Zebrafish Slit2 and Slit3 Act Together to Regulate Retinal Axon Crossing at the Midline.

Slit-Robo signaling regulates midline crossing of commissural axons in different systems. In zebrafish, all retinofugal axons cross at the optic chiasm to innervate the contralateral tectum. Here, the mutant for the Robo2 receptor presents severe axon guidance defects, which were not completely reproduced in a Slit2 ligand null mutant. Since slit3 is also expressed around this area at the stage of axon crossing, we decided to analyze the possibility that it collaborates with Slit2 in this process. We found that the disruption of slit3 expression by sgRNA-Cas9 injection caused similar, albeit slightly milder, defects than those of the slit2 mutant, while the same treatment in the slit2-/-mz background caused much more severe defects, comparable to those observed in robo2 mutants. Tracking analysis of in vivo time-lapse experiments indicated differential but complementary functions of these secreted factors in the correction of axon turn errors around the optic chiasm. Interestingly, RT-qPCR analysis showed a mild increase in slit2 expression in slit3-deficient embryos, but not the opposite. Our observations support the previously proposed "repulsive channel" model for Slit-Robo action at the optic chiasm, with both Slits acting in different manners, most probably relating to their different spatial expression patterns.

Raising overlapping litters: Differential activation of rat maternal neural circuitry after interacting with newborn or juvenile pups.

The maternal behaviour of a rat dynamically changes during the postpartum period, adjusting to the characteristics and physiological needs of the pups. This adaptation has been attributed to functional modifications in the maternal circuitry. Maternal behaviour can also flexibly adapt according to different litter compositions. Thus, mothers with two overlapping litters can concurrently take care of neonate and juvenile pups, mostly directing their attention to the newborns. We hypothesised that the maternal circuitry of these mothers would show a differential activation pattern after interacting with pups depending on the developmental stage of their offspring. Thus, we evaluated the activation of several areas of the maternal circuitry in mothers of overlapping litters, using c-Fos immunoreactivity as a marker of neuronal activation, after interacting with newborns or juveniles. The results showed that mothers with overlapping litters display different behavioural responses towards their newborn and their juvenile pups. Interestingly, these behavioural displays co-occurred with specific patterns of activation of the maternal neural circuitry. Thus, a similar expression of c-Fos was observed in some key brain areas of mothers that interacted with newborns or juveniles, such as the medial preoptic area and the nucleus accumbens, whereas a differential activation was quantified in the ventral region of the bed nucleus of the stria terminalis, the infralimbic and prelimbic subregions of the medial prefrontal cortex and the basolateral and medial nuclei of the amygdala. We posit that the specific profile of activation of the neural circuitry controlling maternal behaviour in mothers with overlapping litters enables dams to respond adequately to the newborn and the juvenile pups.

The Expression of Hypoxia-Induced Gene 1 (Higd1a) in the Central Nervous System of Male and Female Rats Differs According to Age.

HIGD1A (hypoxia-induced gene domain protein-1a), a mitochondrial inner membrane protein present in various cell types, has been mainly associated with anti-apoptotic processes in response to stressors. Our previous findings have shown that Higd1a mRNA is widely expressed across the central nervous system (CNS), exhibiting an increasing expression in the spinal cord from postnatal day 1 (P1) to 15 (P15) and changes in the distribution pattern from P1 to P90. During the first weeks of postnatal life, the great plasticity of the CNS is accompanied by cell death/survival decisions. So we first describe HIGD1A expression throughout the brain during early postnatal life in female and male pups. Secondly, based on the fact that in some areas this process is influenced by the sex of individuals, we explore HIGD1A expression in the sexual dimorphic nucleus (SDN) of the medial preoptic area, a region that is several folds larger in male than in female rats, partly due to sex differences in the process of apoptosis during this period. Immunohistochemical analysis revealed that HIGD1A is widely but unevenly expressed throughout the brain. Quantitative Western blot analysis of the parietal cortex, diencephalon, and spinal cord from both sexes at P1, P5, P8, and P15 showed that the expression of this protein is predominantly high and changes with age but not sex. Similarly, in the sexual dimorphic nucleus, the expression of HIGD1A varied according to age, but we were not able to detect significant differences in its expression according to sex. Altogether, these results suggest that HIGD1A protein is expressed in several areas of the central nervous system following a pattern that quantitatively changes with age but does not seem to change according to sex.

Expression of dmrt1 and sox9 during gonadal development in the Siberian sturgeon (Acipenser baerii).

The sex differentiation period of the Siberian sturgeon was investigated through expression profiling of two testicular markers (dmrt1 and sox9). At the molecular level, a clear sexual dimorphism of dmrt1 and sox9 was observed in 3-year-old fish with immature gonads, in which males showed higher expression of these genes. Among 16-month-old sturgeons cultured in Uruguay, gonad morphology analyses showed one group of fish with undifferentiated gonads and a second group which had started their histological differentiation into ovaries or testes. dmrt1 showed a significantly higher expression in testes of recently differentiated fish, but this was not the case for sox9. In undifferentiated fish, we observed two clearly different groups in terms of expression: one group of fish over-expressing male markers (dmrt1, sox9) and another group of fish showing very low expression of these genes. This suggests that fish undergoing male differentiation can be identified by their profiles of gene expression before they undergo morphological differentiation.

Expression and phylogeny of candidate genes for sex differentiation in a primitive fish species, the Siberian sturgeon, Acipenser baerii.

The molecular mechanisms underlying testis differentiation in basal actinopterygian fish remains poorly understood. The sex differentiation period was investigated in the Siberian sturgeon, Acipenser baerii, by expression profiling of Sertoli cell transcription factors (dmrt1, sox9) that control testis differentiation in vertebrates; Leydig cell factors (cyp17a1, star) affecting androgen production; the androgen receptor (ar); a growth factor controlling testis development (igf1); and a gene coding for a gonadotropin hormone (lh). Two genes were characterised for the first time in the Siberian sturgeon (dmrt1, cyp17a1), while the others came from public databases. Sturgeon gonad development is very slow, with a late sexual differentiation time during their juvenile stage, and are still immature at 3 years of age. Immature fish showed a sex-dimorphic pattern; all the genes studied displayed a higher expression level in male gonads. We took advantage of the presence of juvenile fish with pre- and post-differentiated gonads (16 and 18 months old) to characterise them at the molecular level. The post-differentiated fish displayed a sex dimorphism of gene expression in their gonads for all genes studied, with the exception of sox9. The trends in undifferentiated fish lead us to propose that sturgeons undergoing male differentiation express high levels of Sertoli cell factors (dmrt1, sox9) and of genes involved in the production and receptivity of androgens (cyp17a1, star and ar) together with lh. Expression profiles and phylogenetic studies suggest that these genes are potential regulators of testis development in the Siberian sturgeon.

Temporal distribution of Hig-1 (hypoxia-induced gene 1) mRNA and protein in rat spinal cord: changes during postnatal life.

Several cellular and molecular events responsible for the development of the central nervous system (CNS), particularly those related to the development of ordered neural connections, occur during the first days of postnatal life, being days 1 through 10 a critical period to reach maturity and establish innervations. We have previously characterized hypoxia-induced gene 1 (Hig-1) and described an increase in its expression from day 1 to 15 of postnatal life in the spinal cord. Hig-1 mRNA has an open reading frame for a 93 amino acid protein, but its function has not been completely elucidated. Recently, several analyses in many cell types have related Hig-1 expression with differentiation or cell death/survival balance. With the aim of further characterizing the presence of Hig-1 in the CNS, we analyzed the cellular distribution of HIG-1 protein in rat's spinal cord at postnatal days 1, 8, 15, and 90 (P1-P90). We found an interesting change in the protein expression pattern, shifting from neurons at P1 to glial cells at P90, which points towards a functional role for this protein in the spinal cord throughout development. We also compared the protein distribution with the cellular distribution of the mRNA and of an antisense RNA.

Evidence of two co-circulating genetic lineages of canine distemper virus in South America.

Canine distemper virus (CDV) is the etiological agent of a multisystemic infection that affects different species of carnivores and is responsible for one of the main diseases suffered by dogs. Recent data have shown a worldwide increase in the incidence of the disease, including in vaccinated dog populations, which necessitates the analysis of circulating strains. The hemagglutinin (H) gene, which encodes the major antigenic viral protein, has been widely used to determine the degree of genetic variability and to associate CDVs in different worldwide circulating lineages. Here, we obtained the sequence of the first full-length H gene of field South American CDV strains and compared it with sequences of worldwide circulating field strains and vaccine viruses. In South America, we detect two co-circulating lineages with different prevalences: the Europe 1 lineage and a new South America 2 lineage. The Europe 1 lineage was the most prevalent in South America, and we suggest renaming it the Europe 1/South America 1 lineage. The South America 2 lineage was found only in Argentina and appears related to wild CDV strains. All South American CDV strains showed high amino-acid divergence from vaccine strains. This genetic variability may be a possible factor leading to the resurgence of distemper cases in vaccinated dog populations.

Early thyroid hormone-induced gene expression changes in N2a-ß neuroblastoma cells.

Thyroid hormone has long been known to regulate neural development. Hypothyroidism during pregnancy and early postnatal period has severe neurological consequences including even mental retardation. The purpose of this study was to characterize gene expression pattern during thyroid hormone-induced differentiation of neuro-2a ß cells in order to select "direct response genes" for further analysis. In this neuroblastoma cell line, thyroid hormone blocks proliferation and induces differentiation. Changes in gene expression level were examined after a T3 treatment of 3 and 24 h using cDNA arrays. Sixteen genes were significantly up-regulated and 79 down-regulated by T3 treatment. Five up-regulated genes not previously described as regulated by thyroid hormone and selected for their putative significance to understand T3 action on cell differentiation, were verified by RT-PCR analysis. The transcription factors Phox2a and basic helix-loop-helix domain containing, class B2 mRNAs exhibited a clear increase after 3- and 24-h treatment. The guanine-nucleotide exchange factor RalGDS was greatly up-regulated after 3-h treatment but not 24 h after. The results suggest an early involvement of these genes in T3 action during neuroblastoma cell differentiation probably mediating later changes in gene expression pattern.

Characterization of hypoxia induced gene 1: expression during rat central nervous system maturation and evidence of antisense RNA expression.

Although recent studies have provided a detailed understanding of cellular interactions occurring during the development of the CNS, little is known about the molecular signals which during the peri and postnatal periods ensure its maturation and functionality. Using the mammalian spinal cord as a model, we have designed experiments to examine the main changes in gene expression occurring during this critical transition. In this paper we describe the cloning and characterization of the rat hypoxia induced gene-1 (Hig-1), its expression pattern during spinal cord maturation and in situ localization of its mRNA. We show an increase in Hig-1 expression between P1 and P15 in the spinal cord and a differential spatial pattern. In the P1 spinal cord we observed preferential expression in regions of dorsal laminae II and III and laminae IX ventrally; while in P8, the distribution was more widespread and overall expression was increased. Hig-1 is also widely expressed in the brain. Results of in situ hybridization experiments, as well as particular features concerning ESTs, led us to propose the expression of an antisense mRNA. Primer-specific RTPCR demonstrates the presence of this aHig-1 transcript whose structure has not yet been characterized. The high homology between putative rHig-1 protein and human- and murine-predicted sequences, as well as its characteristic expression in the Central Nervous System, are indicative of a specific role which could be related to apoptosis signaling during postnatal maturation.