The Strategy of the Genes

During pregnancy, the energy requirements of the fetus impose changes in maternal metabolism. Increasing insulin resistance in the mother maintains nutrient flow to the growing fetus, whereas prolactin and placental lactogen counterbalance this resistance and prevent maternal hyperglycemia by driving expansion of the maternal population of insulin-producing beta cells. However, the exact mechanisms by which the lactogenic hormones drive beta cell expansion remain uncertain. Here we show that serotonin acts downstream of lactogen signaling to stimulate beta cell proliferation. Expression of serotonin synthetic enzyme tryptophan hydroxylase-1 (Tph1) and serotonin production rose sharply in beta cells during pregnancy or after treatment with lactogens in vitro. Inhibition of serotonin synthesis by dietary tryptophan restriction or Tph inhibition blocked beta cell expansion and induced glucose intolerance in pregnant mice without affecting insulin sensitivity. Expression of the G alpha(q)-linked serotonin receptor 5-hydroxytryptamine receptor-2b (Htr2b) in maternal islets increased during pregnancy and normalized just before parturition, whereas expression of the G alpha(i)-linked receptor Htr1d increased at the end of pregnancy and postpartum. Blocking Htr2b signaling in pregnant mice also blocked beta cell expansion and caused glucose intolerance. These studies reveal an integrated signaling pathway linking beta cell mass to anticipated insulin need during pregnancy. Modulators of this pathway, including medications and diet, may affect the risk of gestational diabetes.

https://escholarship.org/content/qt57p1w163/qt57p1w163.pdf?t=qag5o5

Serotonin regulates pancreatic beta cell mass during pregnancy.

Purpose of reviewTo examine the roles of the placental and pituitary hormones in the control of maternal metabolism and fetal growth.Recent findingsIn addition to promoting growth of maternal tissues, placental growth hormone (GH-V) induces maternal insulin resistance and thereby facilitates the mob

Placental hormones and the control of maternal metabolism and fetal growth.

Inadequate β-cell mass can lead to insulin insufficiency and diabetes. During times of prolonged metabolic demand for insulin, the endocrine pancreas can respond by increasing β-cell mass, both by increasing cell size and by changing the balance between β-cell proliferation and apoptosis. In this paper, we review recent advances in our understanding of the mechanisms that control the adaptive expansion of β-cell mass, focusing on the islet's response to pregnancy, a physiological state of insulin resistance. Functional characterization of factors controlling both β-cell proliferation and survival might not only lead to the development of successful therapeutic strategies to enhance the response of the β-cell to increased metabolic loads, but also improve islet transplantation regimens.

/pdf/expansion-of-b-cell-mass-in-response-to-pregnancy-m33823d70m.pdf

Expansion of β-cell mass in response to pregnancy

During pregnancy, the mother must adapt her body systems to support nutrient and oxygen supply for growth of the baby in utero and during the subsequent lactation. These include changes in the cardiovascular, pulmonary, immune and metabolic systems of the mother. Failure to appropriately adjust maternal physiology to the pregnant state may result in pregnancy complications, including gestational diabetes and abnormal birth weight, which can further lead to a range of medically significant complications for the mother and baby. The placenta, which forms the functional interface separating the maternal and fetal circulations, is important for mediating adaptations in maternal physiology. It secretes a plethora of hormones into the maternal circulation which modulate her physiology and transfers the oxygen and nutrients available to the fetus for growth. Among these placental hormones, the prolactin-growth hormone family, steroids and neuropeptides play critical roles in driving maternal physiological adaptations during pregnancy. This review examines the changes that occur in maternal physiology in response to pregnancy and the significance of placental hormone production in mediating such changes.

/pdf/the-role-of-placental-hormones-in-mediating-maternal-58kkdb3ehs.pdf

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

Increased islet mass is an adaptive mechanism that occurs to combat insulin resistance during pregnancy. Prolactin (PRL) can enhance β-cell proliferation and insulin secretion in vitro, yet whether it is PRL or other pregnancy-related factors that mediate these adaptive changes during pregnancy is unknown. The objective of this study was to determine whether prolactin receptor (Prlr) is required for normal maternal glucose homeostasis during pregnancy. An ip glucose tolerance test was performed on timed-pregnant Prlr+/+ and heterozygous null Prlr+/− mice on d 0, 15, and 18 of pregnancy. Compared with Prlr+/+ mice, Prlr+/− mice had impaired glucose clearance, decreased glucose-stimulated insulin release, higher nonfasted blood glucose, and lower insulin levels during but not before pregnancy. There was no difference in their insulin tolerance. Prlr+/+ mice show a significant incremental increase in islet density and β-cell number and mass throughout pregnancy, which was attenuated in the Prlr+/− mice. Prlr...

/pdf/prolactin-receptor-is-required-for-normal-glucose-2hp9vtwyc5.pdf

Prolactin Receptor Is Required for Normal Glucose Homeostasis and Modulation of β-Cell Mass during Pregnancy

The ELT-2 GATA factor normally functions in differentiation of the C. elegans endoderm, downstream of endoderm specification. We have previously shown that, if ELT-2 is expressed sufficiently early, it is also able to specify the endoderm and to replace all other members of the core GATA-factor transcriptional cascade (END-1, END-3, ELT-7). However, such rescue requires multiple copies (and presumably overexpression) of the end-1p::elt-2 cDNA transgene; a single copy of the transgene does not rescue. We have made this observation the basis of a genetic screen to search for genetic modifiers that allow a single copy of the end-1p::elt-2 cDNA transgene to rescue the lethality of the end-1end-3 double mutant. We performed this screen on a strain that has a single copy insertion of the transgene in an end-1end-3 background. These animals are kept alive by virtue of an extrachromosomal array containing multiple copies of the rescuing transgene; the extrachromosomal array also contains a toxin under heat shock control to counterselect for mutagenized survivors that have been able to lose the rescuing array. A screen of ∼14,000 mutagenized haploid genomes produced 17 independent surviving strains. Whole genome sequencing was performed to identify genes that incurred independent mutations in more than one surviving strain. The C. elegans gene tasp-1 was mutated in four independent strains. tasp-1 encodes the C. elegans homolog of Taspase, a threonine-aspartic acid protease that has been found, in both mammals and insects, to cleave several proteins involved in transcription, in particular MLL1/trithorax and TFIIA. A second gene, pqn-82, was mutated in two independent strains and encodes a glutamine-asparagine rich protein. tasp-1 and pqn-82 were verified as loss-of-function modifiers of the end-1p::elt-2 transgene by RNAi and by CRISPR/Cas9-induced mutations. In both cases, gene loss leads to modest increases in the level of ELT-2 protein in the early endoderm although ELT-2 levels do not strictly correlate with rescue. We suggest that tasp-1 and pqn-82 represent a class of genes acting in the early embryo to modulate levels of critical transcription factors or to modulate the responsiveness of critical target genes. The screen’s design, rescuing lethality with an extrachromosomal transgene followed by counterselection, has a background survival rate of

A Strategy To Isolate Modifiers of Caenorhabditis elegans Lethal Mutations: Investigating the Endoderm Specifying Ability of the Intestinal Differentiation GATA Factor ELT-2.

Figure 1: A. Needleman-Wunsch alignment of the N-terminal region of the Human LEMD2 protein and the C. elegans LEM-2 protein. Highlighted in yellow is the conserved Leucine residue that is changed to Arginine in the human mutation. B. Schematic summary of the CRISPR-induced changes in the C. elegans lem-2 gene introducing the Leucine to Arginine mutation at amino acid residue 16. Protein sequence is shown above the DNA sequence. The leucine ttg codon is changed to arginine cgg codon (red), thereby introducing a BsrbI restriction site (underlined). The reverse complement of the CRISPR/Cas9 PAM sequence is highlighted in yellow. C. Differential interference contrast (DIC) image of typical arrested lem-2(ca19) embryos whose mothers had been treated with emr-1 RNAi. D. DAPI-stained JM311 lem-2(ca19) embryo whose mother had been treated with emr-1 RNAi. E. Total brood sizes measured for 4-5 days following the L4 stage for strains N2 (wildtype); VC1317 lem-2(ok1807) and JM311 lem-2(ca19). “***” indicates t-test probability <<0.001. Beeswarm-boxplots were assembled in RStudio. F. Body length measurements (microns) measured for arrested non-Green L2 larvae segregating from strains JM312 and JM313, i.e. emr-1(gk119); lem-2(ok1807) or emr-1(gk119); lem2(ca19) larvae segregating from mothers homozygous for the respective lem-2 allele but heterozygous for emr-1(gk119). “*” indicates the (one-sided) t-test probability that lem-2(ca19) larvae are shorter than lem-2(ok1807) < 0.05. Beeswarmboxplots were assembled in RStudio. G. Rates of pharyngeal pumping measured in strains N2 (wildtype), VC1317 and JM311. Beeswarm-boxplots were assembled in RStudio. The three lowest pumping rates for each data set were assessed 6/29/2020 Open Access

https://www.micropublication.org/pdf/micropub-biology-000273

Frances Snider

Papers

Prolactin Receptor Is Required for Normal Glucose Homeostasis and Modulation of β-Cell Mass during Pregnancy

A Strategy To Isolate Modifiers of Caenorhabditis elegans Lethal Mutations: Investigating the Endoderm Specifying Ability of the Intestinal Differentiation GATA Factor ELT-2.

-Using the C. elegans lem-2 Gene to Reconstruct the Human LEMD2 Mutation Associated with Hutterite-type Cataract/Cardiomyopathy.