Embryo development in Mexican Axolotl (Ambystoma mexicanum); a stage morphological study

Fernando García-González ^1* Erika Servín ¹ Alma Lilia Álvarez Guerreo ² Alicia Alcantar-Rodriguez ¹ Alfredo Medrano ¹

• ¹ Faculty of Higher Studies Cuautitlán, National Autonomous University of Mexico, Cuautitlán Izcalli, Mexico
• ² Faculty of Sciences, National Autonomous University of Mexico, Mexico City, México, Mexico

Ambystoma mexicanum is a critically endangered amphibian, however is an important model for regeneration research. In this work we analyze axolotl embryo development, identifying and describing the stages from zygote until hatching with high quality images. We analyzed and described a total of 49 development stages that were grouped in 5 phases: (1) fertilized oocyte, (2) cleavage, (3) gastrulation, (4) neurulation, and (5) organogenesis. Time from fertilization to hatching took about 350 hours under the management conditions set up in our laboratory; it can be considered that the complete development of the axolotl embryo until hatching takes two weeks approximately. The embryos were maintained in natural conditions at 16°C, inside their jelly layers the whole study period to take images that show the natural development. Results of this work may allow researchers in developmental biology, as well as those working on the conservation of the species including assisted reproduction techniques, to have recent material to carry out studies that favor the understanding and conservation of this Mexican species. KEYWORDS: Axolotl, embryo development, Ambystoma mexicanum, amphibian development 1 INTRODUCTION The Mexican Axolotl (Ambystoma mexicanum) is a urodele amphibian, endemic to the Mexico basin. It is classified as a Critically Endangered species, in its native habitat, by the International Union for Conservation of Nature (IUCN, 2020), this is due to the habitat destruction by pollution and urbanization, but also by the introduction of invasive species (SEMARNAT, 2018). This species has been relevant in the Mexican culture but is globally well known as a model to study tissue such as limb regeneration (Bryant et al., 2017). Even when the regeneration and genetic studies have been carried out recently in Ambystoma mexicanum, there are other biological topics which have no current information such as embryo development. The first reports on this subject date from 1975and 1989(Schreckenberg and Jacobson, 1975;Bordzilovskaya et al., 1989).