The ancient source of a distinct gene family encoding proteins featuring RING and C(3)H zinc-finger motifs with abundant expression in developing brain and nervous system.

Intronless genes can arise by germline retrotransposition of a cDNA originating as mRNA from an intron-containing source gene. Previously, we described several members of a family of intronless mammalian genes encoding a novel class of zinc-finger proteins, including one that shows imprinted expression and one that escapes X-inactivation. We report here the identification and characterization of the Makorin ring finger protein 1 gene (MKRN1), a highly transcribed, intron-containing source for this family of genes. Phylogenetic analyses clearly indicate that the MKRN1 gene is the ancestral founder of this gene family. We have identified MKRN1 orthologs from human, mouse, wallaby, chicken, fruitfly, and nematode, underscoring the age and conservation of this gene. The MKRN gene family encodes putative ribonucleoproteins with a distinctive array of zinc-finger motifs, including two to four C(3)H zinc-fingers, an unusual Cys/His arrangement that may represent a novel zinc-finger structure, and a highly conserved RING zinc-finger. To date, we have identified nine MKRN family loci distributed throughout the human genome. The human and mouse MKRN1 loci map to a conserved syntenic group near the T-cell receptor beta cluster (TCRB) in chromosome 7q34-q35 and chromosome 6A, respectively. MKRN1 is widely transcribed in mammals, with high levels in murine embryonic nervous system and adult testis. The ancient origin of MKRN1, high degree of conservation, and expression pattern suggest important developmental and functional roles for this gene and its expressed family members.

Concerted regulation and molecular evolution of the duplicated SNRPB'/B and SNRPN loci.

The human small nuclear ribonucleoprotein SNRPB ' /B gene is alternatively spliced to produce the SmB or SmB' spliceosomal core proteins. An ancestral duplication gave rise to the closely related SNRPN paralog whose protein product, SmN, replaces SmB'/B in brain. However, the precise evolutionary and functional relationship between these loci has not been clear. Genomic, cDNA and protein analyses presented here in chicken, two marsupials (South American opossum and tammar wallaby), and hedgehog, suggest that the vertebrate ancestral locus produced the SmB' isoform. Interestingly, three eutherians exhibit radically distinct splice choice expression profiles, producing either exclusively SmB in mouse, both SmB and SmB' in human, or exclusively SmB' in hedgehog. The human SNRPB ' /B locus is biallelically unmethylated, unlike the imprinted SNRPN locus which is unmethyl-ated only on the expressed paternal allele. Western analysis demonstrates that a compensatory feedback loop dramatically upregulates SmB'/B levels in response to the loss of SmN in Prader-Willi syndrome brain tissue, potentially reducing the phenotypic severity of this syndrome. These findings imply that these two genes encoding small nuclear ribonucleoprotein components are subject to dosage compensation. Therefore, a more global regulatory network may govern the maintenance of stoichiometric levels of spliceosomal components and may constrain their evolution.

Ketamine blocks a conditioned taste aversion (CTA) in neonatal rats.

These experiments explored the effects of glutamate, N-methyl-D-aspartate (NMDA) receptor blockade on the formation, retention, and expression of conditioned taste aversion (CTA) in young rats. Previous data from our laboratory suggested that ketamine administration potentiates a CTA in E18 rat fetuses. The current studies investigated this phenomenon in neonates. High-pressure liquid chromatography (HPLC) methods were used to determine the amount of ketamine that must be injected intraperitoneally (i.p.) to achieve brain ketamine levels in neonates comparable to those found in the fetuses from our previous experiments. Then, on their day of birth, Sprague-Dawley rat pups received injections of either 0.1, 10, or 70 mg/kg of ketamine HCI, i.p. or a Sal control injection. One-half hour later, pups were injected orally with either Saccharin (Sac; 10 microL of 0.3%) or water followed by an injection of either lithium chloride (LiCl; 81 mg/kg) or Sal (i.p.). The CTA was evaluated in two different tests. Two weeks after conditioning, the dam was anesthetized and the frequency with which pups attached to Sac-painted nipples versus nipples painted with water was measured (i.e., the nipple taste test, NTT). Controls for state-dependent learning were run in which 10 mg/kg of ketamine or saline (Sal) was administered before both taste aversion conditioning and the NTT. After weaning, the CTA was also evaluated by measuring the amount of Sac (0.3%) or water consumed during a two-bottle test. Neonates that received Sal control injections before the Sac + LiCl pairing acquired CTAs and avoided Sac-painted nipples. However, the pups injected with ketamine on the conditioning day only (P0) did not avoid Sac-painted nipples (as compared to controls). Pups that had ketamine both at the time of CTA training and testing, or just before the NTT, also failed to avoid Sac-painted nipples. Ketamine's acute effects apparently influenced the outcome of the NTT of state-dependent control subjects. Rat pups that received the highest doses of ketamine (10 or 70 mg/kg) and tasted Sac on P0 later failed to show a neophobia for Sac-painted nipples. Whereas, rat pups that received the high dose of ketamine and water on P0, later exhibited a neophobic response. These data suggest that ketamine did not impair the animal's ability to taste Sac. These data reflecting a ketamine-induced blockade of neonatal CTAs may be contrasted with our previous findings in which ketamine potentiated fetal CTAs. However, they are in consonance with data from adult rats suggesting that ketamine can cause an amnesia for CTAs. NMDA receptor blockade may shape memory formation in a manner that is dependent on the stage of brain development.