Karyotypes of Manatees: New Insights into Hybrid Formation (Trichechus inunguis × Trichechus m. manatus) in the Amazon Estuary.

Great efforts have been made to preserve manatees. Recently, a hybrid zone was described between Trichechus inunguis (TIN) and the Trichechus manatus manatus (TMM) in the Amazon estuary. Cytogenetic data on these sirenians are limited, despite being fundamental to understanding the hybridization/introgression dynamics and genomic organization in Trichechus. We analyzed the karyotype of TMM, TIN, and two hybrid specimens ("Poque" and "Vitor") by classical and molecular cytogenetics. G-band analysis revealed that TMM (2n = 48) and TIN (2n = 56) diverge by at least six Robertsonian translocations and a pericentric inversion. Hybrids had 2n = 50, however, with Autosomal Fundamental Number (FNA) = 88 in "Poque" and FNA = 74 in "Vitor", and chromosomal distinct pairs in heterozygous; additionally, "Vitor" exhibited heteromorphisms and chromosomes whose pairs could not be determined. The U2 snDNA and Histone H3 multi genes are distributed in small clusters along TIN and TMM chromosomes and have transposable Keno and Helitron elements (TEs) in their sequences. The different karyotypes observed among manatee hybrids may indicate that they represent different generations formed by crossing between fertile hybrids and TIN. On the other hand, it is also possible that all hybrids recorded represent F1 and the observed karyotype differences must result from mechanisms of elimination.

Isolation and establishment of skin-derived and mesenchymal cells from south American bat Artibeus planirostris (Chiroptera - Phyllostomidae).

Animal models represent a crucial tool for biological research, so the establishment of new cultures is fundamental for the discovery of new therapies and the understanding of mechanisms of cell development in the most diverse animals. Here, we report the successful establishment of two new primary cell cultures derived from a South American bat (Artibeus planirostris). The establishment of a new bat culture can help in the investigation of new zoonoses since bats have been proposed as carriers of these diseases. We evaluated the chromosomal stability of cells from different passages. Primary cultures were collected from ear tissues and bone marrow of A. planirostris. Cultures were expanded, and osteogenic and adipogenic inductions were conducted for 21 days. For osteogenic differentiation, the medium was supplemented with 0.1 µM dexamethasone, 3 mM ß-glycerophosphate, and 10 µM L-ascorbic acid 2-phosphate. For adipogenic differentiation, the medium was supplemented with 5 µM rosiglitazone, 0.4 µM insulin, 0.1 mM indomethacin, and 0.1 µM dexamethasone. After the induction period, the cells were stained with Alizarin Red to assess osteogenic differentiation and Oil Red O to assess adipogenic differentiation. We observed the appearance of lipid droplets in adipocytes and the extracellular deposition of calcium matrix by osteocytes, indicating that bone marrow-derived cells and skin-derived cells of A. planirostris could successfully differentiate into these lineages. Also, the number of chromosomes remained stable for both primary cultures during passages 2, 4, 6, and 8.

Cryptic Species in Proechimys goeldii (Rodentia, Echimyidae)? A Case of Molecular and Chromosomal Differentiation in Allopatric Populations.

The spiny rats of the genus Proechimys have a wide distribution in the Amazon, covering all areas of endemism of this region. We analyzed the karyotype and cytochrome b (Cyt b) sequences in Proechimys goeldii from 6 localities representing 3 interfluves of the eastern Amazon. A clear separation of P. goeldii into 2 monophyletic clades was observed, both chromosomally and based on Cyt b sequences: cytotype A (2n = 26x2640;/27x2642;, NF = 42) for samples from the Tapajos-Xingu interfluve and cytotype B (2n = 24x2640;/25x2642;, NF = 42) for samples from the Xingu-Tocantins interfluve and east of the Tocantins River. The karyotypes differ in a pericentric inversion and a centric fusion/fission and an average nucleotide divergence of 6.1%, suggesting cryptic species. Meiotic analysis confirmed the presence of a XX/XY1Y2 multiple sex chromosome determination system for both karyotypes. The karyotypes also vary from the literature (2n = 24, NF = 42, XX/XY). The autosome translocated to the X chromosome is different both in size and morphology to P. cf. longicaudatus, which also has a multiple sex chromosome determination system (2n = 14x2640;/15x2640;x2642;/16x2640;/17x2642;, NF = 14). The Xingu River is a barrier that separates populations of P. goeldii, thus maintaining their allopatric nature and providing an explanation for the molecular and cytogenetic patterns observed for the Xingu River but not the Tocantins River.

Protein markers of synaptic behavior and chromatin remodeling of the neo-XY body in phyllostomid bats.

The XX/XY system is the rule among mammals. However, many exceptions from this general pattern have been discovered since the last decades. One of these non-conventional sex chromosome mechanisms is the multiple sex chromosome system, which is evolutionary fixed among many bat species of the family Phyllostomidae, and has arisen by a translocation between one original gonosome (X or Y chromosome), and an autosome, giving rise to a "neo-XY body." The aim of this work is to study the synaptic behavior and the chromatin remodeling of multiple sex chromosomes in different species of phyllostomid bats using electron microscopy and molecular markers. Testicular tissues from adult males of the species Artibeus lituratus, Artibeus planirostris, Uroderma bilobatum, and Vampyrodes caraccioli from the eastern Amazonia were analyzed by optical/electron microscopy and immunofluorescence of meiotic proteins involved in synapsis (SYCP3 and SYCE3), sister-chromatid cohesion (SMC3), and chromatin silencing (BRCA1, γ-H2AX, and RNApol 2). The presence of asynaptic axes-labeled by BRCA1 and γ-H2AX-at meiotic prophase in testes that have a normal development of spermatogenesis, suggests that the basic mechanism that arrests spreading of transcriptional silencing (meiotic sex chromosome inactivation (MSCI)) to the autosomal segments may be per se the formation of a functional synaptonemal complex between homologous or non-homologous regions, and thus, this SC barrier might be probably related to the preservation of fertility in these systems.

Proechimys (Rodentia, Echimyidae): characterization and taxonomic considerations of a form with a very low diploid number and a multiple sex chromosome system.

BACKGROUND: Proechimys is the most diverse genus in family Echimyidae, comprising 25 species (two of which are polytypic) and 39 taxa. Despite the numerous forms of this rodent and their abundance in nature, there are many taxonomic problems due to phenotypic similarities within the genus and high intraspecific variation. Extensive karyotypic variation has been noted, however, with diploid numbers (2n) ranging from 14 to 62 chromosomes. Some heteromorphism can be found, and 57 different karyotypes have been described to date. RESULTS: In the present work, we describe a cytotype with a very low 2n. Specimens of Proechimys cf. longicaudatus were collected from two different places in northern Mato Grosso state, Brazil (12°54″S, 52°22″W and 9°51'17″S, 58°14'53″W). The females and males had 16 and 17 chromosomes, respectively; all chromosomes were acrocentric, with the exception of the X chromosome, which was bi-armed. The sex chromosome system was found to be XY1Y2, originating from a Robertsonian rearrangement involving the X and a large acrocentric autosome. Females had two Neo-X chromosomes, and males had one Neo-X and two Y chromosomes. NOR staining was found in the interstitial region of one autosomal pair. CONCLUSIONS: Comparison of this karyotype with those described in the literature revealed that Proechimys with similar karyotypes had previously been collected from nearby localities. We therefore suggest that this Proechimys belongs to a different taxon, and is either a new species or one that requires reassessment.