Generation of mice lacking DUF1220 protein domains: effects on fecundity and hyperactivity.

Sequences encoding DUF1220 protein domains show the most extreme human lineage-specific copy number increase of any coding region in the genome and have been linked to human brain evolution. In addition, DUF1220 copy number (dosage) has been implicated in influencing brain size within the human species, both in normal populations and in individuals associated with brain size pathologies (1q21-associated microcephaly and macrocephaly). More recently, increasing dosage of a subtype of DUF1220 has been linked with increasing severity of the primary symptoms of autism. Despite these intriguing associations, a function for these domains has not been described. As a first step in addressing this question, we have developed the first transgenic model of DUF1220 function by removing the single DUF1220 domain (the ancestral form) encoded in the mouse genome. In a hypothesis generating exercise, these mice were evaluated by 197 different phenotype measurements. While resulting DUF1220-minus (KO) mice show no obvious anatomical peculiarities, they exhibit a significantly reduced fecundity (χ(2) = 19.1, df = 2, p = 7.0 × 10(-5)). Further extensive phenotypic analyses suggest hyperactivity (p < 0.05) of DUF1220 mice and changes in gene expression levels of brain associated with distinct neurological functions and disease. Other changes that met statistical significance include an increase in plasma glucose concentration (as measured by area under the curve, AUC 0-30 and AUC 30-120) in male mutants, fasting glucose levels, reduce sodium levels in male mutants, increased levels of the liver functional indicator ALAT/GPT in males, levels of alkaline phosphatase (also an indicator of liver function), mean R and SR amplitude by electrocardiography, elevated IgG3 levels, a reduced ratio of CD4:CD8 cells, and a reduced frequency of T cells; though it should be noted that many of these differences are quite small and require further examination. The linking of DUF1220 loss to a hyperactive phenotype is consistent with separate findings in which DUF1220 over expression results in a down-regulation of mitochondrial function, and potentially suggests a role in developmental metabolism. Finally, the substantially reduced fecundity we observe associated with KO mice argues that the ancestral DUF1220 domain provides an important biological functionthat is critical to survivability and reproductive success.

DUF1220 protein domains drive proliferation in human neural stem cells and are associated with increased cortical volume in anthropoid primates.

Genome sequences encoding DUF1220 protein domains show a burst in copy number among anthropoid species and especially humans, where they have undergone the greatest human lineage-specific copy number expansion of any protein coding sequence in the genome. While DUF1220 copy number shows a dosage-related association with brain size in both normal populations and in 1q21.1-associated microcephaly and macrocephaly, a function for these domains has not yet been described. Here we provide multiple lines of evidence supporting the view that DUF1220 domains function as drivers of neural stem cell proliferation among anthropoid species including humans. First, we show that brain MRI data from 131 individuals across 7 anthropoid species shows a strong correlation between DUF1220 copy number and multiple brain size-related measures. Using in situ hybridization analyses of human fetal brain, we also show that DUF1220 domains are expressed in the ventricular zone and primarily during human cortical neurogenesis, and are therefore expressed at the right time and place to be affecting cortical brain development. Finally, we demonstrate that in vitro expression of DUF1220 sequences in neural stem cells strongly promotes proliferation. Taken together, these data provide the strongest evidence so far reported implicating DUF1220 dosage in anthropoid and human brain expansion through mechanisms involving increasing neural stem cell proliferation.

DUF1220-domain copy number implicated in human brain-size pathology and evolution.

DUF1220 domains show the largest human-lineage-specific increase in copy number of any protein-coding region in the human genome and map primarily to 1q21, where deletions and reciprocal duplications have been associated with microcephaly and macrocephaly, respectively. Given these findings and the high correlation between DUF1220 copy number and brain size across primate lineages (R(2) = 0.98; p = 1.8 × 10(-6)), DUF1220 sequences represent plausible candidates for underlying 1q21-associated brain-size pathologies. To investigate this possibility, we used specialized bioinformatics tools developed for scoring highly duplicated DUF1220 sequences to implement targeted 1q21 array comparative genomic hybridization on individuals (n = 42) with 1q21-associated microcephaly and macrocephaly. We show that of all the 1q21 genes examined (n = 53), DUF1220 copy number shows the strongest association with brain size among individuals with 1q21-associated microcephaly, particularly with respect to the three evolutionarily conserved DUF1220 clades CON1(p = 0.0079), CON2 (p = 0.0134), and CON3 (p = 0.0116). Interestingly, all 1q21 DUF1220-encoding genes belonging to the NBPF family show significant correlations with frontal-occipital-circumference Z scores in the deletion group. In a similar survey of a nondisease population, we show that DUF1220 copy number exhibits the strongest correlation with brain gray-matter volume (CON1, p = 0.0246; and CON2, p = 0.0334). Notably, only DUF1220 sequences are consistently significant in both disease and nondisease populations. Taken together, these data strongly implicate the loss of DUF1220 copy number in the etiology of 1q21-associated microcephaly and support the view that DUF1220 domains function as general effectors of evolutionary, pathological, and normal variation in brain size.