Genesis

A standard development embryological series is the primary basis to organize information of any embryological study and is also used to determine the age of eggs and embryos in field conditions. In this article, we calibrate developmental series of the broad‐snouted caiman, Caiman latirostris, against an established series for Alligator mississippiensis. Morphometric measures and extend of the opaque‐shell banding were also related to embryo age. In earlier stages, external morphological features alone can account for embryo age, but we suggest that morphometric measurements should be introduced later in the development. Unlike morphologic and morphometric attributes, the opaque patch was not a useful age predictor. As expected, a close correlation between embryonic development of C. latirostris and A. mississippiensis was observed. genesis 46:401–417, 2008. © 2008 Wiley‐Liss, Inc.

Summary: Cre transgenic mice can be used to delete gene sequences flanked by loxP sites in specific somatic tissues. We have generated vavCre transgenic mice, which can be used to inactivate genes specifically in adult hematopoietic and endothelial cells. In these animals, a Cre transgene is expressed under control of murine vav gene regulatory elements. To assess their usefulness, vavCre transgenic mice were bred with R26R mice, which express a lacZ reporter gene only in cells where Cre‐mediated recombination has occurred. VavCre/R26R double‐heterozygous offspring were analyzed by β‐galactosidase histochemistry and flow cytometry. VavCre‐mediated recombination occurred in most hematopoietic cells of all hematopoietic organs, including the hematopoietic progenitor‐rich bone marrow. Recombination also occurred in most endothelial and germ cells, but only rarely in other cell types. The recombination in both hematopoietic and endothelial lineages may partly reflect their putative shared ontogeny and provides a unique tool for simultaneous pan‐hematopoietic and endothelial mutagenesis. genesis 34:251–256, 2002. © 2002 Wiley‐Liss, Inc.

Summary: The Pax2 gene is expressed in the developing otocyst, kidney, and midbrain–hindbrain boundary. We generated Pax2‐Cre transgenic lines by modification of a Pax2 bacterial artificial chromosome (BAC). In one Pax2‐Cre line, Cre mRNA starts to be expressed in the otic placode at the late presomite stage. R26R reporter mouse analysis revealed that the Cre expression is sufficient to delete the loxP‐flanked sequences in most of the cells in the inner ear. Reporter‐positive cells are also detected in other Pax2‐expressing tissues such as midbrain, cerebellum, olfactory bulb, and kidney, suggesting that these cells are the descendants of Pax2‐expressing cells in these tissues and that Pax2‐Cre transgenic mice can delete genes efficiently in these tissues. genesis 38:195–199, 2004. © 2004 Wiley‐Liss, Inc.

Tbx1 is required for the expansion of second heart field (SHF) cardiac progenitors destined to the outflow tract of the heart. Loss of Tbx1 causes heart defects in humans and mice. We report a novel Tbx1^Cre knock‐in allele that we use to fate map Tbx1‐expressing cells during development in conjunction with a reporter and 3D image reconstruction. Tbx1 descendants constitute a mesodermal cell population that surrounds the primitive pharynx and approaches the arterial pole of the heart from lateral and posterior, but not anterior directions. These cells populate most of the outflow tract with the exception of the anterior portion, thus identifying a population of the SHF of distinct origin. Both myocardial and underlying endocardial layers were labeled, suggesting a common origin of these cell types. Finally, we show that Tbx1^Cre‐positive and Tbx1^Cre‐negative cell descendants occupy discrete domains in the outflow tract throughout development. genesis 45:470–475, 2007. Published 2007 Wiley‐Liss, Inc.

Mammalian development is highly sensitive to Tbx1 gene dosage reduction. Gene function insights can also be learned from increased or ectopic expression. The authors generated a novel mouse transgenic line, named COET, which expresses Tbx1 upon Cre‐mediated recombination. The authors crossed this transgenic line with Tbx1^Cre animals to activate expression in the Tbx1‐expression domain. Compound mutant COET;Tbx1^Cre/+ animals died after birth and showed heart enlargement. At E18.5, compound mutants showed ventricular septal defects and thymic abnormalities. The authors crossed compound mutants into a Tbx1 null background to understand whether this phenotype is caused by gene overdosage. Results showed that gene dosage reduction at the endogenous locus could not rescue heart and thymic defects, although the transgene rescued the loss of function phenotype. Thus, the transgenic phenotype appears to be due to gain of function. Resultant data demonstrate that Tbx1 expression must be tightly regulated to be compatible with normal embryonic development. genesis 47:188–195, 2009. © 2009 Wiley‐Liss, Inc.

Postmortem studies have revealed a downregulation of the transcription factor Pax5 in GABAergic neurons in bipolar disorder, a neurodevelopmental disorder, raising the question whether Pax5 in GABAergic neurons has a role in normal brain development. In a genetic approach to study functions of Pax5 in GABAergic neurons, Pax5 was specifically deleted in GABAergic neurons from Pax5 floxed mice using a novel Gad1‐Cre transgenic mouse line expressing Cre recombinase in Gad1‐positive, that is, GABAergic neurons. Surprisingly, these mice developed a marked enlargement of the lateral ventricles at approximately 7 weeks of age, which was lethal within 1–2 weeks of its appearance. This hydrocephalus phenotype was observed in mice homozygous or heterozygous for the Pax5 conditional knockout, with a gene dosage‐dependent penetrance. By QTL (quantitative trait loci) mapping, a 3.5 Mb segment on mouse chromosome 4 flanked by markers D4Mit237 and D4Mit214 containing approximately 92 genes including Pax5 has previously been linked to differences in lateral ventricular size. Our findings are consistent with Pax5 being a relevant gene underlying this QTL phenotype and demonstrate that Pax5 in GABAergic neurons is essential for normal ventricular development. genesis 51:234–245. © 2013 Wiley Periodicals, Inc.

unpaired (upd) encodes a ligand for the Jak/STAT signaling pathway in Drosophila. In the second instar and early third larval eye disc, upd is expressed in the center of the posterior margin. upd loss‐of‐function mutations caused eye size reduction and upd overexpression caused eye enlargement. Upd regulates eye size through the Dome/Jak(Hop)/STAT92 signaling pathway to promote cell proliferation. Interestingly, the effect of Upd is only on cells located anterior to the morphogenetic furrow (MF), but has no effect on the second mitotic wave, which is posterior to MF. Overexpression of upd behind MF can nonautonomously induce cell proliferation up to 20 rows of cells anterior to MF. The G1 cyclin, cycD transcript level was also enhanced anterior to MF. Consistent with the long‐range effect, we found that the extracellular Upd protein can be detected over a comparable long range, suggesting that Upd acts directly over a long distance as a signaling molecule. genesis 39:141–153, 2004. © 2004 Wiley‐Liss, Inc.