Expanded expression of pro-neurogenic factor SoxB1 during larval development of gastropod Lymnaea stagnalis suggests preadaptation to prolonged neurogenesis in Mollusca.

Introduction: The remarkable diversity observed in the structure and development of the molluscan nervous system raises intriguing questions regarding the molecular mechanisms underlying neurogenesis in Mollusca. The expression of SoxB family transcription factors plays a pivotal role in neuronal development, thereby offering valuable insights into the strategies of neurogenesis. Methods: In this study, we conducted gene expression analysis focusing on SoxB-family transcription factors during early neurogenesis in the gastropod Lymnaea stagnalis. We employed a combination of hybridization chain reaction in situ hybridization (HCR-ISH), immunocytochemistry, confocal microscopy, and cell proliferation assays to investigate the spatial and temporal expression patterns of LsSoxB1 and LsSoxB2 from the gastrula stage to hatching, with particular attention to the formation of central ring ganglia. Results: Our investigation reveals that LsSoxB1 demonstrates expanded ectodermal expression from the gastrula to the hatching stage, whereas expression of LsSoxB2 in the ectoderm ceases by the veliger stage. LsSoxB1 is expressed in the ectoderm of the head, foot, and visceral complex, as well as in forming ganglia and sensory cells. Conversely, LsSoxB2 is mostly restricted to the subepithelial layer and forming ganglia cells during metamorphosis. Proliferation assays indicate a uniform distribution of dividing cells in the ectoderm across all developmental stages, suggesting the absence of distinct neurogenic zones with increased proliferation in gastropods. Discussion: Our findings reveal a spatially and temporally extended pattern of SoxB1 expression in a gastropod representative compared to other lophotrochozoan species. This prolonged and widespread expression of SoxB genes may be interpreted as a form of transcriptional neoteny, representing a preadaptation to prolonged neurogenesis. Consequently, it could contribute to the diversification of nervous systems in gastropods and lead to an increase in the complexity of the central nervous system in Mollusca.

Gonadotropin-Releasing Hormone in Regulation of Thymic Development in Rats: Profile of Thymic Cytokines.

An increasing body of recent experimental data confirms the impact of neurohormones on fetal development and function of different body systems. The synthesis of many neurohormones starts in fetal tissues before the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal systems are formed, and their high levels are detected in the bloodstream. Here, we studied the role of gonadotropin-releasing hormone (GnRH) in rat thymus development and tried to reveal possible mechanisms underlying the GnRH effects in early development. Western blotting and reverse transcription-polymerase chain reaction allowed us to identify receptor for GnRH in the fetal thymus with peak expression on embryonic days 17-18 (ED17-18). Blocking the receptors in utero on ED17 by a GnRH antagonist suppressed the concanavalin A-induced proliferative response of T cells in adults. GnRH (10-7 M) increased mRNA expression of interleukin (IL)-4, IL-10, IL-1ß, interferon γ (IFNγ), and tumor necrosis factor α (TNFα) in the thymus of 18-day fetuses after an ex vivo culture for 24 h. The increased mRNA levels of the cytokines in the thymus were accompanied by increased numbers of CD4+ T helpers. Overall, the data obtained confirm the regulatory or morphogenetic effect of GnRH on fetal thymus development mediated by synthesis of thymic cytokines.

Abolition of prenatal lipopolysaccharide-induced reproductive disorders in rat male offspring by fulvestrant.

During prenatal and early postnatal periods of development, multiple environmental factors have profound and long-lasting effects on the immune and reproductive functions. The aim of this study was to investigate the effects of maternal lipopolysaccharide (LPS) exposure (50 mg/kg, i.p.) at day 12 of pregnancy and estradiol antagonist treatment (fulvestrant, 1.5 mg/kg, s.c. in neck) at postnatal days 5-14 (PND5-14) with high estradiol levels on reproductive parameters in adult rat males. Serum steroid concentrations were measured in male offspring at PND80 by ELISA. Body, testis weights and ano-genital distance (AGD) were recorded at different stages of postnatal development. Testis was also processed to cytohistological studies at PND80. Our results demonstrate that body weight was decreased from PND14 to 30 after prenatal LPS treatment and was increased after fulvestrant treatment. AGD was decreased after prenatal LPS treatment and was increased after fulvestrant injections. Testis weight, testosterone level, seminiferous tubule diameter, and number of Sertoli and spermatid cells were also decreased in rats exposed prenatally to LPS and were restored to the normal control level after fulvestrant treatment. According to results, we can conclude that the development of sexual disorders in males after prenatal immune stress is potentiated by estradiol during the pre-pubertal period.

Disruptions in the hypothalamic-pituitary-gonadal axis in rat offspring following prenatal maternal exposure to lipopolysaccharide.

Postnatal treatment with bacterial endotoxin lipopolysaccharide (LPS) changes the activity of the hypothalamic-pituitary-gonadal (HPG) axis and the gonadotropin-releasing hormone (GnRH) surge in rats. Exposure to an immune challenge in the critical periods of development has profound and long-lasting effects on the stress response, immune, metabolic, and reproductive functions. Prenatal LPS treatment delays the migration of GnRH neurons associated with increased cytokine release in maternal and fetal compartments. We investigated the effects of a single maternal exposure to LPS (18 µg/kg, i.p.) on day 12 (embryonic day (E)12) of pregnancy on reproductive parameters in rat offspring. Hypothalamic GnRH content, plasma luteinizing hormone (LH), testosterone, and estradiol concentrations were measured in both male and female offsprings at different stages of postnatal development by RIA and ELISA (n = 10 each per group). Body weight and in females day of vaginal opening (VO) were recorded. In offspring exposed to LPS prenatally, compared with controls, body weight was decreased in both sexes at P5 and P30; in females, VO was delayed; hypothalamic GnRH content was decreased at postnatal days 30-60 (P30-P60) in both sexes; plasma LH concentration was decreased at P14-P60 in females; plasma concentrations of testosterone/estradiol were increased at P14 in females, and plasma estradiol was increased at P14 in males. Hence activation of the maternal immune system by LPS treatment at a prenatal critical period leads to decreased GnRH and LH levels in pre- and postpubertal life and sex steroid imbalance in the prepubertal period, and delayed sexual maturation of female offspring.

Ontogenesis of rat immune system: Proteasome expression in different cell populations of the developing thymus.

Immune proteasomes in thymus are involved in processing of self-antigens, which are presented by MHC class I molecules for rejection of autoreactive thymocytes in adults and probably in perinatal rats. The distribution of immune proteasome subunits LMP7 and LMP2 in thymic cells have been investigated during rat perinatal ontogenesis. Double immunofluorescent labeling revealed LMP7 and LMP2 in thymic epithelial and dendritic cells, as well as in CD68 positive cells - macrophages, monocytes - at all developmental stages. LMP2 and LMP7 were also detected by flow cytometry in almost all thymic CD90 lymphocytes through pre- and postnatal ontogenesis. Our results demonstrate that the immune proteasomes are expressed in all types of thymic antigen presenting cells during perinatal ontogenesis, suggesting the establishment of the negative selection in the thymus at the end of fetal life. The observation of the immune proteasome expression in T lymphocytes suggests their role in thymocyte differentiation besides antigen processing in thymus.