Neurogenesis in the neonatal rat hippocampus is regulated by sexually dimorphic epigenetic modifiers.

BACKGROUND: Neurogenesis in the hippocampus endures across the lifespan but is particularly prolific during the first postnatal week in the developing rodent brain. The majority of new born neurons are in the dentate gyrus (DG). The number of new neurons born during the first postnatal week in the DG of male rat pups is about double the number in females. In other systems, the rate of cell proliferation is controlled by epigenetic modifications in stem cells. We, therefore, explored the potential impact of DNA methylation and histone acetylation on cell genesis in the developing DG of male and female rats. METHODS: Cell genesis was assessed by quantification of BrdU + cells in the DG of neonatal rats following injections on multiple days. Methylation and acetylation were manipulated pharmacologically by injection of well vetted drugs. DNA methylation, histone acetylation and associated enzyme activity were measured using commercially available colorimetric assays. mRNA was quantified by PCR. Multiple group comparisons were made by one- or two-way ANOVA followed by post-hoc tests controlling for multiple comparisons. Two groups were compared by t test. RESULTS: We found higher levels of DNA methylation in male DG and treatment with the DNA methylating enzyme inhibitor zebularine reduced the methylation and correspondingly reduced cell genesis. The same treatment had no impact on either measure in females. By contrast, treatment with a histone deacetylase inhibitor, trichostatin-A, increased histone acetylation in the DG of both sexes but increased cell genesis only in females. Females had higher baseline histone deacetylase activity and greater inhibition in response to trichostatin-A treatment. The mRNA levels of the proproliferative gene brain-derived neurotrophic factor were greater in males and reduced by inhibiting both DNA methylation and histone deacetylation only in males. CONCLUSIONS: These data reveal a sexually dimorphic epigenetically based regulation of neurogenesis in the DG but the mechanisms establishing the distinct regulation involving DNA methylation in males and histone acetylation in females is unknown.

Multiple GnRHs present in a teleost species are encoded by separate genes: analysis of the sbGnRH and cGnRH-II genes from the striped bass, Morone saxatilis.

GnRH is a neuropeptide which plays an essential role in the control of reproductive fitness for all vertebrates. Increasing evidence suggests that multiple forms of GnRH may exist in most vertebrate brains. Southern blot analysis of the three GnRHs known to be present in perciform fish, the seabream (sb)GnRH, the salmon(s) GnRH and the chicken (c) GnRH-II, demonstrates that each is present as a single gene copy in the genome of the striped bass, Morone saxatilis. In order to investigate the physiological consequences of multiple GnRHs in a single vertebrate species, we have isolated and characterized two of the GnRH genes, those for sbGnRH and cGnRH-II. Computer analysis of 3.5 kb of sequence upstream of the sbGnRH gene reveals a number of consensus DNA binding sites which implicate steroids, such as estrogen and glucocorticoids, and the steroidogenic transcription factor, SF-1, as being involved in the regulation of sbGnRH gene expression. Sequence analysis of the cGnRH-II gene reveals evidence of multiple promoters. Expression studies using (1) solution hybridization-RNAse protection mapping with several RNA probes directed at various regions of the proGnRH gene, (2) primer extension assays using two specific oligonucleotide primers, and (3) reverse transcription PCR with several oligonucleotide primers on cGnRH-II transcripts demonstrate that the cGnRH-II gene initiates transcription at numerous sites using a TATA-less promoter within the brains of sexually mature striped bass. This study is the first to characterize and compare the promoter structures of two GnRH genes present in a single vertebrate species.