To "Bee or Not to Bee" Male or Female? an Educational Primer for Use with "The Am-Tra2 Gene Is an Essential Regulator of Female Splice Regulation at Two Levels of the Sex Determination Hierarchy of the Honeybee"

Article excerpt

SUMMARY An article by Nissen et al. in the November 2012 issue of GENETICS emphasizes the importance of alternative splicing in the sex determination cascade of the honeybee Apis mellifera. This study demonstrates the application of reverse transcriptase PCR and RNA interference screens as genetic tools to better understand the regulation of transcription and splicing. It also provides the opportunity to explore the evolutionary origins of genes by considering the functions of orthologs and paralogs in different species. This Primer article provides background information and explanations of the concepts and findings of Nissen et al. and offers discussion questions for use in the classroom.

Related article in GENETICS: Nissen, I., M. Müller, and M. Beye, 2012 The Am-tra2 gene is an essential regulator of female splice regulation at two levels of the sex determination hierarchy of the honeybee. Genetics 192: 1015-1026.

Background

THE origins of beekeeping and honey collecting in human civilizations can be traced back thousands of years. Honeybee colony management has thrived because of the important role played by honeybees in crop pollination and because human cultures worldwide consume hive products (honey, beeswax, and propolis). Importantly, bees also shape natural ecosystems by facilitating gene flow among plants.

Honeybees are eusocial insects that live in colonies of tens of thousands of individuals. A colony usually consists of three types of bees: queens, drones, and workers. The female queen (usually one per colony) is selected early in larval development and fed a diet of royal jelly. As an adult, the queen lays unfertilized and fertilized eggs. Male drones, whose main role is to mate with the queen, develop from unfertilized eggs. Female workers (the majority of bees in a colony) are the laborers that perform tasks required for colony growth and maintenance (e.g., cleaning, defense, foraging for food). Workers will produce eggs only if the colony is queen-less. Because of this social structure, honeybees are important models for studying behavior, learning, and memory as well as the genetics of sex determination.

The signal transduction cascade that directs sex determination in honeybees (i.e., development as a male drone or female queen/worker) directs developmental fate and, in turn, has a significant influence on the social structure of a colony. Over 150 years ago Johannes Dzierson hypothesized that male bees develop from unfertilized eggs and females from fertilized eggs (reviewed by Page et al. 2012). However, research to understand the genetics that controls male vs. female developmental fate is ongoing. The publication of the DNA sequence of the European honeybee (Apis mellifera) genome in 2006 (Honeybee Genome Sequencing Consortium 2006) provided important resources for studying bee genetics, including the molecular basis of sex determination. Martin Beye and his team of researchers at Heinrich Heine University in Dusseldorf, Germany, have made significant contributions in this field. In their most recent article, Beye and colleagues Inga Nissen and Miriam Müller examine the expression pattern of the gene transformer-2 (tra-2) in A. mellifera and how it regulates the splicing and expression of other genes in the sex determination cascade. Their results enhance our understanding of the mechanisms of gene regulation that lead to either female or male development in the honeybee A. mellifera.

Sex determination in honeybees: the complementary sex determiner locus

What determines whether an animal develops as a male or female? There is no universal answer, but in many animals, sex determination is triggered very early in development by chromosomal differences, such as a specific complement of sex chromosomes. For example, in humans (and many animals) males are heterogametic, having two different sex chromosomes, X and Y, while females are homogametic, having two copies of X. …