A little over 5 years ago, the U.S. National Institutes of Health (NIH) announced the intention to develop policies to require applicants to report plans to balance male and female cells and animals in preclinical investigations. Soon thereafter, the NIH issued a request for information from the scientific community and consulted with various stakeholders. The feedback received was considered during development of policy requiring the consideration of sex as a biological variable (SABV) in NIH-funded research on vertebrate animals and humans, which went into effect for applications due on or after January 25, 2016. We identified NIH programs related to SABV and reviewed SABV-relevant scientific literature. We find that the application of SABV throughout the research process can serve as a guiding principle to improve the value of biomedical science. The NIH is engaged in ongoing efforts to develop resources to help investigators consider SABV in their research. We also provide an update on lessons learned, highlight ways that different disciplines consider SABV, and describe the opportunities for scientific discovery that applying SABV offers. We call on NIH's various stakeholders to redouble their efforts to integrate SABV throughout the biomedical research enterprise. Sex-and gender-aware investigations are critical to the conduct of rigorous and transparent science and the advancement of personalized medicine. This kind of research achieves its greatest potential when sex and gender considerations are integrated into the biomedical research enterprise in an end-to-end manner, from basic and preclinical investigations, through translational and clinical research, to improved health care delivery.

We have identified two cDNAs encoding dipeptidyl aminopeptidase-like proteins (DPPXs) in both bovine and rat brains that have different N-terminal cytoplasmic domains but share an identical transmembrane domain and a long C-terminal extracellular domain. In both species, one of the cDNAs encodes a protein (designated DPPX-S) of 803 amino acid residues with a short cytoplasmic domain of 32 amino acids, and the other cDNA encodes a protein (designated DPPX-L) with a longer cytoplasmic domain-the bovine cDNA encodes 92 amino acids and the rat cDNA encodes 88 amino acids. The membrane topology of DPPX-S and -L is similar to that of other transmembrane peptidases, and DPPXs share -30% identity and 50% similarity with reported yeast and rat liver dipeptidyl aminopeptidase amino acid sequences, suggesting that DPPX is a member of the dipeptidyl aminopeptidase family. DPPX-S mRNA is expressed in brain and some peripheral tissues including kidney, ovary, and testis; in contrast, DPPX-L mRNA is expressed almost exclusively in brain. No transcripts for either form are found in heart, liver, or spleen. In situ hybridization studies show that the two transcripts have different distributions in the brain. DPPX-L mRNA is expressed in limited regions of brain with the highest level of expression in the medial habenula. More widespread expression is seen for DPPX-S mRNA. The differential distribution of mRNAs for the DPPX-S and -L suggests that these proteins are involved in the metabolism of certain localized peptides and that the cytoplasmic domain may play a key role in determining the physiological specificity of DPPX.

Glutamate and related amino acids mediate fast excitatory neurotransmission in the vertebrate CNS via ligand-gated cationic channels in the neuronal membrane. These channels are composed of different subunits that assemble into a functional receptor/channel complex. Although studies have shown that these subunits are differentially expressed in neurons, few studies have quantitatively addressed the cell-specific expression of glutamate subunits in relation to known glutamatergic pathways. In the vertebrate auditory system, glutamate is the proposed neurotransmitter of the auditory nerve and parallel fiber pathways. In situ hybridization histochemistry was used to localize AMPA-selective glutamate receptor subunit mRNAs in seven cell types of the rat cochlear nucleus. GluR1-GluR4 AMPA-selective subunits were all expressed in cochlear nucleus neurons; however, the subunits expressed in identified cells varied with the cell type. Granule cells, previously not known to receive glutamatergic input, expressed GluR2 and GluR4 subunits. Cartwheel and stellate interneurons in the dorsal cochlear nucleus, which receive parallel fiber input, expressed all four subunits. Neurons receiving synaptic input from the auditory nerve, including globular, round, spherical, and fusiform cells, expressed GluR2, GluR3, and GluR4 subunits. Furthermore, a subpopulation of round cells in the ventral cochlear nucleus, and fusiform cells in the dorsal cochlear nucleus, expressed the GluR3 subunit at greatly reduced levels compared to neighboring cells. The results confirm the auditory nerve and parallel fiber pathways as glutamatergic and identify a third synaptic population, projecting to granule cells, which is likely glutamatergic. The data suggest that the composition of GluR1-GluR4 subunits on neurons in the cochlear nucleus may be related to presynaptic input; moreover, heterogeneous patterns of expression of the GluR3 subunit, in addition, suggest that variability in mRNA levels within one population of morphologically defined cells is present.