Differences in Oral Structure and Tissue Interactions during Mouse vs. Human Palatogenesis: Implications for the Translation of Findings from Mice

Clefting of the secondary palate is one of the most common human birth defects and results from failure of the palatal shelves to fuse during embryonic development. Palatogenesis is traditionally considered to be a highly conserved developmental process among mammalian species. However, cleft palate phenotypes in humans are considerably more variable than those seen in mice, the most common animal model for studying palatal development and pathogenesis of cleft palate. In this investigation, we utilized macroscopic observations, histology and 3D imaging techniques to directly compare palate morphology and the oral-nasal cavity during palate closure in mouse embryos and human conceptuses. We showed that mouse and human palates display distinct morphologies attributable to the structural differences of the oral-nasal cavity. We further showed that the palatal shelves interact differently with the primary palate and nasal septum in the hard palate region and with pharyngeal walls in the soft palate region during palate closure in mice and humans. Knowledge of these morphological differences is important for improved translation of findings in mouse models of human cleft lip/palate and, as such, should ultimately enhance our understanding of human palatal morphogenesis and the pathogenesis of cleft lip/palate in humans.

Transcriptional landscape of the prenatal human brain

The anatomical and functional architecture of the human brain is largely determined by prenatal transcriptional processes. We describe an anatomically comprehensive atlas of mid-gestational human brain, including de novo reference atlases, in situ hybridization, ultra-high resolution magnetic resonance imaging (MRI) and microarray analysis on highly discrete laser microdissected brain regions. In developing cerebral cortex, transcriptional differences are found between different proliferative and postmitotic layers, wherein laminar signatures reflect cellular composition and developmental processes. Cytoarchitectural differences between human and mouse have molecular correlates, including species differences in gene expression in subplate, although surprisingly we find minimal differences between the inner and human-expanded outer subventricular zones. Both germinal and postmitotic cortical layers exhibit fronto-temporal gradients, with particular enrichment in frontal lobe. Finally, many neurodevelopmental disorder and human evolution-related genes show patterned expression, potentially underlying unique features of human cortical formation. These data provide a rich, freely-accessible resource for understanding human brain development.

Global gene expression in the human fetal testis and ovary

This study describes a temporal profile of gene expression from normal human fetal testes and ovaries. Gonads from 34 fetuses between 9 wk and 20 wk of gestation were obtained from the Department of Pathology and the Birth Defects Research Laboratory at the University of Washington. Relative transcript levels were determined using the Affymetrix Human Genome U133A Plus 2.0 arrays. Sex determination occurs in the human gonad at approximately 6 wk of gestation with development of the testis driven by expression of SRY. In this study, SRY transcript was present and elevated at 9 wk of gestation in the testis but was absent in the ovary. The transcript levels of other testis-specific factors SOX9 and AMH and the steroidogenic genes CYP17A1, CYP11A1, STAR, and HSD17B3 were all significantly higher in the testis. In contrast, transcripts known to be involved in meiosis, including STRA8, SPO11, SYCP3, TEX11, TEX14, and STAG3, showed highest expression in the fetal ovary beginning at Week 12. These gene expression profiles will be a resource for understanding and defining normal gonad development and provide the opportunity to dissect abnormal development.

FISHing for acrocentric associations between chromosomes 14 and 21 in human oogenesis

OBJECTIVE

The purpose of this study was to search for cytologic evidence of robertsonian translocation formation that involves chromosomes 14q and 21q in human oogenesis with the use of dual color fluorescent in situ hybridization with whole chromosome paints.

STUDY DESIGN

The oocytes from a chromosomally normal fetus at 23.5 weeks of gestation underwent cohybridization with chromosome specific DNA libraries from chromosomes 14 and 21. The nuclei were scored for the proportion of meiosis I prophase substages and for hybridization efficiency and were evaluated for the presence of hybridization signals that were suggestive of heterologous associations between chromosomes 14q and 21q in zygotene, pachytene, and diplotene.

RESULTS

A total of 1769 meiotic nuclei were analyzed. Of 272 informative nuclei at zygotene, pachytene, and diplotene, 1 nucleus at pachytene demonstrated hybridization signals for chromosomes 14 and 21 that could be consistent with a robertsonian translocation.

CONCLUSION

A heterologous association between chromosomes 14q and 21q that possibly represent robertsonian translocation formation was observed cytologically with the use of fluorescent in situ hybridization.