Freshwater fish and the Cretaceous/Palaeogene boundary: a critical assessment of survivorship patterns.

Mass extinctions are major influences on both the phylogenetic structure of the modern biota and our ability to reconstruct broad-based patterns of evolutionary history. The most recent mass extinction is also the most famous-that which implicates a bolide impact in defining the Cretaceous/Palaeogene boundary (K/Pg). Although the biotic effects of this event receive intensive scrutiny, certain ecologically important and diverse groups remain woefully understudied. One such group is the freshwater ray-finned fishes (Actinopterygii). These fish represent 25% of modern vertebrate diversity, yet the isolated and fragmentary nature of their K/Pg fossil record limits our understanding of their diversity dynamics across this event. Here, we address this problem using diversification analysis of molecular-based phylogenies alongside a morphotype analysis of fossils recovered from a unique site in the Denver Basin of western North America that provides unprecedented K/Pg resolution. Our results reveal previously unrecognized signals of post-K/Pg diversification in freshwater clades and suggest that the change was driven by localized and sporadic patterns of extinction. Supported inferences regarding the effects of the K/Pg event on freshwater fish also inform our expectations of how freshwater faunas might recover from the current biodiversity crisis.

Myeloid expression of the AP-1 transcription factor JUNB modulates outcomes of type 1 and type 2 parasitic infections.

Activation of macrophages is a key step in the initiation of immune responses, but the transcriptional mechanisms governing macrophage activation during infection are not fully understood. It was recently shown that the AP-1 family transcription factor JUNB positively regulates macrophage activation in response to Toll-like receptor agonists that promote classical or M1 polarization, as well as to the cytokine interleukin-4 (IL-4), which elicits an alternatively activated or M2 phenotype. However, a role for JUNB in macrophage activation has never been demonstrated in vivo. Here, to dissect the role of JUNB in macrophage activation in a physiological setting, mice lacking JUNB specifically in myeloid cells were tested in two infection models: experimental cerebral malaria, which elicits a pathological type 1 immune response, and helminth infection, in which type 2 responses are protective. Myeloid-restricted deletion of Junb reduced type 1 immune activation, which was associated with reduced cerebral pathology and improved survival during infection with Plasmodium berghei. Myeloid JUNB deficiency also compromised type 2 activation during infection with the hookworm Nippostrongylus brasiliensis, leading to diminished cytokine production and eosinophil recruitment and increased parasite burden. These results demonstrate that JUNB in myeloid cells shapes host responses and outcomes during type 1 and type 2 infections.

Systematic analysis of the MAPK signaling network reveals MAP3K-driven control of cell fate.

The classic network of mitogen-activated protein kinases (MAPKs) is highly interconnected and controls a diverse array of biological processes. In multicellular eukaryotes, the MAPKs ERK, JNK, and p38 control opposing cell behaviors but are often activated simultaneously, raising questions about how input-output specificity is achieved. Here, we use multiplexed MAPK activity biosensors to investigate how cell fate control emerges from the connectivity and dynamics of the MAPK network. Through chemical and genetic perturbation, we systematically explore the outputs and functions of all the MAP3 kinases encoded in the human genome and show that MAP3Ks control cell fate by triggering unique combinations of MAPK activity. We show that these MAPK activity combinations explain the paradoxical dual role of JNK signaling as pro-apoptotic or pro-proliferative kinase. Overall, our integrative analysis indicates that the MAPK network operates as a unit to control cell fate and shifts the focus from MAPKs to MAP3Ks to better understand signaling-mediated control of cell fate.

[Genetic characteristics of hantavirus from rodents in port area of Ningde , Fujian province in the summer of 2020].

Objective: To explore the genetic characteristics and evolution of hantavirus carried by rodents in port area of Ningde in Fujian province in the summer of 2020. Methods: Rodents were captured in the port area of Ningde, the RNA was extracted from rodent lung tissues and detected by using specific kit. The positive samples were used for whole-genome sequencing of the virus. Bioinformatics software was used for the analysis on the similarity and genetic variation of the sequences. Results: A total of 112 rodents were captured, including 5 Rattus norvegicus and 2 Rattus flavipectus, the positive rate of hantavirus was 6.25% (7/112). By virus gene sequencing, two hantavirus complete genome sequences were obtained (named as FJ35 and FJ36, GenBank accession numbers: MW449188-MW449193). The genetic analysis results showed that the hantavirus detected in positive samples were SEOV and shared 99% nucleotide similarity with hantavirus strains LZSF21 and JX20140581 isolated from Shandong province. Phylogenetic analysis using the maximum likelihood method showed that the hantavirus detected in positive samples belonged to S3 subtype, sharing the same subtype with hantavirus strains Z37 from Zhejiang province, LZSF21 from Shandong province, and zy27 and Gongzhuling 415 from northeastern China. Compared with FJ372, the amino acid variation of N259S was observed at sites 251-264 of nucleoprotein, which might be related to antigenicity. Another variation of Q81R was observed in glycoprotein compared with SEOV 80-39 segment of coded amino acid of international reference strain, which might also cause the change in antigenicity. Conclusion: The high positive rate of hantavirus in rodents in the port area of Ningde- would increase the risk of natural human infection and epidemic in local area. The hantavirus positive rodents in this focus might be from an endemic area in Shandong. It is necessary to strengthen the imported rodent control in the port area of Ningde. The virus detected in 2 positive samples belonged to SEOV subtype Ⅲ and shared high homologies of nucleotides and amino acid sequences with the hantavirus strains in surrounding area. However, some slight variations occurred in glycoprotein and nucleoprotein amino acid sequences, which might cause changes in its antigeniity.

Role of dimerization of the membrane-associated growth factor kit ligand in juxtacrine signaling: the Sl17H mutation affects dimerization and stability-phenotypes in hematopoiesis.

The Kit ligand (KL)/Kit receptor pair functions in hematopoiesis, gametogenesis, and melanogenesis. KL is encoded at the murine steel (Sl) locus and encodes a membrane growth factor which may be proteolytically processed to produce soluble KL. The membrane-associated form of KL is critical in mediating Kit function in vivo. Evidence for a role of cytoplasmic domain sequences of KL comes from the Sl17H mutation, a splice site mutation that replaces the cytoplasmic domain with extraneous amino acids. Using deletion mutants and the Sl17H allele, we have investigated the role of the cytoplasmic domain sequences of KL in biosynthetic processing and cell surface presentation. The normal KL protein products are processed for cell surface expression, where they form dimers. Both Sl17H and the cytoplasmic deletion mutants of KL were processed to the cell surface; however, the rate of transport and protein stability were affected by the mutations. Deletion of cytoplasmic domain sequences of KL did not affect dimerization of KL. In contrast, dimerization of the Sl17H protein was reduced substantially. In addition, we have characterized the hematopoietic cell compartment in Sl17H mutant mice. The Sl17H mutation has only minor effects on hematopoiesis. Tissue and peritoneal mast cell numbers were reduced in mutant mice as well as in myeloid progenitors. Interestingly, long-term bone marrow cultures from Sl17H mice did not sustain the long-term production of hematopoietic cells. In addition, homing of normal hematopoietic progenitors to the spleen of irradiated Sl17H/Sl17H recipient mice was diminished in transplantation experiments, providing evidence for a role of Kit in homing or lodging. These results demonstrate that the membrane forms of KL exist as homodimers on the cell surface and that dimerization may play an important role in KL/Kit-mediated juxtacrine signaling.

Differential expression and processing of two cell associated forms of the kit-ligand: KL-1 and KL-2.

The c-kit ligand, KL, and its receptor, the proto-oncogene c-kit are encoded, respectively, at the steel (Sl) and white spotting (W) loci of the mouse. Both Sl and W mutations affect cellular targets in melanogenesis, gametogenesis, and hematopoiesis during development and in adult life. Although identified as a soluble protein, the predicted amino acid sequence of KL indicates that it is an integral transmembrane protein. We have investigated the relationship between the soluble and the cell associated forms of KL and the regulation of their expression. We show that the soluble form of KL is generated by efficient proteolytic cleavage from a transmembrane precursor, KL-1. An alternatively spliced version of KL-1, KL-2, in which the major proteolytic cleavage site is removed by splicing, is shown to produce a soluble biologically active form of KL as well, although with somewhat diminished efficiency. The protein kinase C inducer phorbol 12-myristate 13-acetate and the calcium ionophore A23187 were shown to induce the cleavage of both KL-1 and KL-2 at similar rates, suggesting that this process can be regulated differentially. Furthermore, proteolytic processing of both the KL-1 and KL-2 transmembrane protein products was shown to occur on the cell surface. The relative abundance of KL-1 and KL-2 is controlled in a tissue-specific manner. Sld, a viable steel allele, is shown to encode a biologically active secreted mutant KL protein. These results indicate an important function for both the soluble and the cell associate form of KL. The respective roles of the soluble and cell associated forms of KL in the proliferative and migratory functions of c-kit are discussed.

Effects of simulated Fowler-Stephens orchiopexy on testicular structure and function in rats.

To determine the effects of the Fowler-Stephens orchiopexy (FSO) on testicular structure and function, young rats underwent simulated FSO and concurrent contralateral orchiectomy, unilateral orchiectomy, or no operation. Rats were killed at 1, 2, 4, 6, 8, and 10 weeks postoperation, and serum testosterone, as well as testicular concentrations of the enzymes LDH & SDH, protein markers of testicular germinal cell development, were measured at the time of death. Although LDH and SDH concentrations decreased by 45 per cent in testes after simulated FSO at 4 weeks, control testes showed a 5 per cent increase in these enzymes. Serum testosterone decreased to one-fourth the initial value in rats after FSO, whereas control rats showed a slight increase. Within 2 weeks after simulated FSO, spermatocytes and sperm were sparse and there was marked disruption of tubular morphology; after 4 weeks interstitial fibrosis became prominent. Only a rare testis with good collateral vessels and resultant good histologic appearance and enzyme profile survived the FSO procedure, and these testes were considerably smaller than the controls.

[Testicular morphological and biochemical changes after Fowler-Stephens orchiopexy in rats].

Fowler-Stephens orchiopexy is the most common method of treating high-positioned undescended testes. Its success rate has been reported to be as high as 50-70% based on palpation or in a few circumstances on biopsy. Although it is convenient to evaluate testicular function by palpation and/or biopsy, this method is very subjective and is not scientific enough. To determine testicular function more precisely and objectively, we performed the Fowler-Stephens orchiopexy on Sprague-Dawley rats and observed the morphological and biochemical changes, including assays of LDH, SDH and the testosterone level. In our morphological study, with the use of Fowler-Stephens orchiopexy, only 17% (3/18) of the rat tests could be salvaged. The others revealed either necrosis or fibrosis. Testicular LDH, checked at the 4th postoperative week, revealed 0.62 +/- 0.04 U/mg which was statistically different (p less than 0.05) from that of the control group and the hemicastrated group (0.77 +/- 0.05 U/mg and 0.76 +/- 0.07 U/mg, respectively). The SDH obtained from the testes also revealed significant differences between the study group and the control and hemicastrated groups. Values obtained were 2.67 +/- 0.15 mU/mg, 3.77 +/- 0.4 mU/mg and 3.77 +/- 0.33 mU/mg, respectively (p less than 0.05). Using electrophoresis, 3 out of 18 rats had typical X bands, which is the classical picture of a normal mature testis. In contrast, the others showed faint X bands at the 2nd postoperative week, which subsequently faded thereafter. During testicular ischemia, the Leydig cells are more resistant than the Sertoli cells and the germinal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence and risk factors for age-related macular degeneration in the elderly Chinese population in south-western Taiwan: the Puzih eye study.

AIM: This study aimed to ascertain the prevalence of and the risk factors associated with early and late age-related macular degeneration (AMD) among Chinese individuals aged ≥65 years residing in Puzih, Taiwan. METHODS: This population-based cross-sectional study graded digital colour photographs of the ocular fundus of 673 individuals using the Wisconsin Age-Related Maculopathy Grading System. We compared the characteristics of individuals with early and late AMD using χ(2)-analyses and described risk factors for early and late AMD using odds ratios and 95% confidence intervals. RESULTS: Individuals with late AMD were significantly older and more likely to have hypertension. Further, their sunlight exposure time was longer than that of those with early AMD, only drusen, or no AMD lesions (P<0.01). A history of hyperlipidaemia for >10 years was a significant risk factor for early AMD, while old age, hypertension for >10 years, and exposure to sunlight for >8 h per day were associated with late AMD. CONCLUSIONS: The prevalence rate of early AMD in the present study was 15.0%, which is similar to that reported for Caucasians and Japanese included in the European Eye Study and the Hisayama Study, respectively. The late AMD prevalence rate of 7.3% found among our study participants was comparable to that reported by the Greenland Inuit Eye Study and Reykjavik Study, but considerably lower than that reported for Caucasians, indicating that late AMD might be less prevalent among Asians than Caucasians.

Hipk2 cooperates with p53 to suppress γ-ray radiation-induced mouse thymic lymphoma.

A genome-wide screen for genetic alterations in radiation-induced thymic lymphomas generated from p53+/- and p53-/- mice showed frequent loss of heterozygosity (LOH) on chromosome 6. Fine mapping of these LOH regions revealed three non-overlapping regions, one of which was refined to a 0.2 Mb interval that contained only the gene encoding homeobox-interacting protein kinase 2 (Hipk2). More than 30% of radiation-induced tumors from both p53+/- and p53-/- mice showed heterozygous loss of one Hipk2 allele. Mice carrying a single inactive allele of Hipk2 in the germline were susceptible to induction of tumors by γ-radiation, but most tumors retained and expressed the wild-type allele, suggesting that Hipk2 is a haploinsufficient tumor suppressor gene for mouse lymphoma development. Heterozygous loss of both Hipk2 and p53 confers strong sensitization to radiation-induced lymphoma. We conclude that Hipk2 is a haploinsufficient lymphoma suppressor gene.

Amyloid vs FDG-PET in the differential diagnosis of AD and FTLD.

OBJECTIVE: To compare the diagnostic performance of PET with the amyloid ligand Pittsburgh compound B (PiB-PET) to fluorodeoxyglucose (FDG-PET) in discriminating between Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD). METHODS: Patients meeting clinical criteria for AD (n = 62) and FTLD (n = 45) underwent PiB and FDG-PET. PiB scans were classified as positive or negative by 2 visual raters blinded to clinical diagnosis, and using a quantitative threshold derived from controls (n = 25). FDG scans were visually rated as consistent with AD or FTLD, and quantitatively classified based on the region of lowest metabolism relative to controls. RESULTS: PiB visual reads had a higher sensitivity for AD (89.5% average between raters) than FDG visual reads (77.5%) with similar specificity (PiB 83%, FDG 84%). When scans were classified quantitatively, PiB had higher sensitivity (89% vs 73%) while FDG had higher specificity (83% vs 98%). On receiver operating characteristic analysis, areas under the curve for PiB (0.888) and FDG (0.910) were similar. Interrater agreement was higher for PiB (κ = 0.96) than FDG (κ = 0.72), as was agreement between visual and quantitative classification (PiB κ = 0.88-0.92; FDG κ = 0.64-0.68). In patients with known histopathology, overall classification accuracy (2 visual and 1 quantitative classification per patient) was 97% for PiB (n = 12 patients) and 87% for FDG (n = 10). CONCLUSIONS: PiB and FDG showed similar accuracy in discriminating AD and FTLD. PiB was more sensitive when interpreted qualitatively or quantitatively. FDG was more specific, but only when scans were classified quantitatively. PiB slightly outperformed FDG in patients with known histopathology.

Increased apoptosis, p53 up-regulation, and cerebellar neuronal degeneration in repair-deficient Cockayne syndrome mice.

Cockayne syndrome (CS) is a rare recessive childhood-onset neurodegenerative disease, characterized by a deficiency in the DNA repair pathway of transcription-coupled nucleotide excision repair. Mice with a targeted deletion of the CSB gene (Csb-/-) exhibit a much milder ataxic phenotype than human patients. Csb-/- mice that are also deficient in global genomic repair [Csb-/-/xeroderma pigmentosum C (Xpc)-/-] are more profoundly affected, exhibiting whole-body wasting, ataxia, and neural loss by postnatal day 21. Cerebellar granule cells demonstrated high TUNEL staining indicative of apoptosis. Purkinje cells, identified by the marker calbindin, were severely depleted and, although not TUNEL-positive, displayed strong immunoreactivity for p53, indicating cellular stress. A subset of animals heterozygous for Csb and Xpc deficiencies was more mildly affected, demonstrating ataxia and Purkinje cell loss at 3 months of age. Mouse, Csb-/-, and Xpc-/- embryonic fibroblasts each exhibited increased sensitivity to UV light, which generates bulky DNA damage that is a substrate for excision repair. Whereas Csb-/-/Xpc-/- fibroblasts were more UV-sensitive than either single knockout, double-heterozygote fibroblasts had normal UV sensitivity. Csb-/- mice crossed with a strain defective in base excision repair (Ogg1) demonstrated no enhanced neurodegenerative phenotype. Complete deficiency in nucleotide excision repair therefore renders the brain profoundly sensitive to neurodegeneration in specific cell types of the cerebellum, possibly because of unrepaired endogenous DNA damage that is a substrate for nucleotide but not base excision repair.

Neurotrophins: roles in neuronal development and function.

Neurotrophins regulate development, maintenance, and function of vertebrate nervous systems. Neurotrophins activate two different classes of receptors, the Trk family of receptor tyrosine kinases and p75NTR, a member of the TNF receptor superfamily. Through these, neurotrophins activate many signaling pathways, including those mediated by ras and members of the cdc-42/ras/rho G protein families, and the MAP kinase, PI-3 kinase, and Jun kinase cascades. During development, limiting amounts of neurotrophins function as survival factors to ensure a match between the number of surviving neurons and the requirement for appropriate target innervation. They also regulate cell fate decisions, axon growth, dendrite pruning, the patterning of innervation and the expression of proteins crucial for normal neuronal function, such as neurotransmitters and ion channels. These proteins also regulate many aspects of neural function. In the mature nervous system, they control synaptic function and synaptic plasticity, while continuing to modulate neuronal survival.

Cleavage of membrane-anchored growth factors involves distinct protease activities regulated through common mechanisms.

The membrane-anchored forms of transforming growth factor-alpha (TGF-alpha) and stem cell growth factors (Kit ligands) KL-1 and KL-2 are converted to soluble growth factor forms by a regulated proteolytic cleavage process. Each of these proteins is cleaved at a distinct site, however their cleavage is activated via a common set of intracellular signaling mechanisms. By using a panel of protease inhibitors, we show here that at least two cell-associated serine protease activities with distinct specificities participate in membrane growth factor cleavage. Two serine protease inhibitors of broad specificity, diisopropylfluorophosphate and 3,4-dichloroisocoumarin, prevent the cleavage of proTGF-alpha and KL-1 but not that of KL-2. Of the agents tested, N-tosyl-L-phenylalanine chloromethyl ketone and various haloenol lactone derivatives are the most potent inhibitors of cleavage of all three membrane growth factors. It is concluded that cleavage of membrane-anchored growth factors involves a proteolytic system with multiple serine protease activities regulated through common mechanisms.

Deleterious effects of testicular venous occlusion in young rats.

To determine the differences between testicular arterial and venous obstruction, the spermatic artery or vein, or both, were occluded for varying periods of time in young rats. Two months later, at the conclusion of the study, the testes were examined. Histologic degeneration after vascular obstruction was graded by a modified Johnsen's tubular biopsy score (TBS). The testicular concentrations of enzymes (lactic dehydrogenase and sorbitol dehydrogenase), known to decrease with testicular injury, were measured. TBS and seminiferous tubule diameter (STD) were found to decrease significantly after two hours of vascular occlusion and were similar regardless of whether the obstruction was produced by occlusion of arterial inflow or venous drainage, or both. Testicular concentration of enzymes decreased significantly after permanent ligation of the spermatic artery and vein, but decreased minimally when the vascular obstruction lasted less than 120 minutes. Testicular injury produced by venous occlusion was equally severe and occurred as rapidly as injury produced by arterial or combined arteriovenous occlusion. No significant injury was noted in the contralateral testes in any group.

Hepatitis B and C coinfections and persistent hepatitis B infections: clinical outcome and liver pathology after transplantation.

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are common complications after orthotopic liver transplantation (OLT), but the liver pathology and clinical outcomes of HBV infection with HCV coinfection have not been thoroughly examined. In this study, we used the polymerase chain reaction (PCR) to detect HBV and HCV in pre- and post-OLT sera of 38 patients and correlated the findings with clinical outcome and liver pathology. Of 13 patients who were HBV and HCV negative before OLT, 9 acquired HBV infection, and 4 developed acquired HBV and HCV coinfections after OLT. Persistent HBV infections were present in 10 patients. Three patients with pre-OLT HBV infections developed persistent HBV and acquired HCV coinfections after OLT; 5 with pre-OLT HCV infections developed acquired HBV and persistent HCV coinfections after OLT, and 7 had persistent HBV and HCV coinfections before and after OLT. Portal/periportal inflammation was the same in all groups; however, lobular inflammation and fibrosis were more severe in patients with persistent HBV infections and in those with acquired HBV and HCV coinfections. Two major histopathological patterns were present in patients with HBV and HCV coinfections, one with predominant features of HCV infection, and the other with those of HBV infection. Patients with post-OLT HBV and HCV coinfections had survival rates similar to those with acquired HBV infection, whereas patients with persistent HBV infections experienced more allograft loss caused by chronic hepatitis or fibrosing cytolytic hepatitis, and had a more dire clinical outcome than the others. Although the limited numbers reported in this study prevent a definitive conclusion, our data suggest that in patients with HBV and HCV coinfections, the presence of HCV may improve the clinical outcome as compared with the expected outcome of persistent HBV infection alone.

POU domain factor Brn-3a controls the differentiation and survival of trigeminal neurons by regulating Trk receptor expression.

Mice lacking the POU domain-containing transcription factor Brn-3a have several neuronal deficits. In the present paper, we show that Brn-3a plays two distinct roles during development of the trigeminal ganglion. In this ganglion, neurons expressing the neurotrophin receptors, TrkB and TrkC, are born between E9.5 and E11.5. In the absence of Brn-3a, very few neurons ever express TrkC, but TrkB-expressing neurons are present at E12.5 in elevated numbers, suggesting that Brn-3a may be a constituent of a regulatory circuit determining which Trk receptor is expressed by these early-born neurons. Most neurons expressing the neurotrophin receptor TrkA are generated between E11.5 and E13.5 in this ganglion and their initial generation is not prevented by absence of Brn-3a. However, after E12. 5, absence of Brn-3a results in a progressive loss in neuronal TrkA and TrkB expression, which leads to a massive wave of apoptosis that peaks at E15.5. Despite complete absence of the Trk receptors at E17. 5 and P0, approximately 30% of the normal complement of neurons survive to birth in Brn-3a mutants. Approximately 70% of these express the GDNF receptor subunit, c-ret; many can be sustained by GDNF, but not by NGF in culture. Thus, the vast majority of surviving neurons are probably sustained in vivo by trophic factor(s) whose receptors are not regulated by Brn-3a. In conclusion, our data indicate the specific functions of Brn-3a in controlling the survival and differentiation of trigeminal neurons by regulating expression of each of the three Trk receptors.

Formation of a full complement of cranial proprioceptors requires multiple neurotrophins.

Inactivation of neurotrophin-3 (NT3) completely blocks the development of limb proprioceptive neurons and their end organs, the muscle spindles. We examined whether cranial proprioceptive neurons of the trigeminal mesencephalic nucleus (TMN) require NT3, brain-derived neurotrophic factor (BDNF) or neurotrophin-4 (NT4) for their development. Complements of TMN neurons and masticatory muscle spindles were decreased by 62% in NT3 null mutants, 33% in BDNF null mutants, and 10% in NT4 null mutant mice at birth. The extent of proprioceptive deficiencies differed among different masticatory muscles, particularly in NT3 null mice. Masticatory muscles of embryonic mice heterozygous for the NT3(lacZneo) or BDNF(lacZ) reporter genes expressed both NT3 and BDNF, consistent with target-derived neurotrophin support of TMN neurons. Although more than 90% of TMN neurons expressed TrkB as well as TrkC receptor proteins by immunocytochemistry in wild-type newborns, TrkC or TrkB null mice exhibited only partial proprioceptive deficiencies similar to those present in NT3 or BDNF;NT4 null mice. Thus, in terms of the survival outcome, two main subpopulations of TMN neurons may exist during embryogenesis, one dependent on TrkC/NT3 functioning and the other utilizing TrkB/BDNF signaling. The differential dependence of TMN neurons on neurotrophins may reflect differential accessibility of the neurons to limiting amounts of NT3, BDNF, or NT4 in target tissues, especially if the tissue distribution or levels of BDNF, NT3, and NT4 were dynamically regulated both spatially and temporally.

Brn3a is a transcriptional regulator of soma size, target field innervation and axon pathfinding of inner ear sensory neurons.

The POU domain transcription factors Brn3a, Brn3b and Brn3c are required for the proper development of sensory ganglia, retinal ganglion cells, and inner ear hair cells, respectively. We have investigated the roles of Brn3a in neuronal differentiation and target innervation in the facial-stato-acoustic ganglion. We show that absence of Brn3a results in a substantial reduction in neuronal size, abnormal neuronal migration and downregulation of gene expression, including that of the neurotrophin receptor TrkC, parvalbumin and Brn3b. Selective loss of TrkC neurons in the spiral ganglion of Brn3a(-/-) cochlea leads to an innervation defect similar to that of TrkC(-/-) mice. Most remarkably, our results uncover a novel role for Brn3a in regulating axon pathfinding and target field innervation by spiral and vestibular ganglion neurons. Loss of Brn3a results in severe retardation in development of the axon projections to the cochlea and the posterior vertical canal as early as E13.5. In addition, efferent axons that use the afferent fibers as a scaffold during pathfinding also show severe misrouting. Interestingly, despite the well-established roles of ephrins and EphB receptors in axon pathfinding, expression of these molecules does not appear to be affected in Brn3a(-/-) mice. Thus, Brn3a must control additional downstream genes that are required for axon pathfinding.