Igor O. Nasonkin

A novel sulfonylurea receptor family member expressed in the embryonic Drosophila dorsal vessel and tracheal system.

Sulfonylurea receptors (SURx) are required subunits of the ATP-sensitive potassium channel. SURx alone is electrophysiologically inert. However, when SURx is combined with an inward rectifier Kir6.2 subunit, ATP-sensitive potassium channel activity is generated. We report the identification, characterization, and localization of Dsur, a novel Drosophila gene that is highly related to the vertebrate SUR family. The Dsur coding sequence contains structural features characteristic of the ABC transporter family and, in addition, harbors 1.7 kilobases of a distinctive sequence that does not share homology with any known gene. When Dsur alone is expressed in Xenopus oocytes glibenclamide-sensitive potassium channel activity occurs. During Drosophilaembryogenesis, the Dsur gene is specifically expressed in the developing tracheal system and dorsal vessel. Studies of theDrosophila genome support that only a singleDsur gene is present. Our data reveal conservation of glibenclamide-sensitive potassium channels in Drosophilaand suggest that Dsur may play an important role duringDrosophila embryogenesis. The lack of gene duplication in the Drosophila system provides a unique opportunity for functional studies of SUR using a genetic approach.

Genetic variation in C57BL/6 ES cell lines and genetic instability in the Bruce4 C57BL/6 ES cell line

Genetically modified mouse strains derived from embryonic stem (ES) cells are powerful tools for gene function analysis. ES cells from the C57BL/6 mouse strain are not widely used to generate mouse models despite the advantage of a defined genetic background. We assessed genetic variation in six such ES cell lines with 275 SSLP markers. Compared to C57BL/6, Bruce4 differed at 34 SSLP markers and had significant heterozygosity on three chromosomes. BL/6#3 and Dale1 ES cell lines differed at only 3 SSLP makers. The C2 and WB6d ES cell lines differed at 6 SSLP markers. It is important to compare the efficiency of producing mouse models with available C57BL/6 ES cells relative to standard 129 mouse strain ES cells. We assessed genetic stability (the tendency of cells to become aneuploid) in 110 gene-targeted ES cell clones from the most widely used C57BL/6 ES cell line, Bruce4, and 710 targeted 129 ES cell clones. Bruce4 clones were more likely to be aneuploid and unsuitable for ES cell-mouse chimera production. Despite their tendency to aneuploidy and consequent inefficiency, use of Bruce4 ES cells can be valuable for models requiring behavioral studies and other mouse models that benefit from a defined C57BL/6 background.

Aged PROP1 Deficient Dwarf Mice Maintain ACTH Production

Humans with PROP1 mutations have multiple pituitary hormone deficiencies (MPHD) that typically advance from growth insufficiency diagnosed in infancy to include more severe growth hormone (GH) deficiency and progressive reduction in other anterior pituitary hormones, eventually including adrenocorticotropic hormone (ACTH) deficiency and hypocortisolism. Congenital deficiencies of GH, prolactin, and thyroid stimulating hormone have been reported in the Prop1null (Prop1-/-) and the Ames dwarf (Prop1df/df) mouse models, but corticotroph and pituitary adrenal axis function have not been thoroughly investigated. Here we report that the C57BL6 background sensitizes mutants to a wasting phenotype that causes approximately one third to die precipitously between weaning and adulthood, while remaining homozygotes live with no signs of illness. The wasting phenotype is associated with severe hypoglycemia. Circulating ACTH and corticosterone levels are elevated in juvenile and aged Prop1 mutants, indicating activation of the pituitary-adrenal axis. Despite this, young adult Prop1 deficient mice are capable of responding to restraint stress with further elevation of ACTH and corticosterone. Low blood glucose, an expected side effect of GH deficiency, is likely responsible for the elevated corticosterone level. These studies suggest that the mouse model differs from the human patients who display progressive hormone loss and hypocortisolism.

Cloning, characterization, and embryonic expression analysis of the Drosophila melanogaster gene encoding insulin/relaxin-like peptide.

Insulin is one of the key peptide hormones that regulates growth and metabolism in vertebrates. Evolutionary conservation of many elements of the insulin/IGF signaling network makes it possible to study the basic genetic function of this pathway in lower metazoan models such as Drosophila. Here we report the cloning and characterization of the gene for Drosophila insulin/relaxin-like peptide (DIRLP). The predicted protein structure of DIRLP greatly resembles typical insulin structure and contains features that differentiate it from the Drosophila juvenile hormone, another member of the insulin family. The Dirlp gene is represented as a single copy in the Drosophila melanogaster genome (compared to multiple copies for Drosophila juvenile hormone) and shows evolutionary conservation of genetic structure. The gene was mapped to the Drosophila chromosome 3, region 67D2. In situ hybridization of whole-mount Drosophila embryos with Dirlp antisense RNA probe reveals early embryonic mesodermal/ventral furrow expression pattern, consistent with earlier observation of the insulin protein immunoreactivity in Drosophila embryos. The in situ hybridization pattern was found to be identical to that obtained during immunohistochemistry analysis of the Drosophila embryos using various insulin monoclonal and polyclonal antibodies that do not recognize Drosophila juvenile hormone, supporting the idea that Dirlp is a possible Drosophila insulin ortholog. Identification of the gene for DIRLP provides a new approach for study of the regulatory pathway of the insulin family of peptides.

Structure of the mouse calcitonin/calcitonin gene-related peptide alpha and beta genes

We report the cloning, genomic organization and sequence of the mouse α-CALC and β-CALC genes. The two genes share extensive sequence homology. The transcription units of both genes contain 6 exons. Transcripts of the α-CALC gene were found to alternatively include exon 4 or exons 5 and 6. For the β-CALC gene exon 4 was not detected in transcripts derived from this gene. The predicted mouse α-CGRP was found to be identical to rat α-CGRP, however, β-CGRP predicted amino acid sequences revealed three amino acid differences suggesting these residues are not critical to CGRP function.

20 – Pituitary Gland Development

Pituitary gland is a small endocrine gland located at the base of the brain under the optic chiasm and the arachnoid membrane, in a bony indentation called the sella turcica. Its name comes from the Greek hypophysis, which means undergrowth. The role of the pituitary gland is the regulated synthesis and secretion of polypeptide hormones that are essential for the development and function of many other organs in the body. Releasing hormones and inhibiting factors reach the anterior pituitary via hypothalamic neurons that terminate in the capillary beds of the median eminence, just dorsal to the pituitary gland. These capillary beds are connected to the hypophyseal portal vessels that nourish the anterior pituitary. In response to these stimulatory stimulatory factors, pituitary hormones are released into hypophyseal portal blood vessels and carried through the blood stream to their target organs. An intriguing feature of pituitary development is the initial organization of the cell types into discrete patches and the loss of this spatial organization as the organ expands. The rodent pituitary is composed of three lobes. The posterior pituitary (neurohypophysis or pars nervosa) is derived from neural ectoderm and contains the nerve terminals that secrete oxytocin and vasopressin. The intermediate lobe (pars intermedia) and anterior lobe are both derived from oral ectoderm. The bulk of the anterior lobe (pars distaIis) is at the same level as the intermediate lobe, but a portion of it known as the pars tuberalis extends dorsally along the pituitary stalk.

Cre-mediated recombination in pituitary somatotropes

We report a transgenic line with highly penetrant cre recombinase activity in the somatotrope cells of the anterior pituitary gland. Expression of the cre transgene is under the control of the locus control region of the human growth hormone gene cluster and the rat growth hormone promoter. Cre recombinase activity was assessed with two different lacZ reporter genes that require excision of a floxed stop sequence for expression: a chick β‐actin promoter with the CMV enhancer transgene and a ROSA26 knock‐in. Cre activity is detectable in the developing pituitary after initiation of Gh transcription and persists through adulthood with high penetrance in Gh expressing cells and lower penetrance in lactotropes, a cell type that shares a common origin with somatotropes. This Gh‐cre transgenic line is suitable for efficient, cell‐specific deletion of floxed regions of genomic DNA in differentiated somatotropes and a subset of lactotrope cells of the anterior pituitary gland. genesis 47:55–60, 2009.

Role of PITX2 in the Pituitary Gland

The pituitary gland is a neuroendocrine organ composed of specialized peptide hormone-producing cells that control many bodily functions. Pituitary development depends on the combined activity of extrinsic signaling molecules and intrinsic transcription factors. One of the earliest acting transcription factors in pituitary development is PITX2, a homeobox transcription factor required for expansion of the pituitary primordium, Rathke’s pouch. Analysis of an allelic series in mice revealed that pituitary gland size and the specification of individual pituitary cell types are also dependent upon Pitx2, and this dependence is sensitive to Pitx2 gene dosage. Mechanistically this pituitary phenotype results from the inability of low levels of PITX2 to activate gene expression of several lineage specific transcription factors, such as Gata2, Sf1 (Nr5a1), Egr1 and Pit1. Our understanding of Pitx2 gene dosage effects on pituitary development suggests a basis for dosage sensitive defects in other organs of Rieger syndrome patients. In addition, analysis of the allelic series in mice raises the possibility of gonadotropin and PIT1 lineage defects in individuals with loss of PITX2 function.

A Novel ABC Transporter of the Sulfonylurea Receptor Family Expressed Specifically in the Drosophila Embryonic Heart and Tracheal System

A Novel ABC Transporter of the Sulfonylurea Receptor Family Expressed Specifically in the Drosophila Embryonic Heart and Tracheal System