A yeast-based recombinogenic targeting toolset for transgenic analysis of human disease genes

Lymphotoxin targeted to salivary and lacrimal glands induces tertiary lymphoid organs and cervical lymphadenopathy and reduces tear production

To investigate the role of lymphotoxin (LT) in Sjögren's syndrome (SS) and in mucosal associated lymphoid tissue (MALT)-lymphoma, we made transgenic mice (Amy1-LTαβ) that targeted LTα and LTβ to the salivary and lacrimal glands. Amy1-LTαβ mice developed atrophic salivary and lacrimal glands that contained tertiary lymphoid organs (TLOs) and had reduced tear production. Amy1-LTαβ mice developed cervical lymphadenopathy but not MALT-lymphoma. TLO formation in the salivary and lacrimal glands of Amy1-LTαβ was not sufficient to induce autoimmunity as measured by autoantibody titres.

Functional and molecular features of the Id4+ germline stem cell population in mouse testes

Chan et al. generated transgenic mice in which spermatogonial stem cells expressed an Id4-Gfp transgene. Id4-Gfp⁺ cells exist primarily as a subset of the type A_single pool and eventually comprise ∼2% of the undifferentiated spermatogonial population in adulthood. RNA sequencing analysis revealed genes whose expression is unique for the Id4-Gfp⁺/stem cell and Id4-Gfp⁻/progenitor fractions. These findings provide evidence that stem cells exist as a rare subset of the A_single pool and reveal transcriptome features distinguishing stem cell and progenitor states within the mammalian male germline.

The maintenance of cycling cell lineages relies on undifferentiated subpopulations consisting of stem and progenitor pools. Features that delineate these cell types are undefined for many lineages, including spermatogenesis, which is supported by an undifferentiated spermatogonial population. Here, we generated a transgenic mouse line in which spermatogonial stem cells are marked by expression of an inhibitor of differentiation 4 (Id4)-green fluorescent protein (Gfp) transgene. We found that Id4-Gfp⁺ cells exist primarily as a subset of the type A_single pool, and their frequency is greatest in neonatal development and then decreases in proportion during establishment of the spermatogenic lineage, eventually comprising ∼2% of the undifferentiated spermatogonial population in adulthood. RNA sequencing analysis revealed that expression of 11 and 25 genes is unique for the Id4-Gfp⁺/stem cell and Id4-Gfp⁻/progenitor fractions, respectively. Collectively, these findings provide the first definitive evidence that stem cells exist as a rare subset of the A_single pool and reveal transcriptome features distinguishing stem cell and progenitor states within the mammalian male germline.

Lymphotoxin and TNF: how it all began-a tribute to the travelers

The journey from the discoveries of lymphotoxin (LT) and tumor necrosis factor (TNF) to the present day age of cytokine inhibitors as therapeutics has been an exciting one with many participants and highs and lows; the saga is compared to that in "The Wizard of Oz". This communication summarizes the contributions of key players in the discovery of the cytokines and their receptors, the changes in nomenclature, and the discovery of the LT family's crucial role in secondary and tertiary lymphoid organs. The remarkable advances in therapeutics are detailed as are remaining problems. Finally, special tribute is paid to two pioneers in the field who have recently passed away: Byron H. Waksman and Lloyd Old.

Lymphatic vessel function in head and neck inflammation

BACKGROUND

Serious infections of the head and neck cause lymphedema that can lead to airway compromise and oropharyngeal obstruction. Lymphangiogenesis occurs in the head and neck during infection and after immunization. The goal of this project was to develop tools to image lymphatic vessels in living animals and to be able to isolate individual lymphatic endothelial cells in order to quantify changes in single cells caused by inflammation.

METHODS

The ProxTom transgenic red-fluorescent reporter mouse was developed specifically for the purpose of imaging lymphatic vessels in vivo. Prox1 is a transcription factor that is necessary for lymphangiogenesis in development and for the maintenance of lymphatics in adulthood. Mice were immunized and their lymphatic vessels in lymph nodes were imaged in vivo. Individual lymphatic endothelial cells were isolated by means of their fluorescence.

RESULTS

The ProxTom transgene has the red-fluorescent reporter td-Tomato under the control of Prox1 regulatory elements. tdTomato was faithfully expressed in lymphatic vessels coincident with endogenous Prox1 expression. We show lymphangiogenesis in vivo after immunization and demonstrate a method for the isolation of lymphatic endothelial cells by their tdTomato red-fluorescence.

CONCLUSIONS

The faithful expression of the red-fluorescent reporter in the lymphatic vessels of ProxTom means that these mice have proven utility for in vivo study of lymphatic vessels in the immune response. ProxTom has been made available for distribution from the Jackson Laboratory: http://jaxmice.jax.org/strain/018128.html .

Generation of transgenic mice with megabase-sized human yeast artificial chromosomes by yeast spheroplast-embryonic stem cell fusion

Introducing human genes into mice offers the opportunity to analyze their in vivo function or to obtain therapeutic molecules. For proper gene regulation, or in case of multigene families, megabase (Mb)-sized DNA fragments often have to be used. Yeast artificial chromosome (YAC)-mediated transgenesis is irreplaceable for this purpose, because alternative methods such as the use of bacterial artificial chromosomes (BACs) cannot introduce DNA fragments larger than 500 kb into the mouse germ line. However, YAC libraries often contain only partial gene loci. Time-consuming reconstruction of YACs, genetic instability and the difficulty in obtaining intact YAC DNA above a certain size impede the generation of humanized mice. Here we describe how to reconstruct YACs containing Mb-sized human DNA, such as the T cell receptor-α (TRA) gene locus, thus facilitating the introduction of large DNA fragments into the mouse germ line. Fusion of YAC-containing yeast and embryonic stem (ES) cells avoids the need for YAC DNA purification. These ES cells are then used to stably introduce the functional TRA gene locus into the mouse germ line. The protocol takes ∼1 year to complete, from reconstruction of the entire TRA gene locus from YACs containing partial but overlapping TRA regions to germline transmission of the YAC.

ProxTom lymphatic vessel reporter mice reveal Prox1 expression in the adrenal medulla, megakaryocytes, and platelets

Lymphatic vessels (LVs) are important structures for antigen presentation, for lipid metabolism, and as conduits for tumor metastases, but they have been difficult to visualize in vivo. Prox1 is a transcription factor that is necessary for lymphangiogenesis in ontogeny and the maintenance of LVs. To visualize LVs in the lymph node of a living mouse in real time, we made the ProxTom transgenic mouse in a C57BL/6 background using red fluorescent LVs that are suitable for in vivo imaging. The ProxTom transgene contained all Prox1 regulatory sequences and was faithfully expressed in LVs coincident with endogenous Prox1 expression. The progenies of a ProxTom × Hec6stGFP cross were imaged using two-photon laser scanning microscopy, allowing the simultaneous visualization of LVs and high endothelial venules in a lymph node of a living mouse for the first time. We confirmed the expression of Prox1 in the adult liver, lens, and dentate gyrus. These intensely fluorescent mice revealed the expression of Prox1 in three novel sites: the neuroendocrine cells of the adrenal medulla, megakaryocytes, and platelets. The novel sites identified herein suggest previously unknown roles for Prox1. The faithful expression of the fluorescent reporter in ProxTom LVs indicates that these mice have potential utility in the study of diseases as diverse as lymphedema, filariasis, transplant rejection, obesity, and tumor metastasis.