40 + 30 days; Group 2: 45 + 25 days; Group 3: 50 + 20 days) and water conductivity (high: 180 μS/cm, followed by low: 15 μS/cm conductivity, respectively). The control group was kept in low water conductivity throughout the 70-day trial. Based on the results, 93%, 94%, and 86% of mass gonadal maturation of Gymnotus cf. carapo could be achieved by keeping the fish in high water conductivity (180 μS/cm) for 40, 45, or 50 days, and subsequently in low conductivity (15 μS/cm). The sexing and maturation assessment of the fish using ultrasound imaging was fundamental for effectively evaluating the mass gonadal maturation protocol. The combined use of these techniques proved safe in reproductive studies with banded knifefish.

Examination of the effects of inbreeding on reproductive capacity in the Pacific oyster, Crassostrea gigas

The Pacific oyster (Crassostrea gigas) has been widely cultured as a commercially important bivalve. Intercrossing of inbred strains is regarded as an efficient method to increase yield (heterosis), so the development of inbred lines is common in the breeding strategies of C. gigas. However, inbreeding usually reduces physiological efficiency or reproductive capacity. The effects of inbreeding on gonadal development and reproductive capacity remain to be explored in oysters. In the present study, the monthly gonadal development of an inbred and a control population was observed. Compared with the control population, the delayed gonadal development in the inbred population may require more time and cost for breeders in the artificial breeding process. We investigated how inbreeding influenced female and male gametic traits, including reproductive effort, egg diameter, fertilization rate, hatching rate, sperm motility, sperm longevity, and sperm curvilinear velocity, as well as sperm competitiveness based on a male's share of paternity. We found no inbreeding depression for egg diameter, fertilization rate, or sperm motility. However, maternal inbreeding decreased reproductive effort and hatching rate, and paternal inbreeding decreased sperm longevity, curvilinear velocity, and competitiveness. Our results show evidence of inbreeding depression in the gonadal development and reproductive capacity of C. gigas, which could help us in a better understanding and management of inbreeding in oyster aquaculture.

Preliminary Study on Expression and Function of the Chicken W Chromosome Gene MIER3 in Embryonic Gonads.

The sex chromosomes of birds are designated Z and W. The male is homogamous (ZZ), and the female is heterogamous (ZW). The chicken W chromosome is a degenerate version of the Z chromosome and harbors only 28 protein-coding genes. We studied the expression pattern of the W chromosome gene MIER3 (showing differential expression during gonadogenesis) in chicken embryonic gonads and its potential role in gonadal development. The W copy of MIER3 (MIER3-W) shows a gonad-biased expression in chicken embryonic tissues which was different from its Z copy. The overall expression of MIER3-W and MIER3-Z mRNA and protein is correlated with the gonadal phenotype being higher in female gonads than in male gonads or female-to-male sex-reversed gonads. Chicken MIER3 protein is highly expressed in the nucleus, with relatively lower expression in the cytoplasm. Overexpression of MIER3-W in male gonad cells suggested its effect on the GnRH signaling pathway, cell proliferation, and cell apoptosis. MIER3 expression is associated with the gonadal phenotype. MIER3 may promote female gonadal development by regulating EGR1 and αGSU genes. These findings enrich our knowledge of chicken W chromosome genes and support a more systematic and in-depth understanding of gonadal development in chickens.

Influence of different feeding rates of polychaete worms, Eulalia viridis (Annelida, Polychaeta), on the gonad development of male Penaeus semisulcatus (Decapoda, Dendrobranchiata) under captive conditions

Abstract Penaeus semisulcatus is a large growing species, attaining a maximum size of about 250 mm in total length. It is more resistant to white spot syndrome virus (WSSV) than other cultivable penaeid shrimps, which makes it a potential candidate for culture. The present study evaluated the influence of a different feeding rate of polychaete worms on the gonad development of male P. semisulcatus under captive conditions. P. semisulcatus sub-adults were obtained in the wild. The shrimps were fed with three different concentrations of polychaete worms, viz., ad libitum (T1), 5% of body weight (BW) (T2) and 10% BW (T3), and fresh sardines were fed as a Control (C) diet, all for a period of 60 days. Sampling was done once in 15 days and the bio-growth parameters were recorded. The gonads were harvested for histological analysis. The maximum weight gain (10.19 g), mean weight gain percentage (85.20%), mean daily growth rate (DGR) (0.169833) and mean specific growth rate (SGR) (0.45) were found in shrimps fed with the polychaete worm diet at 5% BW. The estimated bio-growth parameter values were statistically significant when analysed using One way ANOVA (). Histological sections of the testis showed variations in the development of the gonad between the treatments with different feeding rates during the 60 days trials. Indeed in all aspects, the development was higher in shrimps fed with polychaete worms at 5% BW. It can be concluded that feeding polychaete worms at 5% BW created a regime able to improve growth rates, gonad maturation, and quality in the development of the captive male brood stock.

A comparative account of the embryonic lineage and gonad development in two species of Rhabditidae (Nematoda)

ABSTRACT Nematodes serve as excellent models for developmental studies, with a good number of favourable properties. The family Rhabditidae is a paraphyletic group of bacterivorous nematodes showing diversity in the structure of gonads, mode of reproduction, cleavage pattern, etc. In the present paper, two species of Rhabditidae, namely Mesorhabditis paucipapillata Paetzold, 1955 and Cephaloboides anisospiculus Tahseen et al., 2017, with monodelphic and didelphic types of gonads, respectively, were selected for a comparative analysis of the embryonic patterns and trends in gonad development. The cleavage patterns of the early cell lineages were observed to vary considerably with the division of EMS after three consecutive divisions in the AB line in C. anisospiculus. The patterns of gonad development differed, with the number of branches being the key factor in determining the shape and orientation of the primordium; in contrast, vulva formation largely depended on the position and shape of the vulval opening.